Quantitative Studies on Human Urinary Metabolites Of

The metabolism of n-tryptophan in man was recently studied by Langner and Berg (l), who found that about one-third to one-half of a 2 gm. dose was excreted unchanged in the urine. Considerable n-kynurenine and traces of indolepyruvic acid and acetyltryptophan were also excreted by their subjecm. Langner and Volkmann (2) found that acetyl-n-tryptophan was poorly absorbed and most of the compound was accounted for in the feces and urine. Only 5 to 10 per cent of acetyl-L-tryptophan was found in the stool, and a small amount was excreted in the urine. Rose, Coon, Lambert, and Howe (3) have found that acetyl-L-tryptophan was essentially as good as L-tryptophan in the maintenance of nitrogen balance in human subjects who were deprived of t.ryptophan. Other studies in this field have been cited in these recent publications (l-3). Methods for the quantitative determination of several metabolites of tryptophan have recently been developed and applied in studies on the urinary metabolites of L-tryptophan in man and other species (4,5). These determinations included kynurenine, N”-acetylkynurenine, o-aminohippuric acid, anthranilic acid, anthranilic acid glucuronide, kynurenic acid, N-methyl-2-pyridone-5-carboxamide (pyridone), and some related compounds. Similar studies have now been carried out with the urinary metabelites of D-, DL-, acetyl-L-, and acetyl-n-tryptophan in man. Ingestion of acetyl-n-tryptophan failed to alter the urinary excretion of the metabolites studied. The total yield of metabolites from acetyl-ntryptophan and n-tryptophan was about 50 per cent less and 50 per cent more, respectively, than the yield of metabolites from a comparable dose of L-tryptophan. The yield of metabolites from 19.6 mmoles of nn-tryptophan was close to that expected from the same amount of the amino acid administered as separate doses of the D and L isomers. This suggested that