Na+/H+ exchange subtype 1 inhibition reduces endothelial dysfunction in vessels from stunned myocardium

Abstract

Myocardial ischemia and reperfusion cause myocyte and vascular dysfunction, frequently termed "stunning". We hypothesized that inhibiting the Na+/H+ exchanger subtype 1 isoform (NHE1) during ischemia and reperfusion limits myocardial and coronary microvascular stunning. Anesthetized rats completed 2×10-min coronary artery occlusions separated by 5-min of reperfusion, followed by 15 or 60 min of reperfusion. Vehicle (saline) or the NHE1 inhibitor cariporide (HOE-642) was administered 15 min before ischemia and was continued throughout each protocol. After reperfusion, hearts were excised, and the reactivity of resistance arteries (internal diameter, ∼120 μm) was assessed. The first derivative of left ventricular (LV) pressure, LV developed pressure, and LV systolic wall thickening were depressed (P<0.05) similarly in vehicle- and cariporide-treated rats during ischemia and after 15 or 60 min of reperfusion compared with shamoperated animals that were not exposed to ischemia (i.e., controls). In vessels obtained after 15 min of reperfusion, the maximal response to acetylcholine-induced relaxation (10-8-10-4 M) was blunted (P<0.05) in vessels from vehicle-(∼35%) and cariporide-treated rats (∼55%) compared with controls (∼85%). However, the percent relaxation to acetylcholine was greater (P<0.05) in cariporide-treated rats compared with vehicle-treated rats. Maximal contractile responses to endothelin-1 (10-11-10-7 M) were increased (P<0.05) similarly in vehicle- and cariporide-treated rats compared with controls. Relaxation to sodium nitroprusside (10-4 M) was not different among groups. Results were similar in vessels obtained from animals after 60 min of reperfusion. These findings suggest that NHE1 inhibition before coronary occlusion lessens ischemia-induced microvascular dysfunction for 15-60 rain aider reperfusion but does not alter myocardial contractile function in the area at risk.