α-adrenergic receptors

adrenergic receptors that respond to norepinephrine and to such blocking agents as phenoxybenzamine and phentolamine. They are subdivided into two types: α₁, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation, and α₂, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion. Called also alpha or alpha-adrenergic receptors.