Effects of propranolol on myocardial infarct size with and without coronary artery reperfusion in the dog

The ability of propranolol to limit myocardial infarct size (IS) following coronary artery occlusion with and without reperfusion into a critical stenosis was assessed in the dog. IS was determined by the nitrobluetetrazolium staining method and expressed as percent of the left ventricle (free wall plus septum). In Series 1 dogs the left circumflex coronary artery (LCX) was ligated at its origin. IS at 6 h was similar in groups pretreated with saline (36.0 +/- 1.3%) or propranolol (0.2 mg . kg-1, 34.7 +/- 1.7%; 1.0 mg . kg-1, 36.7 +/- 1.5%; 4.4 mg . kg-1, 34.8 +/- 0.3%). In Series 2 dogs a relatively small infarction was produced by ligating the largest branch of the LCX between the left anterior descending and posterior descending arteries. IS at 6 h was not significantly different in dogs pretreated with saline (8.1 +/- 1.7%) or propranolol (0.2 mg . kg-1, 7.1 +/- 2.5%; 1.0 mg . kg-1, 4.6 +/- 1.2%). In Series 3 dogs the LCX was ligated approximately 10 mm from its origin for 60 min followed by reperfusion into a critical stenosis. IS determined at 24 h was significantly less in dogs treated with propranolol (1.0 mg . kg-1) before LCX occlusion (4.6 +/- 0.6%) or 5 min after LCX reperfusion (9.5 +/- 1.8%) than in dogs treated with saline (22.6 +/- 2.8%). In Series 4 dogs treatment was exactly as in Series 3 except that reperfusion was not instituted. IS was similar in dogs pretreated with saline (29.0 +/- 1.5%) or propranolol (31.1 +/- 3.0%). Thus, in the present study, propranolol limited IS in the presence but not in the absence of reperfusion. In the reperfusion model propranolol was effective when administered before coronary occlusion or after initiation of reperfusion.