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The effects of bulbocapnine, an aporphine isoquinoline alkaloid, on dopamine content in PC12 cells were investigated. Bulbocapnine decreased the dopamine content dose-dependentl y (39.2% inhibition at 2OmcM for 24 hr). The IC50 value of bulbocapnine was 22.7mcM. Dopamine content was lowered at 6 hr after exposure to bulbocapnine. And then, the decreased dopamine level was almost maintained at 36 hr and recovered to the control level at about 60 hr. Tyrosine hydroxylase, the rate limiting enzyme in the catecholamine blosynthetic pathway, was also inhibited at 20mcM of bulbocapnine by 23.1% relative to control. We, therefore, hypothesized that the inhibition of tyrosine hydroxylase by bulbocapnine with a single treatment might be partially contributed to the decrease in dopamine content in PC12 cells.
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