SIGNIFICANCE OF ISATIN, AN ENDOGENOUS MAO INHIBITOR, ON BLOOD-PRESSURE CONTROL AND MONOAMINE LEVELS IN RATS

Isatin is an endogenous monoamine oxidase (MAO) inhibitor. The present study was undertaken to elucidate the physiological role of this endo genous MAO inhibitor on blood pressure control and monoamine levels in rats. Tribulin, which has an inhibitory action on brain, kidney and u rine, was purified with ethyl acetate. After chronic administration of isatin (200 mg/kg/day, p. o.) for 4 weeks, the systolic blood pressur e (SEP) of Wistar Kyoto rats (WKY) significantly increased. The urinar y norepinephrine (NE) and dopamine (DA) concentrations increased 4 wee ks after treatment with isatin. Serotonin (5-HT) concentration in the kidney after a 4-week isatin administration significantly increased. T ribulin also significantly inhibited MAO activity like isatin. Exogeno usly administered isatin increased tribulin-like activity from its bas eline in a dose-dependent manner. Although the mechanism of decreased MAO activity induced by isatin has not been elucidated, it can be post ulated that increased blood pressure may be involved in the increased monoamine concentrations induced by isatin.