title: Does sildenafil citrate affect myometrial contractile response to nifedipine in vitro?
abstract: OBJECTIVE
  We sought to test the hypothesis that sildenafil citrate (SC) at low concentrations potentiates the tocolytic effects of nifedipine in vitro.
  
  
  METHODS
  Myometrial biopsies were obtained from 22 term nonlaboring women undergoing scheduled cesarean delivery. Tissue strips were suspended in organ chambers for isometric tension recording, and incubated for 30 minutes with either SC at 231 ng/mL or solvent. The effects of cumulative doses (10(-10) to 10(-5) mol/L) of nifedipine on spontaneous and oxytocin-induced uterine contractility were then determined. Areas under the contraction curve were compared using 1-way analysis of variance with Tukey post hoc test (significance: P < .05).
  
  
  RESULTS
  Nifedipine significantly inhibited spontaneous and oxytocin-induced myometrial contractility. Preincubation with SC increased response to nifedipine and significantly potentiated its inhibitory effect at 10(-8) mol/L, without affecting oxytocin-induced contractile response.
  
  
  CONCLUSIONS
  At concentrations within a therapeutic window, SC increases myometrial sensitivity to nifedipine.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, TX, USA. gichioss@utmb.edu
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Chiossi
authors.forename: Maged M
authors.initials: MM
authors.lastname: Costantine
authors.forename: Ancizar
authors.initials: A
authors.lastname: Betancourt
authors.forename: Gary D V
authors.initials: GD
authors.lastname: Hankins
authors.forename: Monica
authors.initials: M
authors.lastname: Longo
authors.forename: George R
authors.initials: GR
authors.lastname: Saade
authors.forename: Egle
authors.initials: E
authors.lastname: Bytautiene
mesh_terms: D000328:Adult; D001706:Biopsy; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D009215:Myometrium / Q000187:drug effects / Q000473:pathology; D009543:Nifedipine / Q000494:pharmacology*; D010120:Oxytocics / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology*; D011247:Pregnancy; D011687:Purines / Q000494:pharmacology; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology*; D014590:Uterine Contraction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D002121:Calcium Channel Blockers; D010120:Oxytocics; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D010121:Oxytocin; D000068677:Sildenafil Citrate; D009543:Nifedipine