Effect of Propranolol on the Infarct Size and Extent of the Border Zone in Coronary Ligated Rats

The present study was attempted in order to investigate the effectiveness of propranolol in limiting of myocardial infarct size following ligation of the left coronary artery in Wistar rats. The non-infarcted ischemic zone, the border zone, was significantly larger in the rats sacrificed 3 hours after the ligation (25.6±4.9% LV) than in those sacrificed 6 hours after ligation (10.7±6.6%LV). No border zone was demonstrated when the rats were sacrificed 12 hours after the ligation. Nor were any differences in the size of the area at risk found among the above 3 groups. The size of the infarcted area was significantly smaller than in the control group (46. 0±5.5%LV) when propranolol was administered intraperitoneally before (25.3±4.6%LV), immediately after (35.0±4.1%LV) or 3 hours after ligation (36.6±4.7%LV). However, propranolol could not reduce infarct size when administered 6 hours (44.1±8.5%LV) or 12 hours (46.2±3.6%LV) after ligation of the coronary artery.The present study clearly demonstrates the presence of a non-infarcted ischemic zone, a border zone, until at least 6 hours after the ligation of the coronary artery and reduction of the infarcted area by propranolol when administered until at least 3 hours after the ligation. Thus, the author postulated the usefulness of beta-blocking agents in the early phase of acute myocardial infarction.