The effect of in situ freezing of the urinary bladder on
sodium o-phenylphenate (
OPP-Na)-induced urinary bladder
tumor development was investigated in male F344 rats. Freezing was performed at the start of the experiment by touching the serosal surface of the bladder with a frozen steel rod. As a result, three out of 27 rats (11%) developed
bladder tumors within 78 weeks when 0.5%
OPP-Na feeding was started 2 weeks after freezing and one out of 27 rats (4%) when the feeding was started 12 weeks after freezing. 0.5%
OPP-Na alone did not induce any bladder lesions. In a second experiment, 19 out of 25 rats (76%) developed
bladder tumors (
carcinomas in 12 rats and
papillomas in seven rats) when 2%
OPP-Na was administered from 6 weeks after freezing, whereas only one rat (5%) demonstrated a bladder
carcinoma in the group given 2%
OPP-Na without prior freezing. In neither experiment were
tumors induced by freezing alone.
Enzyme histochemistry revealed no remarkable changes in
enzyme activities of regenerative
hyperplasia induced by freezing. The results indicate that in situ freezing of the urinary bladder acts as a trigger of rapid development of
OPP-Na-induced rat urinary bladder
tumors.