Effect of culture age on drug metabolizing enzymes and their induction in primary cultures of rat hepatocytes.

In order to further establish optimal and reproducible conditions for the use of primary hepatocyte cultures in studies of drug metabolism, the effect of culture age on the basal and induced activities of ethoxycoumarin O-deethylase (ECDE), UDP-glucuronyltransferase (GT) [methylumbelliferone (MU) and p-nitrophenol (pNP) as substrates] and sulfotransferase (MU) were measured. In contrast to the monooxygenase activity conjugating activities were maintained for 2-3 weeks in culture, although especially sulfate conjugation showed a transient decline during the first days, and GT activity increased later on during culture. Low induction of ECDE with both phenobarbital (PB) and 3-methylcholanthrene (MC) was seen during the first day in culture, and maximum induction was obtained when inducer was added on the second or third day. The MC inducible GT (pNP) exhibited a similar behaviour indicating that the coordinated induction of the MC inducible activities is preserved in culture. The results show that primary cultures of hepatocytes can be used to study conjugating enzymes and their regulation. However, each functional parameter that is to be investigated in hepatocyte cultures should first be studied as a function of culture age to establish the optimum time.