RECOVERY OF MESSENGER-RNA EXPRESSION OF TRYPTOPHAN 2,3-DIOXYGENASE AND SERINE DEHYDRATASE IN LONG-TERM CULTURES OF PRIMARY RAT HEPATOCYTES

Expression of tryptophan 2,3-dioxygenase (TO) and serine dehydratase ( SDH) has not previously been maintained or re-induced in long-term cul tured hepatocytes. In the present study, we succeeded in inducing expr ession of TO and SDH mRNAs in adult rat hepatocytes cultured in serum- free L-15 medium supplemented with epidermal growth factor and 2% dime thyl sulfoxide (DMSO), After the start of culture, the expression of T O mRNA rapidly disappeared and at 96 h it was less than 10% of that at isolation, However, after the addition of 2% DMSO from 96 h, the tran script level gradually increased and reached about 40% of that of the isolated cells at day 14. In addition, the expression of TO mRNA was e nhanced in cells treated with both 10(-5) M dexamethasone and 10(-7) M glucagon, In contrast, the expression of SDH mRNA decreased very rapi dly and we could not detect it after 24 h of culture, Furthermore, 2% DMSO failed to induce it, However, when both 10(-5) M dexamethasone an d 10(-7) M glucagon were added to the culture medium at day 9, we obse rved dramatic induction of SDH mRNA 24 h later. Primary hepatocytes cu ltured by this method could express and maintain highly differentiated hepatic functions for a long time, Thus, this in vitro system is suit able for the investigation of hepatic functions.