Endothelium‐Derived Nitroxyl‐Mediated Relaxation Is Resistant To Superoxide Scavenging And Preserved In Diabetic Rat Aorta

Abstract

The aim of this study is to investigate whether acute exposure to oxidative stress or diabetes affects the contribution of HNO to endothelium‐dependent relaxation in the rat aorta. Vascular responses to the endothelium‐dependent relaxant, ACh, the HNO donor, Angeli's salt and the NO donor, DEANONOate, were determined using organ bath techniques. Exposure to the superoxide generator pyrogallol (100 μM) significantly reduced the sensitivity to DEANONOate (pEC50: control, 8.03±0.10 vs. pyrogallol, 7.48±0.09, n=6, p<0.01) but had no effect on responses to Angeli's salt. In the presence of L‐cysteine (a selective HNO scavenger), pyrogallol caused a further inhibition to ACh‐induced NO‐mediated relaxation. In contrast, the addition of pyrogallol to hydroxocobalamin (HXC, a selective NO scavenger) did not cause any further inhibition of ACh‐induced relaxation, indicating that HNO‐mediated relaxation was resistant to superoxide. Similarly, in the diabetic aorta, responses to ACh were not affected when NO was abolished by HXC, indicating a preserved HNO‐mediated relaxation. Conversely, when HNO was inhibited with L‐cysteine, the responses to ACh (pEC50: normal, 7.01±0.04 vs. diabetic, 6.72±0.1, n=7–9, p<0.05), were significantly decreased in diabetic aorta, suggesting that NO was impaired by diabetes. These findings demonstrate that HNO component of relaxation is unaffected by oxidative stress.