Relationships between pregnancy and vitamin B-6 nutriture on hepatic tryptophan 2,3-dioxygenase activity in mice

Abstract

The kynurenine pathway is responsible for the majority of tryptophan metabolism. Pregnant women have an abnormal distribution of tryptophan metabolites, which is suggestive of an alteration in the kynurenine pathway. The first, and rate limiting enzyme, tryptophan 2,3-dioxygenase (TDO) is stimulated by estrogens and adrenal cortical hormones, and it has been suggested that TDO activity is increased in pregnancy as a result of hormonal stimulation. We measured TDO activity in control and pregnant A and DBA mice fed diets containing 0.5, 2.0 or 7.0 mg pyridoxine-HCl (PN-HCl). We found a significant effect of dietary level of vitamin B-6 on TDO activity that was more pronounced in the A mice. There was no effect of pregnancy on TDO activity in either strain of mouse at any dietary level of PN-HCl.