RECEPTOR FUNCTION IN HEART-FAILURE

In patients with congestive heart failure, down-regulation of beta-adrenoceptors is present, probably as a result of sympathetic overstimulation. In end-stage dilated cardiomyopathy, beta-1-adrenoceptor density is markedly reduced, while beta-2-adrenoceptor density is normal. This latter finding does not necessarily imply normal sensitivity to beta-2-stimulation, due to possible alterations in the beta-adrenoceptor/adenylate cyclase complex beyond the receptor. In some disease states, such as ischemic cardiomyopathy and mitral valve disease, there seems to be a concomitant reduction of the beta-1- and beta-2-adrenoceptor density. The finding of beta-adrenoceptor down-regulation has stimulated the search for novel therapeutic approaches in heart failure patients. Beta-agonists could even further down-regulate beta-receptors, and this perhaps explains why they seem not to be useful in long-term use. Agents that directly stimulate adenylate cyclase activity, such as forskolin, or that increase cyclic adenosine monophosphate degradation, such as the phosphodiesterase inhibitors, are being tested. Beta-adrenoceptor blocking agents were used in treatment of heart failure before beta-adrenoceptor down-regulation was recognized in these patients. It is tempting to speculate that the beneficial clinical and hemodynamic effects seen in these patients treated with metoprolol is indeed due to an antagonism of the beta-adrenoceptor down-regulation. Studies testing whether beta-adrenoceptor blocking agents can improve survival in congestive heart failure patients are on-going.