Objective: To investigate whether immature hearts experiencing global ischemia and reperfusion injury could be protected by ischemic preconditioning( IPC) and probe the possible mechanism. Methods : Aerobically perfused in Langendorff mode at 39t

isolated immature rabbit hearts( 14 -21 days old)were subjected to a IPC stimulus consisting of 5 minutes of global ischenmia plus 10 minutes of reperfusion. This was followed by 45 minutes of global ischemia and 40 minutes of reperfusion. Left ventricular developed pressure( LVDP)

change of myocardial enzyme (CK - MB) in the coronary effluent

myocardial energy metabolism and morphology were de termined. Cold crystalloid cardioplegia was used to cause the hearts to arrest before the prolonged global I/R. Re sults : The LVDP value in IPC group was significantly higher than that in control. The CK - MB leakage in IPC group was decreased significantly (24.58 ± 5.09 U/L versus 32.80 ± 5.32 U/L in controls P<0. 01). The myocardial levels of ATP in preconditioned group at the end of the reperfusion was significantly preserved(208. 14 ±24. 2ug /g versus 174.52 ± 15. 69ugg/g in controls P<0. 05). Light and electron microscopic findings of myocardium showed the preconditioned hearts were less severely damaged. Conclusion : IPC has a protective effect on the immature rabbit hearts suffering from global I /R injury

which is possibly connected with the preservation of ATP level in myocardium tissue.