Responsiveness of hepatocytes from dichloroacetic acid or phenobarbital treated mice to growth factors in primary culture.

Hepatocytes isolated from male B6C3F1 mice and maintained in primary culture were exposed to epidermal growth factor (EGF), hepatocyte growth factor (HGF), acidic fibroblast growth factor (aFGF) alone or in combination with the mitoinhibitory transforming growth factor beta 1 (TGF-beta 1). Groups of mice were exposed to 3.5 g/l dichloroacetic acid (DCA), 0.1% phenobarbital (PB) or the drinking water vehicle for 0, 2, 5, 10, 20, 30, 60, or 90 days. Following a 2 h attachment period, the growth factors with or without TGF-beta 1 were added together with [3H]thymidine. The cells were harvested 48 h later and the incorporation of the labeled thymidine into cellular DNA was determined. Basal DNA synthesis was enhanced following 2 days of PB treatment after which it declined to levels significantly below that in the untreated mice. No early time enhancement of DNA synthesis was measured in the hepatocyte cultures for animals exposed to DCA, but the late time inhibition was also seen. Primary cultures of hepatocytes isolated from control and DCA treated mice exhibited similarly enhanced DNA synthesis in response to eGF, HGF, or aFGF alone or in combination with TGF-beta 1. In contrast, hepatocytes from PB treated animals were refractory to the effects of the growth factors at all time periods. These data suggest that the early depression of cell proliferation we have seen during DCA induced hepatocellular cancer is not due to an impaired ability of hepatocytes to respond to growth factors and that the mechanisms of liver tumorigenesis in the mouse induced by PB and DCA are dissimilar.