Discovery of dopamine glucuronide in rat and mouse brain microdialysis samples using liquid chromatography tandem mass spectrometry.

A liquid chromatographic-electrospray/tandem mass spectrometric (LC-ESI-MS/MS) method was developed for the analysis of dopamine and its phase I and phase II metabolites from brain microdialysis samples. The method provides for the first time the analysis of intact dopamine glucuronide and sulfate without hydrolysis. The paper describes also an enzymatic synthesis method using rat liver microsomes as biocatalysts and characterization of dopamine glucuronide as a reference compound. The method was validated for quantitative analysis by determining limits of detection and quantitation, linearity,repeatability, and specificity. Dopamine glucuronide was found for the first time in rat and mouse brain microdialysis samples. The concentrations of dopamine and its glucuronide in the microdialysates collected from the striatum of rat brains were approximately equal (2 nM).Dopamine sulfate was not detected in the microdialysates(limit of detection 0.8 nM). The main metabolites of dopamine were dihydroxyphenylacetic acid (DOPAC,1200 nM) and homovanillic acid (HVA, 700 nM).