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on January 5, 2004

A more recent version of this article appeared on February 1, 2004

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Submitted on September 30, 2003
Revised on November 6, 2003

Tempol Lowers Blood Pressure and Sympathetic Nerve Activity But Not Vascular O₂^- in DOCA-Salt Rats

Hui Xu^*; Gregory D. Fink; and James J. Galligan

From the Department of Pharmacology and Toxicology and The Neuroscience Program, Michigan State University, East Lansing, Mich.

^* To whom correspondence should be addressed. E-mail: xuhui2{at}msu.edu.

Abstract--This study tested the hypothesis that depressor responses caused by tempol are not associated with reductions in vascular O₂^- levels in urethane-anesthetized deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We compared the effects of intravenous (IV) administration of tempol, apocynin, superoxide dismutase-polyethylene glycol (PEG-SOD), and SOD on mean arterial blood pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA). In DOCA-salt rats, tempol (30 to 300 µmol/kg) dose-dependently decreased RSNA, MAP, and HR. Tempol (300 µmol/kg) decreased MAP from 140±5 to 83±4 mm Hg (P<0.05). HR decreased from 435±15 to 390±12 bpm (P<0.05). RSNA was reduced by 54%±6% from baseline. However, in the same rats, tempol did not reduce dihydroethidium-induced fluorescent signals in the aorta and vena cava. Apocynin (200 µmol/kg) did not lower MAP (142±5 mm Hg versus 140±6 mm Hg) or HR (428±15 bpm versus 420±13 bpm) and apocynin did not potentiate depressor responses caused by tempol. PEG-SOD (10 000 U/kg, bolus or 5000 U/kg bolus followed by a 30-minutes infusion of 500 U/kg/min) or SOD (25 000 U/kg, bolus or 10 000 U/kg bolus followed by a 30-minutes infusion of 1000 U/kg per minute) did not alter MAP or HR. It is concluded that depressor responses and decreases in HR and RSNA caused by acute tempol treatment are caused by direct sympathetic nerve activity inhibition that is not accompanied by SOD-mimetic action in the aorta or vena cava.

Key words: super oxide • antioxidants • blood pressure

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