Infarct-sparing effect of propranolol in an occlusion-reperfusion dog model

1. To test the hypothesis that early pharmacological protection of the ischemic myocardium can enhance the effects of late reperfusion, 32 mongrel dogs were submitted to 6 h of left anterior descending coronary (LAD) occlusion and 18 h of reperfusion. 2. Arterial pressure and ECG were monitored. Area at risk was determined with methylene blue during coronary occlusion. Myocardial infarct size, measured with triphenyl tetrazolium chloride and by planimetry, was reported as percent of the area at risk of necrosis. 3. Ten dogs received no treatment and were used as controls (Group I); Group II (9 dogs) and Group III (13 dogs) received 2.0 and 4.0 mg/kg propranolol, iv, respectively, 30 min after LAD occlusion. 4. The hemodynamic effects of propranolol were not significantly different among groups during ischemia or reperfusion. Area at risk was similar in the 3 groups. 5. Following reperfusion, salvage of ischemic myocardium was 13 +/- 3% of area at risk in Group I, and 18 +/- 8% (Group II) and 25 +/- 5% (Group III) in propranolol-treated animals. The differences between Groups I and II or II and III were not significant. However, preservation was significantly greater in Group III than in Group I (P less than 0.05). 6. Therefore, early propranolol administration during ischemia improves the effects of subsequent reperfusion.