Abstract
The present paper describes the metabolism of a chiral drug propranolol (PL) using isolated hepatocytes freshly prepared from untreated, PB- or 3-MC-pretreated rats. In order to examine not only the existence of enantioselectivity but also the effect of enzyme inducer (PB or 3-MC) on PL metabolism, 500 μM PL (RS-PL, R(+)-PL or S(–)-PL) was incubated at 37°C using 8×106 cells/ml isolated rat hepatocytes. Then, the elimination amount of PL and the formation amounts of eight kinds of the metabolites including ring hydroxylated metabolites (4-OH-, 5-OH- and 7-OH-PL) and side chain metabolites (NDP, AcNDP, PGL, NLA and NAA) were simultaneously determined by HPLC. By 3-MC- and PB-pretreatment, a significant increase was noticed in PL elimination and also in the formation of PL metabolites, NDP, NLA and NAA. Furthermore, the presence of enantioselectivity was observed, i.e. the substrate R(+)-PL was always eliminated faster than the substrate S(–)-PL. Regarding the metabolite formation, NDP, AcNDP and NAA were dominantly produced from R(+)-PL, and NLA, PGL and the ring hydroxylated metabolites from S(–)-PL. In all cases of PL elimination and the metabolite formation, the amounts of the metabolites derived from RS-PL indicated the mean values of the respective amounts derived from R(+)-PL and S(–)-PL. Using the three kinds of isolated rat hepatocytes mentioned above, the kinetic parameters of NDP-formation at 37°C for 10 min were calculated using RS-PL, R(+)-PL or S(–)-PL as a substrate. From the pseudo values of V′max/K′m (μl/min・8×106 cells), the easiest formation of NDP from R(+)-PL was observed in the rat hepatocyte system pretreated with 3-MC.
