Does isatin interact with rat brain monoamine oxidases in vivo?

Isatin is a reversible endogenous monoamine oxidase (MAO) inhibitor found in the brain. The influence of isatin on the degree of irreversible MAO inhibition by phenelzine and pargyline has been studied in vitro and in vivo experiments. In vitro 10 and 100 μM isatin reduced irreversible inhibition of MAO A and MAO B assayed after mitochondria wash. Pretreatment of rats with `anxiogenic dose' of isatin (10 mg/kg) protected neither MAO A nor MAO B against subsequently administered phenelzine (10 mg/kg). `Anticonvulsant' dose of isatin (80 mg/kg) reduced phenelzine-dependent inhibition of MAO B but not MAO A. Data obtained suggest that the anticonvulsant effect of isatin does not result from the inhibition of MAO A and the increase of monoamine level in the brain reported in few laboratories is apparently stipulated by a mechanism that does not involve MAO A inhibition.