Tissue damage and regeneration of ureteric smooth muscle in rats with obstructive uropathy

To investigate regeneration in obstructed ureters and to elucidate the role of hyperplasia in the thickening of the smooth muscle layer in the late stages of complete ureteric obstruction.

The expression of Ki-67 antigen, c-Fos, c-Jun and c-Myc in the smooth muscle layer of obstructed ureters was determined using immunohistochemistry in 40 Sprague-Dawley rats. After unilateral ligation of the ureter, five rats each were killed for examination at 1, 3, 7, 10, 14, 21, 28 and 42 days after ligation: dive rats that underwent a sham operation were also examined as controls.

The severity of hydroureter and thickening of the smooth muscle layer progressed consistently in the ligated ureters, but no mitosis was detected in myocytes within 14 days of ligation. Fibrosis in the smooth muscle layer appeared 21 days after ligation and progressed. There was no expression of Ki-67 antigen and oncoproteins until 14 days after ligation. The expression of Ki-67 and c-Myc increased gradually to a peak after 28 days, then declined. However, the expression of c-Fos and c-Jun was low and transient.

Cell regeneration is impaired in the damaged muscle layer of obstructed ureters. Only hypertrophy and not hyperplasia of the smooth muscle layer developed during the course of complete ureteric obstruction in this rat model of obstructive uropathy.