Selective Induction of Prostate Carcinomas in F344 Rats Treated with Intraperitoneal Injections of N‐Hydroxy‐3,2′‐dimethyl‐4‐aminobiphenyl

Groups of F344 and Wistar rats were given an intraperitoneal injection of N‐hydroxy‐3,2′‐dimethyl‐4‐aminobiphenyl (N‐OH‐DMAB) at a dose of 5 mg/kg body weight with a 1‐week dietary pretreatment with ethinyl estradiol (EE), and this regimen was repeated 10 times at one‐week intervals. Additional groups were given N‐OH‐DMAB 10 times without the dietary EE pretreatment. The total experimental period was 60 weeks. Carcinomas and atypical hyperplasias of the prostate developed in 8 (42%) and 16 (84%) of 19 F344 rats without the dietary EE treatment and in 1 (6%) and 7 (39%) of 18 rats with the EE diet, respectively. No prostatic tumors were found in Wistar rats, although atypical hyperplasias were observed in 6 of 18 rats with and 4 of 8 rats without the EE supplementation. Tumor yields in other organs were extremely low, resulting in good survival of the animals. A comparison of the results with those obtained for DMAB suggests that intraperitoneal administration of N‐OH‐DMAB in F344 provides a better induction method for models of prostate carcinogenesis.