Ischemic Preconditioning In Immature Rabbit Hearts

Objective: Protection offered by ischemic preconditioning (IPC) against myocardial ischemia has been extensively reported in adult hearts of all species studied. This study was designed to investigate whether immature hearts could be preconditioned and to probe the effects of IPC on immature myocardium. Method: The aorta of isolated immature rabbit hearts(14-21days old) was connected to Langendorff preparation within 30 s after excision. The hearts were perfused with oxygenated (95%O2 : 5%CO2) Krebs-Henseleit buffer(KHB) at 60 cmH2O. 16 immature rabbit hearts were equally divided into 2 groups: control group and IPC group. In IPC group the hearts were first subjected to an IPC stimulus consisting of 5 minutes of global ischemia plus 10 minutes of reperfusion. The hearts in both groups were subjected to 30 minutes of global ischemia and 40 minutes of reperfusion. The change of myocardial hemodynamics, arrhythmia quantification, cardiac ischemia-beating time, myocardial enzyme in the coronary effluent, myocardial energetic metabolism and morphology were also determined. Results: CF,HR,LVDP and ±dp/dtmax recovery were expressed as percent of their baseline values at post-reperfusion 5,10,20,30,40 minutes respectively. The four indexes have not significant difference between the IPC group and the controls. Arrhythmia scores were also comparable between the two groups. It took the IPC group much longer time in cardiac ischemia-beating [(16.23±1.74)min versus(13.50±1.82)min in controls P<0.01]. The CK-MB leakage in IPC group was increased, but the result was not significantly different from that in controls. The ATP levels of myocardium in IPC group at the end of the reperfusion was significantly decreased [( 123.85±17.42)μg/g.wet versus (167.21±16.53)μg/g.wet in controls P<0.01]. Light and electron microscopic findings of myocardium showed the preconditioned hearts were similarly damaged. Conclusions: Single IPC can not protect the cardiac function and decrease the arrhythmia incidence of immature rabbit hearts experiencing with global ischemia and reperfusion. On the contrary, it may lead to injury of the myocardium. The reason for these may be related to longer lasting cardiac ischemia-beating time and more energy consumption .