Superoxide anion production is increased in a model of genetic hypertension - Role of the endothelium

The hypothesis that the decreased nitric oxide (NO) availability observed i n spontaneously hypertensive stroke-prone rats (SHRSP) is due to excess sup eroxide (O-2(-)) was examined. O-2(-) generation, measured by lucigenin che miluminescence, was studied in 12- to 16-week male and female Wistar-Kyoto rats (WKY) and SHRSP. In addition, expression of the gene encoding endothel ial 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 3.8 4+/-0.28 nmol O-2(-) . min(-1) . mg(-1) respectively) compared with their W KY 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 addit ion 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 1.3 2+/-0.16 nmol . min(-1) . mg(-1) (P<0.0001, 95% CI 2.36, 2.83). Similar red uctions were observed in females. L-arginine had no significant effect, but tetrahydrobiopterin significantly decreased O-2(-) generation in SHRSP fro m 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 sh ow that O-2(-) generation is increased in SHRSP and that the tissue and enz ymatic sources of this excess O-2(-) appear to be the endothelium and eNOS, respectively. The increase in O-2(-) generation could explain the decrease d availability of basal NO observed in this model of genetic hypertension.