Tryptophan Metabolism in Man *

Abstract

The urinary excretion of 12 tryptophan metabolites was studied in 10 children (5 male, 5 female) and in 16 adults (8 male, 8 female) before and after tryptophan loading. It was similar in the 3 groups for the preload period; but after loading a significant difference was observed between the adult females and the other 2 groups: a higher percentage of conversion of administered tryptophan by the women, reflecting much higher excretion of metabolites of the kynurenine pathway: kynurenine and acetylkynurenine, 3-hydroxy-kynurenine, 3-hydroxyanthranilic acid, anthranilic acid and glucuronide, kynurenic acid, and xanthurenic acid. No differences were seen in 3-indoleacetic acid and indican excretion. The effect of intravenous vs. oral administration of tryptophan was studied in 3 normal children. Excretion rates and percentage of conversion were similar for the 2 routes, suggesting that tryptophan is completely absorbed from the upper intestinal tract, and that observed tryptophan abnormalities in such disease states as phenylketonuria and the blue diaper syndrome (hypercalcemia, indicanuria, nephrocalcinosis, and tryptophan abnormalities) may reflect absorption defects. Link of tryptophan metabolism to serum Ca levels, suggested by the blue diaper syndrome patient, was confirmed in normal subjects, many of whom had a transient increase in serum Ca levels after tryptophan loading.