Urinary Excretion of Indoxyl Sulfate (Indican) by Human Subjects Ingesting a Semisynthetic Diet Containing Variable Quantities of l-Tryptophan

Abstract

The excretion of indoxyl sulfate by four groups of disease-free human subjects ingesting a semisynthetic diet containing variable quantities of l-tryptophan was measured. As the tryptophan content of the diet was altered, the urinary excretion of indican varied directly. When tryptophan was administered to one of the groups at least 8 hours after the ingestion of the other amino acids, then indoxyl sulfate excretion was not augmented. Over a wide range of dietary tryptophan levels, a constant fraction of about 3 per cent appeared in the urine as indican. As the dietary tryptophan concentration became very low and approached zero, abundant quantities of indican continued to be excreted in the urine. These data suggested that tryptophan derived from gastrointestinal secretions, shed mucosal cells, intestinal bacteria or transported from the serosal to the mucosal side of the intestine provided a significant source of indican.