Inhibition of rat brain monoamine oxidase-B by some monoamine reuptake inhibitors as antidepressants

Monoamine oxidase (MAO) activities in rat forebrain homogenate were determined by using serotonin and benzylamine as respective substrates of MAO-A and -B. Effects of the antidepressants, imipramine, maprotiline, nomifensine and zimelidine on MAO activity were determined. All of these compounds inhibited both MAO-A and -B activity, but the inhibition was not strong. The inhibitory potency of MAO-A and -B was not changed by preincubation of homogenates with these compounds. Each compound competitively inhibited MAO-A, but MAO-B inhibition was shown to be mixed-type inhibition by Lineweaver-Burk plots.