Placental lactogen receptors in maternal sheep liver: effects of fasting and refeeding

In a recent study we demonstrated that fasting of the pregnant ewe reduces the number of placental lactogen (PL) receptors in fetal sheep liver. In the present study we examined the effects of a 72-h fast on the number and affinity of PL receptors in maternal sheep liver. Fasting caused a 57% reduction in the number of hepatic ovine PL receptors; this effect was reversed by refeeding. There were no changes in the affinity of the PL receptor, the subunit structure of the receptor, or the extent of occupancy of the receptor by endogenous circulating maternal hormones. The number of hepatic PL receptors was correlated positively with the maternal plasma concentrations of glucose and insulin, suggesting that these factors may regulate PL binding to maternal tissues during pregnancy. In addition, PL receptor number was correlated positively with maternal plasma insulin-like growth factor I (IGF-I) concentrations, suggesting that a reduction in hepatic ovine PL binding may contribute to the reduction in maternal IGF-I during fasting. Fasting produced a 72% reduction in the number of ovine growth hormone receptors in maternal liver and an 83% increase in hepatic insulin binding. These findings indicate that fasting of the pregnant ewe reduces the number of PL receptors in maternal and fetal liver. The reduction in PL binding may contribute to maternal and fetal hyposomatomedinemia and may play a role in the pathogenesis of the intrauterine growth retardation that accompanies maternal nutritional deprivation.