ROLE OF RENAL NERVES IN NATRIURESIS OF L-NMMA INFUSION IN SHR AND WKY RATS

The purpose of this study was to determine the role of the renal nerves in the natriuresis and diuresis that is observed with the systemic infusion of a high dose of N-G-monomethyl-L-arginine (L-NMMA) to inhibit nitric oxide synthesis in the Okamoto spontaneously hypertensive rat (SHR) and the Wistar-Kyoto (WKY) rat. All rats in this study underwent a unilateral nephrectomy similar to 2 wk prior to the acute experiment. On the day of the acute experiment, renal denervation of the remaining left kidney was performed in one group of SHR (n = 6) and one group of WKY rats (n = 9). Another group of SHR (n = 6) and WKY rats (n = 10) had an innervated kidney. A control clearance period was taken, and then an L-NMMA (15 mg/kg bolus followed by 500 mu g . kg(-1). min(-1) continuous infusion) infusion period followed in all four groups of rats. In the innervated SHR and WKY rats, the increases in fractional excretion of sodium (FE(Na)) were 5.11 +/- 0.70 and 3.58 +/- 0.38%, respectively, with the infusion of L-NMMA and were associated with significant increases in fractional excretions of phosphate (FE(Pi); 18.18 +/- 5.33 and 6.34 +/- 2.29%, respectively), suggesting a reduction in proximal tubule reabsorption. In the SHRs with acute renal denervation, FE(Na) was significantly increased by L-NMMA; however, FE(Na) was significantly reduced (2.03 +/- 0.70%; P < 0.05) in comparison with innervated SHRs and was associated with no increase in FE(Pi) (FE(Pj) -0.72 +/- 1.23%). In contrast, the natriuretic [FE(Na) = 2.88 +/- 0.75%; not significant (NS)] and phosphaturic (FE(Pi) = 5.04 +/- 3.40%; NS) responses to L-NMMA infusion were similar in WKY rats with acute renal denervation in comparison with innervated WKY rats. These results suggest that in the SHR the inhibition of reabsorption by the proximal tubule with L-NMMA infusion requires the presence of the renal nerves and that the natriuretic and diuretic responses to nitric oxide synthesis inhibition are partially dependent on renal innervation.