Placental vascular responses to 6-keto-prostaglandin E₁ in the near-term sheep

6-Keto-prostaglandin E₁ (6-keto-PGE₁) is a biologically active, stable metabolite of prostaglandin I₂ (PGI₂). It has vasoactive properties similar to those of PGI₂ and it has been shown to decrease the resistance of the renal, mesenteric, and pulmonary vascular beds. PGI₂ is synthesized by the pregnant uterus and is vasoactive in the ovine placenta. The effects of 6-keto-PGE₁ on uterine and placental blood flow in pregnant ewes were determined for comparison with those of PGI₂. Near-term ewes and their fetuses were chronically catheterized to permit the measurement of regional blood flow by the radioactive microsphere method. In six sheep a 5-minute maternal jugular infusion of 3.25 μg/kg/min of 6-keto-PGE₁ decreased mean arterial blood pressure from 89 ± 4.8 to 63 ± 7.1 mm Hg. Uterine vascular resistance decreased from 0.55 ± 0.11 to 0.35 ± 0.05 peripheral resistance units (PRU), but maternal cotyledonary resistance increased from 0.19 ± 0.04 to 0.27 ± 0.03 PRU. In five sheep a fetal intravenous infusion of 18 μg/min of 6-keto-PGE₁ decreased mean fetal blood pressure from 43 ± 2 to 29 ± 2 mm Hg. Cotyledonary vascular resistance increased from 0.30 ± 0.02 to 0.55 ± 0.09 PRU · kg^-1. In these sheep there were no significant changes in maternal uterine, renal, or cotyledonary blood flows. These results indicate that 6-keto-PGE₁ is similar to PGI₂ in that it produces maternal cotyledonary vasoconstriction, hypotension, and vasodilation in other organs.