al·pha–re·cep·tor noun \ˈal-fə-ri-ˌsep-tər\
: any of a group of receptors that are present on cell surfaces of some effector organs and tissues innervated by the sympathetic nervous system and that mediate certain physiological responses (as vasoconstriction, relaxation of intestinal muscle, and contraction of most smooth muscle) when bound by specific adrenergic agents—compare beta-receptor
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