Effect of types and amount of dietary fat during the initiation phase of hepatocarcinogenesis

The effects of various levels of corn oil and lard fed during the initiatio n stage of azoxymethane (A OM)-induced hepatocarcinogenesis were studied in male Fischer 344 rats. The animals were fed diets containing 5%, 13.6%, an d 23.5% corn oil or lard two weeks before, during, and until one week after injections of AOM (15 mg/kg body wt sc) once weekly for two weeks. One wee k after A OM treatment, groups of animals fed the 13.6% and 23.5% corn oil or lard diet were transferred to their respective 5% corn oil or lard diet and fed these diets until the termination of the study (34 wk). Immunohisto chemical staining of glutathione S-transferase placental form was performed in the liver, and the number of glutathione S-transferase placental form p ositive foci was determined. Density, average area, and unit area of foci w ere significantly inhibited in the animals fed the 13.6% and 23.5% lard die ts compared with those fed the 13.6% and 23.5% corn oil diets. These result s indicate that the effect of dietary fat during the initiation phase of A OM-induced hepatocarcinogenesis depends on the type of fat and its fatty ac id composition. Additionally, the enhancing effect of a corn oil diet in he patocarcinogenesis is mainly present during the initiation phase of carcino genesis compared with a lard diet.