Abstract 144: Endothelium-Derived Nitroxyl-Mediated Relaxation Is Resistant to Superoxide Scavenging and Preserved in Diabetic Rat Aorta

Abstract

Nitric oxide (NO)-mediated relaxation is impaired in diabetes due to oxidative stress. Nitroxyl (HNO) also contributes to endothelium-dependent relaxation however its role in diabetes-induced oxidative stress is not known. 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 standard organ bath techniques. Pharmacological tools (3 mM L-cysteine), a selective HNO scavenger and 100 μM hydroxocobalamin (HXC, a selective NO scavenger), were used to distinguish between NO and HNO-mediated relaxation. Exposure to the superoxide generator pyrogallol (100 μM) significantly reduced the sensitivity to DEANONOate (pEC 50 : 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 rat aorta (pEC 50 : control, 7.30±0.15 vs. pyrogallol, 7.31±0.08, n=5-6, p>0.05). In the presence of L-cysteine, pyrogallol caused a further inhibition to ACh-induced NO-mediated relaxation. In contrast, the addition of pyrogallol to HXC did not cause any further inhibition of endothelium-dependent relaxation (R max : HXC, 80±2% vs. pyrogallol+HXC, 67±7%, n=7, p>0.05), indicating that HNO-mediated relaxation was not affected by superoxide. Similarly, in the diabetic aorta, responses to ACh were not affected when the contribution of NO to relaxation was abolished by HXC (R max : normal, 55±7% vs. diabetic, 60±8%, n=8-9, p>0.05), indicating a preserved HNO-mediated relaxation. Conversely, when the contribution of HNO was inhibited with L-cysteine, the responses to ACh (pEC 50 : normal, 7.01±0.04 vs. diabetic, 6.72±0.1, n=7-9, p<0.05), were significantly decreased in diabetic compared to normal aorta, suggesting that the contribution of NO was impaired by diabetes. These findings demonstrate that NO-mediated relaxation is impaired in the presence of oxidative stress but the HNO component of relaxation is preserved under those conditions.