GLUTAMINE GLUTAMATE EXCHANGE BETWEEN PLACENTA AND FETAL LIVER

The hypothesis that glutamine shuttles nitrogen between placenta and f etal liver via interconversion with glutamate was explored by infusing L-[1,2-C-13(2)]glutamine in six fetal sheep chronically catheterized for sampling of the umbilical and hepatic circulations. Fetal plasma g lutamine disposal rate was 19.9 +/- 1.3 mu mol.min(-1).kg fetus(-1). E ntry of glutamine from the placenta accounted for similar to 60% of th e total glutamine entry rate in fetal plasma. Glutamine was taken up b y fetal liver, and 45.3 +/- 7.9% of the glutamine taken up was release d as glutamate. The fetal liver released large quantities of glutamate , as evidenced by a sixfold increase in plasma glutamate concentration in the blood flowing through the left hepatic lobe and a hepatic glut amate output-to-O-2 uptake molar ratio of 0.149 +/- 0.013. In conjunct ion with a previous study of fetal glutamate metabolism, these data de monstrate that glutamine entering the fetal circulation is converted t o glutamate by the fetal liver at a rate of similar to- 3-4 mu mol.min (-1).kg fetus(-1).