Manuchair EbadiPiyarat GovitrapongUniversity of Nebraska at OmahaMahidol University2018-10-122018-10-121981-01-01Drug Development Research. Vol.1, No.2 (1981), 129-13610982299027243912-s2.0-0019721017https://repository.li.mahidol.ac.th/handle/20.500.14594/30269The mechanism of the nullification of the therapeutic effects of levodopa by pyridoxine in parkinsonian patients is not known and is still a subject of much speculation. Among other suggestions, it has been proposed that pyridoxine and levodopa may form tetrahydroisoquinoline derivatives in vivo, which may in turn inhibit dopa decarboxylase or act as a false transmitter. This possibility was tested by synthesizing six tetrahydroisoquinoline derivatives and by studying their effects on dopa decarboxylase in brain homogenates. These compounds in concentrations of 50 mM did not inhibit dopa decarboxylase or pyridoxal kinase, which synthesizes pyridoxal phosphate. Copyright © 1981 Alan R. Liss, Inc.Mahidol UniversityPharmacology, Toxicology and PharmaceuticsArticleSCOPUS10.1002/ddr.430010205