Absorption of prostaglandin E2 and uterine sensitivity of the non-pregnant and pregnant monkey in vivo

Radioactive (11-³H) prostaglandin E₂(PGE₂) levels in plasma of non-pregnant Rhesus and Japanese monkeys were determined by radioimmunoassay. The amounts of PGE₂ in plasma increased gradually and reached a peak 90 minutes after oral administration. Comparatively low levels were detected 24 hours after oral administration. Plasma PGE₂ levels increased rapidly and disappeared within 5 minutes when 5 μg/kg of PGE₂ was administered intravenously.Uterine contractile sensitivity to PGE₂ and F_2α was measured by the threshold of a venous dosage required to evoke an elevation of uterine contractility in non-pregnant and pre- and post-labor Japanese monkeys. Uterine sensitivity to PGE₂ in the non-pregnant monkey appear to vary in accordance with the sexual life span. At term of pregnancy, PGE₂ was much more potent in causing uterine contraction than PGF_2α. During labor and at postpartum period with lactation, effectiveness of PGE₂ appear to be less than that of PGF_2α. The non-pregnant and pregnant uterus of the third trimester are more sensitive to PGE₂ than the laboring and postpartum uterus.The long latency of the elevation of uterine contractility induced by the intravenous administration of PG suggests that the PG compounds have potent actions on the central nervous system.