[Isatin: possible role in functional interaction of natriuretic peptides and monoamines]

Isatin is an endogenous compound recently discovered in mammalian tissues and body fluids. It has a distinct distribution in rat brain, with a highest concentration, in the hippocampus, of 0.1 microgram/g. Its origin and metabolic pathways remain unclear. In vitro, isatin selectively inhibits monoamine oxidase (MAO) B (IC50 3-8 microM, Ki approximately 20 microM) and, more potently, atrial natriuretic peptide(ANP) binding (IC50, 0.4 microM). Convulsant doses of pentylene tetrazole result in increased isatin level in the brain. Small amounts of isatin are anxiogenic in rodent models, but higher doses cause sedation and possess anticonvulsant action. Isatin administration also increases monoamine levels in the brain and reduces daily urine output.