Effects of a Xanthine Oxidase/Hypoxanthine Free Radical and Reactive Oxygen Species Generating System on Endothelial Function in New Zealand White Rabbit Aortic Rings

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We investigated the effects of the xanthine oxidase (XO)/hypoxanthine (HX) free radical (FR) generating system on the relaxant properties of aortic rings from New Zealand White rabbits. This system generates superoxide anions, hydroxyl radicals, and H2O2. We wished to identify which of these species is responsible for impairment of vascular function. After obtaining dose-response curves to phenylephrine (PE) and carbachol or sodium nitroprusside (SNP), we exposed rings to the FR generating system or H2O2 for 30 min, either with or without a range of potentially protective agents. Doseresponse curves to carbachol or SNP were then repeated. Exposure to the XO/HX system impaired endotheliumdependent, carbachol-induced relaxation. The hydroxyl radical scavengers mannitol, N-(2-mercaptopropionyl)-glycine (MPG), and captopril offered no protection. Superoxide dismutase (SOD) increased the impairment of response, catalase provided partial protection, and a combination of SOD and catalase completely prevented impairment of the response. H2O2 mimicked the effects of XO/HX system. H2O2 appears to be the primary species involved in mediating the toxic effects of the XO/HX FR generating system, but the superoxide anion is probably responsible for some of the loss of relaxation and a role for intracellular generation of hydroxyl radicals cannot be excluded

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