Rat brain flavin-containing monooxygenase: catalytic activity and sex-related difference

Abstract

The presence of flavin-containing monooxygenase (FMO) activity was examined in brain microsomes from rats. FMO-mediated oxidation of N,N-di-methylaniline (DMA) and methimazole (MEM) was observed in rat brain microsomes. No sex difference was observed in FMO-mediated metabolism of DMA. However, a constitutive sex difference was observed in FMO-mediated metabolism of MEM. Incubation of male brain microsomes at room temperature for .5 hr did not have any effect on DMA or MEM oxidation, while 80% of female brain microsomal FMO-mediated oxidation of MEM was lost on similar incubation. Thus a distinct sex-related difference was observed in FMO-mediated oxidation of MEM as indicated by apparent Km and Vmax and sensitivity to temperature. Results may relate to psychoactive drugs (e.g., chlorpromazine, imipramine) that are substrates for FMO and are detoxified by FMO mediated reactions.