Is the balance between nitric oxide and superoxide altered in spontaneously hypertensive rats with endothelial dysfunction?

Background. Increases in oxidant stress, i.e. excessive production of superoxide anion (.O-2(-)), have been reported in different models of hypertension. This study was-designed to test the hypothesis that increased .O-2(-) production, more than diminished nitric oxide (NO) generation, plays a critical role in endothelial dysfunction present in spontaneously hypertensive rats (SHR). Methods. The study was performed in 30-week-old normotensve Wistar-Kyoto rats (WKY) and SHR. In addition, 16-week-old SHR were treated with oral irbesartan (average dose 20 mg/kg per day) for 14 weeks (SHR-I). Aortic nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase activity was determined, by-use of chemiluminescence with lucigenin. Aortic constitutive nitric oxide synthase (cNOS) activity:was determined by measuring the conversion of L-arginine to L-citrulline. Vascular responses to acetylcholine were determined by isometric tension studies. Results. Whereas systolic blood pressure (SBP) was significantly increased in SHR compared with WKY, no differences were observed in SEP between SHR-I and WKY. In SHR compared with WKY, we found significantly greater NADH/NADPH-driven .O-2(-) production, similar cNOS-mediated NO production and an impaired vasodilation in response to acetylcholine. Treated SHR had similar NADH/NADPH oxidase activity and significantly lower cNOS activity than the WKY group. Vasodilation in response to acetylcholine was improved in SHR-I. Conclusions. These findings suggest that a diminished availability of NO secondary to an enhanced NADH/ NADPH oxidase-dependent .O-2(-) production may play a critical role in endothelial dysfunction of adult SHR.