Determination of Normetanephrine, 3,4-Dihydroxyphenylethyleneglycol (Free and Total), and 3-Methoxy-4-Hydroxyphenylethyleneglycol (Free and Total) in Rat Brain by High-Performance Liquid Chromatography with Electrochemical Detection and Effects of Drugs on Regional Concentrations

A new, fast and sensitive assay for normetanephrine (NM), free and total 3,4-dihydroxyphenylethyleneglycol (DOPEG), and free and total 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) in brain tissue is described. The method is based on high-performance liquid chromatography with electrochemical detection. Small Sephadex G 10 columns were used for prepurification. This permitted the additional isolation and quantification of tyrosine, 3,4-dihydroxyphenylalanine, noradrenaline, dopamine, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid. The compounds were determined in six brain areas (striatum, cortex, hippocampus, hypothalamus, brainstem, and cerebellum). Most DOPEG and MOPEG in rat brain was present in the conjugated form, except for the cerebellum, where about 80% of MOPEG was nonconjugated. No postmortem effects on MOPEG levels were observed; a slight increase in DOPEG in certain brain areas was found in microwave-killed rats. The effects of clonidine, yohimbine, N,N-dipropyl-5,6-ADTN, and chlorpromazine on the concentrations of the five noradrenaline (NA) metabolites were determined. Free and total DOPEG and MOPEG provide similar information on NA metabolism, whereas NM (after monoamine oxidase inhibition) reflects a different type of interaction of drugs with NA metabolism. The similarity in the pattern of drug-induced changes in NA metabolism in the various brain areas suggests that adrenoreceptors mediating NA metabolism are homogeneously distributed throughout the brain.