Contribution of Myocyte Apoptosis to Myocardial Injury in an in Vivo Rabbit Preparation of Ischemia-Reperfusion

Objective: Exposure of the heart to repeated, brief episodes of coronary oc-clusion/reperfusion prevents lethal myocyte injury. Necrosis and apoptosis, two seemingly distinct mechanisms of cell death caused by ischemia could contribute independently to progressive loss of myocardium. Studies suggest that ischemic conditioning (IC) lessens myocyte injury by decreasing apoptosis. The goal of this study was to examine cell death in rabbit hearts subject to ischemia-reperfusion injury without (nIC) or with pretreatment by IC. Methods: In the control study, anesthetized, male rabbits (n = 4/group) un-derwent 30-min regional coronary occlusion (CO) and either 3, 6 or 24 h reperfusion (REP). In the IC study, rabbits were pretreated by IC (2 cycles of 5-min CO and 10-min REP) before 30-min CO and subsequent REP. Addi-tional groups were evaluated with 60, or 120-min CO followed by up to 96 h REP. Agarose electrophoresis was used to detect DNA laddering and poly (ADP-ribose) polymerase (PARP; chromatin bound nuclear DNA repair enzyme) was assessed in myocardial biopsies. Results: Genomic DNA from nIC and IC hearts showed no oligonucleosomal fragmentation. In addition, we did not detect any cleavage of PARP; however, myocardial PARP levels decreased when CO and REP durations were prolonged. Conclusion: Absence of genomic DNA fragmentation or PARP cleavage in an in vivo preparation of ischemia-reperfusion injury does not support the view that apoptosis contributes markedly to post-ischemic tissue necrosis.