Ethoxycoumarin O-deethylation (ECOD) activity in rat liver slices exposed to beta-naphthoflavone (BNF) in vitro.

Precision-cut rat liver slices (0.5 mm) were incubated at 30 degrees C in William's Medium E up to 24 hrs. Our incubation conditions seem to be suitable for maintaining slice function, indicated by constant contents of tissue protein, potassium and glutathione. Thiobarbituric acid reagible substances (TBARS) released into the incubation medium did not significantly increase. Addition of DMSO (0.2 % v/v) or BNF (50 microM) to the incubation medium had no influence on most parameters described above except for increased TBARS release. If ECOD activity was determined in intact liver slices without addition of any cofactor, but substrate only, the main amount of metabolite was found in the medium, and the amount of metabolite retained within the tissue could be neglected. In slices incubated for 24 hrs, no significant changes of ECOD activity occurred for control and DMSO groups, compared with slices incubated for 2 hrs, but in the BNF group activities were more than 3.5 times as high. If ECOD activity was determined in slice homogenate, i.e. with addition of cofactors, decreased activities were measured in all groups after 24 hrs of incubation. This decrease was highest in the control group, lowest in the BNF group. We conclude that intact liver slices can be used as a simple tool to investigate in vitro enzyme induction of BNF type.