THE NUTRITIONAL REGULATION OF CIRCULATING PLACENTAL-LACTOGEN IN FETAL SHEEP

Maternal and fetal plasma ovine placental lactogen (oPL), insulin, and IGF-I levels were measured in response to the starvation and refeeding of pregnant sheep on two defined planes of nutrition. Chronically catheterized pregnant ewes were placed on either a high plane (n = 5) or low plane (n = 5) of nutrition at least 1 wk before the experiment. At 125 to 135 d gestation, the ewes were starved for 72 h and then an i.v. infusion of 10% glucose was administered over 4 h, followed by refeeding at the designated nutritional plane. Plasma oPL levels of fetuses whose mothers had been on a high plane of nutrition were significantly higher during starvation (p < 0.05) than those of fetuses whose mothers had been on a low plane (high + 0.54 +/- 0.17 and low -0.02 +/- 0.17 nmol/L from mean control levels). Intravenous glucose infusion to the ewes at the end of starvation caused a marked rise in fetal plasma oPL levels in both groups (increments of 2.61 +/- 1.4 nmol/L in the high group and 2.81 +/- 1.16 nmol/L in the low group). Maternal oPL levels did not differ significantly between the two nutritional groups during starvation and did not change during glucose infusion. Fetal and maternal plasma IGF-I levels both fell during starvation. Maternal IGF-I levels fell faster in the high group (-17.9 +/- 4.5 at 24 h versus -4.7 +/- 7.2 nmol/L in the low group), but the groups were not different at the end of starvation. There were significant differences (p < 0.05) in maternal and fetal plasma insulin levels between the two groups during starvation. The fall in maternal and fetal plasma insulin was greater in the high group (fetal -0.13 +/- 0.06 and maternal -0.25 +/- 0.13 nmol/L) versus the low group (fetal -0.01 +/- 0.01 and maternal -0.02 +/- 0.08 nmol/L). These observations demonstrate that preexisting maternal nutritional status affects oPL responses to acute starvation and that oPL may have a role in metabolite partitioning between mother and fetus.