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Ischemic preconditioning prevents in vivo hyperoxygenation in postischemic myocardium with preservation of mitochondrial oxygen consumption

¹The Center for Biomedical Electron Paramagnetic Resonance Spectroscopy and Imaging, Davis Heart and Lung Research Institute, and the Division of Cardiovascular Medicine, Department of Internal Medicine, The Ohio State University College of Medicine, Columbus, Ohio; and ²Key Laboratory of Organ Transplantation, Ministry of Education Institute of Organ Transplantation, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China

Submitted 1 March 2007 ; accepted in final form 17 May 2007

Ischemic preconditioning (IPC) strongly protects against ischemia-reperfusion injury; however, its effect on subsequent myocardial oxygenation is unknown. Therefore, we determine in an in vivo mouse model of regional ischemia and reperfusion (I/R) if IPC attenuates postischemic myocardial hyperoxygenation and decreases formation of reactive oxygen/nitrogen species (ROS/RNS), with preservation of mitochondrial function. The following five groups of mice were studied: sham, control (I/R), ischemic preconditioning (IPC + I/R, 3 cycles of 5 min coronary occlusion/5 min reperfusion) and IPC + I/R N^G-nitro-L-arginine methyl ester treated, and IPC + I/R eNOS knockout mice. I/R and IPC + I/R mice were subjected to 30 min regional ischemia followed by 60 min reperfusion. Myocardial PO₂ and redox state were monitored by electron paramagnetic resonance spectroscopy. In the IPC + I/R, but not the I/R group, regional blood flow was increased after reperfusion. PO₂ upon reperfusion increased significantly above preischemic values in I/R but not in IPC + I/R mice. Tissue redox state was measured from the reduction rate of a spin probe, and this rate was 60% higher in IPC than in non-IPC hearts. Activities of NADH dehydrogenase (NADH-DH) and cytochrome c oxidase (CcO) were reduced in I/R mice after 60 min reperfusion but conserved in IPC + I/R mice compared with sham. There were no differences in NADH-DH and CcO expression in I/R and IPC + I/R groups compared with sham. After 60 min reperfusion, strong nitrotyrosine formation was observed in I/R mice, but only weak staining was observed in IPC + I/R mice. Thus IPC markedly attenuates postischemic myocardial hyperoxygenation with less ROS/RNS generation and preservation of mitochondrial O₂ metabolism because of conserved NADH-DH and CcO activities.

ischemia reperfusion; reactive oxygen species; free radicals; nitric oxide; peroxynitrite; redox; mitochondria