Losartan-sensitive renal damage caused by chronic NOS inhibition does not involve increased renal angiotensin II concentrations

Abstract

Chronic nitric oxide synthase (NOS) inhibition results in hypertension, proteinuria, and renal morphological changes. Continuous angiotensin II (Ang II) blockade prevents these effects, suggesting an essential role of Ang II. However, it is not known whether renal Ang II concentrations are primarily increased or whether the scarcity of NO allows normal concentrations of Ang II to cause these detrimental effects. Therefore, we measured renal Ang II concentrations before and during the development of renal damage. Group 1 served as controls. Groups 2 through 5 received the NOS inhibitor Nomega-nitro-L-arginine (L-NNA; 40 mg/kg/day) for 4, 7, 14, and 21 days, respectively. Systolic blood pressure (SBP), proteinuria, glomerular filtration rate (GFR), and renal and blood Ang II were measured. In a separate experiment, rats were treated with L-NNA + the Ang II AT1 receptor blocker losartan to determine the functional effects of endogenous Ang II during chronic NOS inhibition. L-NNA treatment resulted in an increase in SBP from day 4 (161 +/- 4 vs. 135 +/- 4 mm Hg in control, P < 0.05) to day 21 (230 +/- 9 mm Hg). GFR was decreased from day 4 (1.9 +/- 0.2 vs. 2.5 +/- 0.2 ml/min in control, P < 0.05) to day 21 (1.2 +/- 0.2 ml/min). Proteinuria was increased from day 14 (85 +/- 14 vs. 6 +/- 1 mg/day in control, P < 0.05) to day 21 (226 +/- 30 mg/day). L-NNA treatment during four days resulted in a significant decrease in renal Ang II (183 +/- 32 vs. 454 +/- 40 fmol/g in control, P < 0.05). On day 7, 14, and 21, renal Ang II was not significantly different from the control. Blood Ang II was not significantly different from the control on days 4, 7, and 14 but was significantly increased after 21 days of L-NNA treatment (215 +/- 35 vs. 78 +/- 13 fmol/ml in control, P < 0.05). Ang II type-1 (AT1) receptor blockade prevented the severe renal injury and hypertension induced by chronic NOS inhibition. Losartan-sensitive renal damage caused by chronic NOS inhibition does not involve increased renal Ang II concentrations. This suggests that the detrimental effects of endogenous Ang II are increased during chronic NOS inhibition. Thus, when NO levels are low, normal Ang II concentrations can cause renal injury and hypertension.