The effect of the nutritional state on uterine prostaglandin F metabolite concentrations in the pregnant ewe during late gestation.

The effects of nutritional state and nutrient availability on arterial and uterine venous concentrations of 13, 14 dihydro-15-ketoprostaglandin F2 alpha (PGFM) have been investigated in chronically catheterized pregnant ewes during late gestation (120-144 d; term = 147 d). Before the daily feed of concentrates was given, a significant positive venous-arterial (V-A) difference in plasma PGFM concentration was observed across the uterus, irrespective of the number of fetuses or the gestational age (mean value at 135 +/- 2 d: 0.42 +/- 0.06 ng/ml, n = 13, P less than 0.01). However, by 3-5 h after feeding, no significant difference in PGFM concentration could be detected across the uterus. Withdrawal of food but not water for 48 h increased the plasma PGFM levels and widened the V-A difference in PGFM concentration across the uterus at all gestational ages studied but had the greatest effect in late gestation (greater than 137 d). These changes in plasma PGFM were accompanied by a fall in glucose and a rise in free fatty acid (FFA) concentration in the arterial plasma. When these metabolite changes were reversed at the end of the fast either by refeeding or by glucose infusion, there was a rapid fall in PGFM concentration and a narrowing of the uterine V-A difference. Induction of hypoglycaemia by infusion of insulin also led to a widening of the V-A difference in PGFM concentration across the uterus. There was a significant inverse correlation between the arterial plasma glucose level and the V-A difference in PGFM concentration across the uterus during feeding, fasting and insulin infusion. The V-A difference in PGFM concentration was also positively correlated with the arterial plasma FFA level under these conditions. When arterial plasma concentrations of PGFM rose above 3 ng/ml, during fasting or insulin induced hypoglycaemia, the ewes lambed within 12-24 h of restoring the metabolite concentrations. These observations indicate that the output of PGFM by the uterus is controlled in some way by the availability of nutrients and emphasize the importance of a regular food intake during late gestation in the ewes.