Tryptophan metabolism in depression.

Psychiatric patients suffering from endogenous depression and a control group without endogenous depression were given oral loads of L-tryptophan and urinary excretion determined of the tryptophan metabolites on the pyrrolase pathway: kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid. Female endogenously depressed subjects excreted significantly more kynurenine and 3-hydroxykynurenine but not the subsequent metabolite 3-hydroxyanthranilic acid than did female control subjects. Variability of excretion of kynurenine and 3-hydroxykynurenine at different times by the same subject was much greater in the endogenously depressed than in the control group. There was no consistent temporal relationship between excretion of metabolites and severity of the depressive illness. The possible significance of the findings in relation to defective tryptophan metabolism in the brain in endogenous depression is commented upon.