Antagonism by growth hormone of insulin action in fetal sheep

Insulin, glucose, lactate and alpha-amino acid nitrogen concentrations were measured in the plasma of ewes and their hypophysectomized fetal lambs during intravenous infusions of GH, prolactin or saline into the fetus in utero. Prolactin and saline had no effect on mother or fetus. Infusion of GH at 1.2 mg/kg per day for 2 days or at 0.4 mg/kg per day for 4 days caused a sustained twofold increae in the level of insulin and a smaller, but sustained, increase in the level of glucose in fetal plasma. We suggest that GH antagonizes the action of insulin in the fetus. Glucose supplies to the fetal brain and placenta may be protected by such antagonism of insulin use during glucose shortage.