[Tetrahydroisoquinolines in connection with Parkinson's disease]

Tetrahydroisoquinoline (TIQ) derivatives have been assumed to be substances closely related to parkinsonism because of their structural similarity to MPTP, which induces parkinsonism. TIQ and 1-methyltetrahydroisoquinoline (1MeTIQ) could be detected in human brains. The 1MeTIQ content in the frontal lobe of parkinsonian cases was markedly reduced than in non-parkinsonian cases. In addition, it could be recognized that 1MeTIQ content was decreased with aging both in the control and parkinsonians. It can be presumed that 1MeTIQ plays a role in protecting the brain from parkinsonism or aging processes. TIQ and 1MeTIQ were also present in a number of foods. It can be pointed out the possibility of TIQ intake from some foods. Metabolism of TIQ was defective in female DA, rat an animal model of a poor debrisoquine metabolizer. The female DA rat showed significantly higher brain accumulation of TIQ. These results suggest that the metabolic detoxication process is depressed and TIQ accumulation in the brain is enhanced in a poor debrisoquine metabolizer, which may be one possible explanation for poor debrisoquine metabolizers being susceptible to Parkinson's disease.