Initiation/promotion assay for chemical carcinogens in rat liver

A short-term initiation/promotion bioassay has been developed in rat liver using putative preneoplastic foci as the endpoint for the detection of chemical carcinogens. The two protocols of the bioassay used in this study were varied according to the time 2/3 partial hepatectomy was performed in relation to when the initiator or test substance was given. After 7 weeks of promotion with phenobarbital in the drinking water, the rats were killed and the liver was sectioned, stained and scored for gamma-glutamyl transpeptidase (GGTase)-positive foci. The appearance of GGTase-positive foci was taken as an indication of initiation of carcinogenesis by the chemical. Acetylaminofluorene (AAF), aflatoxin B1 (AFB1), benzo(a)pyrene (BaP), diethylnitrosamine (DENA), 7,12-dimethylbenzo(a)anthracene, (DMBA), dimethylhydrazine (DMH), dimethylnitrosamine (DMN) and urethane were positive in the assay, while benzene and N-methyl-N-nitro-N-nitrosoguanidine (MNNG) were negative. Phenobarbital promoted the response of AAF, AFB1, BaP, DENA, DMBA, DMH and DMN. Partial hepatectomy 24 h prior to initiation increased the response of AAF, BaP, DENA, DMBA and DMH. The initiation/promotion assay in rat liver which includes (1) partial hepatectomy at 24 h prior to administering the test chemical; (2) phenobarbital promotion, and (3) GGTase-positive foci as an indication of carcinogenic activity: appears to be sensitive to a wide variety of chemical carcinogens.