Myocardial Protection by Na + -H + Exchange Inhibition in Ischemic, Reperfused Porcine Hearts

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Abstract
Background Studies in isolated myocytes and isolated heart preparations have suggested that Na + -H + exchange is an important mechanism for myocardial ischemia–reperfusion injury. This study was undertaken to determine whether inhibition of Na + -H + exchange limits infarct size and improves regional systolic shortening in regional ischemia and reperfusion in intact pigs. Methods and Results The left anterior descending coronary artery was occluded in 18 anesthetized and thoracotomized pigs for 45 minutes and then reperfused for 24 hours. As main end points of this study, regional systolic shortening (sonomicrometry) and infarct size (percentage of infarcted to ischemic myocardium) were determined at the end of the experiments. Infarcted myocardium was assessed by histochemistry (tetrazolium stain) and by quantitative histology of one heart slice. The Na + -H + exchange inhibitor Hoe 694 was administered intravenously at a dose of 3 mg/kg in 6 pigs each either 10 minutes before ischemia (group A) or 10 minutes before the onset of reperfusion (group B). Six pigs served as controls (group C). Treatment with Hoe 694 before ischemia decreased histochemical infarct size from 65±18% (control group) to 13±8% ( P <.01) and histological infarct size from 49±20% (control group) to 14±4% ( P <.01). Histochemical (55±19%) and histological (42±15%) infarct sizes of group B were insignificantly reduced by 15%. Myocardial protection in group A was associated with an attenuated contracture after 10 minutes of reperfusion and an improved regional systolic shortening after 24 hours of reperfusion (group A, 25±12%; control group, 6±5%; P =.01). These parameters remained unaffected in group B. Conclusions This study clearly demonstrates that Na + -H + exchange is an important mechanism for cell death in myocardial ischemia and reperfusion in intact pigs; thus, inhibition of this exchange system may prove a promising new strategy in the clinical treatment of myocardial ischemia and reperfusion.

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