Slow increase of homovanillic acid in cerebrospinal fluid after levodopa administration

Concentrations of major catabolites of dopamine were followed in the ventricular cerebrospinal fluid (CSF) in five patients undergoing intracranial pressure monitoring for chronic hydrocephalus. Determinations were made every 2 h following the administration of carbidopa/levodopa 25/250 mg (one Sinemet capsule) given 8 h apart. The rise of homovanillic acid (HVA) concentrations was slow and progressive, reaching the level of statistical significance (p < or = 0.01) only 8 h after the second administration of Sinemet. The rise in 3,4-dihydroxyphenylacetic acid (DOPAC) was faster than the rise in HVA, with the peak value detected 4 h after the first administration of Sinemet. These data are interpreted as a confirmation, in humans, of a slow pool of exogenous levodopa, previously demonstrated in animal studies.