The cardioprotective effect of hypoxic and ischemic preconditioning in dogs with myocardial ischemia-reperfusion injury using a double-bypass model.

The effects of preconditioning on cardioprotection have mainly been studied in vitro. No sufficient in vivo experiments have been performed to optimize ischemic preconditioning (IPC) or hypoxic preconditioning (HPC) for clinical applications. The purpose of this study was to establish a canine double-bypass model to examine the effect of IPC and HPC on cardiomyocytes and heart function. A double-bypass procedure to enable independent control of systemic and coronary circulation was established in dogs. The animals were divided into control, HPC, and IPC groups (n=6 each). Indicators of cardiac function, including cardiodynamics, hemodynamics, ATP, and cardiac troponin I (cTnI) levels; myocardium morphology; and myocardiocyte apoptosis were determined. Both IPC and HPC attenuated the reperfusion-induced decrease in left ventricular end systolic pressure seen in the control group. Both the HPC and IPC groups had lower serum cTnI levels, better myocardiocyte histology, and lower rates of apoptosis compared to the control group without preconditioning. HPC reduced the abnormal cardiomyocyte histology and apoptosis to a greater extent than IPC, and only HPC significantly restored the depletion of ATP. This study demonstrates the effectiveness of the double-bypass model for the optimized study of both HPC and IPC. The results suggest that HPC may provide better cardioprotection than IPC.