Production of reversible papillary proliferation of the urinary bladder in rats

A rapid and reproducible method for the production of ulcers and regenerative hyperplasia of the bladder of rats is described. Ulceration was produced by applying a steel rod, 5 mm in diameter, frozen in dry ice acetone (-78°), to the serosal surface of the bladder. Preliminary experiments had determined that an exposure of 2 sec, twice, with 5 sec between the exposures while the rod was reimmersed in dry ice acetone resulted in ulceration. Sequential histologic observations showed that the ulcers were accompanied by necrosis of the entire thickness of the bladder wall and that after 1 day, there was a marked exudate consisting of polymorphonuclear leukocytes, red blood cells, fibrin, and cellular debris. Regenerative hyperplasia was evident near the edge of the ulcer by the second day. The hyperplasia increased until day 5 when it became marked including a fibrovascular core indicating papillary and nodular formation. By the 10th day no ulcer remained. Hyperplastic mucosal proliferation was slight to moderate by day 7, and only minimum hyperplasia was observed at 15 days although slight fibrosis in the muscular and submucosal layers was observed.