The heterotopically transplanted rat urinary bladder as a model for detection of tumor-promoting urinary growth factor(s).

The heterotopically transplanted rat urinary bladder (HTB) was developed in our laboratory as a model to study the role of urine in urinary bladder carcinogenesis. With this model, normal urine was found to enhance urinary bladder carcinogenesis initiated by N-methyl-N-nitrosourea or N-butyl-N-(4-hydroxybutyl)nitrosamine. Two crude urinary components (Fractions I and II) were obtained by gel filtration chromatography; they stimulated ornithine decarboxylase (ODC) in a test bladder carcinoma cell line 804G, and promoted carcinogenesis in the HTB system. Fraction I was found to stimulate growth of 804G cells in vitro. Preliminary data indicate that Fraction I contains at least one, and possibly two heat-stable ODC-inducible and mitogenic components. Further characterization of these components is in progress. The HTB system has been demonstrated to be useful for other investigations; for example, alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ODC, when instilled repeatedly to the bladder lumen, inhibited tumorigenesis in HTBs.