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 in spontaneously hypertensive stroke-prone rats (SHRSP) is due to excess superoxide (O2-) was examined. O2- 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. O2- generation was increased in male and female SHRSP (4.11+/-0.24 and 3. 84+/-0.28 nmol O2-. 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 O2-. 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 O2- generation in SHRSP but not WKY. In males, removal of the endothelium reduced O2- 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 O2- 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 O2- generation is increased in SHRSP and that the tissue and enzymatic sources of this excess O2- appear to be the endothelium and eNOS, respectively. The increase in O2- generation could explain the decreased availability of basal NO observed in this model of genetic hypertension.
Kerr
S
S
Department of Medicine and Therapeutics, Western Infirmary, Glasgow, UK.
Brosnan
M J
MJ
McIntyre
M
M
Reid
J L
JL
Dominiczak
A F
AF
Hamilton
C A
CA
D000818:Animals; D001012:Aorta, Abdominal / Q000378:metabolism*; D001013:Aorta, Thoracic / Q000201:enzymology*; D001794:Blood Pressure; D004730:Endothelium, Vascular / Q000502:physiology / Q000503:physiopathology; D005260:Female; D006973:Hypertension / Q000235:genetics* / Q000378:metabolism* / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000235:genetics*; D052250:Nitric Oxide Synthase Type III; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012727:Sex Characteristics; D013045:Species Specificity; D013481:Superoxides / Q000378:metabolism*; D014158:Transcription, Genetic
D012333:RNA, Messenger; D013481:Superoxides; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat