Placental PGE2 and the Initiation of Parturition in the Sheep

The possibility that prostaglandin E2 (PGE2) has a central action in the fetal lamb arises from studies by Ratter et al. and Robinson. The Prostaglandin E (PGE) release into the fetus may help to preserve fetal growth by decreasing nonessential fetal muscular activity, e.g., fetal breathing movements, thereby sparing glucose. PGE may also maintain a minimum glucose utilization by stimulating insulin release and enhancing pancreatic sensitivity to glucose. PGE2 concentrations in fetal plasma have been shown to increase during late gestation in sheep and this increase parallels the increase in fetal cortisol concentrations. The site of action of PGE2 has also been studied in newborn lambs in which plasma cortisol concentrations increased when PGE2 was infused into the brachiocephalic trunk, but not when infused into the descending aorta. Decreased placental perfusion, caused by placing a clamp on the common iliac artery, results in an increase in fetal cortisol concentrations, which may be secondary to increased fetal PGE2 concentrations.