Impaired renal blood flow autoregulation in two-kidney, one-clip hypertensive rats is caused by enhanced activity of nitric oxide.

Abstract

Increases in renal perfusion pressure will induce shear stress-mediated nitric oxide (NO) release, which could oppose autoregulation of renal blood flow (RBF). Although cardiac, cerebral, and mesenteric autoregulation is enhanced during nitric oxide (NO) synthesis inhibition, this has not been reported for renal autoregulation of blood flow. In the present study, the lower limit and efficiency of RBF autoregulation (as assessed by the degree of compensation) were studied before and during NO inhibition in normotensive Sprague Dawley rats (control; n = 9) and in the non-clipped kidney of two-kidney, one-clip Goldblatt hypertensive animals (2K1C; n = 9; 3 wk; 0.25-mm silver clip). In both groups, renal autoregulation curves were obtained before and during infusion of N(G) -nitro-L-arginine (L-NNA) (bolus 1.5 mg/kg intravenously, infusion 10 microg/kg per min intravenously), using a transit-time flow probe around the left renal artery. In control rats, mean arterial pressure (MAP) increased, RBF decreased, and renal vascular resistance (RVR) increased in response to L-NNA infusion. The lower limit of autoregulation in control animals did not significantly change during L-NNA infusion (78 +/- 3 to 70 +/- 2 mmHg). The degree of compensation in these rats slightly increased during L-NNA infusion, however, this was only significant below 90 mmHg. The 2K1C rats had elevated MAP under baseline conditions. L-NNA infusion resulted in a decrease in RBF and an increase in MAP and RVR. During L-NNA infusion, RVR in 2K1C rats greatly exceeded RVR in control rats. A significant decrease was observed in the lower limit of autoregulation from 85 +/- 3 to 72 +/- 5 mmHg (P < 0.05). In the contralateral kidney of 2K1C rats, the degree of compensation was lower than in control rats under baseline conditions. L-NNA infusion resulted in significantly higher degrees of compensation compared to baseline. In conclusion, the contralateral kidney displayed a high NO dependency, as RBF greatly decreased and RVR dramatically increased in response to L-NNA infusion. The contralateral kidney of 2K1C rats exhibited impaired RBF autoregulation, which was improved by NO inhibition, as judged from a decrease in the lower limit of autoregulation and an increase in the degree of compensation. This study indicates that perfusion pressure-dependent NO release can oppose autoregulation in the kidney. However, the enhanced influence of NO on pressure-dependent RBF may facilitate the preservation of renal function in the nonclipped kidney of 2K1C rats.