SC-51316

Chronic unilateral ureteral obstruction results in interstitial fibrosis of the affected kidney. Both an angiotensin-converting enzyme inhibitor, enalapril, and an angiotensin II receptor antagonist, SC-51316, ameliorate the increased production of extracellular matrix protein in the tubulointerstitium of the obstructed kidney. Blockade of angiotensin II synthesis or inability of angiotensin II to bind to its receptor lessened the increased levels of mRNA for transforming growth factor-beta and collagen IV found in the obstructed kidney of untreated rats. A monocyte/macrophage infiltration was present in the obstructed kidney of untreated rats or rats treated with the angiotensin II receptor antagonists. In contrast, this infiltrate was almost completely absent in the obstructed kidney of rats treated with enalapril. The reason for this different effect of enalapril compared with the angiotensin II receptor antagonist on the macrophage infiltrate seen in obstructive nephropathy has not been elucidated. We conclude that both an angiotensin-converting enzyme inhibitor (enalapril) and a receptor antagonist of angiotensin II ameliorate the tubulointerstitial fibrosis that follows complete unilateral ureteral obstruction in the rat. We suggest that an increased level of angiotensin II has a major role in the development of tubulointerstitial fibrosis following ureteral obstruction.

Unilateral ureteral obstruction (UUO) results in tubulointerstitial fibrosis of the obstructed kidney (OBK). In this study we report that a specific angiotensin II (Ang II) receptor antagonists, SC-51316, ameliorates the expansion of the renal cortical interstitium in the OBK of the rat at five days of UUO. This is similar to the effect of an angiotensin converting enzyme (ACE) inhibitor, enalapril. SC-51316 (20 mg/liter in the drinking water) or enalapril (200 mg/liter in the drinking water) was administered beginning 24 hours before UUO and continued through five days after UUO. The relative volume of the tubulointerstitium (Vv) was measured by a point-counting method, and monocyte/macrophage infiltration, alpha smooth muscle actin (alpha SMA), proliferating cell nuclear antigen (PCNA), and collagen type IV (collagen IV) protein deposition were examined histologically using specific antibodies. We also examined the mRNA levels of transforming growth factor beta 1 (TGF-beta 1) and collagen IV by reverse transcription polymerase chain reaction. In untreated rats with UUO, Vv was remarkably expanded; collagen IV and alpha SMA protein deposition in the interstitium and PCNA labeling of nuclei were increased. These changes were significantly ameliorated by administration of an ACE inhibitor or an Ang II receptor antagonist. A monocyte/macrophage infiltration was evident in the OBK of untreated or Ang II receptor antagonist treated rats but was greatly reduced in the OBK of rats given enalapril. Increased expression of TGF-beta 1 mRNA and collagen IV mRNA was blunted (40 to 75%) by the administration of Ang II receptor antagonist or enalapril. The Ang II receptor antagonist or the ACE inhibitor did not affect the contralateral kidney of rats with UUO or the control kidney of normal rats. This study indicates that the renin-angiotensin system has a major role in the pathogenesis of the tubulointerstitial fibrosis of obstructive nephropathy. The tubulointerstitial fibrosis of obstructive nephropathy is most likely mediated by an increased level of Ang II in renal tissue.