Prostaglandin production in the umbilical and uterine circulations in pregnant sheep at 129-136 days gestation

Prostaglandins circulating in the maternal and foetal blood have been implicated in important physiological systems. These functions include foetal adrenal function, maintenance of patency of the ductus arteriosus, regulation of uterine and umbilical circulations, and labor and delivery type myometrial contractions. The placenta is a major site of prostaglandin production in pregnancy. Limited data are available which combine measurements of veno-arterial differences across the uterine and umbilical circulations with blood flow in these circulations to enable calculation of umbilical-placental and utero-placental production rates for the prostaglandins. In chronically instrumented pregnant ewes, between 129 and 136 days of gestation, prostaglandin F2(α)(PGF(2α)), 13,14 dihydro-15-keto prostaglandin F(2α) (PGFM), prostaglandin E₂ (PGE₂) were measured in the maternal carotid artery and uterine vein. Foetal PGE₂, and 6-keto-prostaglandin F(1α) (6-keto-PGF(1α)) (the major metabolite of prostacyclin) were measured in umbilical venous and foetal descending aorta arterial plasma. Umbilical and uterine blood flow were measured using the diffusion-equilibrium technique. Uterine blood flow was 1693 ± 137 ml.min^-1 (mean ± SEM); uterine production rates were 480 ± 88 ng.min^-1 for PGF(2α). 517 ± 144 ng.min^-1 for PGFM, and 165 ± 27 ng.min^-1 for PGE₂. Umbilical blood flow was 147 ± 17 ml.min^-1.kg^-1 foetal body weight. Umbilical production rates into the foetal circulation were 11 ± 2 ng.min^-1.kg^-1 for PGE₂ and 6 ± 2 ng. ng.min^-1.kg^-1 foetal body weight for PGI₂.