ABSTRACT

One of the major problems in the study of experimental carcinogenesis is that of organ specificity. Review of data reveals that not all tissues of the mouse and rat are equally at risk for neoplasia. Spontaneous neoplasms of the rodent urinary bladder are rare (1,2 ); however, the urinary bladder of the rodent serves as an excellent target for urinary bladder carcinogenesis, as evidenced by the induction of urinary bladder tumors in both rats and mice with a variety of carcinogens (3-7). The primary metabolically active cells of the urinary bladder are the transitional epithe­ lial cells that line the entire lower urinary tract. These cells have a very low normal mitotic index in the postweaning animal. However, they readily respond to stimuli such as crystals, calculi, and chemicals (8-10) within the urine and are susceptible to injury because of their location. The urinary bladder is the most susceptible area of the lower urinary tract, apparently because of its storage function and extended exposure time to urinary toxicants.