Genesis of renal tubular atrophy in experimental hydronephrosis in the rat. Role of apoptosis.

A morphological study was undertaken to assess the role of cell deletion by apoptosis in experimental hydronephrosis. Male Sprague-Dawley rats (200 +/- 20 gm) were used. The left ureter was ligated or a sham operation was carried out. Animals were killed from 4 days to 12 weeks after operation. Two parallel studies were undertaken: one to demonstrate and quantitate specific morphological changes in the affected kidney using light and electron microscopy, and the other to measure changes in dry kidney weights. Renal tubular atrophy is an inevitable consequence of chronic occlusion of the ureter. As expected, the present study showed a progressive loss of tissue mass in the hydronephrotic kidney. This occurred from 1 week after permanent ureteric ligation, and was most rapid between 2 and 4 weeks. The tubular epithelium contained cells undergoing a distinct form of cell death termed apoptosis, characterized ultrastructurally in its early stage by the presence of rounded cells with condensed cytoplasm and condensed and marginated nuclear chromatin, and later by the presence of discrete membrane-bounded intact cellular fragments (apoptotic bodies), which were phagocytosed and digested by adjacent viable cells, or were shed into the tubular lumens. Numbers of apoptotic cells or clusters of apoptotic bodies were increased significantly in all animals with ureteric obstruction in comparison with controls. The greatest increases occurred at 2 and 4 weeks, when loss of renal mass was occurring rapidly. Diminished blood flow in hydronephrosis has been well-documented by others, and therefore our results are consistent with studies which have shown mild ischemia to be the cause of tissue atrophy involving apoptosis. We conclude that cell deletion by apoptosis plays an important role in the pathogenesis of renal tubular atrophy associated with hydronephrosis.