title: Survey of various chemicals for initiating and promoting activities in a short-term in vivo system based on generation of hyperplastic liver nodules in rats.
abstract: The effects of pre- (initiation stage) and post- (promotion stage) administration of 17 chemical carcinogens (including both hepatic and non-hepatic carcinogens), 3 promoters and 2 non-carcinogenic analogs, on the induction of liver hyperplastic nodules were investigated in rats. Test chemicals were administered during the initiation stage after which rats were fed dietary N-2-fluorenylacetamide (2-FAA) for 2 weeks in conjugation with necrogenic CCl4 to enhance production of nodules initiated by test chemicals. Alternatively, effects of test chemicals administered during the promotion phase were evaluated in rats given a combination of dietary 2-FAA for 2 weeks and necrogenic CCl4. This initiation regimen resulted in very few nodules unless a promoter was subsequently used. All chemical carcinogens administered during the initiation stage induced more frequent, larger hyperplastic nodules than did control treatments. However, neither the promoters nor the non-carcinogenic analogs induced hyperplastic nodules if they were administered during the initiation stage. In contrast, hepatocarcinogens and a promoter of hepatocarcinogenesis (phenobarbital) administered in the promotion stage had enhancing (promoting) activity on hyperplastic liver nodules, whereas non-hepatocarcinogens, a promoter for skin carcinogenesis (12-O-tetradecanoylphorbol-13-acetate) and a promoter for urinary bladder carcinogenesis (saccharin) did not. Non-carcinogenic analogs were not active when administered during either the initiation or promotion stages. These findings demonstrated the utility of employing short-term in vivo assays for both initiating and enhancing (promoting) activities of chemicals. By our system, chemicals were classified into 4 main groups, namely, (i) hepatocarcinogens which have both initiating and enhancing activity, (ii) non-hepatocarcinogens with initiating activity only, (iii) promoters of hepatocarcinogenesis which have promoting activity and (iv) non-carcinogens and non liver promoters which did not initiate nor promote nodule development. This is a more discriminating means of assaying carcinogenic activity than is possible with short-term in vitro screening assays for mutagenicity.
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene; D001580:Benzopyrenes / Q000633:toxicity; D002273:Carcinogens / Q000633:toxicity*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D005001:Ethionine / Q000633:toxicity; D006965:Hyperplasia; D008099:Liver / Q000187:drug effects / Q000473:pathology*; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D001580:Benzopyrenes; D002273:Carcinogens; D001564:Benzo(a)pyrene; D005001:Ethionine