Nitric oxide synthesis inhibition retards surgical reversal of one-kidney Goldblatt hypertension in rats

Sympathoactivation and rho-kinase-dependent baroreflex function in experimental renovascular hypertension with reduced kidney mass

BACKGROUND

Dysregulation of the autonomic nervous system is frequent in subjects with cardiovascular disease. The contribution of different forms of renovascular hypertension and the mechanisms contributing to autonomic dysfunction in hypertension are incompletely understood. Here, murine models of renovascular hypertension with preserved (2-kidneys-1 clip, 2K1C) and reduced (1-kidney-1 clip, 1K1C) kidney mass were studied with regard to autonomic nervous system regulation (sympathetic tone: power-spectral analysis of systolic blood pressure; parasympathetic tone: power-spectral analysis of heart rate) and baroreflex sensitivity of heart rate by spontaneous, concomitant changes of systolic blood pressure and pulse interval. Involvement of the renin-angiotensin system and the rho-kinase pathway were determined by application of inhibitors.

RESULTS

C57BL6N mice (6 to 11) with reduced kidney mass (1K1C) or with preserved kidney mass (2K1C) developed a similar degree of hypertension. In comparison to control mice, both models presented with a significantly increased sympathetic tone and lower baroreflex sensitivity of heart rate. However, only 2K1C animals had a lower parasympathetic tone, whereas urinary norepinephrine excretion was reduced in the 1K1C model. Rho kinase inhibition given to a subset of 1K1C and 2K1C animals improved baroreflex sensitivity of heart rate selectively in the 1K1C model. Rho kinase inhibition had no additional effects on autonomic nervous system in either model of renovascular hypertension and did not change the blood pressure. Blockade of AT1 receptors (in 2K1C animals) normalized the sympathetic tone, decreased resting heart rate, improved baroreflex sensitivity of heart rate and parasympathetic tone.

CONCLUSIONS

Regardless of residual renal mass, blood pressure and sympathetic tone are increased, whereas baroreflex sensitivity is depressed in murine models of renovascular hypertension. Reduced norepinephrine excretion and/or degradation might contribute to sympathoactivation in renovascular hypertension with reduced renal mass (1K1C). Overall, the study helps to direct research to optimize medical therapy of hypertension.

Nitric oxide modulates the development and surgical reversal of renovascular hypertension in rats

OBJECTIVE

To evaluate the role of nitric oxide (NO) in the development and unclipping-induced reversal of blood pressure and bilateral renal function in two-kidney, one clip (2K1C) Goldblatt hypertensive rats.

METHODS

Goldblatt hypertensive rats were prepared by clipping the left renal artery 4 weeks before unclipping experiments. NG-nitro-L-arginine methyl ester (L-NAME) was administered after clipping and during unclipping to inhibit nitric oxide (NO) synthesis. Blood pressure and bilateral renal responses were measured.

RESULTS

Chronic L-NAME treatment accelerated and aggravated blood pressure elevations and increased plasma nitrite and nitrate levels in 2K1C rats. Surgical removal of the renal artery clip induced profound reductions in blood pressure in rats with and without L-NAME treatment. However, the magnitude of the unclipping-induced depressor response at the first post-unclipping hour was significantly smaller in L-NAME-treated rats compared to those without L-NAME administration (15 +/- 1 versus 22 +/- 1%, P < 0.05). Two hours after unclipping, blood pressure of both groups fell to a comparable, normal level. Acute intravenous infusion of L-NAME in established 2K1C hypertensive rats further increased blood pressure. Subsequent unclipping caused a depressor response similar to that observed in hypertensive rats treated chronically with L-NAME. Despite the marked decreases in blood pressure, unclipping induced striking increases in glomerular filtration rate (GFR), urine flow and sodium and potassium excretion rates in the ipsilateral kidney. However, the magnitudes of increases in GFR and the diuretic and natriuretic responses in rats without L-NAME treatment were significantly greater than in rats with L-NAME administration. In contrast, unclipping reduced these function indices in the contralateral kidney to a similar level in rats with and without L-NAME treatment.

CONCLUSIONS

NO exerts vasodilator action and thereby lessens renal artery clipping-induced blood pressure elevation. Furthermore, unclipping-induced release of NO partially contributes to the early reduction in blood pressure and changes in bilateral renal function but does not directly mediate the normalization of blood pressure after unclipping in this hypertension model.