Large scale spatio-temporal forcing of pelagic-coastal coupling: disentangling the effects of environmental change on intertidal invertebrate recruitment
- Authors: Muñiz, Carlota Fernández
- Date: 2019
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/75317 , vital:30400
- Description: Marine systems are driven by the relationships among organisms and environmental conditions. Anthropogenic-induced changes during the past decades have started to alter climatic drivers which have the potential to alter the physical, chemical and biological environment. In coastal systems, biogeography is influenced by the temporal variability in the conditions of the water mass. In addition, many marine benthic organisms develop in the water mass and rely on the conditions that link the pelagic and benthic systems for population maintenance. Such pelagic-coastal coupling indicates that changes in the trophic system during development can be transferred to the adult populations through changes in propagule supply. Thus, changes in environmental conditions can influence benthic populations directly (e.g. through larval advection) or indirectly, through their influence on the phytoplankton community (e.g. through the development of HABs). The South African coastline shows clear alongshore patterns of faunal biomass and species richness. On the south coast, strong longitudinal patterns of recruitment of intertidal organisms exist, with areas of particularly high recruitment. HABs of unprecedented spatio-temporal magnitude have recently developed along the south coast, including the areas where benthic recruitment is most intense. The present thesis used these blooms to study changes in intertidal recruitment directly or indirectly associated with their occurrence. Using a combination of remote sensing data to study the environmental conditions of the water mass in the innermost part of the Agulhas Bank, and estimates of mussel and barnacle recruitment rates to integrate the effects of conditions in the water mass during larval development, this thesis aimed to: (1) understand the conditions that triggered the development of an HAB of the dinoflagellate Lingulodinium polyedrum during summer of 2014, (2) determine the direct or indirect effects of that bloom on recruitment of intertidal organisms, and understand the factors that affect recruitment along the coast, (3) determine if the environmental factors during bloom development produced any carryover effects on recruit growth and mortality, and (4) determine the factors that drive changes in community biomass and composition along the south coast, the long-term trends in those factors, and possible changes experienced in recent years. Water column stability during spring, before the development of the red tide, followed by alternating periods of upwelling and relaxation during summer and autumn, seemed to promote the development and persistence of L. polyedrum. Recruitment of mussels and barnacles was estimated during the reproductive season of mussels in 2014, coinciding with the red tide, and during the following year. Alongshore patterns in recruitment were found, with higher mussel recruitment in the absence of the red tide and the opposite pattern in barnacles. Alongshore patterns in SST and chlorophyll matching those of recruitment were also found, with higher SSTs and lower chlorophyll during the red tide than the following year. Growth and mortality rates in barnacles did not differ between years during the first five months after settlement. This suggests that the factors which produced differences in recruitment between years did not produce carryover effects detectable at the temporal scales studied. Further analysis of 15 years of satellite-derived environmental data showed significant cooling trends potentially driven by a long-term seasonal acceleration of the Agulhas Current in autumn around two upwelling centres on the south coast, coinciding temporally with the reproductive period of mussels and barnacles, and spatially with the areas of highest recruitment. In addition, the comparison of SST and chl-a conditions during the first and the second half of the period of study showed that seasonality of both variables has changed in large areas over the shelf, with increasing importance of shorter-term variability, which would in turn decrease environmental predictability. Thus, the conditions observed during the present study, particularly during 2015, when upwelling seemed to be more intense, may presage the potential effects of identified long-term cooling trends at the upwelling centres. Although the general trend shows cooling around those areas, conditions can vary greatly among years, favouring different taxa. Changes in the Agulhas Current System are affected by changes in distant areas in the Indian Ocean basin. Such tele-connection is unlikely to be unique to this system and indicates the importance of understanding trends in major large scale climatic drivers and their regional effects in order to make predictions about coastal systems.
- Full Text:
- Authors: Muñiz, Carlota Fernández
- Date: 2019
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/75317 , vital:30400
- Description: Marine systems are driven by the relationships among organisms and environmental conditions. Anthropogenic-induced changes during the past decades have started to alter climatic drivers which have the potential to alter the physical, chemical and biological environment. In coastal systems, biogeography is influenced by the temporal variability in the conditions of the water mass. In addition, many marine benthic organisms develop in the water mass and rely on the conditions that link the pelagic and benthic systems for population maintenance. Such pelagic-coastal coupling indicates that changes in the trophic system during development can be transferred to the adult populations through changes in propagule supply. Thus, changes in environmental conditions can influence benthic populations directly (e.g. through larval advection) or indirectly, through their influence on the phytoplankton community (e.g. through the development of HABs). The South African coastline shows clear alongshore patterns of faunal biomass and species richness. On the south coast, strong longitudinal patterns of recruitment of intertidal organisms exist, with areas of particularly high recruitment. HABs of unprecedented spatio-temporal magnitude have recently developed along the south coast, including the areas where benthic recruitment is most intense. The present thesis used these blooms to study changes in intertidal recruitment directly or indirectly associated with their occurrence. Using a combination of remote sensing data to study the environmental conditions of the water mass in the innermost part of the Agulhas Bank, and estimates of mussel and barnacle recruitment rates to integrate the effects of conditions in the water mass during larval development, this thesis aimed to: (1) understand the conditions that triggered the development of an HAB of the dinoflagellate Lingulodinium polyedrum during summer of 2014, (2) determine the direct or indirect effects of that bloom on recruitment of intertidal organisms, and understand the factors that affect recruitment along the coast, (3) determine if the environmental factors during bloom development produced any carryover effects on recruit growth and mortality, and (4) determine the factors that drive changes in community biomass and composition along the south coast, the long-term trends in those factors, and possible changes experienced in recent years. Water column stability during spring, before the development of the red tide, followed by alternating periods of upwelling and relaxation during summer and autumn, seemed to promote the development and persistence of L. polyedrum. Recruitment of mussels and barnacles was estimated during the reproductive season of mussels in 2014, coinciding with the red tide, and during the following year. Alongshore patterns in recruitment were found, with higher mussel recruitment in the absence of the red tide and the opposite pattern in barnacles. Alongshore patterns in SST and chlorophyll matching those of recruitment were also found, with higher SSTs and lower chlorophyll during the red tide than the following year. Growth and mortality rates in barnacles did not differ between years during the first five months after settlement. This suggests that the factors which produced differences in recruitment between years did not produce carryover effects detectable at the temporal scales studied. Further analysis of 15 years of satellite-derived environmental data showed significant cooling trends potentially driven by a long-term seasonal acceleration of the Agulhas Current in autumn around two upwelling centres on the south coast, coinciding temporally with the reproductive period of mussels and barnacles, and spatially with the areas of highest recruitment. In addition, the comparison of SST and chl-a conditions during the first and the second half of the period of study showed that seasonality of both variables has changed in large areas over the shelf, with increasing importance of shorter-term variability, which would in turn decrease environmental predictability. Thus, the conditions observed during the present study, particularly during 2015, when upwelling seemed to be more intense, may presage the potential effects of identified long-term cooling trends at the upwelling centres. Although the general trend shows cooling around those areas, conditions can vary greatly among years, favouring different taxa. Changes in the Agulhas Current System are affected by changes in distant areas in the Indian Ocean basin. Such tele-connection is unlikely to be unique to this system and indicates the importance of understanding trends in major large scale climatic drivers and their regional effects in order to make predictions about coastal systems.
- Full Text:
The symbolic consumption and identity construction through luxury branded clothing among Rhodes University students
- Authors: Chinomona, Perpetua
- Date: 2017
- Subjects: Group identity , Peer pressure , Brand choice -- South Africa -- Makhanda , Consumer behavior -- South Africa -- Makhanda , Consumer behavior -- Psychological aspects -- South Africa -- Makhanda , Luxuries -- Psychological aspects -- South Africa -- Makhanda , Rhodes University -- Students -- Attitudes
- Language: English
- Type: Thesis , Masters , MSocSc
- Identifier: http://hdl.handle.net/10962/6853 , vital:21193
- Description: The purpose of this study is to explore how Rhodes University (RU) students construct identity through the symbolic consumption of luxury branded clothing and the role played by reference groups in the consumption behaviour. The study employed the Social Identity Theory (SIT) as a theoretical framework which explains the underpinnings of the cognitions and behaviour with the use of group processes (Trepte, 2006). The central principle of SIT lies in individuals classifying themselves and others into in-group (reference groups) and out-group social categories respectively. There has been a gap in the literature pertaining to a full understanding of the identity construction process through symbolic consumption of luxury brands in South Africa (Reed, 2002). The significance of the study is to provide a foundation for an enhanced theory of consumer behaviour in this context. This study employed a qualitative research approach. A non-probability convenience sampling technique was used, and a total of 12 undergraduate and postgraduate students were interviewed. The chosen data collection method was semi-structured in-depth interviews and data were analysed using thematic analysis. The findings of the study revealed that participants consume luxury branded clothing for both functional and symbolic purposes. Various factors emerged that influence the choice of the symbolic consumption behaviour such as income, buying frequency, spending patterns, perceptions and habits around retail shopping and the shopping experience. In addition, results indicated that reference groups (celebrities, family and peers) play a significant role in the symbolic consumption and construction of identity among the participants. In addition, the results also indicated that the RU participants engaged in a ‘save to spend’ technique whereby they save their pocket money so that they spend it on their favourite luxury branded clothing when they leave for the holidays. There was a common reference group that emerged from the study, namely the peer in-group. The influence of reference groups on youth consumers in South Africa may assist with marketing strategies that can be employed when targeting the Generation Y. Additionally, results indicate that luxury branded clothing have an impact on identity construction within the South African context. The respondents tie their identity to their luxury branded clothing as an indication of ‘who they are’ and as an extension of the ‘self’.
- Full Text:
- Authors: Chinomona, Perpetua
- Date: 2017
- Subjects: Group identity , Peer pressure , Brand choice -- South Africa -- Makhanda , Consumer behavior -- South Africa -- Makhanda , Consumer behavior -- Psychological aspects -- South Africa -- Makhanda , Luxuries -- Psychological aspects -- South Africa -- Makhanda , Rhodes University -- Students -- Attitudes
- Language: English
- Type: Thesis , Masters , MSocSc
- Identifier: http://hdl.handle.net/10962/6853 , vital:21193
- Description: The purpose of this study is to explore how Rhodes University (RU) students construct identity through the symbolic consumption of luxury branded clothing and the role played by reference groups in the consumption behaviour. The study employed the Social Identity Theory (SIT) as a theoretical framework which explains the underpinnings of the cognitions and behaviour with the use of group processes (Trepte, 2006). The central principle of SIT lies in individuals classifying themselves and others into in-group (reference groups) and out-group social categories respectively. There has been a gap in the literature pertaining to a full understanding of the identity construction process through symbolic consumption of luxury brands in South Africa (Reed, 2002). The significance of the study is to provide a foundation for an enhanced theory of consumer behaviour in this context. This study employed a qualitative research approach. A non-probability convenience sampling technique was used, and a total of 12 undergraduate and postgraduate students were interviewed. The chosen data collection method was semi-structured in-depth interviews and data were analysed using thematic analysis. The findings of the study revealed that participants consume luxury branded clothing for both functional and symbolic purposes. Various factors emerged that influence the choice of the symbolic consumption behaviour such as income, buying frequency, spending patterns, perceptions and habits around retail shopping and the shopping experience. In addition, results indicated that reference groups (celebrities, family and peers) play a significant role in the symbolic consumption and construction of identity among the participants. In addition, the results also indicated that the RU participants engaged in a ‘save to spend’ technique whereby they save their pocket money so that they spend it on their favourite luxury branded clothing when they leave for the holidays. There was a common reference group that emerged from the study, namely the peer in-group. The influence of reference groups on youth consumers in South Africa may assist with marketing strategies that can be employed when targeting the Generation Y. Additionally, results indicate that luxury branded clothing have an impact on identity construction within the South African context. The respondents tie their identity to their luxury branded clothing as an indication of ‘who they are’ and as an extension of the ‘self’.
- Full Text:
An investigation of the learning processes that take place during practical work activities when using electrical circuit boards in grade: a case study
- Authors: Accom, Gerald Charles
- Date: 2012
- Subjects: Competency-based education -- South Africa -- Eastern Cape -- Case studies Educational tests and measurements -- South Africa -- Eastern Cape -- Case studies Education -- Evaluation -- South Africa -- Eastern Cape -- Case studies
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1961 , http://hdl.handle.net/10962/d1009687
- Description: Since the introduction of Outcomes Based Education (OBE) as a preferred method of teaching and learning with Curriculum 2005 in 1997, its existence has come under continuous threat for the past thirteen years. Its teething experiences included a revision in 2004 which saw the introduction of the Revised National Curriculum Statements (RNCS) and most recently, we are now standing on the threshold of the implementation of the Curriculum Assessment Policy Statements (CAPS) in 2012. Throughout the turbulent educational milieu, social constructivism has always been upheld as the preferred teaching and learning methodology and millions of rands have been invested in this regard. This study is thus premised on the concern that now after all the years of actively promoting social constructivist methodologies, the implementation of the CAPS could seriously negate reasonable strides made in this regard. Triggered by these curricular issues, a qualitative case study was conducted at a school in Grahamstown in the Eastern Cape, South Africa, investigating the learning processes occurring in group work sessions during lessons involving practical work in electricity using circuit boards in grade 8. Underpinned by an interpretivist paradigm, the study took place in two phases. The data was mainly generated through audio and video recording of two focus groups. An open coding system was employed to derive analytical categories and frequency tables were used to establish trends. In order to validate the data, two observer teachers were involved throughout the research process and this was followed up with semistructured interviews after the second phase. The two case studies, involving learners fitting a similar profile in respect of mother-tongue and age group, were engaged in a similar activity for almost a year apart. This study anticipated the revelation of the extent to which group practical activities in electricity promoted learning, how knowledge is constructed in group-settings and whether practical activities involving electrical circuit boards in grade 8 enhance learning? The main findings of my study revealed that these practical activities can promote learning and therefore should remain a preferred method of teaching.
- Full Text:
- Authors: Accom, Gerald Charles
- Date: 2012
- Subjects: Competency-based education -- South Africa -- Eastern Cape -- Case studies Educational tests and measurements -- South Africa -- Eastern Cape -- Case studies Education -- Evaluation -- South Africa -- Eastern Cape -- Case studies
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1961 , http://hdl.handle.net/10962/d1009687
- Description: Since the introduction of Outcomes Based Education (OBE) as a preferred method of teaching and learning with Curriculum 2005 in 1997, its existence has come under continuous threat for the past thirteen years. Its teething experiences included a revision in 2004 which saw the introduction of the Revised National Curriculum Statements (RNCS) and most recently, we are now standing on the threshold of the implementation of the Curriculum Assessment Policy Statements (CAPS) in 2012. Throughout the turbulent educational milieu, social constructivism has always been upheld as the preferred teaching and learning methodology and millions of rands have been invested in this regard. This study is thus premised on the concern that now after all the years of actively promoting social constructivist methodologies, the implementation of the CAPS could seriously negate reasonable strides made in this regard. Triggered by these curricular issues, a qualitative case study was conducted at a school in Grahamstown in the Eastern Cape, South Africa, investigating the learning processes occurring in group work sessions during lessons involving practical work in electricity using circuit boards in grade 8. Underpinned by an interpretivist paradigm, the study took place in two phases. The data was mainly generated through audio and video recording of two focus groups. An open coding system was employed to derive analytical categories and frequency tables were used to establish trends. In order to validate the data, two observer teachers were involved throughout the research process and this was followed up with semistructured interviews after the second phase. The two case studies, involving learners fitting a similar profile in respect of mother-tongue and age group, were engaged in a similar activity for almost a year apart. This study anticipated the revelation of the extent to which group practical activities in electricity promoted learning, how knowledge is constructed in group-settings and whether practical activities involving electrical circuit boards in grade 8 enhance learning? The main findings of my study revealed that these practical activities can promote learning and therefore should remain a preferred method of teaching.
- Full Text:
An investigation into the antidepressant activity of hypericum perforatum
- Authors: Stephens, Linda Lee
- Date: 2005
- Subjects: Hypericum perforatum -- Physiological effect Hypericum perforatum -- Therapeutic use Antidepressants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3793 , http://hdl.handle.net/10962/d1003271
- Description: Hypericum perforatum is a herbal medicine that has been used for centuries for the treatment of depression. Many studies have been conducted in the Northern hemisphere on the efficacy of the HP extracts produced there. These studies include clinical trials and pharmacological investigations using a standardised HP extract or a fraction of the HP extract containing certain compounds, such as hypericin, pseudohypericin, hyperforin and several of the flavonoids thought to be responsible for the antidepressant activity. The mechanism of action of HP and its constituents is still not completely clear and it is speculated that the antidepressant activity is the result of several of the compounds acting synergistically. HP is indigenous to and also cultivated in the Western Cape of South Africa. Extracts from these plants are sold in the local health shops and there are no previous studies evaluating the efficacy of these products. The aim of this thesis is to investigate the antidepressant activity of one of these products and two of its constituents, quercetin and caffeic acid, to gain further insight into their mode of antidepressant action and to compare these results with similar studies which used a standardised extract produced in the northern hemisphere. The first study investigated the effect of HP, quercetin and caffeic acid on pineal metabolism. Changes in the synthesis of melatonin produced by the pineal gland have been implicated in depression. The results showed an increase in the level of melatonin produced in the animals treated with quercetin, which suggests that this compound may mediate antidepressant activity through such a mechanism. There are no previous reports on the in vivo effects of HP or any of its constituents on pineal metabolism. The second study investigated the effect of HP, quercetin and caffeic acid on the activity of the liver enzyme, tryptophan-2,3-dioxygenase (TDO). Inhibition of this enzyme has been shown to increase plasma levels of tryptophan, a precursor of serotonin and thereby result in increased serotonin levels in the brain. Low levels of serotonin in the brain have been implicated in depression. This study revealed significant inhibition of TDO by caffeic acid and this suggests that this constituent of HP could be contributing to its antidepressant activity through such a mechanism. There are no previous reports investigating the in vivo effect of HP or any of its constituents on TDO activity. Modulation of the levels of indoleamines, serotonin (5-HT) and dopamine (DA) as well as the metabolites, 3,4 dihydroxyphenyl acetic acid (DOPAC), 5-hydroxyindole acetic acid (5-HIAA) and homovallinic acid (HVA) in the brain have been implicated in the neuropharmacology of depression. Different studies using enzyme-linked immunosorbant assay (ELISA), high performance liquid chromatography with electrochemical detection (HPLC-ECD) and liquid chromatography-mass spectrometry (LC-MS) were used to determine changes in the levels of these indoleamines brought about after treatment with HP caffeic acid and quercetin. The results of the ELISA study showed significant increases in 5-HT levels in the brains of the animals treated with caffeic acid and quercetin. The results of the HPLC-ECD studies also revealed significant increases in 5-HT levels and a decrease in the turnover of 5-HT in the animals treated with quercetin. A significant increase in DA levels in the animals treated with quercetin was shown in both the HPLC-ECD and LC-MS studies. There was also an increase in DA turnover in the animals treated with HP shown in the HPLC-ECD and LC-MS studies. These results suggest that HP and its constituents, quercetin and caffeic acid mediate their antidepressant effects through serotonergic and dopaminergic neurotransmission. Adaptive changes in the density of b-adrenergic (b-AR), 5-HT2 and N-methyl-D-aspartate (NMDA) receptors have been implicated in depression. Several studies, investigating the effect of treatment with HP and quercetin on these different receptor densities, were undertaken using radioactive binding assays. Treatment with HP resulted in significant down regulation of b-AR and NMDA receptor densities and up-regulation of 5HT2 receptors. The effects on the b-AR and 5-HT2 receptors are similar to the results reported using HP in the Northern hemisphere, but the effect on the NMDA receptors is novel providing insight into the mode of action of HP. Apoptosis of neuronal cells has been implicated in neuro-degenerative and depressive disorders. Detection of apoptosis, using fluorescent microscopy observed through the labelling of DNA strand breaks, showed a decrease in the amount of apoptosis in the animals treated with HP and quercetin. This adds further support for the use of HP as an antidepressant and these results are similar to results reported from the Northern hemisphere. The results of all these studies suggest that the quality of the locally produced tincture is similar in efficacy to that of the standardised product of the Northern hemisphere.
- Full Text:
- Authors: Stephens, Linda Lee
- Date: 2005
- Subjects: Hypericum perforatum -- Physiological effect Hypericum perforatum -- Therapeutic use Antidepressants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3793 , http://hdl.handle.net/10962/d1003271
- Description: Hypericum perforatum is a herbal medicine that has been used for centuries for the treatment of depression. Many studies have been conducted in the Northern hemisphere on the efficacy of the HP extracts produced there. These studies include clinical trials and pharmacological investigations using a standardised HP extract or a fraction of the HP extract containing certain compounds, such as hypericin, pseudohypericin, hyperforin and several of the flavonoids thought to be responsible for the antidepressant activity. The mechanism of action of HP and its constituents is still not completely clear and it is speculated that the antidepressant activity is the result of several of the compounds acting synergistically. HP is indigenous to and also cultivated in the Western Cape of South Africa. Extracts from these plants are sold in the local health shops and there are no previous studies evaluating the efficacy of these products. The aim of this thesis is to investigate the antidepressant activity of one of these products and two of its constituents, quercetin and caffeic acid, to gain further insight into their mode of antidepressant action and to compare these results with similar studies which used a standardised extract produced in the northern hemisphere. The first study investigated the effect of HP, quercetin and caffeic acid on pineal metabolism. Changes in the synthesis of melatonin produced by the pineal gland have been implicated in depression. The results showed an increase in the level of melatonin produced in the animals treated with quercetin, which suggests that this compound may mediate antidepressant activity through such a mechanism. There are no previous reports on the in vivo effects of HP or any of its constituents on pineal metabolism. The second study investigated the effect of HP, quercetin and caffeic acid on the activity of the liver enzyme, tryptophan-2,3-dioxygenase (TDO). Inhibition of this enzyme has been shown to increase plasma levels of tryptophan, a precursor of serotonin and thereby result in increased serotonin levels in the brain. Low levels of serotonin in the brain have been implicated in depression. This study revealed significant inhibition of TDO by caffeic acid and this suggests that this constituent of HP could be contributing to its antidepressant activity through such a mechanism. There are no previous reports investigating the in vivo effect of HP or any of its constituents on TDO activity. Modulation of the levels of indoleamines, serotonin (5-HT) and dopamine (DA) as well as the metabolites, 3,4 dihydroxyphenyl acetic acid (DOPAC), 5-hydroxyindole acetic acid (5-HIAA) and homovallinic acid (HVA) in the brain have been implicated in the neuropharmacology of depression. Different studies using enzyme-linked immunosorbant assay (ELISA), high performance liquid chromatography with electrochemical detection (HPLC-ECD) and liquid chromatography-mass spectrometry (LC-MS) were used to determine changes in the levels of these indoleamines brought about after treatment with HP caffeic acid and quercetin. The results of the ELISA study showed significant increases in 5-HT levels in the brains of the animals treated with caffeic acid and quercetin. The results of the HPLC-ECD studies also revealed significant increases in 5-HT levels and a decrease in the turnover of 5-HT in the animals treated with quercetin. A significant increase in DA levels in the animals treated with quercetin was shown in both the HPLC-ECD and LC-MS studies. There was also an increase in DA turnover in the animals treated with HP shown in the HPLC-ECD and LC-MS studies. These results suggest that HP and its constituents, quercetin and caffeic acid mediate their antidepressant effects through serotonergic and dopaminergic neurotransmission. Adaptive changes in the density of b-adrenergic (b-AR), 5-HT2 and N-methyl-D-aspartate (NMDA) receptors have been implicated in depression. Several studies, investigating the effect of treatment with HP and quercetin on these different receptor densities, were undertaken using radioactive binding assays. Treatment with HP resulted in significant down regulation of b-AR and NMDA receptor densities and up-regulation of 5HT2 receptors. The effects on the b-AR and 5-HT2 receptors are similar to the results reported using HP in the Northern hemisphere, but the effect on the NMDA receptors is novel providing insight into the mode of action of HP. Apoptosis of neuronal cells has been implicated in neuro-degenerative and depressive disorders. Detection of apoptosis, using fluorescent microscopy observed through the labelling of DNA strand breaks, showed a decrease in the amount of apoptosis in the animals treated with HP and quercetin. This adds further support for the use of HP as an antidepressant and these results are similar to results reported from the Northern hemisphere. The results of all these studies suggest that the quality of the locally produced tincture is similar in efficacy to that of the standardised product of the Northern hemisphere.
- Full Text:
Isolation and characterization of a novel thermostable and catalytically efficient laccase from Peniophora sp. strain UD4
- Authors: Jordaan, Justin
- Date: 2005
- Subjects: Enzymes Enzymes -- Industrial applications Peniophora Laccase
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3970 , http://hdl.handle.net/10962/d1004029
- Description: Enzymes are becoming an effective tool in industrial processes, from crude applications such as bioremediation to fine processes such as chirally selective biocatalysis. The ligninolytic enzymes have recently received considerable attention for industrial application due to both their broad substrate range and their ability to degrade the most recalcitrant natural polymer, lignin. This group of enzymes was therefore identified as the target group for this study. Improved enzyme properties are constantly being sought to enhance the range of applications for enzymes. Biodiversity provides a wide variety of enzymes. Several researchers have concentrated on extremophiles as their primary source of superior enzymes, consequently neglecting temperate environments in their search for these enzymes. The relatively neglected fungal biodiversity of South Africa provided an opportunity to test the hypothesis that potentially important industrial enzymes with unusual properties could be isolated from mesophilic basidiomycetous fungi. Subsequent screening of Eastern Cape biodiversity for thermostable ligninolytic enzymes from basidiomycetes resulted in the isolation of a novel laccase enzyme from a basidiomycetous species. This fungus was identified as Peniophora sp. UD4 by phylogenetic analysis of rDNA ITS sequences. Initial studies indicated a superior optimum temperature of 70°C and thermostability, indicated by no loss in activity at 60°C over nine hours. Further characterization of the laccase revealed a broader than usual substrate range through its unusual ability to oxidatively couple DMAB and MBTH. The laccase also exhibited a broad pH oxidation range for ABTS (pH 2 – 6.8), and a relatively high affinity (K_m_ = 0.0123 mM) and catalytic efficiency (63 252 mM^(-1)^s^(-1)^) for ABTS as a substrate. The laccase activity from Peniophora sp. UD4 was shown to be comprised of three isozymes with a molecular weight of 62 kDa and pI’s of 6.33, 6.45 and 6.50. Investigation of the nutrient and physical factors affecting ligninolytic enzyme production and growth of Peniophora sp. UD4 indicated that the wild-type organism was unsuitable for large scale production of the thermostable laccase due to the low levels of laccase production. The thermostable laccase was applied to defouling of ultrafiltration membranes, bioremediation of industrial waste streams, biocatalysis, and biosensor technology as potential applications. Application of the Peniophora sp. UD4 laccase to defouling of membranes used for ultrafiltration of brown water showed large flux recoveries of 31, 21 and 21% after the first three defouling recycles respectively, compared to 3% for the control without immobilized enzyme. The novel laccase showed potential for the bioremediation of industrial waste streams, the most successful being that of bleach plant effluent, where a reduction of 66% of the phenolic load was achieved. Application of the novel laccase to biocatalytic oxidation of ferulic acid and (±)-α-pinene showed higher product yield as compared to oxidation of these compounds by Trametes versicolor laccase in mediated and non-mediated systems. The major products of (±)-α-pinene oxidation were identified as verbenol and trans-sorberol. The Peniophora sp. UD4 laccase was successfully applied to biosensor technology, which benchmarked significantly better than Trametes versicolor laccase for the detection of 4-chlorophenol. The biosensor developed with laccase from UD4 by covalent binding to a glassy carbon electrode exhibited the best combination of sensitivity and stability. This thesis shows that a laccase with superior properties was obtained from a mesophilic South African basidiomycete. The catalytic properties displayed by the novel laccase from Peniophora sp. UD4 all contribute to the increased industrial applicability of laccases, and may be the most industrially feasible enzyme of its class isolated to date.
- Full Text:
- Authors: Jordaan, Justin
- Date: 2005
- Subjects: Enzymes Enzymes -- Industrial applications Peniophora Laccase
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3970 , http://hdl.handle.net/10962/d1004029
- Description: Enzymes are becoming an effective tool in industrial processes, from crude applications such as bioremediation to fine processes such as chirally selective biocatalysis. The ligninolytic enzymes have recently received considerable attention for industrial application due to both their broad substrate range and their ability to degrade the most recalcitrant natural polymer, lignin. This group of enzymes was therefore identified as the target group for this study. Improved enzyme properties are constantly being sought to enhance the range of applications for enzymes. Biodiversity provides a wide variety of enzymes. Several researchers have concentrated on extremophiles as their primary source of superior enzymes, consequently neglecting temperate environments in their search for these enzymes. The relatively neglected fungal biodiversity of South Africa provided an opportunity to test the hypothesis that potentially important industrial enzymes with unusual properties could be isolated from mesophilic basidiomycetous fungi. Subsequent screening of Eastern Cape biodiversity for thermostable ligninolytic enzymes from basidiomycetes resulted in the isolation of a novel laccase enzyme from a basidiomycetous species. This fungus was identified as Peniophora sp. UD4 by phylogenetic analysis of rDNA ITS sequences. Initial studies indicated a superior optimum temperature of 70°C and thermostability, indicated by no loss in activity at 60°C over nine hours. Further characterization of the laccase revealed a broader than usual substrate range through its unusual ability to oxidatively couple DMAB and MBTH. The laccase also exhibited a broad pH oxidation range for ABTS (pH 2 – 6.8), and a relatively high affinity (K_m_ = 0.0123 mM) and catalytic efficiency (63 252 mM^(-1)^s^(-1)^) for ABTS as a substrate. The laccase activity from Peniophora sp. UD4 was shown to be comprised of three isozymes with a molecular weight of 62 kDa and pI’s of 6.33, 6.45 and 6.50. Investigation of the nutrient and physical factors affecting ligninolytic enzyme production and growth of Peniophora sp. UD4 indicated that the wild-type organism was unsuitable for large scale production of the thermostable laccase due to the low levels of laccase production. The thermostable laccase was applied to defouling of ultrafiltration membranes, bioremediation of industrial waste streams, biocatalysis, and biosensor technology as potential applications. Application of the Peniophora sp. UD4 laccase to defouling of membranes used for ultrafiltration of brown water showed large flux recoveries of 31, 21 and 21% after the first three defouling recycles respectively, compared to 3% for the control without immobilized enzyme. The novel laccase showed potential for the bioremediation of industrial waste streams, the most successful being that of bleach plant effluent, where a reduction of 66% of the phenolic load was achieved. Application of the novel laccase to biocatalytic oxidation of ferulic acid and (±)-α-pinene showed higher product yield as compared to oxidation of these compounds by Trametes versicolor laccase in mediated and non-mediated systems. The major products of (±)-α-pinene oxidation were identified as verbenol and trans-sorberol. The Peniophora sp. UD4 laccase was successfully applied to biosensor technology, which benchmarked significantly better than Trametes versicolor laccase for the detection of 4-chlorophenol. The biosensor developed with laccase from UD4 by covalent binding to a glassy carbon electrode exhibited the best combination of sensitivity and stability. This thesis shows that a laccase with superior properties was obtained from a mesophilic South African basidiomycete. The catalytic properties displayed by the novel laccase from Peniophora sp. UD4 all contribute to the increased industrial applicability of laccases, and may be the most industrially feasible enzyme of its class isolated to date.
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An assessment of the knowledge processing environment in an organisation : a case study
- Authors: Vlok, Daniël
- Date: 2004
- Subjects: Rhodes University (East London) -- Information Technology Department Knowledge management Organizational behavior Organizational learning Information storage and retrieval systems
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:721 , http://hdl.handle.net/10962/d1003806
- Description: Knowledge Management is associated with organisational initiatives in response to the demands of a knowledge-based economy in which the potential value of knowledge as a source for competitive advantage is recognised. However, the lack of a common understanding about knowledge itself, its characteristics and how it is constructed has led to diverse approaches about how to "manage" it. This study presents a critical overview of traditional and contemporary KM approaches. The main focus of this study was to discover and apply a suitable methodology for assessing an organisation's knowledge processing environment. This includes an analysis of the current practices and behaviours of people within the organisation relating to the creation of new knowledge and integrating such knowledge into day-to-day work. It also includes inferring from the above practices those policies and programmes that affect knowledge outcomes. This research makes extensive use of the Knowledge Life Cycle (KLC) framework and the Policy Synchronisation Method (PSM) developed by advocates of the New Knowledge Management movement. A case study approach was followed using a range of data collection methods, which included personal interviews, a social network survey and focus group discussions. The selected case is the small IT department at the East London campus of Rhodes University. Evidence from the case suggests that the knowledge processing environment within the IT department is unhealthy. The current knowledge processing practices and behaviours are undesirable and not geared towards the creation of new knowledge and the integration of such knowledge within the business processes of the IT department. There is little evidence of individual and organisational learning occurring and the problem solving process itself is severely hampered by dysfunctional knowledge practices. The study concludes that the above state of affairs is a reflection of the quality and appropriateness of policies and programmes in the extended organisation. Equally, the local definition of rules, procedures and the execution thereof at a business unit level is mostly lacking. The study illustrates that a systematic assessment of the knowledge processing environment provides the organisation with a sound baseline from where knowledge-based interventions can be launched.
- Full Text:
- Authors: Vlok, Daniël
- Date: 2004
- Subjects: Rhodes University (East London) -- Information Technology Department Knowledge management Organizational behavior Organizational learning Information storage and retrieval systems
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:721 , http://hdl.handle.net/10962/d1003806
- Description: Knowledge Management is associated with organisational initiatives in response to the demands of a knowledge-based economy in which the potential value of knowledge as a source for competitive advantage is recognised. However, the lack of a common understanding about knowledge itself, its characteristics and how it is constructed has led to diverse approaches about how to "manage" it. This study presents a critical overview of traditional and contemporary KM approaches. The main focus of this study was to discover and apply a suitable methodology for assessing an organisation's knowledge processing environment. This includes an analysis of the current practices and behaviours of people within the organisation relating to the creation of new knowledge and integrating such knowledge into day-to-day work. It also includes inferring from the above practices those policies and programmes that affect knowledge outcomes. This research makes extensive use of the Knowledge Life Cycle (KLC) framework and the Policy Synchronisation Method (PSM) developed by advocates of the New Knowledge Management movement. A case study approach was followed using a range of data collection methods, which included personal interviews, a social network survey and focus group discussions. The selected case is the small IT department at the East London campus of Rhodes University. Evidence from the case suggests that the knowledge processing environment within the IT department is unhealthy. The current knowledge processing practices and behaviours are undesirable and not geared towards the creation of new knowledge and the integration of such knowledge within the business processes of the IT department. There is little evidence of individual and organisational learning occurring and the problem solving process itself is severely hampered by dysfunctional knowledge practices. The study concludes that the above state of affairs is a reflection of the quality and appropriateness of policies and programmes in the extended organisation. Equally, the local definition of rules, procedures and the execution thereof at a business unit level is mostly lacking. The study illustrates that a systematic assessment of the knowledge processing environment provides the organisation with a sound baseline from where knowledge-based interventions can be launched.
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The enzymology of enhanced hydrolysis within the biosulphidogenic recycling sludge bed reactor (RSBR)
- Authors: Enongene, Godlove Nkwelle
- Date: 2004
- Subjects: Hydrolysis , Sewage sludge , Sewage -- Purification -- Anaerobic treatment , Water -- Purification -- Biological treatment
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4132 , http://hdl.handle.net/10962/d1015744
- Description: The hydrolysis of complex organic heteropolymers contained in municipal wastewater to simpler monomers by extracellular hydrolytic enzymes is generally considered the rate-limiting step of the biodegradation process. Previous studies of the Recycling Sludge Bed Reactor (RSBR) revealed that the hydrolysis of complex particulate organics, such as those contained in primary sludge (PS), was enhanced under anaerobic biosulphidogenic conditions. Although the mechanism was not fully understood, it appeared to involve the interaction of sulfide and sludge flocs. The current study was conducted using a 3500 ml laboratory-scale RSBR fed sieved PS at a loading rate of 0.5 kg COD/m³.day and an initial chemical oxygen demand (COD) to sulfate ratio (COD:SO₄) of 1:1. There was no significant accumulation of undigested sludge in the reactor over the 60-day experimental period and the quantity of SO₄ reduced indicated that the yield of soluble products from PS was at least as high as those reported previously for this system (> 50%). In the current study, the specific activities of a range of extracellular hydrolytic enzymes (L-alanine aminopeptidase, L-leucine aminopeptidase, arylsulphatase, α-glucosidase, β- glucosidase, protease and lipase) were monitored in a sulfide gradient within a biosulphidogenic RSBR. Data obtained indicated that the specific enzymatic activities increased with the depth of the RSBR and also correlated with a number of the physicochemical parameters including sulfide, alkalinity and sulfate. The activities of α- glucosidase and β-glucosidase were higher than that of the other enzymes studied. Lipase activity was relatively low and studies conducted on the enzyme-enzyme interaction using specific enzyme inhibitors indicated that lipases were probably being digested by the proteases. Further studies to determine the impact of sulfide on the enzymes, showed an increase in the enzyme activity with increasing sulfide concentration. Possible direct affects were investigated by looking for changes in the Michaelis constant (Km) and the maximal velocity (Vmax) of the crude enzymes with varying sulfide concentrations (250, 400 and 500 mg/l) using natural and synthetic substrates. The results showed no significant difference in both the Km and the Vmax for any of the hydrolytic enzymes except for the protease. The latter showed a statistically significant increase in the Km with increasing sulfide concentration. Although this indicated a direct interaction, this difference was not large enough to be of biochemical significance and was consequently not solely responsible for the enhanced hydrolysis observed in the RSBR. Investigation into the floc characteristics indicated that the biosulphidogenic RSBR flocs were generally small in size and became more dendritic with the depth of the RSBR. Based on the above data, the previously proposed descriptive models of enhanced hydrolysis of particulate organic matter in a biosulphidogenic RSBR has been revised. It is thought that the effect of sulfide on the hydrolysis step is primarily indirect and that the reduction in floc size and alteration of the floc shape to a more dendritic form is central to the success of the process.
- Full Text:
- Authors: Enongene, Godlove Nkwelle
- Date: 2004
- Subjects: Hydrolysis , Sewage sludge , Sewage -- Purification -- Anaerobic treatment , Water -- Purification -- Biological treatment
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4132 , http://hdl.handle.net/10962/d1015744
- Description: The hydrolysis of complex organic heteropolymers contained in municipal wastewater to simpler monomers by extracellular hydrolytic enzymes is generally considered the rate-limiting step of the biodegradation process. Previous studies of the Recycling Sludge Bed Reactor (RSBR) revealed that the hydrolysis of complex particulate organics, such as those contained in primary sludge (PS), was enhanced under anaerobic biosulphidogenic conditions. Although the mechanism was not fully understood, it appeared to involve the interaction of sulfide and sludge flocs. The current study was conducted using a 3500 ml laboratory-scale RSBR fed sieved PS at a loading rate of 0.5 kg COD/m³.day and an initial chemical oxygen demand (COD) to sulfate ratio (COD:SO₄) of 1:1. There was no significant accumulation of undigested sludge in the reactor over the 60-day experimental period and the quantity of SO₄ reduced indicated that the yield of soluble products from PS was at least as high as those reported previously for this system (> 50%). In the current study, the specific activities of a range of extracellular hydrolytic enzymes (L-alanine aminopeptidase, L-leucine aminopeptidase, arylsulphatase, α-glucosidase, β- glucosidase, protease and lipase) were monitored in a sulfide gradient within a biosulphidogenic RSBR. Data obtained indicated that the specific enzymatic activities increased with the depth of the RSBR and also correlated with a number of the physicochemical parameters including sulfide, alkalinity and sulfate. The activities of α- glucosidase and β-glucosidase were higher than that of the other enzymes studied. Lipase activity was relatively low and studies conducted on the enzyme-enzyme interaction using specific enzyme inhibitors indicated that lipases were probably being digested by the proteases. Further studies to determine the impact of sulfide on the enzymes, showed an increase in the enzyme activity with increasing sulfide concentration. Possible direct affects were investigated by looking for changes in the Michaelis constant (Km) and the maximal velocity (Vmax) of the crude enzymes with varying sulfide concentrations (250, 400 and 500 mg/l) using natural and synthetic substrates. The results showed no significant difference in both the Km and the Vmax for any of the hydrolytic enzymes except for the protease. The latter showed a statistically significant increase in the Km with increasing sulfide concentration. Although this indicated a direct interaction, this difference was not large enough to be of biochemical significance and was consequently not solely responsible for the enhanced hydrolysis observed in the RSBR. Investigation into the floc characteristics indicated that the biosulphidogenic RSBR flocs were generally small in size and became more dendritic with the depth of the RSBR. Based on the above data, the previously proposed descriptive models of enhanced hydrolysis of particulate organic matter in a biosulphidogenic RSBR has been revised. It is thought that the effect of sulfide on the hydrolysis step is primarily indirect and that the reduction in floc size and alteration of the floc shape to a more dendritic form is central to the success of the process.
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A description of the language experiences of English Second-Language students entering the academic discourse communities of Rhodes University
- Authors: Reynolds, Judith Marsha
- Date: 1998
- Subjects: English language -- Study and teaching -- Foreign speakers , English language -- Ability testing
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2361 , http://hdl.handle.net/10962/d1002644 , English language -- Study and teaching -- Foreign speakers , English language -- Ability testing
- Description: This study is a description of the language experiences of English Second Language students in their first year at Rhodes University. It took place in the context of the changes that are currently occurring in higher education in South Africa in terms of student populations. More and more students are entering tertiary education institutions, including HWESUs, such as Rhodes University, who are considered non-traditional. These students typically have English as their second, or additional, language, and have not been adequately prepared for university study by their secondary education. This study describes the experiences of three such students in their first year at Rhodes University. Entry into a university is seen not just as acquiring knowledge, but as entering, or attempting to enter, a new culture. It is recognised that all students enter universities with other cultures or literacies already in place. In the case of non-traditional students tbese other literacies are usually at some distance from those of the university. The work of James Gee (1990) is particularly useful in understanding this process of adjusting to the demands of university study and the effect that previous experiences have on this process. This study is an attempt to discover and describe the literacies that these three students brought with them to university and the effect these literacies had on their attempts to enter academic discourse communities of the university. An ethnographic research method was adopted in order to do this. The study is also an attempt to evaluate, from the perspective of the three students, the appropriacy of the various changes that Rhodes University has made since the numbers of non-traditional students has started to increase.
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- Authors: Reynolds, Judith Marsha
- Date: 1998
- Subjects: English language -- Study and teaching -- Foreign speakers , English language -- Ability testing
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2361 , http://hdl.handle.net/10962/d1002644 , English language -- Study and teaching -- Foreign speakers , English language -- Ability testing
- Description: This study is a description of the language experiences of English Second Language students in their first year at Rhodes University. It took place in the context of the changes that are currently occurring in higher education in South Africa in terms of student populations. More and more students are entering tertiary education institutions, including HWESUs, such as Rhodes University, who are considered non-traditional. These students typically have English as their second, or additional, language, and have not been adequately prepared for university study by their secondary education. This study describes the experiences of three such students in their first year at Rhodes University. Entry into a university is seen not just as acquiring knowledge, but as entering, or attempting to enter, a new culture. It is recognised that all students enter universities with other cultures or literacies already in place. In the case of non-traditional students tbese other literacies are usually at some distance from those of the university. The work of James Gee (1990) is particularly useful in understanding this process of adjusting to the demands of university study and the effect that previous experiences have on this process. This study is an attempt to discover and describe the literacies that these three students brought with them to university and the effect these literacies had on their attempts to enter academic discourse communities of the university. An ethnographic research method was adopted in order to do this. The study is also an attempt to evaluate, from the perspective of the three students, the appropriacy of the various changes that Rhodes University has made since the numbers of non-traditional students has started to increase.
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Interaction of selected fungicides with insoluble bovine skin collagen in the presence of the non ionic surfactant Triton X-100
- Authors: Fowler, William Mackenzie
- Date: 1992
- Subjects: Collagenases -- Research Fungicides -- Research Hides and skins -- Preservation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4318 , http://hdl.handle.net/10962/d1004976
- Description: In the leather industry fungicides are often used for the protection of wet-blue leather. These fungicides are usually only sparingly soluble and are therefore formulated together with surfactants in order to increase their solubility and to ensure an even distribution over the surface of the hide after treatment. Solutions containing both fungicides and surfactant are complex. The nature of these solutions was investigated. By means of UV/Vis spectroscopy and viscometry it was shown that the surfactant and fungicides form micelles and mixed micelles in solution. The nature of these micelles and mixed micelles was dependent on the solution temperature as well as on the concentrations of the surfactant and fungicides. At the higher temperatures and concentrations transition to large, possibly rod-shaped, mixed micelles occurred. The interaction between the selected fungicides 2-(thiocyanomethylthio)benzothiazole and n-octyl-4-isothiazol-3-one with bovine skin collagen in the form of both limed and lightly chromed hide powder in the presence of the non ionic surfactant Triton X -100 was investigated. Fungicide uptake was determined by difference measurements on the float solutions at regular intervals during treatment. Binding was rapid with equilibrium being established within the first six hours even for the solutions with the highest surfactant concentration. Binding failed to follow a normal mass-action binding-type isotherm approaching a saturation limit, but increased continuously indicating a co-operative effect whereby binding site affinity actually increased with the amount of ligand bound. Binding was accompanied by a drop in the free surfactant in the solution at the higher biocide levels indicating the formation of complex mixed micelles which bind to the collagen fibres. The uptake and antifungal activity of commercial fomulations of the fungicides on chrome-tanned wet-blue leather was investigated at various treatment temperatures. At lower fungicide treatment concentrations, binding tended to follow a typical mass-action type binding isotherm, increasing slightly with temperature. At higher float concentrations, an inflexion point was apparent beyond which uptake showed a marked increase with concentration. This inflexion point, signifying a change in binding characteristics, occurred at progressively lower concentrations with increasing temperature. Antifungal activity in terms of storage periods to onset of fungal growth was determined on the wet-blue leather cuttings immediately after treatment and drainage and also on sample discs after exhaustive extraction of free fungicide using dichloromethane. Storage performance testing of the various treated wet-blue leathers was carried out by different methods. Residual protective periods showed a curvilinear increase with dosage offer and surface uptake. In the low dosage range treatment temperature had only a relatively slight effect in promoting uptake and improving storage protection. At higher dosages, the influence of temperature on uptake and storage protection was greater due to the increase in surface binding of the fungicides at the elevated temperatures. Only a portion of the fungicide uptake was recovered by direct solvent extraction of the treated wet-blue leather. Solvent extraction reduced storage margins. The storage response in relation to fungicide content was, however comparable after extraction, indicating that both irreversibly bound and physically associated fungicide offered effective protection. Results of the study provide further insight into the mode of interaction of fungicide emulsion dispersion with bovine skin collagen, and the importance of the emulsion dispersions and its stability in determining the uptake of fungicide.
- Full Text:
- Authors: Fowler, William Mackenzie
- Date: 1992
- Subjects: Collagenases -- Research Fungicides -- Research Hides and skins -- Preservation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4318 , http://hdl.handle.net/10962/d1004976
- Description: In the leather industry fungicides are often used for the protection of wet-blue leather. These fungicides are usually only sparingly soluble and are therefore formulated together with surfactants in order to increase their solubility and to ensure an even distribution over the surface of the hide after treatment. Solutions containing both fungicides and surfactant are complex. The nature of these solutions was investigated. By means of UV/Vis spectroscopy and viscometry it was shown that the surfactant and fungicides form micelles and mixed micelles in solution. The nature of these micelles and mixed micelles was dependent on the solution temperature as well as on the concentrations of the surfactant and fungicides. At the higher temperatures and concentrations transition to large, possibly rod-shaped, mixed micelles occurred. The interaction between the selected fungicides 2-(thiocyanomethylthio)benzothiazole and n-octyl-4-isothiazol-3-one with bovine skin collagen in the form of both limed and lightly chromed hide powder in the presence of the non ionic surfactant Triton X -100 was investigated. Fungicide uptake was determined by difference measurements on the float solutions at regular intervals during treatment. Binding was rapid with equilibrium being established within the first six hours even for the solutions with the highest surfactant concentration. Binding failed to follow a normal mass-action binding-type isotherm approaching a saturation limit, but increased continuously indicating a co-operative effect whereby binding site affinity actually increased with the amount of ligand bound. Binding was accompanied by a drop in the free surfactant in the solution at the higher biocide levels indicating the formation of complex mixed micelles which bind to the collagen fibres. The uptake and antifungal activity of commercial fomulations of the fungicides on chrome-tanned wet-blue leather was investigated at various treatment temperatures. At lower fungicide treatment concentrations, binding tended to follow a typical mass-action type binding isotherm, increasing slightly with temperature. At higher float concentrations, an inflexion point was apparent beyond which uptake showed a marked increase with concentration. This inflexion point, signifying a change in binding characteristics, occurred at progressively lower concentrations with increasing temperature. Antifungal activity in terms of storage periods to onset of fungal growth was determined on the wet-blue leather cuttings immediately after treatment and drainage and also on sample discs after exhaustive extraction of free fungicide using dichloromethane. Storage performance testing of the various treated wet-blue leathers was carried out by different methods. Residual protective periods showed a curvilinear increase with dosage offer and surface uptake. In the low dosage range treatment temperature had only a relatively slight effect in promoting uptake and improving storage protection. At higher dosages, the influence of temperature on uptake and storage protection was greater due to the increase in surface binding of the fungicides at the elevated temperatures. Only a portion of the fungicide uptake was recovered by direct solvent extraction of the treated wet-blue leather. Solvent extraction reduced storage margins. The storage response in relation to fungicide content was, however comparable after extraction, indicating that both irreversibly bound and physically associated fungicide offered effective protection. Results of the study provide further insight into the mode of interaction of fungicide emulsion dispersion with bovine skin collagen, and the importance of the emulsion dispersions and its stability in determining the uptake of fungicide.
- Full Text:
Aspects of prostacyclin in experimental hypertension
- Authors: Botha, Julia Hilary
- Date: 1983
- Subjects: Prostacyclin Prostaglandins Prostaglandin endoperoxides Thromboxanes Hypertension
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3825 , http://hdl.handle.net/10962/d1006109
- Description: A new prostaglandin - prostaglandin X (later renamed prostacyclin or prostaglandin I₂ (PGI₂)), was discovered by Moncada, Gryglewski, Bunting and Vane in 1976. This unstable substance was shown to be produced by vascular tissue and to be a vasodilator and the most potent endogenous inhibitor of platelet aggregation known. Because of its properties, it appeared that a lack of it may be related to the development and or maintenance of hypertension, a disorder featuring vasoconstriction and an increased tendency to arterial thrombosis. The present studies aimed to investigate this possibility using a rat model. A bioassay for prostacyclin was first perfected. This consisted of a modification of the method used by Moncada, Higgs and Vane (1977): PGI₂ released by rat aortic strips, during incubation in tris buffer, was measured by assessing the ability of the incubate to inhibit adenosine diphosphate induced aggregation of human platelets, as compared to the inhibitory effect of standard prostacyclin sodium salt. The specificity of the assay for the detection of PGI₂ was tested. The abil ity of hypertensive rat aorta to release prostacycl in was investigated in two studies. The first compared aortas of Wistar rats of the New Zealand genetically hypertensive strain (GH) with those of matched normotensive Wistar controls. In the second study, hypertension was induced by wrappi ng the ri ght kidney with surgical silk and removing the contralateral kidney. Ten weeks later, aortic generation of prostacyclin by these animals was compared with that of matched sham controls which had received identical surgical manipulation but for the application of silk to the right kidney. Contrary to expectation, in both forms of hypertension, aortas of the rats with elevated pressure produced consistently more prostacyclin than those of matched controls. In order to discover more about the relationship between elevated pressure and elevated PGI₂ production, the effect of pressure reduction with hypotensive agents on the ability of GH rat aortas to produce prostacyclin, was investigated. After pressure had been controlled within normal range for one week (achieved by oral administration of furosemide, dihydralazine and reserpine for one month), aortic PGI₂ was reduced in comparison with matched GH controls. However, the reduction was not consistent and statistical significance was not reached. Because it was subsequently reported by other workers, that some of the hypotensive agents which had been employed may effect prostaglandin levels per se, no conclusions could be drawn from this study as to any possible direct relationships between pressure and aortic prostacyclin generating capacity. A further means of reducing elevated pressure (which had no inherent effect on prostaglandin levels) was thus sought. A mechanical method was eventually selected, application of a silver clip to the aortas of GH rats, just below the diaphragm, producing an immediate reduction in pressure distal to the constriction. Eighteen hours with later, PGI₂ production by these distal aortas those of matched sham GH controls and was was compared found to be consistently reduced. These results indicate that the ability to produce PGI₂ may be influenced by prior local pressure changes and that the increased capacity of hypertensive rat aortas to generate prostacyclin may be related to the increased mechanical transmural stress consequent on elevated pressure. Since haemostatic balance must be influenced not only by vascular PGI₂ generation but also by platelet sensitivity to PGI₂, the response of GH platelets to the anti-aggregatory effect of prostacyc1in was also investigated. As it had been shown by Sinzinger, Si1berbauer, Horsch and Gall (1981) that intra-arterial infusion of PGI₂ in humans decreased platelet sensitivity to the substance, the possibility existed that platelet sensitivity in hypertension might be reduced. This hypothesis was, however, invalidated as the sensitivity of GH platelets to the anti-aggregatory effect of PGI₂ was almost identical to that of normotensive controls. The shortcomings of the methodology and the possible importance of these findings in the hypertensive animal are discussed. The idea that elevated PGI₂ in hypertension may play a protective role both with respect to platelet aggregation and in attenuating further pressure rises is considered. It is finally suggested that it will be possible to draw more accurate conclusions as to the meaning of the increased PGI₂ generation in hypertension (both in relation to vascular tone and platelet function) only when details of production of, and sensitivity to, thromboxane A₂ are known. Thromboxane A₂ (TXA₂) is a vasoconstrictor and promotor of aggregation (Hamberg, Svensson and Samuelson, 1975) and it may be that, despite elevated vascular PGI₂ generation, the TXA₂/PGI₂ balance is still tipped in favour of vasoconstriction and platelet aggregation in hypertension.
- Full Text:
- Authors: Botha, Julia Hilary
- Date: 1983
- Subjects: Prostacyclin Prostaglandins Prostaglandin endoperoxides Thromboxanes Hypertension
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3825 , http://hdl.handle.net/10962/d1006109
- Description: A new prostaglandin - prostaglandin X (later renamed prostacyclin or prostaglandin I₂ (PGI₂)), was discovered by Moncada, Gryglewski, Bunting and Vane in 1976. This unstable substance was shown to be produced by vascular tissue and to be a vasodilator and the most potent endogenous inhibitor of platelet aggregation known. Because of its properties, it appeared that a lack of it may be related to the development and or maintenance of hypertension, a disorder featuring vasoconstriction and an increased tendency to arterial thrombosis. The present studies aimed to investigate this possibility using a rat model. A bioassay for prostacyclin was first perfected. This consisted of a modification of the method used by Moncada, Higgs and Vane (1977): PGI₂ released by rat aortic strips, during incubation in tris buffer, was measured by assessing the ability of the incubate to inhibit adenosine diphosphate induced aggregation of human platelets, as compared to the inhibitory effect of standard prostacyclin sodium salt. The specificity of the assay for the detection of PGI₂ was tested. The abil ity of hypertensive rat aorta to release prostacycl in was investigated in two studies. The first compared aortas of Wistar rats of the New Zealand genetically hypertensive strain (GH) with those of matched normotensive Wistar controls. In the second study, hypertension was induced by wrappi ng the ri ght kidney with surgical silk and removing the contralateral kidney. Ten weeks later, aortic generation of prostacyclin by these animals was compared with that of matched sham controls which had received identical surgical manipulation but for the application of silk to the right kidney. Contrary to expectation, in both forms of hypertension, aortas of the rats with elevated pressure produced consistently more prostacyclin than those of matched controls. In order to discover more about the relationship between elevated pressure and elevated PGI₂ production, the effect of pressure reduction with hypotensive agents on the ability of GH rat aortas to produce prostacyclin, was investigated. After pressure had been controlled within normal range for one week (achieved by oral administration of furosemide, dihydralazine and reserpine for one month), aortic PGI₂ was reduced in comparison with matched GH controls. However, the reduction was not consistent and statistical significance was not reached. Because it was subsequently reported by other workers, that some of the hypotensive agents which had been employed may effect prostaglandin levels per se, no conclusions could be drawn from this study as to any possible direct relationships between pressure and aortic prostacyclin generating capacity. A further means of reducing elevated pressure (which had no inherent effect on prostaglandin levels) was thus sought. A mechanical method was eventually selected, application of a silver clip to the aortas of GH rats, just below the diaphragm, producing an immediate reduction in pressure distal to the constriction. Eighteen hours with later, PGI₂ production by these distal aortas those of matched sham GH controls and was was compared found to be consistently reduced. These results indicate that the ability to produce PGI₂ may be influenced by prior local pressure changes and that the increased capacity of hypertensive rat aortas to generate prostacyclin may be related to the increased mechanical transmural stress consequent on elevated pressure. Since haemostatic balance must be influenced not only by vascular PGI₂ generation but also by platelet sensitivity to PGI₂, the response of GH platelets to the anti-aggregatory effect of prostacyc1in was also investigated. As it had been shown by Sinzinger, Si1berbauer, Horsch and Gall (1981) that intra-arterial infusion of PGI₂ in humans decreased platelet sensitivity to the substance, the possibility existed that platelet sensitivity in hypertension might be reduced. This hypothesis was, however, invalidated as the sensitivity of GH platelets to the anti-aggregatory effect of PGI₂ was almost identical to that of normotensive controls. The shortcomings of the methodology and the possible importance of these findings in the hypertensive animal are discussed. The idea that elevated PGI₂ in hypertension may play a protective role both with respect to platelet aggregation and in attenuating further pressure rises is considered. It is finally suggested that it will be possible to draw more accurate conclusions as to the meaning of the increased PGI₂ generation in hypertension (both in relation to vascular tone and platelet function) only when details of production of, and sensitivity to, thromboxane A₂ are known. Thromboxane A₂ (TXA₂) is a vasoconstrictor and promotor of aggregation (Hamberg, Svensson and Samuelson, 1975) and it may be that, despite elevated vascular PGI₂ generation, the TXA₂/PGI₂ balance is still tipped in favour of vasoconstriction and platelet aggregation in hypertension.
- Full Text:
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