THE TEMPORAL RELATIONSHIP BETWEEN THE SEVERITY OF HYDROURETER AND THE DYNAMIC CHANGES OF OBSTRUCTED URETERS IN A RAT MODEL

Objective To investigate dynamic changes in the obstructed rat ureter and to evaluate the usefulness of the rat model in the study of obstructive uropathy. Materials and methods Unilateral ligation of the ureter was performed in 26 rats. After ureteric ligation, four to seven rats were killed and examined after 1, 3, 7, 10, and 14 days. The severity of hydroureter and hydronephrosis was assessed by pyelography and the hydroureter-hydronephrosis index. The middle portion of the ureter was prepared for light and electron microscopic observation, Five rats which received a sham operation were also examined as controls. Results The severity of hydroureter and hydronephrosis in the ligated ureters progressively increased during the period of obstruction (P<0.005) and reached a maximum 10-14 days after ligation. Hypertrophy of the smooth muscle layer developed on the third day after ligation and proliferation of submucosal connective tissue occurred on the 10th day after ligation, The changes in smooth muscle and connective tissue layers also progressed consistently during ureteric obstruction (P<0.001 and <0.005, respectively). The number and size of granular endoplasmic reticulum and Golgi apparatus in the smooth muscle cells increased after ureteric ligation and then caveolae exocytosis developed. Deposition of collagen fibres between muscle cells became apparent later. Conclusion The rat model of hydrouropathy demonstrated a clear temporal relationship between the severity of hydroureter and the dynamic changes in the obstructed ureter and could be used as a conventional method for the study of obstructive ureter.