Summary— The time course of 5‐hydroxytryptophan (5‐HTP), serotonin (5‐HT), and 5‐hydroxyindoleacetic acid (5‐HIAA) concentrations in four rat brain areas (hypothalamus, hippocampus, striatum and olfactory bulbs) were investigated after treatment with l‐dopa (125 mg/kg, ip) + benserazide (50 mg/kg, ip). 5‐HTP levels increased as early as 0.5 h, showed maximum accumulation at 1.5 h and returned to control levels within 4 h, while 5‐HT was markedly decreased in all four structures, with a maximum effect at 1.5 h (approximately − 70%) in the four areas. The decrease in 5‐HT was not accompanied by changes in 5‐HIAA levels. In agreement with previous studies, these data demonstrate that l‐dopa loading interferes with serotonin metabolism in the rat brain. However, in addition to the releasing action of newly‐synthesized dopamine, the accumulation of 5‐HTP and the parallel decrease in 5‐HT indicate a reduction in 5‐HT synthesis. This inhibition could be explained by a competitive effect of l‐dopa for aromatic aminoacid decarboxylase activity.
Fundamental & Clinical Pharmacology – Wiley
Published: Aug 1, 1991
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