Effect of phenobarbital on 7-Ethoxycoumarin-O-deethylase and microsomal epoxide hydrase activities in collagen gel cultures of rat hepatocytes.

Abstract Ethoxycoumarin- O -deethylase (ECOD) and microsomal epoxide hydrase (mEH) activities have been studied in collagen gel cultures of rat hepatocytes under control conditions and after exposure to phenobarbital. The hepatocytes were either sandwiched between two layers of extracellular matrix (type I collagen) or directly mixed with the same type of collagen gel. In preliminary experiments it was first tested whether it was possible to measure ECOD activity directly in intact hepatocytes that were embedded in a collagen gel matrix. Probably by a delay of substrate penetration through the collagen gel, the latter had to be removed by a collagenase digestion before ECOD activity measurements took place. When cultured in control medium, the activity of both phase I enzymes studied decreased as a function of culture time in sandwich as well as in immobilization cultures. After 4 days, however, a steady-state situation was reached and this level of enzymatic activity was observed for at least 2 wk. When the cells were exposed to 3.2 m m phenobarbital, an increased ECOD activity remained detectable for at least 14 days. In sandwich cultures a two- to threefold increase of ECOD activity was observed, whereas in immobilization cultures, increases of only 30 to 46% of the values observed in the control medium were measured. After exposure of the collagen gel cultures to 3.2 m m phenobarbital, the mEH activity was increased to the same extent (factor 2 to 2.5) in both culture models.