THE EFFECT OF VITAMIN SUPPLEMENTATION ON THE URINARY EXCRETION OF TRYPTOPHAN METABOLITES BY PREGNANT WOMEN*

Abstract

The effect of an oral dose of 2.0 g of L-tryptophan on the excretion of kynurenine (KYN), kynurenic acid (KA), acetylkynurenine, hydroxykynurenine (HK), xanthurenic acid (XA), o-aminohippuric acid and N-methyl-2-pyridone-5-carboxamide (PYR) was measured quantitatively in the urine of nonpregnant women, pregnant women without and with vitamin supplementation, and in the same subjects postpartum. During pregnancy, excretion of KA was unchanged or decreased even though large amounts of KYN, HK, and XA were excreted. PYR was also excreted in larger amounts by pregnant subjects suggesting increased efficiency of niacin synthesis from tryptophan during pregnancy. PYR excretion remained high even after pyridoxine supplementation had significantly lowered the excretion of XA, HK and KYN. Administration of vitamins other than pyridoxine had no detectable effect on excretion of metabolites. Subjects studied at various intervals postpartum still excreted slightly elevated levels of several metabolites, suggesting that their metabolism had not completely returned to normal. Normal nonpregnant women when tested just before or just after menstruation, or during ovulation, had normal urinary levels of tryptophan metabolites, with the exception of HK which was significantly decreased after menstruation. The urinary excretion patterns of metabolites suggested a vitamin B6 deficiency in pregnancy, but the patterns were modifed probably by the normal hormonal changes associated with pregnancy.