Role of alpha adrenoceptors in hypertension and in antihypertensive drug treatment.

Recent plethysmographic experiments suggest that both postsynaptic alpha 1 and alpha 2 adrenoceptors in human resistance vessels play an important role in the maintenance and regulation of vascular tone. Central alpha 2 adrenoceptors are assumed to be involved in the central regulation of blood pressure. Radioligand binding studies on the density and characteristics of alpha adrenoceptors have not revealed consistent differences between normotensive and hypertensive subjects, with the exception of pheochromocytoma, in which a consistent down regulation of alpha 2 adrenoceptors in thrombocytes has been demonstrated. The radioligand binding studies are limited, since they cannot be performed on vascular tissues. Alpha adrenoceptors are vitally important as targets of several antihypertensive drugs; the activities of these agents and the principles and clinical relevance of mechanisms involving alpha adrenoceptors are reviewed.