In situ Freezing of the Rat Urinary Bladder: DNA Adduct Formation in the Bladder Epithelium Demonstrated by (32)P‐Postlabeling Assay

In situ freezing of the urinary bladder has been demonstrated to exert tumor‐initiating potential in two‐stage urinary bladder carcinogenesis in the rat. In the present experiment, DNA modification was examined after in situ freezing of the whole urinary bladder performed by pinching with frozen forceps at —15°C or —30°C for 2 s. The (32)P‐postlabeling analysis revealed at least 2 DNA adducts in the epithelial cells of the urinary bladder collected 3 days after freezing. Single‐strand breaks of DNA were also found by means of the alkaline elution assay in the bladder epithelium collected 10 min after freezing. Thus, the previously demonstrated tumor‐initiating activity of in situ freezing in urinary bladder carcinogenesis was revealed to be associated with substantial DNA damage and adduct formation.