The effect of propranolol on microvascular injury in acute myocardial ischemia.

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Abstract
The purpose of this study was to determine whether propranolol, which has been shown to reduce the extent of myocardial infarction, reduces microvascular injury which may play a role in exacerbating ischemia. Saline (10 dogs) or propranolol (2 mg/kg i.v., 7 dogs) was injected prior to a one hour occlusion of the left anterior descending coronary artery. Carbon black (1 ml/kg), which labels damaged and leaky vessels, was injected 5 min after release of the occlusion and allowed to circulate for two hours. By morphometric analysis of 1 micron thick sections, 75 +/- 12% of vessels and 84 +/- 7% of myocardial cells showed damage in untreated dogs; only 2 +/- 1% of vessels and 9 +/- 8% of myocardial cells showed damage in the propranolol-treated dogs (P less than 0.001). The number of carbon black-labeled vessels/10 fields/biopsy from comparable areas of ischemic tissue was 55 +/- 7 in untreated dogs and 27 +/- 3 in propranolol-treated dogs (P less than 0.001). The results suggest that propranolol not only protects the ischemic myocardial cell, but also significantly decreases the ischemic microvascular changes.