REGULATION OF THE EXPRESSION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE AND ALPHA-FETOPROTEIN IN CULTURED FETAL-RAT HEPATOCYTES

The livers of fetal rats were dissociated by collagenase treatment. Tw enty-four hr after the dissociation, dexamethasone (DEX) or epidermal growth factor (EGF) was added to the culture medium, and hepatocytes w ere cultured for 3 more days. After 3 days in culture, clear boundary lines were observed between adjacent hepatocytes in the DEX-added medi um under a phase-contrast microscope. A high level of activity of gamm a-glutamyltranspeptidase (GGT) was observed along these lines by enzym e histochemical staining. On the other hand, the number of hepatocytes showing a positive reaction to immunohistochemical staining of alpha- fetoprotein (AFP) was decreased in the DEX-added medium. Moreover, bun dles of actin filaments were formed along the periphery of cells in he patocytes cultured in the DEX-added medium. In addition, in the same m edium, the quantity of H-3-thymidine incorporated into the hepatocytes was less than that in the pure medium or in the EGF-added medium. Whe n hepatocytes, cultured in the DEX-added medium, were examined under a transmission electron microscope (TEM), an accumulation of glycogen g ranules was observed in the cytoplasm, and bile canaliculuslike struct ures, consisting of large intercellular spaces, were observed between adjacent hepatocytes. In this study, it was indicated in vitro that DE X suppressed the proliferation of rat fetal hepatocytes, induced activ ity of GGT, and depressed the expression of AFP.