Na+/H+ exchanger inhibitor HOE-642 improves cardioplegic myocardial preservation under both normothermic and hypothermic conditions

Background The sarcolemmal Na+/H+ exchanger has been implicated in the pathogenesis of myocardial injury during ischemia/reperfusion. We determined the cardioprotective efficacy of the Na+/H+ exchanger inhibitor HOE-642 (HOE) as an alternative, adjunct, or additive to cardioplegia (CP). Methods and Results In isolated working rat hearts (n=6 per group) subjected to 25 minutes of ischemia at 37 degrees C, the postischemic recovery of aortic flow (AF) was 5+/-3% in controls; this was improved to 18+/-4% by the preischemic infusion of 1 mu mol/L HOE (P<.05 versus control) and to 53+/-7% by CP (P<.05 versus control and HOE). In hearts subjected to CP and 35 minutes of ischemia at 37 degrees C, AF recovered to 9+/-3% with CP alone; this was improved to 18+/-3% by the adjunctive administration of HOE during early reperfusion (CP+repHOE, P<.05 versus CP) and to 27+/-4% by the use of HOE as an additive to CP (CP+HOE, P<.05 versus CP and CP+repHOE). With 120 minutes of ischemia at 28 degrees C, AF recoveries were 16+/-3% in CP, 32+/-3% in CP+repHOE (P<.05 versus CP) and to 50+/-4% in CP+HOE (P<.05 versus CP and CP+repHOE). With 300 minutes of ischemia at 7.5 degrees C, the corresponding values were 30+/-4%, 45+/-5% (P<.05 versus CP), and 63+/-5% (P<.05 versus CP and CP+repHOE). Improved recovery of pump function was often accompanied by a reduction in creatine kinase leakage during reperfusion. Conclusions (i) HOE alone affords significant protection at normothermia but is not a superior alternative to CP, and (ii) the use of HOE as an adjunct or additive to CP provides significant benefit at normothermia, moderate hypothermia, and severe hypothermia.