title: A postsynaptic location of alpha 2 adrenoceptors in vascular smooth muscle: in vivo studies in the conscious rabbit.
abstract: The rise in blood pressure after intravenous administration of a range of alpha-adrenoceptor agonists and the effect of alpha adrenoceptor antagonists was studied in groups of conscious rabbits. Phentolamine was equally effective at blocking the pressor response to the alpha 1 adrenoceptor agonist phenylephrine and the mixed alpha 1/alpha 2 adrenoceptor agonist noradrenaline. Phenoxybenzamine which acts preferentially on alpha 1 adrenoceptors and the more specific alpha 1 adrenoceptor antagonist prazosin were more effective against phenylephrine induced rises in pressure, while yohimbine and alpha yohimbine which preferentially act on alpha 2 adrenoceptors were more effective against noradrenaline. The immediate pressor response to intravenous injections of the alpha 2 adrenoceptor agonists clonidine and guanabenz was blocked more effectively by phentolamine than prazosin when doses which gave a postsynaptic location of both alpha 1 and alpha 2 adrenoceptors both of which mediate vasoconstrictor responses in vascular smooth muscle.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000032:analysis* / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000032:analysis* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011817:Rabbits; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D010656:Phenylephrine; D009638:Norepinephrine