Down-regulation of inducible nitric oxide synthase (iNOS) in rat with congenital hydronephrosis

BACKGROUND: Most of our knowledge concerning obstructive uropathy has been derived mainly from surgically manipulated animal models, and the pathogenesis of congenital obstructive hydronephrosis is not fully elucidated. Nitric oxide (NO) acts as an important biological modulator with diverse physiological functions, which can be either toxic or protective depending on the situation. NO is synthesized from l-arginine by nitric oxide synthase, and in the kidney iNOS is expressed spontaneously. The aim of our study is to investigate the expression of iNOS protein and its relationship with tubulointerstitial fibrosis and tubular cell apoptosis in congenital hydronephrosis. METHODS: We conducted histological studies on 18 kidneys of six-week-old-rats from an inbred colony of congenital hydronephrosis with reference to the histological grading of the affected kidney, tubulointerstitial fibrosis, renal tubular atrophy, and tubular cell apoptosis. Renal transforming growth factor-beta1 (TGF-beta1) level was determined by a sandwich ELISA assay and the expression of iNOS was analyzed by western blotting. RESULTS: Most of the hydronephrotic kidneys were markedly enlarged with dilatation of the collecting system, parenchymal thinning, tubular atrophy, interstitial infiltration and fibrosis. Renal TGF-beta1 level was higher in hydronephrotic kidneys than normal control kidneys (364.81 +/- 52.60 vs. 221.19 +/- 22.53 pg/mg protein, P < 0.05). Tubular apoptotic score in hydronephrotic kidneys was also significantly higher than in the normal control kidneys (1.97 +/- 0.42 vs. 0.14 +/- 0.02/HPF, P < 0.01). The expression of iNOS protein was lower in the affected kidneys compared with the normal control kidneys (8.79 +/- 0.78 vs. 14.00 +/- 0.83 arbitrary unit, P < 0.01). There was a negative correlation between iNOS expression and histological grading in congenital hydronephrosis. The iNOS expression also correlated negatively with renal interstitial fibrosis, TGF-beta1 level and tubular cell apoptosis. CONCLUSION: Our study confirmed the down-regulation of iNOS expression in affected kidneys from rats with congenital hydronephrosis, in which the cytoprotective effect of NO may be lost or weakened.