New developments in alpha-adrenergic receptor pharmacology: implications for the initial treatment of hypertension.

The vascular postsynaptic alpha 1 receptor is the major locus through which adrenergically determined vascular tone is mediated. Therefore, blockade of this receptor is a particularly specific approach to the major pathophysiologic defect in hypertension--an elevation of peripheral vascular resistance. Although the mechanism responsible for this increase in peripheral vascular resistance in hypertension is not known, it is apparent that the sympathetic nervous system plays a key role. In addition, considerable evidence suggests that a common abnormality in hypertension is an increase in the sensitivity of vessels to alpha-adrenergic stimulation, a defect potentially located at the alpha-receptor level. Basic radioligand binding studies of vascular alpha 1 receptors, in fact, demonstrate that the affinity, or avidity, of binding of these sites is under the regulation of both neural and humoral factors. Although diuretics, and more recently, beta-adrenergic blocking agents, have been utilized for the initial treatment of hypertension, recent information about the adverse effects of these agents has led to a reappraisal of the role of alpha-receptor blockade as a rational approach to the initial treatment of hypertension.