In vitro diffusion cell design and validation. I. A stability-indicating high-performance liquid chromatographic assay for betamethasone 17-valerate in purified isopropyl myristate receptor phase
- Authors: Smith, Eric W , Haigh, John M
- Date: 1989
- Language: English
- Type: text , Article
- Identifier: vital:6431 , http://hdl.handle.net/10962/d1006595
- Description: Introduction: The development of a reliable in vitro permeation system necessitates the use of a precise and accurate method of quantifying the amount of permeant partitioning from the membrane into the cell receptor phase. Aqueous donor and receptor chamber fluids have been used in the majority of reported investigations, which makes quantitative permeant analysis relatively facile. Alternatively, radiolabelled diffusants have been used and flux rates monitored by scintillation counting, obviating the need for chromatographic separation of the receptor-phase components. However, this technique is not applicable when nonlabelled compounds or commercial dosage forms are to be evaluated by a cell system. Furthermore, several studies indicate that aqueous receptor phases may not present an optimal partitioning environment for certain lipophilic permeants (1-4), thereby impairing accurate flux monitoring due to limited diffusant solubility. Several attempts have therefore been made to improve the partitioning environment within these systems, by the addition of surfactants for example (4). A lipophilic receptor environment appears beneficial for corticosteroid partitioning, and thus, the use of isopropyl myristate has been investigated because of its bipolar properties that tend to mimic the biochemical composition of the skin (5,6). Betamethasone 17-valerate and its 21-valerate degradation product are highly soluble in isopropyl myristate and this nonaqueous solvent will not augment C-17-to-C-21 ester degradation reactions.
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Rainfall characteristics, rainfall reliability and the definition of drought : Baringo district, Kenya
- Authors: Rowntree, K M
- Date: 1989
- Language: English
- Type: Article
- Identifier: vital:6724 , http://hdl.handle.net/10962/d1006802
- Description: Monthly rainfall data for Kabarnet District Office, together with comments taken from the Baringo District Annual Report, are used here to examine the relationship between rainfall characteristics and agricultural drought experienced over the period 1915 to 1943 in order to establish the meteorological criteria for a definition of drought applicable to the former Kerio Native Land Unit, Baringo District, Kenya. The concept of reliable rainfall as a drought threshold is also examined. The analysis shows that the occurrence of drought was related to both the rainfall total and to the seasonal distribution. The meteorological criteria for drought and for reliable rainfall were found to differ between the upland cultivators and the lowland pastoralists, the latter experiencing a higher frequency of drought.
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The Benthic invertebrate community of a Southern Cape estuary : structure and possible food sources
- Authors: Whitfield, Alan K
- Date: 1989
- Language: English
- Type: text , Article
- Identifier: vital:7154 , http://hdl.handle.net/10962/d1011871
- Description: Cluster analysis of invertebrate communities in the Swartvlei estuary revealed that vegetated (Zostera capensis) sites were distinct from unvegetated ones. `Indicator species' for the eelgrass group included Melita zeylinaca, Loripes clausus, Natica tecta and Palaemon pacificus, whereas those for the bare sand community were Urothoe pulchella, Callianassa kraussi, Iphinoe truncata and Pontogeloides latipes. Infaunal bivalves comprised >60 % of the invertebrate biomass at Zostera sites but <5 % at bare sand sites. Conversely the infaunal anomuran C. kraussi dominated the sandy sites (>80 %) and was a minor component (<5 %) at eelgrass sites. The supratidal invertebrate community was dominated by Orchestia spp. which live and feed on wrack detritus. Litterbag experiments revealed that degradation of Zostera leaf wrack was rapid during the first thirty days after deposition but slow between 40 and 140 days. Laboratory experiments indicated that Orchestia consumption of wrack material could not account for the rapid weight loss recorded in the natural environment. Preliminary diet analyses of intertidal and infratidal zoobenthos revealed that most invertebrate species feed on detritus and associated microorganisms. Filamentous algae and diatoms dominated the gut contents of only three out of 18 macrobenthic species, and living Zostera was not an important food item for any invertebrate examined.
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Travelling stallions in and adjacent to Brycheiniog
- Authors: Lewis, Colin A
- Date: 1989
- Language: English
- Type: Article
- Identifier: vital:6696 , http://hdl.handle.net/10962/d1006732
- Description: [From the introduction]: Horses played a major role in the transport system in Britain until, in the years following the conclusion of the First World War, they were gradually ousted by motor vehicles. In 1917, when the first reasonably complete equine census of Britain was undertaken, there were 2,650,773 horses in the country, 1,115,920 of which were used for agricultural purposes (Chivers, 1976). Horse breeding was therefore of great importance and a variety of attempts was made to improve the quality of horses by subsidising stallions that travelled the countryside during the breeding season, and that were available, at a fee, for the service of mares. This paper describes some of the routes followed by stallions that formerly travelled in Brycheiniog and adjacent counties.
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