Propranolol reduces myocardial hypertrophy in the right cardiac chambers after infarction in rats

The effects of chronic propranolol (Prop) therapy on the postinfarction myocardial hypertrophy of infarcted rats were studied by histological techniques. Male albino rats were submitted to left coronary artery ligation to produce infarction or to sham surgery (Con, N = 6). Infarcted rats (Inf) were divided into 2 groups receiving Prop (2.5 mg/kg, twice a day, N = 6) or saline (N = 6) for one month, respectively. Myocyte diameters were measured in longitudinally oriented sections in the four heart chambers (60 cells/chamber). Inf produced a significant increase in mean diameter of myocytes from the right atrium and ventricle and from the left atrium. In the right ventricle, myocyte diameter increased from 8.9 +/- 0.5 microns in the Con group to 12.5 +/- 0.6 microns in the Inf group (P < 0.05). Under Prop, myocyte diameter was reduced (P < 0.05) to 9.8 +/- 0.9 microns. Similar values were observed in the right atrium. In the left atrium, Prop produced only a partial reversion of the postinfarction hypertrophy. In the left ventricle, myocyte diameter was not significantly changed after Inf or Prop therapy. These data show that beta blockers reduce the myocardial hypertrophy in the right heart chambers after experimental infarcts in rats. This effect can be secondary to reduction of pulmonary hypertension or to blockade of direct effects of catecholamines on myocardial fibers or both.