Drug Metabolism Activities of Isolated Rat Hepatocytes in Monolayer Culture

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Abstract
The levels of cytochrome P‐450 in hepatocytes cultured as monolayers for 22 hrs in Dulbecco's modified Eagle medium supplemented with serum and insulin was reduced to approximately 40% of initial values of freshly isolated hepatocytes. In correspondance with this the activities of the cytochrome P‐450 monooxygenases aryl hydrocarbon (benzo(a)pyrene) hydroxylase (AHH) and ethylmorphine (EM) N‐demethylase were reduced to 40 and 22% of their initial activities, respectively. Modifying the culture medium through omission of cysteine and cystine, and adding dexamethazone and delta‐amino levulinic acid, increased the content of cytochrome P‐450 to 59 % and EM N‐demethylase to 46 % of initial values, but was without effect on AHH activity. However, further modifications by adding high concentrations of asparagine and leucine increased AHH activity to 62% of initial values, but did not further enhance the total content of cytochrome P‐450 or the EM N‐demethylase activity. The activities of cytochrome P‐450 reductase, flavin containing monooxygenase, epoxide hydrolase and glutathione S‐transferase decreased less (to about 70–80% of initial values) than cytochrome P‐450 associated monooxygenase activities, whereas UDP‐glucuronyl transferase decreased to about 50% of initial values. In contrast to what was observed regarding cytochrome P‐450 and associated monooxygenase activities, modification of the incubation conditions did not affect the non‐cytochrome P‐450 enzymatic activities.

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