Effect of nitric oxide inhibition on kidney function in experimental renovascular hypertension

We examined the effect of acute systemic blockade of nitric oxide (NO) synthesis on blood pressure and renal function in rats with angiotensin II dependent two-kidney, one-clip Goldblatt hypertension. Hypertensive animals had significantly higher blood pressures, plasma NO metabolite concentrations and urinary NO metabolite excretion rates than control rats. Intravenous administration of N^G-nitro-L-arginine methylester (L-NAME) (10 mg/kg) increased mean arterial pressure in both hypertensive and control animals with the magnitude of increase being greater in hypertensive than control rats (32 ± 3 vs. 20 ± 2 mmHg, p < 0.05). L-NAME did not affect glomerular filtration rates of normal and clipped kidneys but significantly decreased non-clipped kidney glomerular filtration rate (1.1 ± 0.1 vs. 0.7 ± 0.1 ml/min per g kidney wt, p < 0.05). Blood flow to normal and non-clipped kidneys fell in response to L-NAME. Percent reduction in renal blood flow produced by L-NAME was significantly greater in non-clipped than normal kidneys (38±3 vs. 24±2%, p < 0.05). In contrast, clipped kidney blood flow increased after L-NAME (3.3±0.2 vs. 4.0±0.2 ml/min per g kidney wt, p < 0.05). An identical improvement in clipped kidney blood flow occurred when arterial pressure was raised with aortic constriction indicating that the systemic pressor effect of L-NAME was responsible for this finding. These results indicate that NO plays an important role in systemic and non-clipped kidney hemodynamics in renovascular hypertension. Because NO has little influence on stenotic kidney function, the stimulus for increased NO system activity in this disease appears to be vascular shear stress rather than elevated circulating or intrarenal angiotensin II concentrations.