Fetal membranes inhibit prostaglandin but not oxytocin-induced uterine contractions,

OBJECTIVE: Paracrine signaling in fetal membranes and uterus is hypothesized to play a role in the initiation of labor in women. Numerous fetal membrane signals that stimulate uterine contractions have been described. Recently, by means of the dual-chamber, fetal membrane, uteirne muscle model we showed that fetal membranes inhibit spontaneous uterine 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 mounte dinto the maternal side of a Plexiglas acrylic plastic chamber, Uterino contractions were recorded for 3 hours after the addition of either 50 nmol/L prostaglandin E2 or 0.1 nmol/L oxytocin to the maternal side of the chamber. During the first and third hours no fetal membranes were present (basal condition). At the beginning of the second hour fetal membranes were inserted into the chamber so that they divided the chamber into maternal and fetal compartments. The membranes were removed before the beginning of the third hour. The integrated force of uterine contractions during the second hour, when the muscle was exposed to fetal membranes, was compared with the basal condition (first and third hours) by repeated-measure analysis of variance. RESULTS: Fetal membranes reversibly inhibited prostaglandin E2-induced uterine contractions by 22%. Fetal membranes did not inhibit oxytocin-induced uterine contractions. CONCLUSIONS: Fetal membranes inhibit agonist-induced uterine contractions. The fetal membrane inhibitory system is agonist selective.