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Medical Definition of Alpha-adrenergic receptors
1. Adrenergic receptor's in effector tissues capable of selective activation and blockade by drugs; conceptually derived from the ability of certain agents, such as phenoxybenzamine, to block only some adrenergic receptor's and of other agents, such as methoxamine, to activate only the same adrenergic receptor's. Such receptor's are designated as alpha-receptors. Their activation results in physiological responses such as increased peripheral vascular resistance, mydriasis, and contraction of pilomotor muscles. (05 Mar 2000)