CATECHOLAMINES modulate a host of diverse responses in man. These responses are initiated by the interaction of catecholamines with discrete sites located on the plasma membrane of cells. Adrenergic receptors, like other hormone receptors, are responsible for the selective recognition and binding of specific molecular structures, in this case catecholamines such as epinephrine and related drugs. The demarcation between alpha-adrenergic and beta-adrenergic receptors has long been appreciated,1 as has the existence of beta-adrenergic receptor subtypes (beta1 and beta2).2 Recent advances in the understanding of alpha-adrenergic receptors have led to the appreciation of the existence of subtypes of . . .