3-Methylcholanthrene-inhibition of hepatocarcinogenesis in the rat due to 3'-methyl-4-dimethylaminoazobenzene or 2-acetylamino-fluorene: a comparative study.

Male Leeds strain rats were given a diet containing either 0.06% 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB) or 0.05% 2-acetylaminofluorene (2-AAF), alone or together with 0.0067% 3-methylcholanthrene (MeCh). MeCh both reduced the incidence of hepatic neoplasms induced by 3'-MeDAB and delayed their development. With 2-AAF, however, inhibition of hepatocarcinogenesis by MeCh only appeared to operate during the period of treatment; thereafter the incidence of tumours rose rapidly and this was accentuated if dietary MeCh continued to be administered after the period of combined 2-AAF and MeCh treatment, suggesting a secondary, promoting effect of MeCH. In contrast, the inhibition by MeCh of carcinogenesis of Zymbal's gland due to 2-AAF was almost complete. Thus, in the long term MeCh has different effects upon 3'-MeDAB and 2-AAF carcinogenesis in the rat liver.