The Contribution of 5-Hydroxyindolepyruvic Acid To Cerebral 5-Hydroxyindole Metabolism

The extent of the 5-hydroxyindolepyruvic acid (5-HIPA) bypass to the cerebral metabolism of 5-hydroxyindoles was measured. The presence of 5-HIPA-14C in brain was demonstrated after intravenous 5-HTP-14C through isolation and identification of its 2,4-dinitrophenylhydrazone. The formation of 5-HIPA was significantly affected by various drugs. The rate of synthesis of 5-HIAA via 5-HIPA in rat brain appears to be at least 0.22 n-mol/g/hr. Increased cerebral 5-HT inhibited transamination of 5-HTP but not the hydroxylation of tryptophan. Lack of feedback inhibition of cerebral tryptophan hydroxylase by 5-HT is confirmed.