DNA synthesis in the urinary tract epithelium of the rat induced by ureteric ligation.

The effect of ligating the left ureter on the thymidine-labeling index (LI) of epithelial cells lining the urinary tract in male Wistar rats has been investigated and compared with the LI in appropriate control groups. In experiment 1, the temporal pattern of the response was studied. In the left ureter, the LI above and below the ligature began to increase at about 8 hours and reached a peak approximately 100 times normal control values at 18 hours. At 48 hours, the LI above the ligature was still about 15 times normal, but distal to the ligature it was significantly below normal levels. There were also impressive increases in the LI in the epithelium of the left renal pelvis and in the tubular cells of the left renal cortex. An unexpected observation was a significant increase in the LI in the right ureter and bladder of these animals and similar increases in both ureters and bladders of sham-operated animals and laparotomy controls. Other unusual features were a significant decrease in the LI in the cortical tubular cells in all the sham-operated animals and in some ligated groups, and a highly significant sustained reduction in the LI of hepatocytes in both sham-operated and ligated animals but not in anesthetic controls. In experiment 2, the topographic relationship between the ligature and the changes in thymidine labeling was examined. The highest LIs were in the pieces of ureter neighboring the ligature with successively lower indices as the distance from the ligature increased. Factors potentially responsible for the changes in the LI in different parts of the urinary tract are considered, and conclusions about the mechanisms involved are tentatively drawn.