Abstract
We sought an isolated vascular preparation and experimental setting where the function of alpha2B-adrenoceptors could be demonstrated by non-recombinant technique. ST-91 (2-[2,6-diethylphenylamino]-2-imidazoline), an alpha 2B-adrenoceptor agonist with a mixed alpha adrenergic receptor type/subtype selection profile antagonized the relaxant effect of isoproterenol in endothelium-denuded rat mesenteric artery rings precontracted with phenylephrine. At 10(-7) M of ST-91, the antagonism was characterized by a rightward shift of isoproterenol dose-response curve (A50=6.81+/-1.40 e-7 (n=4) vs the control 1.29+/-0.25 e-7 M (n=4)) with no E(max) depression. At 10(-6) M the Emax depression was prevalent (36.1+/-7.0% (n=4) vs the control 79.9+/-5.1% (n=4)); both actions could be antagonized by the alpha2-adrenoceptor antagonist yohimbine. The not subtype-selective alpha(2)-adrenoceptor agonist xylazine (10(-7) M) did not affect the relaxant action of isoproterenol. Present findings are discussed in the light of previously reported hemodynamic effects attributed to alpha2B-adrenoceptors in receptor subtype-knockout animals.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adrenergic alpha-2 Receptor Agonists*
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Adrenergic alpha-2 Receptor Antagonists
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Adrenergic alpha-Agonists / pharmacology
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Adrenergic beta-2 Receptor Antagonists*
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Analysis of Variance
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Animals
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Aorta / drug effects
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Aorta / physiology
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Clonidine / analogs & derivatives*
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Clonidine / pharmacology
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Dose-Response Relationship, Drug
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In Vitro Techniques
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Isoproterenol / pharmacology
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Male
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Mesenteric Arteries / drug effects*
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Mesenteric Arteries / physiology
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Phenylephrine / pharmacology
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Prazosin / pharmacology
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Rats
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Rats, Wistar
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Receptors, Adrenergic, alpha-2 / physiology
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Receptors, Adrenergic, beta-2 / physiology
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Terbutaline / pharmacology
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Vas Deferens / drug effects
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Vas Deferens / physiology
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Vasodilation / drug effects*
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Vasodilation / physiology
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Xylazine / pharmacology
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Yohimbine / pharmacology
Substances
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Adra2a protein, rat
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Adra2b protein, rat
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Adrenergic alpha-2 Receptor Agonists
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Adrenergic alpha-2 Receptor Antagonists
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Adrenergic alpha-Agonists
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Adrenergic beta-2 Receptor Antagonists
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Receptors, Adrenergic, alpha-2
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Receptors, Adrenergic, beta-2
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Phenylephrine
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Xylazine
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Yohimbine
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ST 91
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Isoproterenol
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Clonidine
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Terbutaline
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Prazosin