Inhibitory effects of noscapine on dopamine biosynthesis in PC12 cells

The effects of noscapine, a phthalide isoquinoline alkaloid, on dopamine biosynthesis and tyrosine hydroxylase (TH) activity in PC12 cells were investigated. Noscapine showed 74.6% inhibition on dopamine content in PC12 cells at a concentration of 20 μM. IC50 of noscapine was 6.8 μM. TH activity was inhibited by the treatment of noscapine in PC12 cells (20.9% inhibition at 20 μM). Therefore, the inhibition of TH activity by noscapine might be involved in at least one component of the reduction of dopamine biosynthesis in PC12 cells.