Effects of late reperfusion on infarct expansion and infarct healing in conscious rats.

We examined the effects of late reperfusion on infarct expansion and infarct healing process in conscious rats. Coronary occlusion and reperfusion were carried out in conscious rats 1 week after appropriate surgical preparations. The rats were randomized into the following four groups: sham operated, permanent occlusion, early reperfusion (i.e., reperfusion performed 1 hour after occlusion), and late reperfusion (i.e., reperfusion performed 6 hours after occlusion). Histological examination was performed 7 days after coronary occlusion. In the early reperfusion group, infarct size and expansion were reduced when compared to the permanent occlusion group. In rats subjected to late reperfusion, infarct size and expansion were not different from those in the permanent occlusion group. The extent of unresorbed necrotic myocardium in areas of infarcted scar was reduced in both early and late reperfusion groups. Infiltration by neutrophilic cells into areas of necrotic myocardium 16 hours after myocardial infarction was increased in both reperfusion groups. Infiltration by macrophages 3 days after infarction was also increased in both reperfusion groups. Late reperfusion, therefore, does not affect infarct expansion, but does contribute to the acceleration of the infarct healing process.