EFFECT OF METOPROLOL ON THE BETA-ADRENOCEPTOR DENSITY OF LYMPHOCYTES IN PATIENTS WITH DILATED CARDIOMYOPATHY

We investigated the effect of the beta1-selective blocker metoprolol o n the beta-adrenergic receptor density of circulating lymphocytes in p atients with dilated cardiomyopathy. Nine men in New York Heart Associ ation functional classes II (six patients) and III were given metoprol ol for 6 months (mean dose 45.6 +/- 18.1 mg). Their cardiac function w as assessed by echocardiography. Although there was no difference in t he heart rate or pressure rate products, the end-systolic and end-dias tolic dimensions significantly decreased in six patients after metopro lol treatment. The ejection fraction, fractional shortening, and mean left ventricular circumferential shortening were significantly increas ed after the treatment. Beta-Adrenoceptor densities of lymphocytes, ex amined by iodine 125-labeled iodocyanopindolol, were reduced in patien ts at entry but recovered to normal levels after the metoprolol treatm ent. The dissociation constants did not differ at any stage of the dis ease. The relationship between beta-adrenoceptor densities in lymphocy tes and echocardiographic parameters showed a positive correlation wit h the plasma norepinephrine concentration. This study thus provides ev idence that long-term metoprolol therapy for dilated cardiomyopathy is associated with beta-receptor up-regulation, and the restoration of m yocardial beta-receptor density may be associated with the improved ca rdiac function as determined by echocardiography.