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

Relationships between Pregnancy and Vitamin B-6 Nutriture on Brain 3-Hydroxykynurenine Concentrations in Mice

The kynurenine (KYN) pathway of tryptophan metabolism produces several neuroactive metabolites, including 3-hydroxykynurenine (3HK). The pathway is subject to regulation by a number of effectors including pregnancy and availability of vitamin B-6. Vitamin B-6 depleted humans and animals excrete abnormally high concentrations of KYN metabolites in urine. In pregnancy, vitamin B-6 deficiency is commonly seen, and tryptophan metabolism is often found to be altered. We measured concentrations of 3HK in brains of DBA/2Ibg and A/Ibg mice as functions of pregnancy and dietary level of vitamin B-6. Pregnant DBA mice are more susceptible to flurothyl-induced seizures than controls, pregnant A mice are not. Significant elevations of 3HK were found in brains of pregnant mice, and the increases were greater in the pregnancy-associated seizure prone DBA, than in the A mice. In the A mice, brain 3HK concentrations were negatively correlated with dietary vitamin B-6 levels, as expected; however, in the DBA mice these correlations were positive, indicating an unusual response to vitamin B-6 restriction. The accumulation of a cytotoxic, excitatory metabolite, 3HK, in brain may contribute to the increased seizure susceptibility of susceptible pregnant mice, perhaps though its effects as an endogenous modulator of excitatory amino acid receptor systems.