APA Dictionary of Psychology

a receptor that binds norepinephrine and causes stimulation of smooth muscle in responses of the sympathetic nervous system, such as pupil dilation and increased vascular resistance (see vasoconstriction). There are two types, α₁-adrenoreceptors and α₂-adrenoreceptors, each of which is divided into subtypes designated by subscript capital letters (α_1A-adrenoreceptor, α_2A-adrenoreceptor, etc.). Also called alpha adrenoceptor; alpha adrenoreceptor; alpha receptor. Compare beta-adrenergic receptor.