Abstract 144: Endothelium-Derived Nitroxyl-Mediated Relaxation Is Resistant to Superoxide Scavenging and Preserved in Diabetic Rat Aorta
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 (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 rat aorta (pEC50: 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 (Rmax: 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 (Rmax: 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 (pEC50: 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.
- © 2012 by American Heart Association, Inc.