Perivascular Superoxide Anion Contributes to Impairment of Endothelium-Dependent Relaxation

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Abstract
Background— Like endothelial and smooth muscle cells, vascular adventitial fibroblasts contain a substantial NAD(P)H oxidase superoxide anion (O 2 − )-generating system activated by angiotensin II (Ang II). Based on the ability of nitric oxide (NO·) to diffuse rapidly through tissue and the fast reaction rate of NO· and O 2 − , we postulated that the interaction between NO· and adventitial NAD(P)H oxidase–derived O 2 − contributes to impairment of endothelium-dependent relaxation (EDR). Methods and Results— C57Bl/6 mouse abdominal aortas were simultaneously perfused intraluminally and suffused adventitially with physiological buffer at 37°C. After constricting the vessels with phenylephrine, an acetylcholine dose-response curve was obtained while monitoring changes in diameter by videomicroscopy. Endogenous O 2 − was increased by treating the adventitial side of the aortas with Ang II (10 pmol/L), leading to impairment of EDR. EDR impairment was reversed by adventitial suffusion of superoxide dismutase (SOD) of aortas from wild-type mice. Ang II–treated aortas from gp91 phox −/− mice, which lack significant adventitial O 2 − , exhibited greater EDR and were not affected by SOD. Adventitially suffused SOD failed to penetrate the media, indicating that the effects of SOD were localized to the adventitia. Adventitial application of the O 2 − -generating system xanthine/xanthine oxidase or the potent NO scavenger oxyhemoglobin impaired EDR. Conclusions— O 2 − derived from adventitial gp91 phox -based NAD(P)H oxidase contributes to impairment of the action of endothelium-derived NO·.