FETAL MEMBRANES INHIBIT PROSTAGLANDIN BUT NOT OXYTOCIN-INDUCED UTERINE CONTRACTIONS

OBJECTIVE: Paracrine signaling in fetal membranes and uterus is hypoth esized to play a role in the initiation of labor in women. Numerous fe tal membrane signals that stimulate uterine contractions have been des cribed. Recently, by means of the dual-chamber, fetal membrane, uterin e muscle model we showed that fetal membranes inhibit spontaneous uter ine contractions. This study was designed to test whether human fetal membranes can also inhibit agonist-induced uterine contractions. STUDY DESIGN: A rat uterine muscle strip was mounted into the maternal side of a Plexiglas acrylic plastic chamber. Uterine contractions were rec orded for 3 hours after the addition of either 50 nmol/L prostaglandin E(2) or 0.1 nmol/L oxytocin to the maternal side of the chamber. Duri ng the first and third hours no fetal membranes were present (basal co ndition). At the beginning of the second hour fetal membranes were ins erted into the chamber so that they divided the chamber into maternal and fetal compartments. The membranes were removed before the beginnin g of the third hour. The integrated force of uterine contractions duri ng the second hour, when the muscle was exposed to fetal membranes, wa s compared with the basal condition (first and third hours) by repeate d-measure analysis of variance. RESULTS: Fetal membranes reversibly in hibited prostaglandin E(2)-induced uterine contractions by 22%. Fetal membranes did not inhibit oxytocin-induced uterine contractions. CONCL USION: Fetal membranes inhibit agonist-induced uterine contractions. T he fetal membrane inhibitory system is agonist selective.