title: Endogenous modulation of the blunted adrenergic response in resistance-sized mesenteric arteries from the pregnant rat.
abstract: OBJECTIVE
  We tested the hypothesis that during pregnancy the endothelium mediates the blunted response to adrenergic vasoconstriction.
  
  
  METHODS
  Mesenteric resistance arteries from late pregnant (n = 6) and age-matched virgin control (n = 6) Sprague-Dawley rats were studied in a myograph.
  
  
  RESULTS
  Arteries from pregnant rats were 35% less sensitive to phenylephrine vasoconstriction than were those from nonpregnant rats (mean effective concentration that produced a 50% response 2.26 vs 1.48 mumol/L, pregnant vs nonpregnant, p < 0.01). Meclofenamate had no effect on the vasoconstrictor response in arteries from either group. Inhibition of endothelium-derived relaxing factor with N(o)-nitro-L-arginine methyl ester or endothelial cell removal had a similar twofold increase in phenylephrine sensitivity in arteries from both the pregnant and nonpregnant rats (mean effective concentration that produced a 50% response 2.26 vs 1.11 mumol/L for pregnant rats and 1.48 vs 0.72 mumol/L for nonpregnant rats, p < 0.01). However, methacholine relaxation response was potentiated in pregnant versus nonpregnant rats (mean effective concentration that produced a 50% response 0.030 vs 0.049 mumol/L, p < 0.01).
  
  
  CONCLUSIONS
  Although the potential for endothelium-dependent relaxation is augmented in mesenteric arteries of the pregnant rat, the decreased sensitivity to phenylephrine during pregnancy is not modulated acutely by endothelium-derived relaxing factor or by prostaglandin products of the cyclooxygenase pathway.
authors: Department of Pediatrics, University of Cincinnati College of Medicine, OH.
authors: S T
authors: ST
authors: Davidge
authors: M K
authors: MK
authors: McLaughlin
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D005260:Female; D008469:Meclofenamic Acid / Q000494:pharmacology; D008638:Mesenteric Arteries / Q000502:physiology*; D016210:Methacholine Chloride / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000037:antagonists & inhibitors; D010656:Phenylephrine / Q000494:pharmacology; D010865:Pilot Projects; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D016210:Methacholine Chloride; D010656:Phenylephrine; D009569:Nitric Oxide; D008469:Meclofenamic Acid; D001120:Arginine; D019331:NG-Nitroarginine Methyl Ester