title: Modulation of vascular tone by nitric oxide and endothelin 1 in myometrial resistance arteries from pregnant women at term.
abstract: OBJECTIVE
  We evaluated the role of endothelium-derived nitric oxide and endothelin 1 in the modulation of myogenic tone, norepinephrine-induced tone, and flow-mediated responses in resistance arteries from pregnant women at term.
  
  
  METHODS
  Arteries (approximately 200 microm at 50 mm Hg; n = 27) were dissected from myometrial biopsies obtained from women undergoing elective cesarean delivery at term and mounted in a pressure arteriograph. Responses to intraluminal flow, pressure, and norepinephrine were studied in the absence and presence of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine and the endothelin-converting enzyme inhibitor phosphoramidon.
  
  
  RESULTS
  Pressure-induced (80 mm Hg) myogenic tone was significantly enhanced after incubation with Nomega-nitro-L-arginine (33% +/- 8% vs 24% +/- 4%; P <.05), whereas phosphoramidon significantly reduced myogenic tone (24% +/- 5% vs 33% +/- 5%; P <.05). A combination of Nomega-nitro-L -arginine and phosphoramidon did not affect myogenic tone. Norepinephrine-induced tone was significantly enhanced after nitric oxide synthase inhibition (49% +/- 6% vs 41% +/- 5%; P <.05) but was not affected by phosphoramidon. Flow-mediated dilatation was increased in the presence of phosphoramidon compared with flow-induced dilatation in physiologic salt solution (maximum dilatation, 57% +/- 12% vs 30% +/- 5%; analysis of variance, P <.05), and all flow-induced dilatation was abolished by Nomega-nitro-L -arginine.
  
  
  CONCLUSIONS
  Nitric oxide and endothelin 1 may play a significant role in modulation of myogenic tone and flow-mediated responses in the resistance vasculature of the uterine circulation in normal pregnancy.
authors.affiliation: Department of Obstetrics and Gynecology, Karolinska Institute, Huddinge University Hospital, Sweden.
authors.forename: K R
authors.initials: KR
authors.lastname: Kublickiene
authors.forename: H
authors.initials: H
authors.lastname: Nisell
authors.forename: L
authors.initials: L
authors.lastname: Poston
authors.forename: K
authors.initials: K
authors.lastname: Krüger
authors.forename: B
authors.initials: B
authors.lastname: Lindblom
mesh_terms: D001158:Arteries / Q000187:drug effects* / Q000502:physiology; D001783:Blood Flow Velocity; D002585:Cesarean Section; D019332:Endothelin-1 / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D018056:Hemorheology; D006801:Humans; D066298:In Vitro Techniques; D009215:Myometrium / Q000098:blood supply*; D009569:Nitric Oxide / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D011247:Pregnancy; D011312:Pressure; D015203:Reproducibility of Results; D014655:Vascular Resistance; D014664:Vasodilation
chemical_list: D019332:Endothelin-1; D004791:Enzyme Inhibitors; D019335:Nitroarginine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D009638:Norepinephrine