Effect of early propranolol treatment in an animal model of congestive cardiomyopathy. II. beta-adrenergic receptors and left ventricular function.

Young turkeys inbred for congestive cardiomyopathy (CCM) were treated with propranolol prior to the development of cardiac enlargement. One-day-old inbred CCM and commercial turkeys received 2 mg X kg-1 X day-1 of propranolol for 1 month and were compared with untreated age matched inbred CCM and commercial turkeys. Heart weight, body weight, and binding characteristics of cardiac beta-adrenergic receptors, using (-)3H-dihydroalprenolol as a ligand, were determined at 10 and 28 days. Left ventricular shortening fraction was determined at 28 days and at 32 days, 4 days after propranolol was discontinued, in treated and untreated inbred CCM and commercial turkeys. Propranolol did not prevent the development of cardiac hypertrophy in inbred CCM turkeys at 28 days of age and did not effect body weight or heart weight in either inbred CCM or commercial turkeys at 10 or 28 days of age. In the inbred CCM turkeys, the maximum number of binding sites (Bmax) and the binding affinity (Kd) of beta-adrenergic receptors were not changed by propranolol treatment. In the propranolol-treated commercial turkeys, Bmax the of beta-receptors was increased at 28 days of age compared with untreated age matched controls, 382 vs 194 fmol X mg-1 (p less than 0.05). Untreated inbred CCM turkeys when compared with untreated age matched commercial turkeys show a significant reduction of binding affinity of beta-receptors at both 10 and 28 days of age, Kd = 10.4 vs 6.2 nmol X litre-1 at 10 days and 11.3 vs 5.2 nmol X litre-1 at 28 days (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)