Purpose: To investigate the effects of chronic subcutaneous administration of reserpine (Res) or propranolol (Prop) on the postinfarction myocardial hypertrophy and the effects of Prop treatment on myocardial contractility in rats.
Methods: Male albino rats (3-month-old) were submitted to left coronary artery ligation to produce myocardial infarction. Rats submitted to a sham-operation were used as controls. Animals submitted to Res (0.5 mg/kg/day) were killed 8-10 days after surgery and those submitted to Prop (2.5 mg/kg twice a day) were killed 15 (G-15) or 30 (G-30) days later. Hypertrophy was evaluated according to cardiac chambers weight corrected to body weights. Isometric force (F) developed by isolated right ventricular (RV) strips was used as a contractile index.
Results: Atrial and RV hypertrophy were completely blocked by Res. Prop treatment did not significantly change infarct extension, evaluated by the fibrous scar area. Prop therapy also reduced atrial and RV hypertrophy. This effect was less intense compared to Res, however. In the G-30, for example, the relative right atrial and RV weights (mg/g) were 0.10 +/- 0.01 and 0.59 +/- 0.03 in sham-operated animals (n = 9), 0.12 +/- 0.01 and 0.079 +/- 0.07 in infarcted animals with Prop (n = 11) and 0.22 +/- 0.03 and 1.11 +/- 0.07 in those infarcted and treated with saline solution (n = 11). Basal F values were 25 to 30% lower in RV strips from infarcted than in sham-operated hearts. This reduction however was only 4% (G-15) and 8% (G-30) in infarcted hearts under Prop treatment.
Conclusion: These data show that sympathetic blockade reduces the postinfarction myocardial hypertrophy and tends to preserve contractility of the surviving myocardium.