adrenergic receptors 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 receptors and of other agents, such as methoxamine, to activate only the same adrenergic receptors. Such receptors are designated as a-receptors. Their activation results in physiologic responses such as increased peripheral vascular resistance, mydriasis, and contraction of pilomotor muscles.
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Examples: glitazone, GI cocktail, etc.