Role of tryptophan metabolites in the hypoglycemia associated with neoplasia

Three patients who had hypoglycemia associated with neoplasia were studied. In one, total tryptophan and protein-free metabolites of tryptophan in blood and tryptophan metabolites in urine were increased during hypoglycemia. In another, total tryptophan and protein-free tryptophan metabolites in serum were increased markedly and tryptophan metabolites in urine were increased mostly during hypoglycemia; during normoglycemia, however, concentration of both total tryptophan and protein-free tryptophan metabolites in serum and of protein-free tryptophan metabolites in urine was mostly normal. In the third, during normoglycemia, concentrations of total tryptophan and protein-free tryptophan metabolites in serum and of protein-free tryptophan metabolites in urine were normal or nearly so. Thus, patients with hypoglycemia associated with neoplasia seemingly have increased concentrations of tryptophan and tryptophan metabolites in serum and urine during hypoglycemic periods. Intraperitoneal administration of indole-3-propionic acid, indole-3-butyric acid, and indole-3-aretic acid caused profound hypoglycemia in normal and alloxandiabetic mice while L-tryptophan and kynurenic acid had no effect.