l-NIL prevents renal microvascular hypoxia and increase of renal oxygen consumption after ischemia-reperfusion in rats

Abstract

Even though renal hypoxia is believed to play a pivotal role in the development of acute kidney injury, no study has specifically addressed the alterations in renal oxygenation in the early onset of renal ischemia-reperfusion (I/R). Renal oxygenation depends on a balance between oxygen supply and consumption, with the nitric oxide (NO) as a major regulator of microvascular oxygen supply and oxygen consumption. The aim of this study was to investigate whether I/R induces inducible NO synthase (iNOS)-dependent early changes in renal oxygenation and the potential benefit of iNOS inhibitors on such alterations. Anesthetized Sprague-Dawley rats underwent a 30-min suprarenal aortic clamping with or without either the nonselective NO synthase inhibitor Nω-nitro-l-arginine methyl ester (l-NAME) or the selective iNOS inhibitor l- N6-(1-iminoethyl)lysine hydrochloride (l-NIL). Cortical (CμPo2) and outer medullary (MμPo2) microvascular oxygen pressure (μPo2), renal oxygen delivery (Do2ren), renal oxygen consumption (V̇o2ren), and renal oxygen extraction (O2ER) were measured by oxygen-dependent quenching phosphorescence techniques throughout 2 h of reperfusion. During reperfusion renal arterial resistance and oxygen shunting increased, whereas renal blood flow, CμPo2, and MμPo2(−70, −42, and −42%, respectively, P < 0.05), V̇o2ren, and Do2ren(−70%, P < 0.0001, and −28%, P < 0.05) dropped. Whereas l-NAME further decreased Do2ren, V̇o2ren, CμPo2, and MμPo2and deteriorated renal function, l-NIL partially prevented the drop of Do2renand μPo2, increased O2ER, restored V̇o2renand metabolic efficiency, and prevented deterioration of renal function. Our results demonstrate that renal I/R induces early iNOS-dependent microvascular hypoxia in disrupting the balance between microvascular oxygen supply and V̇o2ren, whereas endothelial NO synthase activity is compulsory for the maintenance of this balance. l-NIL can prevent ischemic-induced renal microvascular hypoxia.