Alpha-adrenoceptor subtypes in blood vessels: physiology and pharmacology

The existence of alpha 1- and alpha 2-adrenoceptors subtypes is now well established. Presynaptically, alpha 2-adrenergic autoreceptors modulate norepinephrine release. In vascular smooth muscle both alpha 1- and alpha 2-adrenoceptors exist postjunctionally, the alpha 1 subtype being innervated preferentially in most vascular beds. alpha 2-Adrenoceptors may be present on the smooth muscle cell as well as the endothelial cell where they may participate in the release of endothelium derived relaxing and constricting factors. Developing insights into the role of alpha-adrenoceptor subtypes in the cardiovascular system, and into the classification of subtypes of alpha 1- and alpha 2-adrenoceptors may be expected to have, if confirmed, significant therapeutic implications for drug discovery in the cardiovascular system.