Induction of gamma-glutamyl transferase by dexamethasone in cultured fetal rat hepatocytes

Hepatocytes isolated as a relatively pure population from normal fetal rats were maintained in primary monolayer culture for 4-10 days. Hepatocytes exhibited a small increase in basal gamma-glutamyl transferase (GGT) activity over time. Exposure to dexamethasone (10(-6) mol/l) elicited a rise in GGT activity after a lag of 24 h. The presence of the steroid was necessary to maintain induction, and its removal resulted in reversal of induction. The maximal response was 2- to 3-fold, 72 h after exposure to the steroid. After this maximal response, a gradual decay in enzyme activity occurred, despite the continuous presence of the hormone. Actinomycin D or cycloheximide given prior to/or simultaneously with the steroid prevented the induction, thus suggesting that both RNA and protein biosynthesis are necessary for induction to occur.