14C-homovanillic acid in the cerebrospinal fluid of parkinsonian patients after intravenous 14C-L-dopa.

Six patients with Parkinson's disease and five controls were premedicated with probenecid and the peripheral decarboxylase inhibitor alpha-methyldopathydrazine (Carbidopa) before intravenous administration of 50 muc of 14C-L-dopa in tracer quantity. Seven-and-one-half hours later lumbar CSF was obtained. 14C-homovanillic acid (HVA), a major metabolite of brain dopamine, was isolated by thin-layer chromatography and measured. The statistically significant positive correlation between endogenous HVA and 14C-HVA in the entire patient group and the slightly lower values of endogenous HVA and 14C-HVA in the CSF of the parkinsonians support the assumption that the concentration of HVA in the CSF after probenecid treatment reflects brain dopamine turnover. Measurement of labeled HVA here seems to have little advantage over measurement of endogenous HVA alone.