reactive components of effector tissues, most of which are innervated by adrenergic postganglionic fibers of the sympathetic nervous system. Such receptor’s can be activated by norepinephrine and/or epinephrine and by various adrenergic drugs; receptor activation results in a change in effector receptor’s, on the basis of their response to various adrenergic activating and blocking agents. Syn: adrenoceptor, adrenoreceptors.