[Pharmacological role of isatin, an endogenous MAO inhibitor].

Isatin (indole-2,3-dione) has been found in mammalian tissues as one of major components of tribulin, a postulated endogenous marker of stress and anxiety. I previously identified isatin as an endogenous inhibitor of monoamine oxidase (MAO) in the human urine and the brain of stroke-prone spontaneously hypertensive rats (SHRSP) using GC-MS. A single dose of isatin significantly increased norepinephrine (NE) and 5-hydroxytryptamine (5-HT) concentrations measured 2 h later in the various brain regions of normotensive Wistar Kyoto rats (WKY). Striatal acetylcholine (ACh) and dopamine (DA) levels significantly increased 2 h after the administration of isatin. Perfused through a microdialysis probe, isatin also produced a significant and concentration-dependent increase in the ACh and DA concentration in the perfusate from the rat striatum. In the patients with Parkinson's disease, urinary isatin concentrations tended to increase according to the severity of disease, as classified by the Hoehn and Yahr criteria. Isatin significantly increased striatal DA levels in a rat model of Parkinson's disease. Isatin may play a role in the regulation of the brain levels of ACh and DA. Furthermore, isatin has a wide spectrum of biological properties: (a) a marker of stress and anxiety, (b) an inhibitor of a number of enzymes, (c) an anti-seizure agent, (d) an inhibitor of benzodiazepin receptors and ANP binding to its receptors.