To study the regulation of drug metabolism, the expression of cytochrome P-450 isozymes and drug-metabolizing activities were investigated by using the primary cultures of adult rat hepatocytes. We used hexobarbital 1 mM concentration to maintain or induce the ability of drug metabolism of cultured hepatocytes. Addition of hexobarbital to the culture medium showed time-dependent increases of the cytochrome P-450 associated monooxygenases, such as ethoxycoumarin O-deethylase, aryl hydrocarbon hydroxylase, aniline 4-hydroxylase, and ethoxyresolufin O-decthylase. These increments of enzyme activities were abolished by addition of cyclocheximide (1.0 uM). We also could obtain the increase of the 3-methylcholanthrene-inducible cytochrome P-450 isozyme and phenobarbital inducible P-450 isozyme in radioimmunocassay.
In conclusion, it seems that hexobarbital may induce the cytochrome P450 and monooxygenase activities in culture and these induction are dependent on protein synthesis.