Adrenergic beta receptors in anesthesia and intensive care medicine

Abstract

beta-Adrenoceptors (beta-AR) are divided into a beta 1-, a beta 1-, and a recently cloned beta 3-subtype. beta-AR belong to the group of 7-transmembrane spanners which are coupled via GS-proteins to the enzyme adenylyl cyclase. Instead of being static entities, beta-AR undergo dynamic regulation upon repeated or prolonged exposure to agonists (down-regulation) or antagonists (up-regulation). After exposure to agonists, an early desensitisation caused by phosphorylation of amino acid residues can be distinguished from receptor sequestration. Finally, the internalised receptor is digested by proteolytic enzymes. The present article describes the basic patterns of molecular biology of beta-AR, signal transduction, and receptor desensitisation. In the human heart, beta-AR are the most important receptor system to provide positive inotropic and chronotropic effects. The alterations of the beta-adrenergic system in cardiac insufficiency, after heart transplantation, and after extracorporeal circulation, as well as changes induced by surgery and single anaesthetic agents, are reviewed.