METABOLIC ALTERATIONS IN THE FETAL HEPATIC AND UMBILICAL CIRCULATIONSDURING GLUCOCORTICOID-INDUCED PARTURITION IN SHEEP

Fetal hepatic amino acid metabolism has unique features in comparison to postnatal life. Thus, it seemed likely that this metabolism might b e changed by the endocrine changes which precede birth. To explore the changes in placental and fetal carbohydrate and amino acid metabolism that occur during parturition, labor was induced in six ewes at 131 /- 1 d gestation with a fetal infusion of dexamethasone. For purpose o f chemical analysis, blood was withdrawn before and approximately 3 an d 25 h from the start of the infusion from maternal arterial, uterine venous, umbilical venous, fetal arterial, and left hepatic venous cath eters. Fetal oxygenation remained normal. At 25 h, both fetal and mate rnal arterial plasma glucose concentrations increased (p < 0.01 and p < 0.02, respectively) and umbilical glucose uptake decreased (p < 0.05 ). Fetal glutamate showed a significant reduction in its hepatic outpu t (p < 0.05) with a concomitant reduction in fetal arterial plasma con centration (p < 0.05) and placental uptake (p < 0.01). Fetal plasma co ncentrations of several other amino acids were markedly increased. The reduction in placental glutamate uptake was temporally associated wit h a decline in progesterone release by the pregnant uterus. These data suggest the hypothesis that glutamate plays a role in integrating the complex changes in placental and fetal hepatic metabolism that occur during parturition.