Effect of Antioxidant Therapy on Nitric Oxide Synthase (NOS) Expression in Hypertensive Rats

Abstract

P66 Earlier studies have demonstrated evidence for increased reactive oxygen species (ROS) and enhanced nitric oxide synthase (NOS) expression and NO production in spontaneously hypertensive rats (SHR). Given the negative feedback regulation of NOS by NO, we hypothesized that enhanced NO inactivation by ROS may contribute to compensatory upregulation of NOS in SHR. The present study was designed to test this hypothesis. Eight-week old male SHR were treated for three weeks with either a placebo or the potent antioxidant, lazaroid (des-methyltirilazad, 10 mg/kg/day by gastric gavage). A group of age-matched male Wistar Kyoto (WKY) rats served as controls. Tail arterial blood pressure and urinary excretion of NO metabolites (i.e. nitrate and nitrite, NO x ) were measured. In addition, immunodetectable NOS isotype proteins in the vascular, renal, cardiac and cerebral tissues were measured by Western blot. Compared to the WKY group, the placebo-treated SHR group showed a marked elevation of blood pressure (129±6 vs 198±8 mmHg, P<0.01), a significant increase in urinary NOx excretion (714±82 vs 1344±187 μmol/g creatinine, P<0.01) and a significant upregulation of eNOS (given as relative optical density) in the aorta (27±3 vs 165±15*), kidney (99±3 vs 180±8*) and heart (17±4 vs 126±2*). Likewise, inducible NOS (iNOS) expression was increased in the aorta (27±3 vs 163±15*), kidney (7±3 vs 322±57*)and heart (30±1 vs 80±2*) of the untreated SHR when compared to the WKY controls. In addition, nNOS expression was elevated in the brain (10±1 vs 18±1*) and kidney (12±1 vs 20±2*) of the untreated SHR group. Lazaroid therapy ameliorated HTN (144±4 mmHg, P<0.01, vs untreated SHR group) and mitigated upregulation of eNOS in the aorta (85±13*), kidney (129±8*) and heart (59±10*). Similarly, antioxidant therapy lowered iNOS expression in the aorta (85±13*), kidney (99±15*) and heart (41±3*) of the treated SHR. However, it had no significant effect on renal and brain nNOS expressions (18±2 and 16±2, respectively). These findings support the role of oxidative stress in the genesis and/or maintenance of HTN and compensatory up-regulations of eNOS and iNOS expressions in SHR. *P<0.05