Late Phase Preconditioning And Ischemic Postconditioning Protect Heart Ischemia And Reperfusion Injury In Mice

Objective To improve the procedure of establishing animal model of myocardial ischemia and reperfusion (I/R) in mice.Methods Male C57BL/6 mice were anethetized, the chest was opened with a mouse respirator, a 7/0 silk suture was placed around the left anterior descending coronary artery (LAD), a polyethylene tube (PE) was placed under the silk suture. The LAD was ligated for 30 min, reperfusion was achieved by releasing the tension applied to ligature for 24 h.Result A total of 20 C57BL/6 were allocated into I/R group and shame control group. The survival rate in 30-min I/R group is 9/10 after 24 h reperfusion and the infarct area is 32.2±0.7% and the AAR (total left ventricle (LV) area-non-ischemic area) over the area of left ventricle is 59.5±0.9%. Conclusions A repeatable and simple technique for mouse model of myocardial ischemia and reperfusion injury can be established.Objective The late phase ischemic preconditioning (24 hours later) strongly protects against ischemia reperfusion injury. However, its effect on myocardial oxygenation and related mechanism(s) are unknown. Therefore, we determine in an in vivo mouse model of regional ischemia and reperfusion (I/R) whether late phase preconditioning attenuates post-ischemic myocardial hyperoxygenation with preservation of mitochondrial function.Methods Four groups of mice were studied:sham, late phase preconditioning (LPC,3 cycles of 5 min coronary occlusion/5 min reperfusion), ischemia reperfusion (I/R,30 min ischemia followed by 60 min reperfusion), and LPC+I/R mice.Results Tissue Po2 upon reperfusion rose significantly above the pre-ischemic value in the I/R mice. This hyperoxygenation status was attenuated in the PC+I/R mice. Activities of complexⅡandⅢ(SCR) and cytochrome c oxidase (CcO) were increased in the PC group, reduced in the I/R group, but conserved in the PC+I/R group compared with sham control. The activity of NADH dehydrogenase (NADH-DH) showed no significant difference between sham and the PC group, but was reduced in the I/R group and recovered in the PC+I/R group. The expression of Mn-SOD was increased in the PC and PC+I/R group compared with sham control.Conclusion Taken together, these data suggest that the late phase PC attenuates post-ischemic myocardial hyperoxygenation and preserves mitochondrial O2 metabolism due to increased SCR and CcO activities and conserved NADH-DH activity and increased Mn-SOD expression.Objective Ischemic post-conditioning (IPOC) is a powerful method to reduce ischemia and reperfusion injury. Studies also demonstrate that IPOC could be deleterious when the ischemia duration was either too short or too long. Our study is to determine whether there is a salvageable ischemic time window for IPOC and the potential mechanisms involved.Methods C57BL/6 mice underwent 30,45 and 60 min left anterior descending coronary artery (LAD) occlusion followed by reperfusion, w/o IPOC. In vivo tissue oxygenation was monitored with electron paramagnetic resonance (EPR) oximetry. Regional Blood Flow (RBF) was measured by the laser Doppler perfusion monitor. Tissue from the risk area was collected and the activities of mitochondrial were assayed.Results The tissue oximetry data demonstrated that IPOC attenuated tissue hyperoxygenation with 45 but not 30 and 60 min ischemia. IPOC improved the RBF with 30 and 45 but not 60 min ischemia. IPOC preserved the activities of mitochondrial enzymes activities at 30 and 45 but not 60 min ischemia. Infarct size measurement indicated that IPOC protected the heart with 30 min and 45 min but not 60 min ischemia.Conclusions The cardioprotection afforded by IPOC is limited to a time window between 30 and 45 min LAD occlusion in mouse. This salvageable ischemic time window is determined by the effect of IPOC on improving the RBF and mitochondrial function.