OXIDATIVE STRESS AND RENAL AT1R FUNCTION DURING HYPERTENSION

Angiotensin (Ang) II via renal Ang II type 1 receptors (AT1R) modulates proximal tubular Na/K-ATPase such that, low concentrations of Ang II stimulates Na/K-ATPase whereas at high concentrations the stimulatory effect is lost. Studies show that oxidative stress can impair Ang II-induced Na/K-ATPase regulation and can contribute to hypertension. In the present study we first determined whether renal oxidative stress precedes development of hypertension in SHR. We found that at 3-4 weeks of age, SHR are normotensive and do not exhibit proximal tubular oxidative stress. Also, renal AT1R protein expression and Ang II-induced Na/K-ATPase stimulation was similar in SHR and WKY rats. Next we determined if antioxidant treatment at an early age can prevent renal oxidative stress and alleviate increase in blood pressure in SHR. We found that in adult SHR, there was high blood pressure, increased renal oxidative stress and decreased proximal tubular Nrf-2 activation as well as antioxidant activity compared to WKY rats. In WKY rats Ang II exerted a biphasic effect on Na/K-ATPase whereas in SHR, there was loss of biphasic effect such that Ang II produced stimulation at both high and low concentrations. In presence of nitric oxide (NO) synthase (NOS) inhibitor, L-NAME, Ang II (high concentration) produced stimulation of Na/K-ATPase in WKY rats. Ang II via AT1R caused NO iv production in WKY rats but not in SHR. Ang II caused enhanced activation of NADPH oxidase and L-arginine dependent NOS mediated superoxide production in proximal tubules of SHR. NADPH oxidase inhibitor DPI prevented Ang II-induced L-arginine dependent superoxide production and normalized NO production in SHR. There was increased renal NF kappaB activation, Giα protein expression and AT1R-G protein-coupling in SHR compared to WKY rats. Antioxidant resveratrol decreased blood pressure, increased Nrf-2 mediated antioxidant enzymes, reduced oxidative stress, normalized NOS coupling and restored Ang II-induced NO production as well as biphasic effect on Na/K-ATPase. Resveratrol treatment in SHR decreased Giα protein expression and normalized AT1R-G protein-coupling. Together these results demonstrate mechanism by which renal oxidative stress contributes to hypertension in SHR.