Prostaglandin synthase inhibitory activity in the plasma of rhesus monkeys during late pregnancy: effect of dexamethasone.

Plasma from rhesus monkeys during late pregnancy contained a factor(s) that was inhibitory of prostaglandin synthase activity. There was no consistent trend in the inhibitory activity of plasma obtained between 120 days of gestation and term (approximately 167 days of gestation). Administration of dexamethasone (0.125 to 1.0 mg twice daily) consistently increased inhibitory activity in plasma after an initial treatment period of 5-10 days. Administration of dexamethasone for several weeks is associated with prolongation of gestation in rhesus monkeys. We suggest that the action of dexamethasone, to delay parturition is related, in part, to an enhancement of the activity of a circulating factor(s) that is inhibitory of prostaglandin synthase activity.