Abstract: AIMTo assess the sex-difference on flutamide metabolism in rat liver microsomes useing rat cytochrome P450 1A2, inhibitory monoclonal antibody. METHODSLiver microsomes were prepared from male or female rats. Protein concentration and total cytochrome P450 content were determined. Incubation mixture included liver microsomes (1.0 nmol·L^-1), reduced form of nicotinamide adenine dinucleotide phosphate (NADPH, 0.1 nmol·L^-1), CYP1A2 (1∶400) and flutamide (2 mg·L^-1). The incubation time was 30 min. The concentration of flutamide and its major metabolite 2-hydroxyflutamide were analyzed by reverse high-performance liquid chromatography. The mobile phase was a mixture of methanol-acetonitrile-water-diethylether (40∶20∶35∶1) with methyltestosterone as internal standard. The detection wavelength was 234 nm. The reaction mixture was extracted with acetic ether 4 mL. Sex-difference on flutamide metabolism was expressed as the difference between the concentration ratio of 2-hydroxyflutamide to flutamide in male and female rat liver microsomes. RESULTSThe recoveries of flutamide and 2-hydroxyflutamide for the proposed method were more than 75%. The formation of 2-hydroxyflutamide from flutamide was inhibited by CYP1A2 antibodies (1∶400) in male and female rat liver microsome for 30 min of incubation time, but the inhibition of flutamide metabolism in female rat was stronger than that in male. The concentration ratios of 2-hydroxyflutamide to flutamide were (1.5±0.6) and (0.9±0.4) in male and female rat liver microsomes, respectively (P<0.01). CONCLUSIONThe results indicate that the activity of male rat CYP1A2 is higher than that of the female rat. There is difference in sex-related rate of flutamide metabolism in rat liver microsomes.