title: The contractions induced in rat and guinea-pig aortic strips by the alpha 2-adrenoceptor selective agonists B-HT 920 and UK 14,304 are mediated by alpha 1-adrenoceptors.
abstract: The alpha-adrenergic action of the selective alpha 2-adrenoceptor agonists B-HT 920 and UK 14,304 was investigated on helically cut preparations of rat and guinea-pig isolated aorta. The alpha 1-adrenoceptor selective stimulant (-)-phenylephrine was included for comparison. All agonists induced concentration-dependent contractions in both preparations. Calcium entry blockade by D 600 almost abolished the contractions evoked by B-HT 920 and UK 14,304 in rat aorta while those evoked in guinea-pig aorta were less strongly affected. Contractions elicited by (-)-phenylephrine were moderately impaired by D 600 in rat aorta whereas there was only a limited effect in guinea-pig aorta. Analysis of the prazosin and yohimbine antagonism of B-HT 920- and UK 14,304-evoked contractions showed the involvement of alpha 1-like adrenoceptors in rat and guinea-pig aorta, prazosin being approximately 1000 times more potent that yohimbine. The results show that B-HT 920 and UK 14,304 contract rat and guinea-pig aorta via alpha 1-like adrenoceptors which are not identical. It is submitted that rat and guinea-pig alpha 1-adrenoceptors activate different contractile processes.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects; D001381:Azepines / Q000494:pharmacology*; D000068438:Brimonidine Tartrate; D004305:Dose-Response Relationship, Drug; D005711:Gallopamil / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D011224:Prazosin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D013045:Species Specificity; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D005711:Gallopamil; D000068438:Brimonidine Tartrate; C024763:talipexole; D011224:Prazosin