Role of plasma renin activity and the renal nerves in the natriuresis of L-NMMA infusion in rats

The objective of this study was to determine the effect of NI-monomethyl-L- arginine (L-NNMA) infusion on plasma renin activity (PRA) in the presence o r absence of the renal nerves in normotensive Wistar-Kyoto (WKY) rats and O kamoto spontaneously hypertensive rats (SHR). All rats were unilaterally ne phrectomized two weeks before the acute experiment. On the day of the exper iment, acute renal denervation (Dnx) of the remaining kidney was performed in one group of WKY rats (Dnx-WKY; n= 10) and one group of SHRs (Dnx-SHR; n =7). The renal nerves were left intact in a group of WKY rats (Inn-WKY; n=8 ) and SHRs (Inn-SHR; n=9). After a control clearance period, L-NMMA was adm inistered i.v. (15 mg/ky bolus followed by 500 mug/kg/min infusion) and ano ther clearance period of 20 min was taken. In all experimental groups L-NMM A infusion resulted in a significant natriuresis. L-NMMA infusion increased fractional excretion of sodium (FENa) to a greater extent in the Inn-SHR t han in the Inn-WKY (Delta FENa = 5.23 +/- 0.87% vs Delta FENa = 2.87 +/- 0. 73% respectively; P=0.05), PRA did not change in the SHR with the infusion Of L-NMMA. However, in the Inn-WKY group, the natriuresis Of L-NMMA infusio n was associated with a tendency for lower PRA levels, as compared to a gro up of time control Inn-WKY rats. In Dnx-WKY, the natriuresis of L-NMMA infu sion (Delta FENa 4.60 +/- 0.52%) was associated with a significantly lower level of PRA (4.26 +/- 1.18 ng AI/ml/hr) as compared to a group of time con trol Dnx-WKY rats (9.83 +/- 1.32 ng AI/ml/hr; P <0.05). In the Dnx-SHR, the natriuretic response to L-NMMA infusion was significantly attenuated by re nal denervation (Delta FENa = 2.36 +/- 0.34%) and PRA was unchanged. In con clusion, the natriuretic effect of systemic inhibition of nitric oxide (NO) synthesis was associated with decreased PRA in the Dnx-WKY suggesting that a potential interaction exists between NO and the renal nerves in the modu lation of PRA in the normotensive WKY rat. Whereas, the natriuretic effect Of L-NMMA infusion in the SHR in the presence and absence of the renal nerv es, were independent of 2001 Elsevier Science. All rights reserved. chan-es in PRA. (C) 2001 Elsevier Science Inc. All rights reserved.