3-Methoxy-4-hydroxyphenethyleneglycol production by human brain in vivo

Methodological issues in the measurement of urinary MHPG

Reported mean values for urinary 3-methoxy-4-hydroxyphenylglycol (MHPG) for both depressed patients and controls vary substantially between laboratories. The present study describes methodological sources of variance affecting urinary MHPG values. Although intra-assay variance is small (coefficient of variation (CV) = 4.6%), the interassay variance is high (CV = 14.3%) and suggests caution in the interpretation of small group differences. The gas chromatographic (GC) method in this laboratory produces values highly correlated (r = 0.98) with those obtained by a reference gas chromatographic-mass spectrometric (GC-MS) method. The absolute values obtained by GC are 20% higher than those by GC-MS--a problem that may be shared to a varying extent by all GC assays.

IN CONCLUSION

methodological differences do contribute to some of the variation in reported values of urinary MHPG.

Determination of the primary metabolite of central nervous system norepinephrine, 3-methoxy-4-hydroxy-phenethyleneglycol, in mouse brain and brain perfusate by high-performance liquid chromatography with electrochemical detection

Assays are described for the determination of picomole levels of 3-methoxy-4-hydroxy-phenethyleneglycol (MHPG) in mouse brain and in the perfusate of an intact mouse brain. High-performance liquid chromatography with electrochemical detection yielded a MHPG detection limit of 0.37 pmol. This technique offers a sensitive and inexpensive alternative to gas chromatography with mass spectrometry.

Covariance of plasma free 3-methoxy-4-hydroxyphenethyleneglycol and diastolic blood pressure

To test the acute effects of clonidine on plasma levels of 3-methoxy-4-hydroxyphenethyleneglycol (MHPG), the major metabolite of brain norepinephrine (NE), and to examine the relationship between plasma MHPG and concurrently measured blood pressure variables, we performed a series of 31 double blind, placebo controlled, test days in which clonidine (1 and 5 micrograms/kg) or placebo was administered (p.o. at 9:00 a.m.) to six fasting normotensive male subjects. Three h following the 5 micrograms/kg clonidine dose, plasma MHPG reached a nadir significantly below both baseline and placebo levels (P less than 0.05). Mean MHPG concentrations were significantly correlated with diastolic blood pressure (sitting: r = 0.46, df = 88, P less than 0.00001; standing r = 0.49, df = 73, P less than 0.00001). Unexpectedly, this relationship was independent of clonidine dose and sampling time. Under drug-free conditions, the correlation between plasma free MHPG and diastolic blood pressure remained significant (sitting: r = 0.43, df = 40, P = 0.003; standing: r = 0.46, df = 33, P = 0.006). The findings are considered in light of evidence implicating brain NE systems in the regulation of blood pressure.

Norepinephrine metabolism in man using deuterium labelling: the conversion of 4-hydroxy-3-methoxyphenylglycol to 4-hydroxy-3-methoxymandelic acid

4-Hydroxy-3-methoxyphenylglycol (HMPG) labelled with three deuterium atoms was used to study the disposition of peripherally administered HMPG. Five healthy men were given an intravenous pulse dose of 4.3 mumol of labelled HMPG and subsequent plasma and urine levels of endogenous and labelled HMPG as well as those of 4-hydroxy-3-methoxymandelic acid (HMMA, VMA) were determined by gas chromatography-mass spectrometry, using selected ion detection. Approximately 40% of the injected amount of deuterium-labelled HMPG was recovered in the urine as HMMA and another 40% was eliminated as HMPG conjugates. Thus, the HMPG formed from norepinephrine either in the central or peripheral nervous system undergoes both conjugation and extensive oxidation.

Acathisia-syndrome: involvement of noradrenergic mechanisms

The involvement of noradrenergic mechanisms in patients suffering from acathisia was investigated by determination of urinary night-time 3-methoxy-4-hydroxy-phenyl glycol (MHPG)-excretion and was compared both with control patients matched according to age and sex and healthy individuals. A significantly reduced MHPG excretion was found among the acathisia patients. It is suggested that a supersensitivity of the spinal noradrenergically innervated receptors caused by their long-term blocking is responsible for occurrence of the symptoms.

Controlled exercise elevates plasma but not urinary MHPG and VMA

The effect of controlled exercise on plasma and urinary 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and vanillylmandelic acid (VMA) was investigated in normal subjects. After 3 days of bed rest, six normal volunteers engaged in controlled exercise adjusted to a constant 40% of the individual's maximum oxygen intake. The exercise program consisted of 4 miles of walking and a half-hour each of bicycle ergometry and treadmill walking. Both plasma VMA and MHPG were higher on the exercise day than on the resting day, while urinary VMA and MHPG levels did not differ from rest to exercise. The mean urinary MHPG/VMA ratio (0.46) differed markedly from the mean plasma MHPG/VMA ratio (2.3). Plasma and urinary MHPG apparently represent different indices of norepinephrine metabolism.

Toward a biochemical classification of depressive disorders. III: Pretreatment urinary MHPG levels as predictors of response to treatment with maprotiline

Pretreatment urinary MHPG levels were examined in 28 depressed patients as a possible predictor of response to treatment with maprotiline, a tetracyclic antidepressant that exerts potent effects on norepinephrine uptake, but has little effect on serotonin uptake. Maprotiline was administered in doses up to 150 mg/day during the first 2 weeks after which time the dose could be increased incrementally up to 300 mg/day if indicated clinically. At 2 weeks, patients with low pretreatment urinary MHPG levels responded more favorably to treatment than did patients with high MHPG levels. At 4 weeks, patients with low MHPG levels continued to show more favorable responses; however, differences between the two groups were less clear-cut than at 2 weeks. The findings suggest the patients with low pretreatment urinary MHPG levels are more sensitive to, and respond more rapidly to, treatment with maprotiline than patients with high pretreatment urinary MHPG levels.

Amphetamine withdrawal: effects on threshold of intracranial reinforcement

In order to determine whether alterations in sensitivity to rewarding stimuli accompany the biochemical and behavioral changes induced by chronic amphetamine treatment and withdrawal, we explored the effects of chronic administration and withdrawal of d-amphetamine on thresholds of intracranial reinforcement in the rat. Rats were injected with d-amphetamine sulfate according to a chronic, escalating dose schedule. Marked decreases in threshold of intracranial reinforcement were observed immediately (0--1 h) following the last injection of d-amphetamine. In contrast, all animals showed marked increases in thresholds of intracranial reinforcement 24-48 h after the last injection of d-amphetamine. These findings were discussed in relation to amphetamine-induced and naturally occurring depressions in man.

4-methoxy-3-hydroxyphenylglycol as an internal standard for the determination of 3-methoxy-4-hydroxyphenyglycol in urine: results obtained in depressed patients and healthy controls

A modification of the method developed by Dekirmenjian & Maas (1970) Anal. Biochem. 35, 113-122) is described for the determination of 3-methoxy-4-hydroxyphenylglycol in urine. The use of 4-methoxy-3-hydroxyphenylglycol as an internal standard improves the accuracy, simplicity and reproducibility. Therefore, the method is suitable for routine determination in laboratories without gas chromatography/mass spectrometry equipment. Some results obtained in depressed patients and healthy controls are presented.

MHPG excretion in depression

3-Methoxy-4-hydroxyphenylethyleneglycol (MHPG) was measured in 24-hour urine collections obtained from 44 drug-free patients hospitalized for a major depressive disorder, MHPG was significantly lower in a group of three biopolar 1 patients than in a group of unipolar patients. The excretion of MHPG did not significantly differ among patients classified as psychoatic, agitated, or retarded subtypes of depression as compared to patients not assigned to these subtypes.

The need for power, brain norepinephrine turnover and learning

This experiment was designed to explore whether brain norepinephrine (NE) serves as a specific reward system for the power drive. Previous research has indicated that 3-methoxy-4-hydroxyphenyl glycol (MHPG), a urinary metabolite reflecting central NE turnover, is positively correlated with features of assertiveness which one might expect of a person high in the need for power (n power) or in a state of aroused power motivation. Twenty-seven male undergraduates, 13 of whom were high and 14 of whom were low in n power as assessed by a TAT measure, were recruited as subjects. Before and after the laboratory session, subjects voided all urine and concentrations of epinephrine, norepinephrine and MHPG were obtained from samples. The laboratory task consisted of 20 picture-word pairs in which the subject had to learn to anticipate the word associated with each picture before the word was presented. Five pairs of stimuli in each of the following picture-word combinations were presented 12 times: neutral-neutral, neutral-power, power-neutral and power-power. The results revealed that, as predicted, subjects high in n power learn most power-related material faster than subjects low in n power. The need for achievement is unrelated to the learning of any picture-word pairs. The neurochemical data indicated that subjects maintaining a relatively high MHPG excretion rate during the experiment who were also high in n power showed the greatest mastery of power related compared with neutral picture-word pairs. These findings are consistent with the hypothesis that brain NE turnover is specifically related to the learning of power-related responses in subjects high in n power.