title: Dopamine metabolism in the central nervous system after discontinuation of L-dopa therapy in patients with Parkinson disease.
abstract: The dopamine turnover rate in the central nervous system (CNS) of parkinsonian patients was studied by means of the intravenous probenecid test during drug holiday (DH) and alternate day L-dopa therapy (ADDT). After L-dopa therapy was stopped, the dopamine turnover rate decreased more rapidly in patients with the marked wearing-off phenomenon than that in patients without fluctuation of symptoms. The lumbar CSF concentrations of L-dopa and 3-O-methyldopa of patients with and without wearing-off phenomenon were similar during L-dopa therapy. DH improved the effect of L-dopa on parkinsonian symptoms; it did not affect, however, the metabolism of exogenous L-dopa. The dopamine turnover rate in the CNS before L-dopa therapy or on on-days did not differ between patients tolerating and those not tolerating ADDT. However, it was significantly lower on off-days in patients not tolerating ADDT than in those tolerating ADDT. The relationship between dopamine storage in the CNS and the response to L-dopa therapy is discussed.
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D002230:Carbidopa / Q000378:metabolism / Q000627:therapeutic use*; D004298:Dopamine / Q000378:metabolism*; D004334:Drug Administration Schedule; D004359:Drug Therapy, Combination; D005260:Female; D006207:Half-Life; D006801:Humans; D007980:Levodopa / Q000378:metabolism / Q000627:therapeutic use*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D010300:Parkinson Disease / Q000188:drug therapy*; D011339:Probenecid
chemical_list: D007980:Levodopa; D002230:Carbidopa; D011339:Probenecid; D004298:Dopamine