Direct Effects of Testosterone, Dihydrotestosterone and Estrogen on 3,2′‐Dimethyl‐4‐aminobiphenyl‐induced Prostate Carcinogenesis in Castrated F344 Rats

The present experiment was carried out to explore the effect of endogenous androgen on rat prostate carcinogenesis induced by 3,2′‐dimethyl‐4‐aminobiphenyl (DMAB) and testosterone propionate (TP) or 5α‐dihydrotestosterone (DHT) with or without ethinyl estradiol (EE). In order to eliminate the influence of endogenous androgen, F344 rats were orchiectomized just after initiation with the prostate carcinogen, DMAB, and then given TP, DHT, TP plus EE or DHT plus EE for 40 weeks. The results demonstrated that while administration of TP following DMAB treatment causes invasive carcinomas in the lateral and anterior prostate and seminal vesicles, DHT does not exhibit equivalent effects. Synergistic enhancement was also evident with TP plus EE, but not with DHT plus EE. The incidences of prostatic and seminal vesicle lesions in all groups of the present experiment, except for the group given castration without hormonal supplement, were equivalent to those previously found in non‐castrated animals. Therefore, the present findings indicate that endogenous testosterone may not be required for promotion hy TP/EE of DMAB‐initiated prostate carcinogenesis and that it may not contribute to the actions of DHT.