THE EFFECT OF THREE TRYPTAMINE DERIVATIVES ON SEROTONIN METABOLISM IN VITRO AND IN VIVO

¹ Department of Pharmacology, The Upjohn Company, Kalamazoo, Michigan

- Methyltryptamine and -ethyltryptamine inhibited MAO activity both in vitro and in vivo. In vitro the activities of these indoles were of the same order as that of iproniazid. In vivo they differed from iproniazid in that their effect was reversible. 5-Hydroxy--methyltryptamine was less active in vitro than the two other indoles tested and showed no inhibition in vivo in the dose used. -Methyl and -ethyltryptamine, but not 5-hydroxy--methyltryptamine, caused an central stimulation of rats and mice. This effect correlated with the ability to inhibit MAO. -Methyltryptamine and 5-hydroxy--methyltryptamine inhibited 5-hydroxytryptophan decarboxylase in vitro and in vivo as determined by Woolley's diarrhea test in mice. Although it is possible for -methyltryptamine to inhibit both MAO and 5-hydroxytryptophan decarboxylase in vivo the observed effects would indicate that MAO is predominantly affected.