Some Aspects of Tryptophan Metabolism in Human Subjects

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Abstract
The excretion of 10 tryptophan metabolites was measured in the urine of 4 college women maintained on a semi-synthetic diet containing 2.5 mg of niacin per day and varying in tryptophan content from 25 to 810 mg per day. The excretion of all metabolites was very low when the tryptophan intake was 25 mg per day. After stepwise additions of tryptophan to the diet, N-methyl-2-pyridone-5-carboxamide excretion remained at low levels until blood pyridine nucleotide levels were restored. The excretion of the other tryptophan metabolites more closely followed the tryptophan intake. When given a 2.0 gm loading dose of L-tryptophan these subjects excreted essentially the same amounts of these metabolites as did previous subjects ingesting ordinary foods.