Abstract

We previously demonstrated that induction of hepatic cytochrome P4503A (CYP3A) immunoreactive protein is a response in rats, but not rabbits, treated with the antiglucocorticoid, pregnenolone 16 alpha-carbonitrile and in rabbits, but not rats, treated with rifampicin. These striking interspecies differences in response to CYP3A inducers prompted us to compare the effects of a variety of agents on CYP3A expression in primary cultures of hepatocytes from rats, rabbits, and humans, maintained under nearly identified conditions on Matrigel. We used treatment with dexamethasone, the most effective inducer of CYP3A mRNA and CYP3A immunoreactive protein in cultures of rat hepatocytes, to define the 100% response. As expected from their effects in vivo, incubations of cultures with medium containing pregnenolone 16 alpha-carbonitrile or rifampicin induced CYP3A mRNA to high levels exclusively in rat hepatocytes or rabbit hepatocytes, respectively. Pregnenolone 16 alpha-carbonitrile treatment also did not induce CYP3A immunoreactive protein in rabbit hepatocytes, although rifampicin treatment did increase CYP3A immunoreactive protein levels in rat hepatocyte cultures. Additions of phenobarbital to the cultures induced CYP3A mRNA and CYP3A immunoreactive protein to a greater extent in rabbit hepatocytes (94-108% of the dexamethasone response) than in rat hepatocytes (38-57% of the dexamethasone response). In primary cultures of human hepatocytes, dexamethasone and phenobarbital treatments induced CYP3A mRNA (> or = 4.4- and 1.9-fold, respectively, over the amounts of CYP3A mRNA in incubated control cultures).(ABSTRACT TRUNCATED AT 250 WORDS)