| Objectives: Injury to the renal microvasculature may be a major contributing factor to the progression of chronic obstructive uropathy(COU). Although severe disruption of peritubular capillaries (PTC) could lead to marked renal tubular epithetial cell apoptosis and tubulointerstitial scarring, elucidation of that process remains incomplete. The aim of this study is to investigate the morphologic changes in PTC and their likely regulation by vascular endothelial growth factor (VEGF) during the course of experimental obstructive uropathy in weanling male Sprague-Dawley (SD) rats. We also try to explore the relationships between PTC regression and renal tubular cell apoptosis, and to evaluate the protective effect of enalapril on PTC and renal tubular cell apoptosis induced by complete ureteral obstruction.Methods: Under ketamine anesthesia (50mg/Kg), 36 weanling male SD rats were subjected to CUUO by ligation of the left ureteropelvic junction. Six rats each were randomly euthanized to yield left ligated and right contralateral kidneys on the day 0,1,7, 14, and 4 wk after obstruction. Six randomly selected rats were assigned to the treatment group in which the rats began to drink tap water containing enalapril(200mg/L) from the fifth post-obstruction day on. Six sham-operated rats were assigned to control group. The sham-operated and enalapril-treated rats were harvested on day 14. The severity of hydronephrotic kidneys was evaluated on routine hematoxylin and eosin(H&E) stained sections, and the tubulointerstitial fibrosis analyzed morphometrically on Masson's trichrome stained sections. Renal tubular atrophy was assessed on periodic acid Schiff (PAS) stained sections. Changes in PTC density and the expression of VEGF were immunohistochemically detected, and morphologic changes in PTC endothelial cells andrenal tubular epithetial cells were examined by using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) technique and electron-microscopic studies. For quantification of VEGF expression, areas with positive staining were measured by using computer image analysis.Results:1.In the first week of renal obstruction, the immunohistochemical labeling of tubular VEGF was intensified, accompanied by deformation and dilation of adjacent Flk-1-positive PTC lumina, mild renal tubular cell apoptosis and minimal tubulointerstitial fibrosis. On the second week, the tubular VEGF labeling was reduced, and so were the Flk-1 labeled PTC numbers. By the 4th week, the number of Flk-1-positive PTC lumina was significantly decreased in areas of marked renal tubular atrophy and tubulointerstitial scarring.2. Electron microscopic studies demonstrated PTC endothelial cell and tubular cell apoptosis. Renal tubular cell apoptosis(as detected in TUNEL) peaked on the 14th day after ureteral ligation, and thereafter decreased rapidly.3. By the 2nd week of renal obstruction, there was a negative correlation between the number of TUNEL-positive PTC cells and the VEGF labeling area percentage (r =-0.668, P<0.05). The mean number of PTC demonstrated a positive correlation with the VEGF labeling area percentage (r = 0.707, P<0.05), but a negative correlation with the renal tubular cell apoptosis (r=-0.863, P<0.01).4. There was higher VEGF expression, higher PTC density, lower renal tubular cell apoptosis, and less renal tubular interstitial fibrosis in enalapril treatment group than the non-treatment group.Conclusions: Injury to PTC is characterized by progressive PTC endothelial cell apoptosis, followed by collapse of the PTC networks in the unilateral ureteral obstruction model. Our results demonstrated that depletion of VEGF in renal tubular epithelial cells is crucial to the loss of PTC, and PTC regression might contribute to renal tubular cellIVapoptosis and tubulointerstitial scarring. .Administration of enalapril have a renal protective effect by increasing PTC density, alleviating tubular cell apoptosis and interstitial fibrosis, which may be of... |
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