DIFFERENT BIOTRANSFORMATION OF MORPHINE IN ISOLATED LIVER-CELLS FROM GUINEA-PIG AND RAT

The biotransformation of morphine was characterized in freshly isolate d parenchymal and non-parenchymal liver cells from rats and guinea pig s in suspension culture to establish an in vitro model for morphine me tabolism. Liver cells were prepared by a collagenase perfusion techniq ue, and separated by differential centrifugation. Morphine metabolism was investigated at different concentrations (1, 5, 100 and 200 muM). Samples were taken repeatedly during 2-4 hr of incubation, and subsequ ently analysed on a HPLC system employing both UV and electrochemical detection. In suspensions of hepatocytes from both animal species morp hine-3-glucuronide (M3G) was the major metabolite of morphine. and was formed at comparable rates at all concentrations examined. Guinea pig hepatocytes in addition produced considerable quantities of morphine- 6-glucuronide (M6G), whereas this metabolite was detected only intrace llularly in minor quantities in rat hepatocytes. The ratio between the two morphine glucuronides (M3G/M6G) in suspensions of guinea pig hepa tocytes was approximately 4: 1. N-Demethylation of morphine was more p ronounced per mg cell protein in rat hepatocytes compared to guinea pi g cells. Metabolic activity towards morphine was not detected in non-p arenchymal cells of the two species. The morphine glucuronidation patt ern found in guinea pig hepatocytes resembles to a greater extent than that found in rat hepatocytes the pattern found in in vivo studies of humans. It was concluded that isolated guinea pig parenchymal cells a ppeared to be a promising in vitro system for studies of morphine gluc uronidation, and to observe metabolism in general.