HUMAN FETAL MEMBRANES INHIBIT CALCIUM L-CHANNEL ACTIVATED UTERINE CONTRACTIONS

OBJECTIVE: Paracrine signals among fetal membranes, decidua, and uteru s play an important role in the initiation of parturition in women. In previous work we demonstrated that fetal membranes inhibit uterine co ntractions. In the current study we test the hypothesis that the fetal membranes decrease uterine contractions by inhibition of the uterine calcium L-channel. STUDY DESIGN: Our dual-chamber fetal membrane-uteri ne muscle in vitro model was used in this study. Rat uterine muscle st rips were anchored into the maternal sides of the chambers. Fetal memb ranes (or Parafilm controls) were added to the chamber in a removable cassette. Uterine contractions were stimulated with the specific calci um L-channel agonist Bay K 8644. RESULTS: When uterine muscle was expo sed to full-thickness fetal membranes (amnion-chorion with attached de cidua) or to the intact fetal components (chorion-amnion) or to chorio n alone, the Bay K 8644 dose-response curve was significantly shifted to the right. When uterine muscle was exposed to amnion alone or to th e decidua alone, the Bay K 8644 dose-response curve was not shifted. F etal membranes, did not cause a shift in the ionomycin (a calcium iono phore) dose-response curve. CONCLUSION: These results support the hypo thesis and provide evidence that human fetal membranes, most likely ch orion, release an endogenous calcium L-channel inhibitor.