title: Human fetal membranes inhibit calcium L-channel activated uterine contractions.
abstract: OBJECTIVE
  Paracrine signals among fetal membranes, decidua, and uterus play an important role in the initiation of parturition in women. In previous work we demonstrated that fetal membranes inhibit uterine contractions. In the current study we test the hypothesis that the fetal membranes decrease uterine contractions by inhibition of the uterine calcium L-channel.
  
  
  METHODS
  Our dual-chamber fetal membrane-uterine muscle in vitro model was used in this study. Rat uterine muscle strips were anchored into the maternal sides of the chambers. Fetal membranes (or Parafilm controls) were added to the chamber in a removable cassette. Uterine contractions were stimulated with the specific calcium L-channel agonist Bay K 8644.
  
  
  RESULTS
  When uterine muscle was exposed to full-thickness fetal membranes (amnion-chorion with attached decidua) or to the intact fetal components (chorion-amnion) or to chorion alone, the Bay K 8644 dose-response curve was significantly shifted to the right. When uterine muscle was exposed to amnion alone or to the decidua alone, the Bay K 8644 dose-response curve was not shifted. Fetal membranes, did not cause a shift in the ionomycin (a calcium ionophore) dose-response curve.
  
  
  CONCLUSIONS
  These results support the hypothesis and provide evidence that human fetal membranes, most likely chorion, release an endogenous calcium L-channel inhibitor.
authors.affiliation: Department of Obstetrics and Gynecology, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Collins
authors.forename: J J
authors.initials: JJ
authors.lastname: Moore
authors.forename: E
authors.initials: E
authors.lastname: Idriss
authors.forename: T M
authors.initials: TM
authors.lastname: Kulp
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D002823:Chorion / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005321:Extraembryonic Membranes / Q000502:physiology*; D005260:Female; D006801:Humans; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D014590:Uterine Contraction
chemical_list: D015220:Calcium Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester