Abstract P232: Superoxide Increases Renin Activity, Renal Angiotensin II Type 1 Receptor (at1r) Function and Blood Pressure in Rats

Abstract

We examined role and mechanism of superoxide in renal AT1R function contributing to hypertension in Sprague-Dawley rats. Rats were divided into 4 groups and treated with 1. vehicle, 2. superoxide dismutase (SOD) inhibitor diethylthiocarbamate (DETC, 10mg/kg, i.p./daily for 2 weeks), 3. DETC+tempol (an SOD mimetic, 2 mM in drinking water), and 4. tempol only. Rats were sacrificed, blood plasma and kidneys obtained for biochemical studies. Superoxide [Fluorescence Unit (FU): control vs DETC vs DETC+tempol vs tempol, 0.10±0.006 vs 0.13±0.01 vs 0.09±0.007 vs 0.09±0.004] but not hydrogen peroxide levels increased in the renal tissues of DETC-rats than in vehicle-rats, which decreased in DETC+tempol rats. Nuclear levels of acetylated-Sp3 transcription factor, an index of its activity, (Density Unit: control vs DETC vs DETC+tempol vs tempol, 0.10±0.01 vs 0.17±0.02 vs 0.10±0.01 vs 0.13±0.02) and membranous AT1R proteins levels (Density Unit: control vs DETC vs DETC+tempol vs tempol, 0.98±0.32 vs 2.93±0.40 vs 0.99±0.24 vs 0.77±0.23) increased in DETC-rats, which were attenuated in DETC-tempol-rats. Moreover, plasma renin activity (FU: control vs DETC vs DETC+tempol vs tempol: 0.13±0.006 vs 0.19±0.04 vs 0.12±0.005 vs 0.13±0.01) increased in DETC-rats, which decreased in DETC+tempol-rats. Second set of rats underwent the same treatment as above, anesthetized, blood pressure (BP) and renal AT1R function (in terms of natriuresis) in response to AT1R blocker candesartan (10μg/kg, i.v. bolus) were determined. Systolic BP increased in DETC-rats than in vehicle-rats, which decreased in DETC+tempol-rats (mmHg: control vs DETC vs DETC+tempol vs tempol: 118.6±2.72 vs 136.7±2.96 vs 118.1±3.81 vs 123.1±6.88). Natriuresis in response to candesartan (cande) increased in vehicle-rats, which further increased in DETC-rats while decreased in DETC+tempol-rats (μmols/min: control vs control+cande vs DETC vs DETC+cande vs DETC+tempol vs DETC+tempol+cande vs tempol vs tempol+cande, 0.32±0.07 vs 0.58±0.10 vs 0.19±0.05 vs 1.06±0.34 vs 0.23±0.05 vs 0.49±0.14 vs 0.27±0.04 vs 0.66±0.11). Taken together, our results suggest that superoxide via Sp3 activation increases renin activity, membranous AT1R levels and function contributing to hypertension in rats.