Cardioprotection induced by hypoxic preconditioning and ischemic preconditioning in in vivo hearts of dogs: using double CPB circuits

Objective To evaluate the cardioprotection induced by ischemic preconditioning(IPC)and hypoxic preconditioning(HPC)which were carried out by using the double cardiopulmonary bypass(CPB) circuits in in vivo hearts of dogs. Methods Eighteen healthy male dogs, weighing 17.5-24.5 kg, aged 13-24 months, were divided into 3 groups (n=6 each) using a random number table: myocardial ischemia-reperfusion group (group I/R), IPC group and HPC group.The double CPB circuits were established as follows: systemic and coronary circulation, and independent systemic and coronary circulation was carried out.In group IPC, the aorta was clamped, and the coronary circulation pump was suspended for 5 min followed by 5 min opening, repeating for 3 cycles.In group HPC, the aorta was clamped, the coronary circulation was started, and pure nitrogen was insufflated for 5 min followed by 5 min of oxygen insufflation, repeating for 3 cycles.CPB was performed for 1 h starting from the time point immediately after IPC or HPC.Before splitting of sternum (T1), after establishment of double CPB circuits (T2), at the end of preconditioning (T3), and at 60 and 120 min after restoration of spontaneous heart beat (T4, 5), heat rate, mean arterial pressure, central venous pressure, left ventricular end-systolic pressure, left ventricular end-diastolic pressure and the maximum rate of increase/decrease of left ventricular pressure were recorded.Blood samples were collected from the right internal jugular vein at T1 and T4, 5 for determination of serum cardiac troponin I concentrations.The animals were sacrificed after determination of the parameter or after blood sampling at T5, myocardial specimens were obtained for examination of the ultrastructure and for detection of apoptosis in cardiomyocytes, and apoptosis index was calculated.Before aortic clamping, immediately after aortic unclamping and at 30 min after aortic unclamping, myocardial specimens were obtained for determination of ATP contents in cardiomyocytes. Results Compared with I/R group, left ventricular end-systolic pressure was significantly increased, and the serum cardiac troponin I concentrations were significantly decreased at T4, 5, the myocardial ATP contents were significantly increased immediately after aortic unclamping and at 30 min after aortic unclamping, apoptosis index was significantly decreased (P<0.05 or 0.01), and the pathological changes were significantly attenuated in IPC and HPC groups.Compared with group IPC, the myocardial ATP contents were significantly increased(P<0.05), and the pathological changes were attenuated in group HPC. Conclusion Both HPC and IPC can exert cardioprotection when carried out by using the double CPB circuits, and HPC provides better cardioprotection than IPC in in vivo hearts of dogs. Key words: Ischemic preconditioning, myocardial; Anoxia; Myocardial reperfusion injury