Stimulation of DNA synthesis in carcinogen-induced diploid hepatocytes in vitro

Diploid hepatocytes induced by a combination of diethylnitrosamine and 2-acetylaminofluorene were isolated and separated from polyploid hepatocytes by centrifugal elutriation. The diploid and polyploid cell fractions were approximately 90% pure and contained between 1 and 1.5 x 10(7) cells. When kept in monolayer cultures both cell populations responded to the mitogenic effect of EGF and insulin. However, the percentage of labelled nuclei was higher in predominantly diploid compared to predominantly tetraploid hepatocyte cultures at all epidermal growth factor (EGF) concentrations used in this study. At 10 ng EGF/ml and 10 mU insulin/ml the labelling index was twice as high in the diploid liver cells. Further work is required to show the relevance of the stronger response of the diploid cell fraction to mitogens in the process of carcinogenesis.