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 undenaken to elucidate the physiological role of this endogenous MAO inhibitor on blood pressure control and monoamine levels in rats. Tribulin, which has an inhibitory action on brain, kidney and urine, was purified with ethyl acetate. After chronic administration of isatin (200 mg/kg/day, p. o.) for 4 weeks, the systolic blood pressure (SBP) of Wistar Kyoto rats (WKY) significantly increased. The urinary norepinephrine (NE) and dopamine (DA) concentrations increased 4 weeks after treatment with isatin. Serotonin (5-HT) concentration in the kidney after a 4-week isatin administration significantly increased. Tribulin also significantly inhibited MAO activity like isatin. Exogenously administered isatin increased tribulin-like activity from its baseline in a dose-dependent manner. Although the mechanism of decreased MAO activity induced by isatin has not been elucidated, it can be postulated that increased blood pressure may be involved in the increased monoamine concentrations induced by isatin.