Free catecholamines

Dutton, J., Hodgkinson, A. J., Hutchinson, G., and Roberts, N. B., Evaluation of a new method for the analysis of free catecholamines in plasma using automated sample trace enrichment with dialysis and HPLC, Clin. Chem., 45, 394, 1999. 

Thyroxine and catecholamine are examples of hormones that are derived from amino acids they are water soluble and circulate in plasma either bound to proteins (thyroxine) or free (catecholamines). Thyroxine binds avidly to three binding proteins and has a half-life of about 7 to 10 days, and the free and unbound catecholamines such as epinephrine have a very short half-life of a minute or less. As do the water-soluble peptide and protein hormones, these hormones interact with membrane-associated receptors and use a second messenger system. 

A method for measuring plasma free catecholamines based on HPLC with amperometric detection is available on this book s accompanying Evolve site and representative adult reference intervals for plasma catecholamines are shown in Table 29-7. 

Earlier fluorometric methods for analysis of urinary free catecholamines have been replaced by HPLC methods that allow selective quantitation of epinephrine, norepinephrine, and dopamine. Preliminary extraction of urine is stid required and numerous preanalytical cleanup techniques are available. An alumina extraction procedure is typically coupled with ion-exchange or adsorption chromatography. Alumina pretreatment usually involves a batch extraction technique in which catechols are first adsorbed at pH 8.6 and then eluted with boric acid, which forms a complex with cis-diol groups. Purification on boric acid affinity gels provides an alternative procedure for selective adsorption of catecholamines. 

Premel-Cabic A, Turcant A, AUain P. Normal reference intervals for free catecholamines and their add metabolites in 24-h urines from children, as determined by liquid chromatography with amperometric detection. Clin Chem 1986 32 1585-7. 

Rosano TG. Liquid-chromatographic evaluation of age-related changes in the urinary excretion of free catecholamines in pediatric patients. Chn Chem 1984 30 301-3. 

Eiquid- or solid-phase extraction methods have been adopted for the isolation of catecholamines and their metabolites from urine samples. The liquid extraction system is ordinarily based on the formation of a complex, in alkaline medium, between diphenylborate and the diol group in the catecholamines. However, the liquid extraction methods reported in the literature are relatively tedious and often involved multiple extraction steps.For the more widely used solid-phase extraction methods, catecholamines may be selectively isolated from the urine sample by adsorption with activated alumina," " phenylboronic acid or cation-exchange resins. All the specimen preparative procedures are specific for the free catecholamines, i.e. the extracted catecholamines do not include the conjugated fraction. 

F. Boomsma, G. Alberts, F.A. van der Hoorn, A.J. Man in t Veld and M.A.D.H. Schalekamp, Simultaneous determination of free catecholamines and epinine and estimation of total epinine and dopamine in plasma and urine by high-performance hquid chromatography with fluorimetric detection, J. Chromatogr, 51A, 109-117 (1992). 

G.M. Anderson, J.G. Young, PI. Jatlow and D.J. Cohen, Urinary free catecholamines determined by liquid chromatography-fluorometry, Clin. Chem., 27, 2060-2063 (1981). 

B.L. Lee, S.K. Chia and C.N. Ong, Measurement of urinary free catecholamines using high-performance liquid chromatography with electrochemical detection, J. Chromatogr., 494,303-309 (1989). 

O. Nozaki, H. Kawamoto and H. Moriyama, Total free catecholamines assay by identiflcation of its two functional groups and micro-flow injection chemiluminescence. Luminescence, 14, 369-374 (1999). 

Stanosz S, Kuligowski D, Pieleszek A, et al. 1994a. Concentration of dopamine in plasma, activity of dopamine -hydroxylase in serum and urinary excretion of free catecholamines and vanillylmandelic acid in women chronically exposed to carbon disulfide. Int J Occup Med Environ Health 7 257-261. 

Catecholamines and their metabolites The catecholamines, adrenaline, noradrenaline, and dopamine are essential components of the central nervous system acting as neurotransmitters both within the brain and at peripheral nerves. All are synthesized in the adrenal medulla from phenylalanine or tyrosine and are metabolized by a mixture of enzymatic side chain oxidation and methylation of the hydroxy groups on the ring. If the metabolism is complete, adrenaline and noradrenaline are degraded to 4-hydroxy-3-methoxy mandelic acid (HMMA, commonly called vanillylmandelic acid - VMA), while dopamine is broken down to homovanillic acid (HVA). Urinary excretion of these metabolites and their conjugates is the major route of elimination of catecholamines from the body, although small amounts are excreted unchanged as the free catecholamines. 

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