Modulation of Bovine Placental Prostaglandin Synthesis by an Endogenous Inhibitor*

Abstract

An endogenous, heat-labile, inhibitor of prostanoid synthesis in maternal caruncle tissue of bovine placentomes was studied. Inhibitory activity was present in caruncle extracts from days 120-250 of gestation, but was not detectable at term (260-280 days). The disappearance of inhibitory activity coincided with an increase in the secretion of prostanoids by dispersed caruncle cells in culture. Coculture of caruncle cells from placentomes of 120-day gestation with fetal cotyledon cells resulted in suppression of prostanoid synthesis by the cotyledon cells. However, this inhibition was not observed in cocultures of dispersed caruncle cells and fetal cotyledon cells from term placentomes. Our findings indicate that an endogenous inhibitor modulates bovine placental prostaglandin synthesis. A decline in the level of this inhibitor at term may be one factor triggering increased prostanoid synthesis required for parturition.