Vascular NADH/NADPH Oxidase Is Involved in Enhanced Superoxide Production in Spontaneously Hypertensive Rats

Abstract

Abstract —This study was designed to test the hypothesis that stimulation of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase is involved in increased vascular superoxide anion (·O ₂ ⁻ ) production in spontaneously hypertensive rats (SHR). The study was performed in 16-week-old and 30-week-old normotensive Wistar-Kyoto rats (WKY ₁₆ and WKY ₃₀ , respectively) and in 16-week-old and 30-week-old SHR (SHR ₁₆ and SHR ₃₀ , respectively). In addition, 16-week-old SHR were treated with oral irbesartan (average dose 20 mg/kg per day) for 14 weeks (SHR ₃₀ -I). Aortic NADH/NADPH oxidase activity was determined by use of chemiluminescence with lucigenin. The expression of p22phox messenger RNA was assessed by competitive reverse transcription–polymerase chain reaction. Vascular responses to acetylcholine were determined by isometric tension studies. Aortic wall structure was studied, determining the media thickness and the cross-sectional area by morphometric analysis. Whereas systolic blood pressure was significantly increased in the 2 groups of hypertensive animals compared with their normotensive controls, no differences were observed in systolic blood pressure between SHR ₃₀ and SHR ₁₆ . No other differences in the parameters measured were found between WKY ₁₆ and SHR ₁₆ . In SHR ₃₀ compared with WKY ₃₀ , we found significantly greater p22phox mRNA level, NADH/NADPH-driven ·O ₂ ⁻ production, media thickness, and cross-sectional area and an impaired vasodilation in response to acetylcholine. Treated SHR had similar NADH/NADPH oxidase activity and p22phox expression as the WKY ₃₀ group. The vascular functional and morphological parameters were improved in SHR ₃₀ -I. These findings suggest that an association exists between p22phox gene overexpression and NADH/NADPH overactivity in the aortas of adult SHR. Enhanced NADH/NADPH oxidase–dependent ·O ₂ ⁻ production may contribute to endothelial dysfunction and vascular hypertrophy in this genetic model of hypertension.