Circulatory response to beta-adrenergic blockade at rest and during exercise

Abstract

The beta adrenoceptors involved in the regulation of the cardiovascular system include the beta 1 subtype in the heart, coronary arteries and juxtaglomerular cells of kidney, and the beta 2 subtype in skeletal muscle resistance vessels and on terminals of sympathetic nerves. The beta 1 receptors are activated primarily by norepinephrine released from the sympathetic nerves, the beta 2 by circulating epinephrine from the adrenal medulla. The function of these receptors is to adjust the circulation to meet the stresses imposed by gravitational forces including those that occur in changing from supine to standing position, in muscular exercise and during emotional stress. In normal subjects, other systems can compensate if the beta receptors are prevented from functioning. Thus, during beta-adrenergic blockade it is only when the cardiovascular system is taxed severely that deficiencies in its performance become apparent. In patients with cardiovascular diseases, other effects of beta blockers, not yet understood, may also be important.