title: Endothelin-1 potentiates the in vitro contractile response of pregnant human myometrium to oxytocin.
abstract: OBJECTIVE
  This study was designed to test the hypothesis that endothelin-1 pretreatment of human myometrium at subcontractile doses in vitro will enhance the contractile response to oxytocin.
  
  
  METHODS
  In vitro contractile oxytocin dose-response curves were generated by use of myometrial strips collected from nonpregnant women (n = 7), pregnant patients at elective cesarean section (n = 7), and patients in active labor (n = 7) in the presence or absence of 10(-9) mol/L endothelin-1. Contractile responses were analyzed by on-line computer, and data were normalized to the maximum response to potassium.
  
  
  RESULTS
  Pretreatment with endothelin-1 significantly increased the maximal contractile response of pregnant myometrium (p < 0.01 compared with control). In marked contrast myometrium from nonpregnant patients was unaffected by endothelin-1 pretreatment. Values for the two-point discrimination and Hill coefficient were not different among the treatment groups.
  
  
  CONCLUSIONS
  Endothelin-1 potentiates the oxytocin response of myometrium from pregnant but not nonpregnant women. We speculate that a high circulating level of a uterotonin-like oxytocin may not be necessary to initiate labor. The synergistic interaction between different uterotonins may be sufficient.
authors.affiliation: Department of Obstetrics and Gynecology, San Bernardino County Medical Center, CA 92415-0935, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Valenzuela
authors.forename: C W
authors.initials: CW
authors.lastname: Hewitt
authors.forename: C A
authors.initials: CA
authors.lastname: Ducsay
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D016232:Endothelins / Q000494:pharmacology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D009215:Myometrium / Q000187:drug effects* / Q000502:physiology; D010121:Oxytocin / Q000494:pharmacology*; D011247:Pregnancy / Q000502:physiology*; D014590:Uterine Contraction / Q000187:drug effects*
chemical_list: D016232:Endothelins; D010121:Oxytocin