American Journal of Clinical Nutrition, Vol 19, 105-112, Copyright © 1966 by The American Society for Clinical Nutrition, Inc.

Quantitative Studies on the Urinary Excretion of Indoxyl Sulfate (Indican) in Man Following Administration of l-Tryptophan and Acetyl-l-Tryptophan

¹ From the Division of Clinical Oncology, University of Wisconsin Medical School, Madison, Wisconsin

During the first 24 hour period following the oral administration of either indole, acetyl-l-tryptophan or l-tryptophan to human subjects free of disease, and ingesting self-selected diets, there was a statistically significant increase in urinary indoxyl sulfate excretion, as measured by diazotization and coupling. About 53 per cent of the indole, and nearly 3 per cent of orally supplemented acetyl-l-tryptophan or l-tryptophan were accounted for as urinary indican. When l-tryptophan was instilled through a long tube into the distal ileum or cecum, a statistically significant increase in urinary indican was observed during the second 24 hour period following supplementation. About 14 per cent of the tryptophan presented in this manner was accounted for as urinary indican. These data suggest that in man l-tryptophan may be the major precursor of urinary indoxyl sulfate. No explanation for the temporal differences in indican excretion observed after tryptophan was administered orally or instilled into the distal small intestine was apparent.