Ischemic preconditioning in immature rabbit hearts

Objective Protection afforded by ischemic preconditioning (IPC) against myocardial ischemia in adult heart has been investigated. This study was designed to examine the effects of IPC on myocardial tolerance to ischemia in immature hearts.Methods The aorta of isolated immature rabbit heart (14-21d old) was connected to Langendorff preparation within 30 s after excision. The hearts were perfused with oxygenated (95%O 2:5%CO 2) Krebs-Henseleit buffer(KHB) at 60 cmH 2O. 16 immature rabbit hearts were equally divided into 2 groups: control group and IPC group. In IPC group the hearts were first subjected to IPC stimulus consisting of 5 min global ischemia followed by 10 min reperfusion. The hearts in both groups were made globally ischemic for 30 min(no perfusion) followed by 40 min reperfusion. At the end of 40 min reperfusion the hearts were harvested for ATP analysis. The coronary flow(C), HR, left ventricle developed pressure(LVDP) and ±dp/dt were monitored and recorded before ischemia and at 5,10,20,30 and 40 min of reperfusion, and calculated as % of pre-ischemia levels. Coronary flow was collected before and after reperfusion for CK-MB determination.Results There were no statistically significant differences in the four parameters between the two groups. Arrhythmia scores were also comparable betweeen the two groups. The CK-MB leakage in IPC group was increased but not significantly different from that in control group. The ATP levels of myocardium at the end of reperfusion was significantly lower than that in the control group [(123.85±17.42)μg/g versus (167.21±16.53)μg/g].Conclusions IPC can not protect immature rabbit hearts from ischemia-reperfusion injury. On the contrary it may lead to myocardial injury due to more energy consumption.