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  • Title: L-5-hydroxytryptophan. Correlation between anticonvulsant effect and increases in levels of 5-hydroxyindoles in plasma and brain.
    Author: Löscher W, Pagliusi SR, Müller F.
    Journal: Neuropharmacology; 1984 Sep; 23(9):1041-8. PubMed ID: 6083501.
    Abstract:
    The effect of L-5-hydroxytryptophan (5-HTP) on the threshold for maximal electroconvulsions was compared with concomitant changes in levels of 5-HTP, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in plasma and brain of rats. A single injection of 5-HTP (100 mg/kg, i.p.) caused significant elevation in seizure threshold which was markedly intensified by pretreatment with the decarboxylase inhibitor carbidopa (10 mg/kg, i.p., 0.5 hr previously). Pretreatment with carbidopa also resulted in behavioural changes, i.e. the characteristic "wet-dog shake" behaviour became much more prominent. Biochemically, administration of 5-HTP gave rise to significant elevation of levels of 5-HTP, 5-HT and 5-HIAA in plasma and brain. Carbidopa increased levels of 5-HTP in the brain, decreased 5-HIAA in the periphery but did not alter the elimination rate of 5-HTP in plasma. In both naive rats and rats pretreated with carbidopa, a significant correlation was found between levels of 5-HTP and 5-HIAA in plasma and brain following injection of 5-HTP. Furthermore, in the absence of carbidopa, the increases of levels of 5-HT in plasma and brain induced by 5-HTP were correlated in a significant fashion. When the changes in the electroconvulsive threshold were compared with respective changes in levels of 5-hydroxyindoles, a significant correlation was obtained between threshold elevations and increases of 5-HTP and 5-HT in the brain. In rats treated with 5-HTP, without decarboxylase inhibitor, a significant correlation was found between increases in 5-HT in plasma and the seizure threshold. The results suggest that analysis of 5-hydroxyindoles in plasma may represent a useful tool for the estimation of 5-HT metabolism in brain.
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