Reduction by Propranolol of Myocardial Necrosis following Temporary Coronary Artery Occlusion in Dogs

The effect of propranolol on the severity of myocardial necrosis following 40 minutes of temporary coronary artery occlusion was assessed in dogs. The circumflex coronary artery was occluded 1-2 cm from the aorta in open-chest dogs anesthetized with sodium pentobarbital. One group of dogs was untreated and a second group received propranolol (5.0 mg/kg, iv) 10 minutes prior to the occlusion. After 40 minutes the clamp was removed and arterial perfusion was restored. Dogs which survived this procedure were killed 2-5 days later for gross and histologic assessment of the necrosis. The relative area of necrosis (percent of fibers involved) in the posterior papillary muscle of each heart was quantified from stained histologic sections prepared from serial longitudinal slices of each posterior papillary muscle. Dogs treated with propranolol showed significantly less necrosis than did untreated controls, but the mechanism of the drug's action remains unknown. During coronary artery occlusion, propranolol-treated dogs exhibited somewhat lower heart rates, systolic blood pressures, and S-T segment elevations than did untreated dogs. However, none of these latter differences between groups was significant.