Vanillylmandelic acid

Vanillylmandelic acid human urine acidification, centrifugation ion-pair CIS Affix EC 65... 

Methoxy-4-hydroxy-mandelic acid Vanillylmandelic acid (VMA)... 

Large doses may decrease urinary excretion of phenolsulfonphthalein. Salicylates in the urine result in falsely elevated vanillylmandelic acid (VMA) with most tests, but falsely decrease VMA determinations by the Pisano method. 

Adrenaline is synthesised in the adrenal medulla and at sympathetic nerve endings from phenylalanine and metabolised by oxidation (monoamine oxidase MAO) or conjugation (catechol 0-methyl transferase COMT). It is excreted in the urine as vanillylmandelic acid. Its main physiological effects are at pi and a adrenoceptors, with less marked effects at (P2... 

Magera MJ, Thompson AL, Stoor AL, Helgeson JK, Matern D, Rinaldo P (2003) Determination of vanillylmandelic acid in urine by stable isotope dilution and electrospray tandem mass spectrometry. Clin Chem 49 825-826... 

Degradation of catecholamines The catecholamines are inacti vated by oxidative deamination catalyzed by monoamine oxidase (MAO), and by O-methylation carried out by catechol-O-methyl-transferase (COMT, Figure 21.15). The two reactions can occur in either order. The aldehyde products of the MAO reaction are axi dized to the corresponding acids. The metabolic products of these reactions are excreted in the urine as vanillylmandelic acid, metanephrine, and normetanephrine. 

The catecholamines are a group of hormones secreted by the adrenal medulla. The major urinary metabolite of norepinephrine and epinephrine is vanillylmandelic acid (VMA). Urinary levels of VMA are considerably higher than those of total catecholamine. From the standpoint of laboratory methodology, VMA estimation is preferable to total catecholamine estimation, although it is not a simple procedure. VMA has been shown to be elevated in some patients who had phenochromocytoma and normal urinary catecholamines, even though patients with neuroblastoma have a normal VMA level and elevated catecholamine levels. 

Potential fates of recaptured norepinephrine Once norepinephrine reenters the cytoplasm of the adrenergic neuron it may be taken up into adrenergic vesicles via the amine transporter system and be sequestered for release by another action potential or persist in a protected pool. Alternatively, norepinephrine can be oxidized by monoamine oxidase (MAO) present in neuronal mitochondria. The inactive products of norepinephrine metabolism are excreted in the urine as vanillylmandelic acid (VMA), metanephrine and normetanephrine. 

Biotransformations Epinephrine, like the other catecholamines, is metabolized by two enzymatic pathways COMT, which has S-adenosylmethionine as a cofactor, and MAO (see Figure 6.3). The final metabolites found in the urine are metanephrine and vanillylmandelic acid. [Note Urine also contains normeta-nephrine, a product of norepinephrine metabolism.]... 

Kahane et al. [169] first oxidized vanillylmandelic acid, after its extraction from urine by the action of sodium periodate, to vanillin. The vanillin was then converted into the methyloxime by reaction with methoxylammonium chloride and finally silylated. The recovery of the total procedure, including extraction from urine, is said to be minimally 95%, with the resulting derivative being highly specific for the compound under analysis. The GC analysis was performed on QF-1 as stationary phase. 

The liver is richly endowed with COMT and MAO it therefore contributes significantly to the degradation of circulating norepinephrine and epinephrine. The end product of the combined actions of MAO and COMT is vanillylmandelic acid. 

Disposition in the Body. Rapidly metabolised before reaching the systemic circulation and therefore ineffective after oral administration poorly absorbed after subcutaneous injection widely distributed throughout the body. The principal metabolic reaction is 0-methylation catalysed by catechol-O-methyltrans-ferase to form normetanephrine this is followed by oxidative deamination catalysed by monoamine oxidase, to form 4-hydroxy-3-methoxymandelic aldehyde which is converted to 4-hydroxy-3-methoxymandelic acid (vanillylmandelic acid) and to... 

Homovanillic and vanillylmandelic acids, the major metabolites of catecholamines, are often tested in urine for neurological diagnosis and for monitoring the... 

Fauler G, Leis HJ, Huber E, Schellauf C, Rerbl R, Urban C, Gleispach H. Determination of homovanil-lic acid and vanillylmandelic acid in neuroblastoma screening by stable isotope dilution GC-MS. J Mass Spectrom 1997 32 507-14. 

Fujita K, Maruta K, Ito S, Nagatsu T. Urinary 4-hydroxy-3-methoxymandehc (vanillylmandelic) acid,... 

Gironi A, Seghieri G, Niccolai M, Mammini P. Simultaneous liquid-chromatographic determmation of urinary vanillylmandelic acid, homovandlic acid, and... 

N.C. Parker, C.B. Levtzow, P.W. Wright, L.L. Woodward and J.F. Chapman, Uniform chromatographic conditions for quantifying urinary catecholamines, metanephrines, vanillylmandelic acid, 5-hydroxyindoleacetic acid, by liquid chromatography with electrochemical detection, Clin. Chem., 32, 1473-1476 (1986). 

I NA, like DA, is metabolised by MAO and COMT (see Table 1.2). The main CNS metabolite of NA is 3-methoxy-4-hydroxypheitylglycol (MHPG). This is in contrast to the peripheiy where it is vanillylmandelic acid (VMA). 

D. D., A quantitative assay for vanillylmandelic acid (VMA) by gas-liquid chromatography. Anal. Biochem. 13, 544-551 (1965). 

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