Quantitative differences in phase I and II metabolism between rat precision-cut liver slices and isolated hepatocytes

Testosterone (250 microM), 7-ethoxycoumarin (25 microM), and 1-chloro-2,4-dinitrobenzene (CDNB, 50 microM) were used as substrates to compare phase I and II metabolism in rat precision-cut liver slices and rat hepatocytes. Overall clearance to metabolites was significantly greater in hepatocytes for testosterone (1.9- to 16.9-fold), 7-ethoxycoumarin (O-deethylation, 14.8-fold; glucuronidation, 3.1-fold), and CDNB (8.7-fold). The same metabolites for each of the substrates were detected in slices and hepatocytes. However, the ratio of sulfate to glucuronide conjugation was higher in slices, in line with the markedly slower rate of formation of 7-hydroxycoumarin. The slower rate of CDNB conjugation could not be explained by differences in the intracellular concentration of glutathione. These data suggest that metabolism in precision-cut slices is limited by diffusion of the substrate. This was illustrated by the use of 2-(5'-chloro-2'-phosphoryloxyphenyl)-6-chloro-4-(3H)-quinazolinone as a fluorescent probe to investigate diffusion in slices and hepatocytes.