Effects of pregnancy and endothelial cell removal on alpha-adrenoceptor-mediated responses of rat thoracic aortae.
1. The possibility was examined that changes in sensitivity of the aorta to alpha-adrenoceptor agonists during pregnancy in the rat are due to changes in smooth muscle receptor-mediated responses and/or endothelial cell-mediated responses. 2. Maximum constrictor responses to phenylephrine (PE) of both endothelium-intact and denuded thoracic aortic rings were greater when tissues were obtained from 20-day pregnant rats compared with non-pregnant ones. For endothelium-denuded thoracic aortic rings, the pA2 value for phentolamine as an antagonist of PE was not significantly different for rings from 20-day pregnant rats compared with rings from non-pregnant rats. 3. Prazosin (1-50 nM) markedly depressed maximum contractile responses to PE of endothelium-intact (but not denuded) thoracic aortic rings from both non-pregnant and 20-day pregnant rats. However, this marked depression of maximum responses by prazosin did not occur in the additional presence of yohimbine (10 nM), and yohimbine alone (10-500 mM) did not affect maximum responses to PE. There was no significant difference between the pA2 value for prazosin against PE-induced contractions of endothelium-denuded aortic rings obtained from either non-pregnant or 20-day pregnant rats (in the presence of yohimbine, 10 nM). 4. These results provide no evidence for a change in aortic smooth muscle alpha-adrenoceptor affinity during pregnancy, although maximum responsiveness of aortic smooth muscle to PE is increased on day 20 of pregnancy (c.f. non-pregnant controls).
Jansakul
C
C
Department of Pharmacology, Monash University, Clayton, Victoria, Australia.
King
R G
RG
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D005260:Female; D066298:In Vitro Techniques; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*
D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D010646:Phentolamine