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1 Medicine, University of Louisville, Louisville, Kentucky, United States
* To whom correspondence should be addressed. E-mail: rbolli{at}louisville.edu.
OBJECTIVES: Brief episodes of ischemia and reperfusion following a lethal ischemic insult confer cardioprotection, a phenomenon termed "ischemic postconditioning". However, all studies reported to date have been conducted in open-chest animal models. We sought to determine whether postconditioning occurs in conscious animals and whether it protects against severe myocardial injury. METHODS: Chronically instrumented rats were assigned to a 30- (Subset 1), 45- (Subset 2) or 60-min (Subset 3) coronary occlusion followed by 24 h of reperfusion. In each subset, rats received no further intervention (control), were preconditioned with 12 cycles of 2-min occlusion/2-min reperfusion immediately (EPC) or 24 h (LPC) before myocardial infarction, or were postconditioned with 20 cycles of 10-s occlusion/10-s reperfusion immediately following myocardial infarction (20-10 PostC). RESULTS: With a 30-min occlusion, infarct size (54.4 2.3% of risk region in control-30) was significantly reduced in EPC-30, LPC-30 and 20-10 PostC-30 groups (by 72, 70, and 47%, respectively; all P<0.05 vs. control-30). With a 45-min occlusion, infarct size (62.2 2.4% in control-45) was reduced in EPC-45 and LPC-45 groups (by 47 and 41%, respectively; all P<0.05 vs. control-45), but not in 20-10 PostC-45 group (55.4 2.3%, P=NS vs. control-45). With a 60-min occlusion, infarct size (72.7 2.2% in control-60) was reduced in EPC-60 (by 20%, P<0.05), but neither in LPC-60 (63.6 2.5%, P=NS) nor in 20-20 PostC group (71.5 3.4%, P=NS). CONCLUSIONS: Both early and late ischemic preconditioning as well as ischemic postconditioning confer protection in conscious rats; however, unlike early preconditioning, postconditioning protects only against coronary occlusions <45 min. In the conscious rat, the cardioprotection afforded by postconditioning is limited to mild to moderate myocardial injury.
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