Production of Xanthurenic Acid From Tryptophan in Pregnancy and in Various States of Nitrogen Balance

¹ From the Atlantic Regional Laboratory, National Research Council, Halifax, Nova Scotia, Canada

Production of xanthurenic acid from tryptophan was studied in pregnant women, in pregnant rats and in rats in vitamin B₆ deficiency and various states of nitrogen balance. Of eight women well advanced in pregnancy only one excreted excessive xanthurenic acid after a test dose of tryptophan, and this pregnancy was complicated by disease. The excessive excretion in this case was reduced by dosage with pyridoxin. Rats late in pregnancy and early in the post-partum period typically excreted abnormally large amounts of xanthurenic acid after test doses of tryptophan. The administration of extra vitamin B₆ or of other B vitamins had no effect. After the same level of dosage with tryptophan the excretion of xanthurenic acid by rats well advanced in vitamin B₆ deficiency was much higher than that by pregnant rats. No conclusive evidence was obtained that the production of xanthurenic acid from tryptophan is associated with the state of nitrogen balance as influenced by pregnancy, vitamin B₆ deficiency, or the intake of protein. Some of the experimental results suggested, however, that outside of vitamin B₆ deficiency it tends to be high when the retention of nitrogen is high.