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Dual effect of clonidine on mesenteric artery adrenoceptors: agonistic (alpha-2) and antagonistic (alpha-1).
Silva, E G; Feres, T; Vianna, L M; Okuyama, P; Paiva, T B.
Afiliação
  • Silva EG; Department of Biophysics, Escola Paulista de Medicina 04023-062, São Paulo, Brazil.
J Pharmacol Exp Ther ; 277(2): 872-6, 1996 May.
Article em En | MEDLINE | ID: mdl-8627569
The effect of clonidine on the mesenteric vascular bed and the isolated mesenteric artery was examined in preparations in which tonus was induced by norepinephrine or endothelin. In preparations precontracted by norepinephrine, clonidine caused a relaxation which was not inhibited by the alpha-2 antagonists yohimbine and idazoxan or by the K+ channel blockers apamine, tetraethylammonium and glibenclamide. In preparations precontracted with endothelin, clonidine increased the depolarization and induced a contraction. Both these effects were inhibited by prazosin. In isolated mesenteric arteries, norepinephrine cause a significant depolarization that was inhibited by clonidine or prazosin. On the other hand, clonidine caused a hyperpolarization which was inhibited by idazoxan or yohimbine, but not by prazosin. This hyperpolarization was also abolished by apamine, tetraethylammonium and glibenclamide. It is concluded that clonidine acts on alpha-1 adrenoceptors as a partial agonist, causing relaxation of the mesenteric artery precontracted with norepinephrine or contraction of preparations precontracted with endothelin. Moreover, clonidine can open K+ channels and hyperpolarize the plasma membrane of mesenteric artery by acting on alpha-2 adrenoceptors.
Assuntos
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Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Clonidina / Agonistas alfa-Adrenérgicos / Antagonistas Adrenérgicos alfa / Agonistas de Receptores Adrenérgicos alfa 2 / Antagonistas de Receptores Adrenérgicos alfa 1 / Artérias Mesentéricas Limite: Animals Idioma: En Revista: J Pharmacol Exp Ther Ano de publicação: 1996 Tipo de documento: Article País de afiliação: Brasil País de publicação: Estados Unidos
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Coleções: 01-internacional Base de dados: MEDLINE Assunto principal: Clonidina / Agonistas alfa-Adrenérgicos / Antagonistas Adrenérgicos alfa / Agonistas de Receptores Adrenérgicos alfa 2 / Antagonistas de Receptores Adrenérgicos alfa 1 / Artérias Mesentéricas Limite: Animals Idioma: En Revista: J Pharmacol Exp Ther Ano de publicação: 1996 Tipo de documento: Article País de afiliação: Brasil País de publicação: Estados Unidos