Preconditioning with Na+/H+ exchange inhibitor HOE642 reduces calcium overload and exhibits marked protection on immature rabbit hearts

Inhibition of Na/H exchanger isoform-1 (NHE1) has shown significant protection in adult myocardium during ischemia/reperfusion injury; however, the effect is unclear in immature myocardium. We evaluated the effects of HOE642 (a potent, highly selective NHE1 inhibitor) preconditioning on immature rabbit hearts. Twenty immature (2-3 weeks old) New Zealand white rabbits were randomly divided into the control group (n = 10) and the HOE642 preconditioning group (n = 10). The immature isolated hearts were subjected to 45 minutes of normothermic global ischemia plus 60 minutes of reperfusion after being established on the Langendorff apparatus. During reperfusion, the recovery rates of cardiac function (LVDP, +dp/dtmax, -dp/dtmax, and coronary flow) were about 90% in the HOE642 treated group and about 50% in the control group (p < 0.05). HOE642 preconditioning can significantly decrease the release of cardiac specific enzymes CK, CK-MB and LDH (p < 0.05) and the myocardial water content (p < 0.05). Meanwhile, HOE642 markedly attenuated intracellular calcium overload (265.8 +/- 41.1 vs. 500.7 +/- 60.8 mg/kg dry wt) (p < 0.01). The blinded ultrastructural assessment under transmission electron microscopy illustrated that preconditioning with HOE642 produced evident myocyte salvage. This study demonstrates that preconditioning with HOE642 provides a significant protection during ischemia/reperfusion injury in immature myocardium, mostly by reducing myocardial calcium overload.