The nutritional regulation of plasma prostaglandin E concentrations in the fetus and pregnant ewe during late gestation.

1. The effects of nutrient availability on the plasma concentrations of prostaglandin E (PGE) were investigated in chronically catheterized ewes and their fetuses during late gestation by varying dietary intake and by experimental manipulation of the fetal plasma concentration of glucose. The aim of the study was to determine whether varying the glucose level altered the fetal and maternal concentrations of plasma PGE. 2. Basal plasma concentrations of PGE increased with increasing gestational age in both the fetus and ewe. Fetal plasma concentrations of PGE were positively correlated with the corresponding uterine venous concentrations throughout the period of study. There was also a significant venous--arterial difference in plasma PGE concentration across the uterus at all gestational ages studied. 3. Withdrawal of food but not water for 48 h increased the plasma PGE concentration in all the fetuses studied irrespective of gestational age. In the pregnant ewe, the effects of fasting depended on gestational age. Before 130 days, fasting only increased the uterine venous concentration of plasma PGE, while after 130 days there were significant increases in both maternal arterial and uterine venous concentrations of plasma PGE. There was also a significant widening of the uterine venous--arterial difference in plasma PGE concentration during fasts begun after 130 days of gestation. Refeeding the fasted animals restored the plasma PGE levels to normal values within 24 h in both the fetus and ewe. 4. The normal daily feeding regime had no apparent effect on plasma PGE concentrations before 130 days of gestation. However, in animals nearer to term, there were significant reductions in plasma PGE in the fetus and uterine vein in the 3-6 h period after feeding. 5. The changes in plasma PGE levels during fasting and in response to the normal daily feeding regime were correlated to the changes in plasma glucose level observed in the fetus. The slope of the line relating the changes in the fetal concentrations of plasma PGE and glucose was significantly steeper in animals older than 130 days than earlier in gestation. 6. Fetal hypoglycaemia induced by fetal infusion of insulin increased fetal concentrations of plasma PGE without any apparent change in maternal plasma PGE values. In contrast, fetal hyperglycaemia produced by infusion of glucose into the fetus had little effect on plasma PGE levels in utero. 7. The results demonstrate that nutrient availability can influence uterine output and plasma concentrations of PGE in the fetus and pregnant ewe.(ABSTRACT TRUNCATED AT 400 WORDS)