Renal baroreceptor-stimulated renin in the eNOS knockout mouse

The role of endothelium-derived nitric oxide (NO) in renal baroreceptor stimulation of renin was tested comparing endothelial nitric oxide synthase (eNOS) deficient mice with C57BL/6J (C57) controls. We measured blood pressure, renal blood flow (RBF), and plasma renin concentration (PRC) in Inactin-anesthetized mice. Blood pressure in eNOS knockout mice was higher than in controls (100 +/-3 vs. 86 +/-1 mmHg, respectively; P<0.001), but RBF was similar (1.71<plus/minus>0.06 vs. 1.66 +/-0.09 ml.min(-1).100 mg kidney wt(-1), respectively), so that renal vascular resistance was also higher in the knockouts (59.81 +/-2.07 vs. 51.81 +/-2.66 resistance units, respectively; P<0.025). PRC was similar (8.24<plus/minus>1.57 in eNOS knockouts vs. 7.10 +/-1.19 ng ANG I.ml(-1).h(-1) in C57). NOS inhibition with nitro-L-arginine methyl ester (L-NAME) in C57 controls increased blood pressure (from 85 +/-2 to 106 +/-1 mmHg, P<0.001) and decreased RBF (from 1.66<plus/minus>0.09 to 1.08 +/-0.02; P<0.005), but L-NAME had no effect in eNOS knockout mice. When renal perfusion pressure was reduced in C57 controls to 55 mmHg, PRC increased from 6.6<plus/minus>0.9 to 14.5 +/-1.9 mg.ml(-1).h(-1) (P<0.025), but this response was blocked by L-NAME. However, in eNOS knockouts, reduced renal perfusion pressure increased PRC from 7.6<plus/minus>1.4 to 15.0 +/-2.8 mg.ml(-1).h(-1) (P<0.001). Thus in the chronic absence of eNOS, blood pressure was elevated, but RBF was normal. Additionally, the absence of eNOS did not modify baroreceptor-stimulated renin, suggesting that eNOS-derived NO does not directly mediate this renin-regulating pathway.