Ta. Aasmundstad et al., DIFFERENT BIOTRANSFORMATION OF MORPHINE IN ISOLATED LIVER-CELLS FROM GUINEA-PIG AND RAT, Biochemical pharmacology, 46(6), 1993, pp. 961-968
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.