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.
Published Version
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