Induction of cytosolic phosphoenolpyruvate carboxykinase in the ovine fetal liver by chronic fetal hypoglycemia and hypoinsulinemia.

Abstract

Fetal glucose production has been observed in the chronically hypoglycemic, hypoinsulinemic (HH) fetal lamb. The purpose of this study was to test the hypothesis that induction of hepatic gluconeogenic enzymes occurs in this condition. The activities of both mitochondrial and cytosolic phosphoenolpyruvate carboxykinase (PEPCK), fructose-1,6-diphosphatase, and glucose-6-phosphatase, three key enzymes of gluconeogenesis, were determined in fetal sheep liver from HH lambs and controls (CONT). Pregnant ewes were maintained chronically hypoglycemic by continuous hyperinsulinemic clamps from approximately 80 d of gestational age (53% of gestation) for 6 wk. Fetuses (gestational age: HH = 136 +/- 2.6, CONT = 133 +/- 3.7 d) were maintained chronically hypoglycemic [HH = 0.51 +/- 0.05 versus CONT = 1.22 +/- 0.11 mmol/L (9.2 +/- 1.0 versus 21.9 +/- 11.9 mg/dL)] and hypoinsulinemic (HH = 3.3 +/- 0.6 versus CONT = 12.0 +/- 2.2 microU/mL) and delivered by cesarean section after measurement of fetal glucose production rate. Hepatic cytosolic PEPCK was 6.0 +/- 1.4 nmol/min/mg protein in CONT and 19.7 +/- 2.5 in HH lamb (p < 0.05), whereas mitochondrial PEPCK was not different between the two groups. Neither fructose-1,6-diphosphatase or glucose-6-phosphatase activities nor plasma glucagon levels were different between groups. These results suggest that chronic fetal hypoglycemia and hypoinsulinemia prematurely induce hepatic cytosolic PEPCK in the fetal lamb. The observed fetal glucose production in the HH fetal lamb may be due to gluconeogenesis.