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1 Cardiovascular-Kidney Institute and Division of Nephrology and Hypertension, Georgetown University, Washington, District of Columbia, United States
* To whom correspondence should be addressed. E-mail: yc53{at}georgetown.edu.
Tempol catalyzes the formation of H2O2 from superoxide (O2.-) and relaxes blood vessels. We tested the hypothesis that the generation of H2O2 by tempol in vascular smooth muscle cells (VSMCs) during oxidative stress contributes to the vasorelaxation. Tempol and nitroblue tetrazolium (NBT) both metabolize O2.- in VSMCs, but only tempol generates H2O2. Rat pressurized mesenteric arteries were exposed for 20 min to the thromboxane-prostanoid receptor agonist, U-46619, or norepinephrine (NE). During U-46619, tempol caused a transient dilation (22±2%), whereas NBT was ineffective (2±1%) and neither dilated vessels constricted with NE which does not cause vascular oxidative stress. Neither endothelium removal nor blockade of K+ channels with 40mM KCl affected the tempol-induced dilation, but catalase blunted the tempol dilation by 53±7%. Tempol, but not NBT, increased H2O2 in rat mesemteric vessels loaded with dichlorofluorescein. To test physiologic relevance in vivo, topical application of tempol caused a transient dilation (184±20%) of mouse cremaster arterioles exposed to angitensin II for 30 min which was not seen with NBT (9±4%). The vasodilation to tempol was reduced by 68±6% by catalase. We conclude that the transient relaxation of blood vessels by tempol after prolonged exposure to U-46619- or angiotensin II is mediated in part via production of H2O2 and is largely independent of the endothelium and potassium channels.
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