Renal baroreceptor-stimulated renin in the eNOS knockout mouse

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Abstract
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 ± 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 ± 1.57 in eNOS knockouts vs. 7.10 ± 1.19 ng ANG I · ml−1· h−1in 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 ± 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 ± 0.9 to 14.5 ± 1.9 μg · 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 ± 1.4 to 15.0 ± 2.8 μg · 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.