AJP - Endocrinology and Metabolism, Vol 258, Issue 2 E338-E346, Copyright © 1990 by American Physiological Society
Placental lactogen receptors in maternal sheep liver: effects of fasting and refeeding
M. Freemark, M. Comer, T. Mularoni, A. J. D'Ercole, A. Grandis and L. Kodack
Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710.
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.
