Enhanced superoxide activity modulates renal function in NO-deficient hypertensive rats

An enhancement of superoxide (O-2(-)) activity was shown to contribute to the development of hypertension induced by NO deficiency. To better understand the mechanistic role of O-2(-) in this NO-deficient hypertension, we evaluated the renal responses to acute intraarterial administration of an O-2(-) scavenger, tempol (50 mu g/min per 100 g of body weight) in anesthetized male Sprague-Dawley rats treated with NO synthase inhibitor nitro-L-arginine methyl ester (15 mg/kg per day in drinking water, n = 7) for 4 weeks, which caused increases in mean arterial pressure (146 +/- 3 versus 124 +/- 2 mm Hg) compared with normotensive control rats (n = 6). Hypertensive rats had higher renal vascular resistance (29 +/- 2 versus 20 +/- 1 mm Hg/mL per minute per gram), as well as lower renal blood flow (5.2 +/- 0.3 versus 6.3 +/- 0.2 mL/min per gram; cortical blood flow, 153 +/- 13 versus 191 +/- 8 perfusion units; medullary blood flow, 43 +/- 2 versus 51 +/- 3 perfusion units) and glomerular filtration rate (0.69 +/- 0.04 versus 0.90 +/- 0.05 mL/min per gram) without a significant difference in urinary sodium excretion (0.81 +/- 0.07 versus 0.86 +/- 0.12 mu mol/min per gram) compared with normotensive rats. Urinary 8-isoprostane excretion rate (6.8 +/- 0.7 versus 4.5 +/- 0.3 pg/min per gram) was higher in hypertensive than normotensive rats. Intraarterial infusion of tempol did not alter renal function in normotensive rats. However, tempol significantly decreased renal vascular resistance by 12 +/- 2% and urinary 8-isoprostane excretion rate by 24 +/- 4% and increased renal blood flow by 10 +/- 2%, cortical blood flow by 9 +/- 2%, medullary blood flow by 15 +/- 6%, glomerular filtration rate by 11 +/- 3%, and urinary sodium excretion by 19 +/- 5% in hypertensive rats. These data indicate that enhanced O-2(-) activity modulates renal hemodynamics and excretory function during reduced NO production and, thus, contributes to the pathophysiology of the NO-deficient form of hypertension.