Gender differences in the renal nitric oxide (NO) system: dissociation between expression of endothelial NO synthase and renal hemodynamic response to NO synthase inhibition.

Many studies have shown that nitric oxide (NO) production is higher in the systemic vasculature of females than males and is stimulated during pregnancy, a high estrogen state. The present study was performed in rats to determine whether females had a greater expression of endothelial NO synthase (eNOS) in kidneys than did males; whether there were gender differences in the excretion of NO metabolites, nitrate/nitrite; and whether there were gender differences in the renal hemodynamic response to NO synthase inhibition. The renal levels of eNOS mRNA (as measured by ribonuclease protection assays) and protein (as measured by Western blot) were 80% higher in kidneys from females than from males (P < .001). Urinary excretion of NO metabolites, nitrate/nitrite, were not different between males and females. To inhibit eNOS, rats were treated with nitro-L-arginine methyl ester (L-NAME, 3 to 4 mg/kg/day) for 2 weeks. Although there were no differences in basal renal hemodynamics between males and females, when factored for kidney weight, chronic L-NAME increased renal vascular resistance by 130% in males but by only 60% in females, and decreased renal plasma flow by 40% in males but had no effect in females. These data show that although the renal levels of eNOS mRNA and protein are higher in females than in males, the renal vasculature of males is more responsive to NO synthase inhibition. The data suggest that the renal vasculature of males may be more dependent on NO than is the renal vasculature in females.