Increased availability of nitric oxide leads to enhanced nitric oxide dependency of tubuloglomerular feedback in the contralateral kidney of rats with 2-kidney, 1-clip Goldblatt hypertension.

Abstract

The contralateral kidney of 2-kidney, 1-clip hypertensive (2K1C) rats is unable to escape the renal vasoconstrictive and sodium-retaining effects of increased circulating angiotensin II levels. Evidence is accumulating that renal function is relatively preserved by enhanced influence of NO in the contralateral kidney. In this study, we investigated (1) whether the high NO dependency of renal hemodynamics in the contralateral kidney is due to increased availability of NO or increased sensitivity to NO and (2) whether elevated NO activity dampens the actions of angiotensin II to enhance tubuloglomerular feedback (TGF) responses in the nonclipped kidney of 2K1C rats. To estimate whether the available NO is increased, the NO clamp technique was applied in rats that underwent sham operation (n=6) and in the contralateral kidney of 2K1C Sprague-Dawley rats (3 weeks old; 0.25-mm silver clip; n=6). During systemic infusion of nitro-L-arginine (L-NNA; 50 microg/kg. min(-1)), sodium nitroprusside (SNP) was infused in the renal artery and the rate was adjusted so that renal vascular resistance (RVR) was restored to baseline levels. In sham rats, RVR increased during L-NNA treatment from 17.2+/-2.0 to 33.0+/-3.6 U (P<0.01) and was restored to baseline values during SNP infusion (17.1+/-2.3 U); 9. 2+/-1.8 nmol/min of SNP was needed to restore RVR to baseline values. In 2K1C rats, RVR increased during L-NNA treatment from 16.7+/-1.1 to 53.4+/-3.5 U (P<0.01). This increase of RVR was significantly larger than in sham rats. RVR was restored to baseline values during SNP infusion (17.4+/-0.9 U); 26.0+/-4.3 nmol/min of SNP was needed to restore RVR to baseline values (P<0.05 versus sham). Furthermore, maximum TGF responses were assessed before and during late proximal tubular infusion of L-NNA in the kidneys of sham rats and the nonclipped kidneys of 2K1C rats. Control maximum TGF responses were 4.7+/-0.7 and 5.1+/-0.4 mm Hg in sham and 2K1C rats, respectively. During intraluminal L-NNA infusion, maximum TGF responses were 15. 4+/-0.9 mm Hg in sham rats and 22.2+/-2.5 mm Hg in 2K1C rats (P<0.05 versus sham). Finally, urinary NO(2)+NO(3) excretion in the nonclipped kidney was significantly higher than in the clipped kidney (P<0.05). In conclusion, (1) as assessed using the NO clamp, ambient intrarenal NO levels are increased in the contralateral kidney of 2K1C rats and (2) the NO dependency of the TGF system is enhanced. These experiments indicate that adaptations in NO activity lead to relatively low TGF responsiveness, which will offset the simultaneous sodium-retaining actions of angiotensin II on proximal tubular reabsorption and TGF responsiveness.