Sympathetic stimulation of renin is independent of direct regulation by renal nitric oxide

Hemodynamic and neural responses to renal denervation of the nerve to the clipped kidney by cryoablation in two-kidney, one-clip hypertensive rats

Renal artery stenosis is increasing in prevalence. Angioplasty plus stenting has not proven to be better than medical management. There has been a reluctance to use available denervation methodologies in this condition. We studied conscious, chronically instrumented, two-kidney, one-clip (2K-1C) Goldblatt rats, a model of renovascular hypertension, to test the hypothesis that renal denervation by cryoablation (cryo-DNX) of the renal nerve to the clipped kidney decreases mean arterial pressure (MAP), plasma and tissue ANG II, and contralateral renal sympathetic nerve activity (RSNA). Five-week-old male Sprague-Dawley rats underwent sham (ShC) or right renal artery clipping (2K-1C), placement of telemetry transmitters, and pair-feeding with a 0.4% NaCl diet. After 6 wk, rats were randomly assigned to cryo-DNX or sham cryotreatment (sham DNX) of the renal nerve to the clipped kidney. MAP was elevated in 2K-1C and decreased significantly in both ShC cryo-DNX and 2K-1C cryo-DNX. Tissue norepinephrine was ∼85% lower in cryo-DNX kidneys. Plasma ANG II was higher in 2K-1C sham DNX but not in 2K-1C cryo-DNX vs ShC. Renal tissue ANG II in the clipped kidney decreased after cryo-DNX. Baseline integrated RSNA of the unclipped kidney was threefold higher in 2K-1C versus ShC and decreased in 2K-1C cryo-DNX to values similar to ShC. Maximum reflex response of RSNA to baroreceptor unloading in 2K-1C was lower after cryo-DNX. Thus, denervation by cryoablation of the renal nerve to the clipped kidney decreases not only MAP but also plasma and renal tissue ANG II levels and RSNA to the contralateral kidney in conscious, freely moving 2K-1C rats.

Neuronal nitric oxide synthase-deficient mice have impaired renin release but normal blood pressure

BACKGROUND

Nitric oxide deficiency is involved in the development of hypertension, but the mechanisms are currently unclear. This study was conducted to further elucidate the role of neuronal nitric oxide synthase (nNOS) in blood pressure regulation and renin release in relation to different sodium loads.

METHODS

Blood pressure and heart rate were measured telemetrically and assessed during periods of physical activity and inactivity. Urinary solute excretion was measured by metabolism cages and plasma renin concentration (PRC) was determined by radioimmunoassay; all in nNOS knockout (nNOS(-/-)) and wild-type (nNOS(+/+)) mice after 10 days of low (0.01% NaCl) and high (4% NaCl) sodium diets.

RESULTS

The resting heart rate was reduced in nNOS(-/-) mice, but the two genotypes had similar blood pressure during the low (nNOS(+/+) 104 +/- 2 mm Hg; nNOS(-/-) 103 +/- 2 mm Hg) and high (nNOS(+/+) 107 +/- 3 mm Hg; nNOS(-/-) 108 +/- 2 mm Hg) sodium diets. During the high sodium diet, PRC did not differ between the genotypes (nNOS(+/+) 743 +/- 115 10(-5) Goldblatt units; nNOS(-/-) 822 +/- 63 10(-5) Goldblatt units), but during the low sodium diet, nNOS(-/-) mice failed to increase PRC (nNOS(+/+) 2164 +/- 220 10(-5) Goldblatt units; nNOS(-/-) 907 +/- 101 10(-5) Goldblatt units) and renal renin mRNA. On the low sodium diet, nNOS(-/-) mice also showed increased urine flow rate and osmolar excretion, observations not made during a high sodium diet.

CONCLUSIONS

Our results show that nNOS is necessary for stimulation of renin in response to sodium restriction. Furthermore, nNOS(-/-) mice are normotensive, and their blood pressure responds normally to an increased dietary sodium intake, indicating that nNOS deficiency does not cause salt-sensitive hypertension.