HYDROXYLATION OF TRYPTOPHAN BY BRAIN TISSUE IN VIVO AND RELATED ASPECTS OF 5-HYDROXYTRYPTAMINE METABOLISM

As an evidence for the hydroxylation of l -tryptophan (Try) to 5-hydroxytryptophan (5-HTP) in the brain, it was demonstrated that intracerebrally injected (14C)- l -Try led to the appearance of (14C)-5-hydroxytryptamine (5-HT) in the brains of pigeons and rats. Under identical conditions, the injection of the d -isomer did not give labeled 5-HT, but it decreased the 5-HT level in the brain. Intraperitoneal injection of(14C)-Try in amounts equal to or 17 times larger than those injected i.e. did not lead to the appearance of labeled 5-HT in the central nervous system. Identification of label in 5-HT was proved by column, paper chromatography, enzymatic conversion to 5-hydroxyindoleacetic acid, and by recovery of (14C)-5-HT from its picrate salt. Results of the studies of the efflux and turnover of Try, 5-HTP, and 5-HT are also presented.