PSYCHOTROPIC DRUGS AND THE METABOLISM OF INTRACEREBRALLY INJECTED TRYPTAMINE, 5-HYDROXYTRYPTAMINE, AND NOREPINEPHRINE

— Rats were injected intracerebrally with labelled tryptamine, 5-hydroxytrypt-amine (5-HT) and norepinephrine (NE). The disappearance of the amines and their metabolites as a function of time was determined. Tryptamine disappeared very rapidly, with a half-life of 5 min in normal animals and of 45 min in rats treated with a monoamine oxidase (MAO) inhibitor. The level of radioactive 5-HT declined in two phases, with half-lives of 45 min and 3 h respectively. The 5-hydroxyindoleacetic acid (5-HIAA) that was formed disappeared with a half-life of approximately 1 h. After inhibition of monoamine oxidase, there was only a single phase of 5-HT disappearance (half-life of 4 h). Reserpine decreased and imipramine increased the amount of 5-HT remaining 4 h after injection. Of the NE injected, 12 per cent was converted to methoxyhydroxyphenylglycol sulphate (MHPGS), which disappeared with a half life of 3 h. Reserpine doubled the amount of methoxyhydroxyphenylglycol sulfate formed, but did not alter its rate of disappearance, its peak concentration occurring about 30 min after injection of NE in both control and reserpine-treated rats.