Long-term angiotensin II inhibition increases mitochondrial nitric oxide synthase and not antioxidant enzyme activities in rat heart

Objective To provide insight into the subcellular mechanisms involved in the improvement of cardiovascular structure and function by long-term inhibition of the renin-angiotensin system. Design The activities of antioxidant enzymes and mitochondrial free radical production were determined in the heart of control (C), enalapril-treated (E), and losartan-treated (L) rats to test the hypothesis of increased antioxidant enzyme activities and participation of mitochondria in the effects of chronic treatments with angiotensin II inhibitors. Methods At 6 and 18 months of treatment, superoxide dismutases (SOD), Se-glutathione peroxidase, and catalase activities were determined in left ventricle homogenates by spectrophotometric methods and nitric oxide (NO) production in submitochondrial membranes by the oxyhemoglobin oxidation assay. The maximal rate of hydrogen peroxide (H2O2) production by submitochondrial membranes was also evaluated at 18 months by the scopoletin-horseradish peroxidase method. Results No significant increase was found in the antioxidant enzymes measured. At 6 months, Mn-SOD was actually decreased in E and catalase in both E and L, whereas at 18 months Se-glutathione peroxidase was decreased in L. Production of NO by submitochondrial particles was 64% higher at 6 months in E and 105% higher at 18 months in E and L. Maximal hydrogen peroxide production was lower at 18 months in both groups. Conclusions Results do not support the hypothesis of an increase in antioxidant enzyme activity by long-term treatment with angiotensin II inhibitors as previously suggested and point towards a role for the NO produced by mitochondrial nitric oxide synthase (mtNOS) in the protective effect of these drugs. (C) 2002 Lippincott Williams Wilkins.