Importance of receptor regulation in the pathophysiology and therapy of congestive heart failure.

The available data indicate that the beta-adrenergic receptors that mediate positive inotropic responses undergo "down-regulation," a cellularly mediated decrease in surface receptor number, in congestive heart failure. This decrease in beta-adrenergic receptor number is proportional to the degree of myocardial dysfunction and the loss of contractility that occurs in congestive heart failure. It appears to be chamber-specific, occurring to the greatest degree in the most severely affected ventricular chamber, and is specific to the beta 1-adrenergic receptor subtype. Beta-adrenergic receptor down-regulation may be the result of the excessively high levels of plasma catecholamines seen in congestive heart failure, inasmuch as a similar phenomenon of beta-adrenergic receptor down-regulation is seen in animals treated with high doses of catecholamines. The specific down-regulation in cardiac beta receptors may be, in part, the cause of the decrease in myocardial function observed during long-term beta-adrenergic receptor stimulation, and an actual decrease in beta-adrenergic receptor number has been observed in myocardial tissue from patients with congestive heart failure. Down-regulation of beta receptors in congestive heart failure results in a decrease or loss of efficacy of beta-adrenergic receptor agonists on long-term administration. This is especially evident for partial agonists, which are more dependent on receptor number for their positive inotropic effects than full agonists. Although beta receptors are down-regulated in congestive heart failure, myocardial alpha 1-adrenergic receptors and histamine H2 receptors do not appear to be subject to this same regulatory process. Inasmuch as stimulation of both of these receptors results in a positive inotropic effect, further study should be given to the potential therapeutic utility of selective stimulation of myocardial alpha 1-adrenergic receptors and histamine H2 receptors in congestive heart failure. It is evident that the status of specific receptor subtypes in pathophysiologic states such as congestive heart failure must be considered when assessing the likelihood of success in treating patients with beta-adrenergic receptor agonists.