Studies on Tryptophan Metabolism in Male Subjects Treated with Hydrocortisone1

The influence of hydrocortisone on urinary excretion of metabolites of the kynurenine pathway of tryptophan metabolism has been studied in male subjects. Hydrocortisone caused increased urinary excretion of tryptophan metabolites (i.e., kynurenine, acetylkynurenine, kynurenic acid, 3-hydroxykynurenine, and xanthurenic acid) after a loading dose of 2 g l-tryptophan, whereas urinary excretion of anthranilic acid metabolites was unchanged. The conversion of tryptophan to nicotinic acid metabolites was inhibited. Vitamin B6 supplementation normalized urinary excretion of tryptophan metabolites and caused an increase in urinary excretion of anthranilic acid metabolites. These results indicate that the capacity of the kynurenine pathway is exceeded by a loading dose of 2 g l-tryptophan when tryptophan pyrrolase, the first step of the kynurenine pathway, is induced by hydrocortisone. On the other hand, hydrocortisone seems to inhibit the extent to which tryptophan enters the NAD pathway.