The paradox of α-adrenergic coronary vasoconstriction revisited

Activation of coronary vascular alpha-adrenoceptors results in vasoconstriction which competes with metabolic vasodilation during sympathetic activation. Epicardial conduit vessel constriction is largely mediated by alpha(1)-adrenoceptors; the constriction of the resistive microcirculation largely by alpha(2)-adrenoceptors, but also by alpha(1)-adrenoceptors. There is no firm evidence that alpha-adrenergic coronary vasoconstriction exerts a beneficial effect on transmural blood flow distribution. In fact, alpha-blockade in anesthetized and conscious dogs improves blood flow to all transmural layers, during normoperfusion and hypoperfusion. Also, in patients with coronary artery disease, blockade of alpha(1)- and alpha(2)-adrenoceptors improves coronary blood flow, myocardial function and metabolism. (C) 2011 Elsevier Ltd. All rights reserved.