The role of adrenoceptors in circulatory and metabolic regulation

This survey covers the classification and subdivisions of alpha- and beta-adrenoceptors, including alpha 1 and alpha 2, beta 1 and beta 2, and pre-and postsynaptic receptor subtypes, together with the distribution and functional relevance of the various adrenoceptor subtypes. The emphasis will be on their relevance in circulatory regulatory processes, especially those of the blood vessels. The alpha- and beta-adrenoceptor antagonists that interact with various receptor subtypes are briefly discussed. The control of alpha 2-adrenoceptors concerned with blood pressure regulation is an important target for centrally acting antihypertensive drugs (such as clonidine or alpha-methyldopa). Changes in adrenoceptor density, particularly the down-regulation of beta 1- adrenoceptors (but not beta 2), are found in congestive heart failure. However, the experimental findings about alpha-and beta-adrenoceptors in essential hypertension remain controversial. Finally, the influence of alpha- and beta-adrenoceptor antagonists on plasma lipids and carbohydrate metabolism is briefly reviewed. The changes found may be only partly explained on the basis of alpha- or beta-receptor blockade.