Antihypertensive response to prolonged tempol in the spontaneously hypertensive rat

Introduction. Tempol is a permeant nitroxide superoxide dismutase (SOD) mimetic that lowers mean arterial pressure (MAP) in spontaneously hypertensive rats (SHRs). We investigated the hypothesis that the antihypertensive response entails a negative salt balance, blunting of plasma renin activity (PRA), endothelin-1 (ET-1), or catecholamines or correction of oxidative stress as indexed by 8-isoprostane prostaglandin F-2 alpha (PGF(2 alpha)) (8-Iso). Methods. Groups (N= 6 to 8) of SHRs were infused for 2 weeks with vehicle or tempol (200 nmol/kg/min) or given tempol (2 mmol/L) in drinking water. Results. Tempol infusion reduced the MAP of anesthetized SHRs (150 +/- 5 vs. 126 +/- 6 mm Hg) (P < 0.005). Oral tempol did not change the heart rate but reduced the MAP of conscious SHRs (-23 +/- 6 mm Hg) (P < 0.01) but not Wistar-Kyoto (WKY) rats. Tempol infusion increased the PRA (2.2 +/- 0.2 vs. 5.0 +/- 0.9 ng/mL/hour) (P < 0.005), did not change excretion of nitric oxide (NO) [NO2+ NO3 (NOx)], ET-1, or catecholamines but reduced excretion of 8-Iso (13.2 +/- 1.4 vs. 9.6 +/- 0.9 ng/24 hours; P < 0.01). Cumulative Na+ balance and gain in body weight were unaltered by tempol infusion. Tempol prevented a rise in MAP with high salt intake. Conclusion. Tempol corrects hypertension without a compensatory sympathoadrenal activation or salt retention. The response is independent of nitric oxide, endothelin, or catecholamines and occurs despite increased PRA. It is accompanied by a reduction in oxidative stress and is maintained during increased salt intake.