Superoxide Anion Production Is Increased in a Model of Genetic Hypertension: Role of the Endothelium

Abstract

Abstract —The hypothesis that the decreased nitric oxide (NO) availability observed in spontaneously hypertensive stroke-prone rats (SHRSP) is due to excess superoxide (O 2 − ) was examined. O 2 − generation, measured by lucigenin chemiluminescence, was studied in 12- to 16-week male and female Wistar-Kyoto rats (WKY) and SHRSP. In addition, expression of the gene encoding endothelial NO synthase, the enzyme involved in NO generation, was investigated. O 2 − generation was increased in male and female SHRSP (4.11±0.24 and 3.84±0.28 nmol O 2 − · min −1 · mg −1 respectively) compared with their WKY counterparts and was significantly higher in male than female WKY (1.22±0.08 in males and 0.8±0.08 nmol O 2 − · min −1 · mg −1 respectively) (SHRSP versus WKY P <0.0001, 95% CI −3.39, −2.51; male versus female WKY P =0.0029, 95% CI −0.67, −0.17). Removal of the endothelium by rubbing or addition of NO synthase inhibitors attenuated O 2 − generation in SHRSP but not WKY. In males, removal of the endothelium reduced O 2 − generation from 3.86±0.12 to 1.35±0.08 nmol · min −1 · mg −1 ( P <0.0001, 95% CI 2.29, 2.81), whereas addition of L-NAME caused a reduction from 4.13±0.17 to 1.32±0.16 nmol · min −1 · mg −1 ( P <0.0001, 95% CI 2.36, 2.83). Similar reductions were observed in females. l -arginine had no significant effect, but tetrahydrobiopterin significantly decreased O 2 − generation in SHRSP from 4.04±0.11 to 2.36±0.40 nmol · min −1 · mg −1 ( P =0.0026, 95% CI 0.89, 2.44). Endothelial NO synthase mRNA expression was significantly greater in SHRSP than in WKY and in WKY males than in WKY females. These results show that O 2 − generation is increased in SHRSP and that the tissue and enzymatic sources of this excess O 2 − appear to be the endothelium and eNOS, respectively. The increase in O 2 − generation could explain the decreased availability of basal NO observed in this model of genetic hypertension.