Progressive growth of rat bladder carcinomas after exposure to prolonged uracil-induced urolithiasis.

Dietary uracil at the 3% level induces urinary bladder tumors in rats through urolithiasis-dependent mechanical irritation. In the present study, comparison of lesions induced by uracil administration over the different periods of 36 weeks (middle-term) and up to 103 weeks (long-term) revealed significant elevation of both incidences and multiplicity of transitional cell carcinomas (TCCs) in the long-term group. Histopathological assessment in terms of tumor biology further demonstrated significantly higher grading on the basis of the degree of cellular and structural atypia, and greater depth of invasion in the long-term group. Application of markers for cell proliferation activities including proliferating cell nuclear antigen (PCNA) and silver-binding nucleolar organizer regions (AgNORs) also revealed significantly elevated AgNOR counts in the long-term group TCC. AgNOR counts and PCNA rates in TCCs showed relation to the histological grades. Thus the present study demonstrated that prolonged uracil-induced urolithiasis causes more biologically aggressive bladder carcinomas with invasive potential. Continuous stimulation of cell proliferation presumably has the potential to facilitate multiple genetic alterations leading to development of more malignant carcinomas. However, it should be borne in mind that the difference in bladder cancer development might also be related to the fact that the animals survived longer and that the early lesions therefore had more time to progress to more advanced stages.