Circadian changes in CSF dopaminergic measures in restless legs syndrome.

BACKGROUND AND PURPOSE: Restless legs syndrome (RLS) has a circadian component with symptoms being prominent at night. The dopaminergic (DAergic) system, which plays a role in RLS, entails circadian changes that parallel RLS symptom changes. The aim of this study was to look for relative and diurnal differences in DAergic activity. PATIENTS AND METHODS: All RLS subjects were treated prior to their enrollment in the study but were all drug-free for at least 2 weeks prior to evaluation. Cerebrospinal fluid (CSF) collected at 10 p.m. was used to determine DA-related co-factors and metabolites. These were compared to CSF values collected in a previous study at 10 a.m. RESULTS: The only significant finding from the 10 p.m. samples (30 RLS; 22 control) was increased 3-ortho-methyldopa (3OMD) for RLS compared to controls. A comparison of the 10 p.m. to 10 a.m. values (16 RLS; 9 controls) showed small, non-significant diurnal changes for controls but large diurnal changes in tetrahydrobiopterin (BH4), HVA:5HIAA ratio and 3OMD for RLS, with the 10 a.m. sample showing increases in all three CSF factors compared to the 10 p.m. sample. CONCLUSIONS: The greater diurnal changes in RLS suggest greater fluctuations than normal in DAergic circadian dynamics. The increased 3OMD concentration in the absence of concurrent exogenous levodopa (l-dopa) suggests changes in synthesis or metabolism of l-dopa in RLS.

Identification of O-methyldopa in the ventricular fluid of patients with Parkinson's disease.

A newly developed liquid chromatographic system with a multiple electrode detector was used for quantification of neurochemical substances in ventricular fluid of patients with Parkinson's disease. During the analysis, an unknown peak was observed at almost the same high-performance liquid chromatography retention time as 5-hydroxytryptophan. Through the use of ion suppression techniques, voltammographic analysis and fast atom bombardment mass spectrometry, the compound was identified as O-methyldopa, the major metabolite of L-dopa.

Comparative pharmacokinetics of D- and L-alphamethyldopa in plasma, aqueous humor, and cerebrospinal fluid in rabbits.

The 2 stereoisomers of alphamethyldopa (alpha MD) were separately injected IV at 3 different doses (3, 10, 30 mg/kg) in anesthetized rabbits. Samples of plasma, aqueous humor (AH), and cerebrospinal fluid (CSF) were collected over a 300-min period. The concentration of the aminoacid (AA) was determined by liquid chromatography and electrochemical detection. Parameters obtained from kinetic analyses of the plasma concentrations were close to the values reported in other species. Linear elimination kinetics were observed in the dose range studied. A marked dose-dependent entry of alpha MD was observed in AH. A stereospecific active transport of alpha MD was evidenced in the AH since the concentration of the L-isomer reached values above the plasma levels. CSF entry of the AA was small when compared to AH kinetics. A limited passive diffusion of the AA in the brain could account for this phenomenon. However, greater availability of the L-stereoisomer was still observed in CSF. These alpha MD kinetic analyses illustrate the adaptation of AH and CSF removal procedures to the pharmacokinetic studies of the brain and ocular entry of AA isomers.

Determination of alphamethyldopa, dihydroxyphenylacetic acid and 5-hydroxyindolacetic acid in the cerebrospinal fluid of the rat: kinetic study.

Cerebrospinal fluid (CSF) was removed at a constant flow rate of 1 microliter min-1 from the third ventricle of rats and directly analyzed by liquid chromatography coupled with electrochemical detection. The effect of alphamethyldopa (alpha MD) on CSF alpha MD, dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindolacetic acid (5-HIAA) concentrations was studied for 5 h. alpha MD ethyl ester administration resulted in higher alpha MD levels in CSF as compared with alpha MD administration, suggesting a higher bioavailability of the ethyl ester vs the free acid. A specific inhibition of dopamine metabolism was reflected by a reduction in DOPAC levels while 5-HIAA concentrations were unchanged.