a site on a cell that, upon interaction with epinephrine or norepinephrine, controls vasoconstriction, intestinal relaxation, pupil dilation, and other physiological processes.
Any of various cell membrane receptors that can bind with norepinephrine and related substances that activate or block the actions of the cells containing such receptors; these cells initiate physiological responses such as vasoconstriction, pupil dilation, and contraction of pilomotor muscles.alpha-receptor
