Catecholamines modulate a wide variety of important physiological processes, alpha-1 Adrenergic receptors play a major role in transducing many of the actions of catecholamines. A particularly prominent action of alpha-1 adrenergic receptors is the promotion of vasoconstriction in a range of vascular beds. Additionally these receptors are found in nonvascular smooth muscle such as vas deferens and uterus, as well as in other tissues such as the liver and heart. Although these receptors influence important cellular responses, it is clear that the physiological response to alpha-1 adrenergic receptor activation is not fixed, but may vary in a range of situations. For example, prolonged exposure to catecholamines may modify the effects of subsequent alpha-1 adrenergic receptor activation. Also, changes in hormonal state or disease processes such as hypertension may alter tissue responsiveness to alpha-1 adrenergic receptor-transduced events.