EFFECTS OF INTERFERON, POLYRIBOINOSINIC ACID POLYRIBOCYTIDILIC ACID AND STEROIDS ON THE CYTOCHROME-P450 SYSTEM OF CULTURED PRIMARY MOUSE HEPATOCYTES

An earlier study from this laboratory showed that the hepatic murine c ytochrome P450 (P450) system was depressed by interferon in vivo but i nduced in cultured primary hepatocytes. The current investigation atte mpted to resolve this contradiction. The P450 content of the cells use d in the earlier study fell precipitously during the first 24 hr of cu lture and remained at the same low level throughout another 48 hr of i ncubation. This failure to maintain the P450 level suggested that the cells may not have been sufficiently viable to support the mechanisms involved in the depressant activity of interferon. Accordingly, a chem ically defined medium containing hydrocortisone was devised which supp orted an acceptable level and function of the P450 system throughout a 72 hr incubation period. Functionality of the P450 system was evaluat ed by measuring aminopyrine N-demethylase and benzo[a]pyrene hydroxyla se activities. When this steroid supplemented medium was used, interfe ron depressed both activities by about 25%; however, neither activity was affected significantly by poly IC. On the other hand, benzo[a]pyre ne hydroxylase activity was depressed by both poly IC and interferon i n hepatocytes induced with dexamethasone or with dexamethasone plus 3- methylcholanthrene. These studies emphasize the necessity of maintaini ng an acceptable level of homeostasis in cultured hepatocytes if one i s to derive meaningful interpretations of certain biological events.