The effect of 6-Methoxy-2-Benzoxazolinone (6-MBOA) on indoleamine regulation and its possible role in depression
- Authors: Tanda, Sindiswa Eunice
- Date: 2000
- Subjects: Tryptophan -- Physiological effect , Tryptophan -- Therapeutic use , Antidepressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3912 , http://hdl.handle.net/10962/d1003971 , Tryptophan -- Physiological effect , Tryptophan -- Therapeutic use , Antidepressants
- Description: Tryptophan is an essential amino acid that is obtained from the diet. Approximately 98 % of ingested tryptophan is metabolized by the enzyme tryptophan 2,3-dioxygenase (TDO). The metabolism of tryptophan by TDO is an important determinant of tryptophan bioavailability to the brain for serotonin (5-HT) biosynthesis, an essential amine in affective disorders such as depression. Studies done on circadian rhythmicity of the enzyme activity have shown that, TDO activity is high during the scoto-phase (dark-phase), which is attributable to the de novo enzyme synthesis that occurs during this phase. 6-Methoxy-2-benzoxazolinontr-(6-MBOA), a structural analogue of melatonin (aMT) was shown to inhibit TDO activity in both the photo-phase (light-phase) and the scoto-phase with greater potency during the light-phase. Further studies were directed at demonstrating the effects of 6-MBOA on the brain tryptophan hydroxylase (TH) activity, which is a rate limiting enzyme in 5-HT biosynthesis and subsequently on 5-HT levels. The findings showed that, 6-MBOA induces TH activity with a concomitant rise in brain 5-HT levels. The blockade of 5-HT re-uptake into the presynaptic neuron leads to an increase in 5-HT available for the stimulatory action of 5-HT receptors. An attempt to establish whether the administration of 6-MBOA would block the binding of 5-HT to receptors on the synaptosomal membrane showed that 6-MBO A only inhibits the binding of 5 -HT at specific concentrations. In view of the positive effects imposed by 6-MBOA on brain 5-HT levels, urinary 5-hydroxyindole acetic acid (5-HIAA) excretion was measured before and after treatment with 6-MBOA. 5-HIAA excretion was found to be significantly increased after 6-MBOA treatment. Extensive research on the biosynthesis of pineal metabolites has been conducted in the past two decades. The pineal metabolites are synthesized from the precursor tryptophan. In order to obtain an overall picture of the effect of6-MBOA on pineal indole metabolism, an organ culture technique was employed. The results obtained showed that although 6-MBOA administration to rats caused a significant increase in aMT production, there was an insignificant increase in NAS production. This is an immediate precursor of aMT. Other pineal indoles were not affected at all by 6-MBOA administration. Furthermore, the production of pineal NAS and aMT showed an inter-individual variation with some animals producing very high, some very low and some produced average levels of these two metabolites in both photo and scoto-phase experiments. A study undertaken to investigate the circadian rhythm in endogenous aMT production using the competitive ELISA technique showed a clear pattern with high levels of aMT produced during the dark-phase and low levels ofaMT produced during the light-phase. Furthermore, the administration of6-MBOA to rats lead to a significant rise in endogenous aMT production.
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- Date Issued: 2000
The effect of tricyclic antidepressant drugs on the uptake and metabolism of serotonin by the pineal gland in organ culture
- Authors: Pillay, Manoranjenni
- Date: 1983 , 2013-04-05
- Subjects: Antidepressants , Pineal gland -- Metabolsim , Serotonin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3828 , http://hdl.handle.net/10962/d1007053 , Antidepressants , Pineal gland -- Metabolsim , Serotonin
- Description: The effect of tricyclic antidepressants (TADs) on a variety of pineal functions was assessed. TADs affected the uptake of ³H-5HT into bovine pineal slices within a particular concentration range of these drugs, DESI, CLOMI and IMI appeared to inhibit uptake slightly, within a limited concentration range. Surprisingly, DESI appeared to be a relatively potent 5HT uptake inhibitor. The 5-HT re-uptake system in the pineal probably differes from that in brain tissue. TADs had a marked effect on the metabolism of ³H-5HT in the rat pineal, in an organ culture system, MEL and N-acetylserotonin synthesis increased for the first 11 days and thereafter a slight decrease was observed. HTOH and HIAA also showed an initial increase followed by a slight decrease in synthesis. The synthesis of MTOH and MIAA was decreased. The possibility that TADs could affect HIOMT and SNAT synthesis and thereby change the metabolic pattern of 5-HT was investigated. TADs appeared to stimulate SNAT initially and thereafter a slight decrease from peak activity was observed. This is probably due to stimulation followed by development of subsensitivity of β-receptors, HIOMT activity also appeared to be affected by TADs. The existence of two types of HIOMT is suggested. There is a possibility that these changes in the metabolism of 5-HT could be implicated in the mechanism of action of TADs. , KMBT_363 , Adobe Acrobat 9.53 Paper Capture Plug-in
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- Date Issued: 1983
The study of the potentiation of anticholinergic side effects of tricyclic antidepressives by female sex steroids
- Authors: Kok, Eric Charl
- Date: 1981
- Subjects: Antidepressants , Steroid hormones
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3822 , http://hdl.handle.net/10962/d1005623 , Antidepressants , Steroid hormones
- Description: It has been recorded that women respond to tricyclic antidepressives with a greater incidence of anticholinergic side effects than men do, particularly women taking an exogenous source of oestrogen. The aim of this study was to investigate the influence that ethinyl oestradiol and Premarin© had on the metabolism of a number of tricyclic antidepressives, and also the influence they had on the binding ability of microsomes to imipramine. Rat hepatocyctes and microsomes were used. Detection techniques used were High Pressure Liquid Chromatography and Spectrophotometry respectively. In addition to these studies, a study of the anticholinergic activity of Nomifensine, tricyclic antidepressives and their derivatives was performed on a rat jujenum. Results conclusively showed that ethinyl oestradiol had a marked influence on the metabolism of the tricyclic antidepressives studied. Premarin© had Iittle, if any influence. However, both ethinyl oestradiol and Premarin© affected the binding of microsomes to imipramine, but ethinyl oestradiol had the greater effect. The parent compound in each case exhibited a higher pAZ value. Results indicate that a possible explanation for the increased anticholinergic side effect is due to an inhibition of the metabolism of the tricyclic antidepressives by oestrogen.
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- Date Issued: 1981
The evaluation of melatonin as a possible antidepressive
- Authors: Skene, Debra Jean
- Date: 1980
- Subjects: Melatonin , Antidepressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3728 , http://hdl.handle.net/10962/d1001465
- Description: Melatonin, a hormone of the pineal gland, was evaluated in a variety of animal models of depression. Measurements of the frog righting reflex and rat locomotor activity showed that low doses of melatonin have a serotonin-like potentiating effect following monoamine oxidase inhibition. High doses of melatonin caused a reduction in the duration of rat immobility in the Porsolt model of depression and exerted a chlorpromazine-like effect on conditioned avoidance behaviour. In view of the indoleamine hypothesis of depressive disorders, the possibility of melatonin being a potential antidepressive is discussed and it is concluded that melatonin might be useful in the treatment of "agitated" depressions
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- Date Issued: 1980