A simplified routine assay for urinary 3-methoxy-4-hydroxyphenylglycol

Urinary 3-methoxy-4-hydroxyphenylglycol (MHPG) level may provide us with a biochemical index for central noradrenergic activity. Previous methods for assaying MHPG in urine often lacked specificity, sensitivity, cost-effectiveness or convenience. We now describe a simplified routine assay for urinary MHPG by high-pressure liquid chromatography using electrochemical detection. For convenience and cost-effectiveness within a typical batch assay of total MHPG, 0.5 mL of urine sample, 50 microL of glusulase and 4 micrograms iso-vanillyl alcohol (internal standard) were used to hydrolyze conjugated MHPG at 37 degrees C overnight. Alternatively, for a same-day operation, it is efficient to hydrolyze the sample at 50 degrees C for 3 hours. Each sample was separated isocratically on a reversed-phase column (Ultracarb 5 ODS) at 25 degrees C with the flow rate at 1 mL/min. Intra- and inter-assay coefficients of variation were found to be 4.0% (n = 10) and 5.0% (n = 27), respectively, for MHPG at a mean concentration of 1.9 mg/L. Sulfatase or glucuronidase can be substituted for glusulase to obtain either sulfate- or glucuronide-conjugated MHPG. This procedure requires smaller sample amounts and less preparation time without compromising sensitivity and reproducibility.

Determination of 3-methoxy-4-hydroxyphenylethylene glycol in urine using reversed-phase liquid chromatography with column switching and electrochemical detection

A column-switching method was developed for the determination of total 3-methoxy-4-hydroxy-phenylethyleneglycol (MHPG) in urine. This was performed by first treating samples with beta-glucuronidase, followed by extraction with ethyl acetate. The reconstituted extracts were injected onto an HPLC system containing an amperometric detector and tandem Nucleosil C18 and C8 reversed-phase columns connected by a switching valve. The total analysis time for MHPG was 12 min. The limit of detection was 0.18 ng, or 9 micrograms/l for 20-microliters injections of a 1.0-ml reconstituted extract prepared from 1.0 ml of urine. The linear range extended up to 80 mg/l. The within-day precision for a urine sample containing 170 micrograms/l total MHPG was +/- 6% and the day-to-day precision was +/- 15%. The average levels determined by this method for total MHPG in normal subjects showed good agreement with previous literature values. This approach could be modified for the determination of free MHPG by using only ethyl acetate extraction for sample pretreatment.

Quantitation of total MHPG in the rat brain using a non enzymatic hydrolysis procedure. Effects of drugs

An acid-catalyzed procedure has been used to hydrolyze MHPG-sulfate in homogenates of rat brain. The samples (in 0.4 mol/L perchloric acid) are treated for 3 min. at 100 degrees C in a water bath and aliquots are injected into a reversed phase HPLC system. Detection is achieved fluorimetrically. The absolute detection limit for MHPG is 150 pg, which allows the reliable determination of either free or total MHPG in rat brain in concentrations down to 15 ng/g, using the described procedure. The concentration of total MHPG found in the brains of saline-treated rats are 101 +/- 21 ng/g (mean +/- S.D.) which is in a good accordance with the concentration value for the same samples obtained using a GC-MS method (115 +/- 19 ng/g). Rats treated with clonidine (300 micrograms/Kg, i.p.) or yohimbine (10 mg/Kg, i.p.) showed brain concentrations of total MHPG of 68 +/- 22 ng/g and 299 +/- 85 ng/g, respectively. The utility of this method for the analysis of brain regions or brain nuclei (e.g. locus coeruleus) is also shown.

Determination of urinary 4-hydroxy-3-methoxyphenylethylene glycol in man by high performance liquid chromatography with electrochemical detection

A reverse phase high performance liquid chromatographic method for determining levels of 4-hydroxy-3- methoxyphenylethylene glycol (MHPG) in human urine that is virtually free of all interfering peaks has been developed. After addition of a homologous internal standard, enzymatic hydrolysis is performed. Samples are then placed onto columns containing AG1-X8, and the MHPG is collected in a phosphate buffer wash of the column. After ethyl acetate extraction and evaporation of the organic solvent, the dry residue is redissolved in mobile phase, and injected onto a reverse phase column. Results obtained with this assay were almost identical (101+/-5.6%, mean+/-SD, n=6) with those obtained using a gas chromatography - mass spectrometry (GCMS) assay.

An improved gas chromatographic determination of urinary catecholamine metabolites

We describe an improved gas chromatographic method for the determination of 3-methoxy-4-hydroxymandelic acid (vanilmandelic acid), 3-methoxy-4-hydroxyphenyacetic-acid (homovanillic acid), and 3-methoxy-4-hydroxyphenylethylene glycol. By incorporating slight modifications to established procedures, this method allows the urinary metabolites to be measured more rapidly and with better resolution. The procedure uses an internal standard and involves ethyl acetate extraction, silylation, and chromatography using a combination of two different stationary phases. The technique is simple and reliable and may be easily incorporated as a routine laboratory procedure.

Free and conjugated 3-methoxy-4-hydroxyphenylglycol in human urine: peripheral origin of glucuronide

The aim of our study was to investigate the endogenous origin of the three forms of 3-methoxy-4-hydroxyphenylglycol (MHPG) present in human urine and to further examine the hypothesis of an independent (peripheral or central) origin of glucuronide and sulfate conjugates. The urinary levels of free, sulfate, and glucuronide MHPG were determined in control subjects under normal conditions in relation to age, sex, and diet and in two experimental situations known to alter sympathetic activity. The mean daily excretion of total MHPG in a group of 14 men and 14 women was 1780 +/- 122 micrograms, with the free, sulfate, and the glucuronide representing 8% +/- 0.5%, 40% +/- 1.5%, and 52% +/- 1.6%, respectively. No influence of sex, age, or diet was observed on any form. Strong physical activity and anticipatory stress increased norepinephrine excretion and selectively increased MHPG glucuronide levels without changing the free or the sulfate excretion. We conclude that the total amounts of free, sulfate, and glucuronide MHPG found in urine originate from endogenous body pools with no interference of dietary components. The sympathetic nervous system seems to be the main source of glucuronide and arguments are given supporting the central origin of sulfate.