RNA silencing in vivo reveals role of p22phox 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 p22phox component of NADPH oxidase is required for this response. Reactive oxygen species were assessed from excretion of 8-isoprostane prostaglandin F2α and blood pressure by telemetry. Two siRNA sequences to p22phox (sip22phox) 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, sip22phox, relative to control siRNA, led to significant (P<0.001; ≈50%) reductions in expression of p22 phox mRNA and protein and of NADPH oxidase activity in the kidney cortex. In Ang II-infused rats, sip22phox decreased protein expression for Nox-1, -2, and -4 but increased p47phox. Three days after sip22phox, conscious rats infused with Ang II had a reduced excretion of 8-isoprostane (10±1 versus 19±2 pg·24 h -1; P<0.01) and a reduced mean arterial pressure (142±5 versus 168±4 mm Hg; P<0.005). An increase in p22phox 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. © 2006 American Heart Association, Inc.