Nitric oxide mediates protective effect of endothelin receptor antagonism during myocardial ischemia and reperfusion

Abstract
Endothelin (ET) receptor antagonism protects from ischemiareperfusion injury. We hypothesized that the cardioprotective effect is related to nitric oxide (NO) bioavailability. Buffer-perfused rat and mouse hearts were subjected to ischemia and reperfusion. At the onset of ischemia, the rat hearts received vehicle, the dual endothelin type A/type B (ETA/ETB) receptor antagonist bosentan (10 μM), the NO synthase inhibitor NG-monomethyl-l-arginine (l-NMMA; 100 μM), the combination of bosentan and l-NMMA or the combination of bosentan, l-NMMA, and the NO substrate l-arginine (1 mM). Hearts from wild-type and endothelial NO synthase (eNOS)-deficient mice received either vehicle or bosentan. Myocardial performance, endothelial function, NO outflow, and eNOS expression were monitored. Bosentan significantly improved myocardial function during reperfusion in rats and in wild-type mice, but not in eNOS-deficient mice. The functional protection afforded by bosentan was inhibited by l-NMMA, whereas it was restored by l-arginine. Myocardial expression of eNOS (immunoblotting) increased significantly in bosentan-treated rat hearts compared with vehicle hearts. Recovery of NO outflow during reperfusion was enhanced in the bosentan-treated rat heart. The endothelium-dependent vasodilator adenosine diphosphate increased coronary flow by 18 ± 9% at the end of reperfusion in the bosentan group, whereas it reduced coronary flow by 7 ± 5% in the vehicle group ( P < 0.001). The response to the endothelium-independent dilator sodium nitroprusside was not different between the two groups. In conclusion, the dual ETA/ETB receptor antagonist bosentan preserved endothelial and cardiac contractile function during ischemia and reperfusion via a mechanism dependent on endothelial NO production.