RNA Silencing In Vivo Reveals Role of p22 phox in Rat Angiotensin Slow Pressor Response

Abstract

The angiotensin II (Ang II) slow-pressor response entails an increase in mean arterial pressure and reactive oxygen species. We used double-stranded interfering RNAs (siRNAs) in Sprague Dawley rats in vivo to test the hypothesis that an increase in the p22 ^phox component of NADPH oxidase is required for this response. Reactive oxygen species were assessed from excretion of 8-isoprostane prostaglandin F _2α and blood pressure by telemetry. Two siRNA sequences to p22 ^phox (sip22 ^phox ) reduced mRNA >85% in cultured vascular smooth muscle cells. Rats received rapid (10 second) IV injections (50 to 100 μg) of 1 of 2 different sip22 ^phox , control siRNA, or vehicle (TransIt in saline) during 14 day SC infusions of Ang II (200 ng · kg ⁻¹ · min ⁻¹ ) or sham infusions. In both groups, sip22 ^phox , relative to control siRNA, led to significant ( P phox mRNA and protein and of NADPH oxidase activity in the kidney cortex. In Ang II–infused rats, sip22 ^phox decreased protein expression for Nox-1, -2, and -4 but increased p47 ^phox . Three days after sip22 ^phox , conscious rats infused with Ang II had a reduced excretion of 8-isoprostane (10±1 versus 19±2 pg · 24 h ⁻¹ ; P P phox is required for increased renal NADPH oxidase activity, expression of Nox proteins and oxidative stress, and contributes ≤50% to hypertension during an Ang II slow-pressor response.