The effect of vitamin supplementation on the urinary excretion of tryptophan metabolites by pregnant women

and Haagen-Smit (1) of the occurrence of xan-thurenic acid in urine of vitamin B6-deficient rats has since been extended and confirmed in a num-ber of species (2-4) including man (5, 6), and the measurement of xanthurenic acid in urine fol-lowing a loading dose of tryptophan has been pro-posed as an index of vitamin B6 nutrition (7). The role of this vitamin in tryptophan metabolism has been studied in intact rats by Dalgliesh (8), and enzyme studies by a number of investigators (9-12) provide a reasonable explanation for the elevated excretion of tryptophan metabolites found in the urine of pvridoxine-deficient animals. Although xanthurenic acid sometimes occurs in elevated amounts in urine, it is not an abnormal tryptophan metabolite. since it can be detected in normal human urine (13). The observations that pregnant women ex-crete elevated amounts of xanthurenic acid (14-16) and other metabolites of tryptophan (17) have been interpreted as signifying a vitamin B6 deficiency in pregnancy, inasmuch as supplemen-tation of the diet with pyridoxine restored the excretion of xanthurenic acid to control levels. Xanthurenic acid excretion was not elevated in pregnant swine (18). rats, guinea pigs, rabbits or dogs (19). However, dietary pyridoxine de-ficiency caused elevated xanthurenic acid excre-tion in most of these species. It has been reported that pre-eclamptic and eclamptic patients excreted more xanthurenic acid than normal pregnant or nonpregnant women (14). However, since there are differing re