Increased renal medullary H2O2 leads to hypertension

We have recently reported that exaggerated oxidative stress in the renal medulla due to superoxide dismutase inhibition resulted in a reduction of renal medullary blood flow and sustained hypertension. The present study tested the hypothesis that selective scavenging of O2*- in the renal medulla would prevent hypertension associated with this exaggerated oxidative stress. An indwelling, aortic catheter was implanted in nonnephrectomized Sprague-Dawley rats for daily measurement of arterial blood pressure, and a renal medullary interstitial catheter was implanted for continuous delivery of the superoxide dismutase inhibitor diethyldithiocarbamic acid (DETC, 7.5 mg x kg(-1) x d(-1)) and a chemical superoxide dismutase mimetic, 4-hydroxytetramethyl piperidine-1-oxyl (TEMPOL, 10 mg. kg-1. d-1). Renal medullary interstitial infusion of TEMPOL completely blocked DETC-induced accumulation of O2*- in the renal medulla, as measured by the conversion rate of dihydroethidium to ethidium in the dialysate and by urinary excretion of 8-isoprostanes. However, TEMPOL infusion failed to prevent DETC-induced hypertension, unless catalase (5 mg x kg(-1) d(-1)) was coinfused. Direct infusion of H2O2 into the renal medulla resulted in increases of mean arterial pressure from 115+/-2.5 to 131+/-2.1 mm Hg, which was similar to that observed in rats receiving the medullary infusion of both TEMPOL and DETC. The results indicate that sufficient catalase activity in the renal medulla is a prerequisite for the antihypertensive action of TEMPOL and that accumulated H2O2 in the renal medulla associated with exaggerated oxidative stress might have a hypertensive consequence.