Maternal-fetal relationship in ammonia metabolism during late gestation in the rat.

The concentrations of the major metabolites for nitrogen excretion and/or transport in maternal and fetal blood and amniotic fluid during the last 2 days of gestation were investigated. Alanine, glutamine, ammonia and allantoin accumulated in amniotic fluid during late gestation. Urea concentrations increased in amniotic fluid though only during the last day of gestation, suggesting that urea is taken up by the mother through the amniotic membranes. Glutamate did not accumulate in amniotic fluid during late gestation although high concentrations of it were found in fetal blood in the same circumstances, suggesting the occurrence of a mechanism for preventing fetal glutamate disposal.