Plasma catecholamines, measurement

Goldstein DS, Stull R, Markey SP, Marks ES, Reiser HR. 1984. Dihydrocaffeic acid A common contaminant in the liquid chromatographic-electrochemical measurement of plasma catecholamines in man. J Chromatogr 311 148-153. 

Interactions. With nonselective monoamine oxidase inhibitors (MAOI), the monoamine dopamine formed from levodopa is protected from destruction it accumulates and also follows the normal path of conversion to noradrenaline (norepinephrine), by dopamine (J-hydroxylase severe hypertension results. The interaction with the selective MAO-B inhibitor, selegiline, is possibly therapeutic (see below). Tricyclic antidepressants are safe. Levodopa antagonises the effects of antipsychotics (dopamine receptor blockers). Some antihypertensives enhance hypotensive effects of levodopa. Metabolites of dopamine in the urine interfere with some tests for phaeochromocytoma, and in such patients it is best to measure the plasma catecholamines directly. 

Findings that none of the traditionally used biochemical tests could reliably detect aU cases of pheochromocytomas led to recommendations that biochemical testing should include a combination of measurements of catecholamines and catecholamine metabolites. VMA is excreted in urine in large amounts, which makes measurement of this metabolite a simple, easy to implement, and time-honored test for diagnosis of pheochromocytomas. Numerous studies have now made it clear, however, that measurements of urinary VMA provide a relatively insensitive diagnostic test with limited value for initial testing for pheochromocytomas. Therefore the usual recommendation has been that biochemical testing should include measurements of urinary or plasma catecholamines and urinary metanephrines. 

Procedure The test is best performed in the morning after an overnight fast. The patient remains recumbent throughout the entire procedure. A forearm venous cannula is placed for baseline and 3-hour blood sampling during the procedure. After at least 20 minutes of supine rest, a baseline blood sample is drawn in a heparinized tube. Clonidine, 4.3 pg/kg of body weight, is then given orally, and a repeat blood sample is drawn 3 hours later. The samples are analyzed for plasma catecholamines, with plasma normetanephrine measurement also recommended. 

Catecholamines and Metabolites HPLC, coupled with electrochemical or fiuorometric detection, now provides the most widely used assay method for measurements of urinary or plasma catecholamines in the routine clinical laboratory. Once equipment is pur-... 

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. 

Boomsma F, Alberts G, van Eijk L, Man in t Veld AJ, Schalekamp MA. Optimal collection and storage conditions for catecholamine measurements in human plasma and urine. Clin Chem 1993 39 2503-8. 

The patient s plasma PTH should be measured and, if increased, a diagnosis of primary hyperparathyroidism can be made. However, hyperparathyroidism with a serum calcium of 2.8 mmol/1 is usually asymptomatic and thus another cause for his hypertension, headaches and anxiety should be sought. If the symptoms were episodic this would suggest the possibility of a phaeochromocytoma which is associated with hyperparathyroidism in families with MEN. The patient should have his urinary catecholamines measured and, if the diagnosis is made, it is important that other members of his family be screened for hyperparathyroidism and phaeochromocytoma. 

LC with electrochemical detection offers a sensitive method for measuring human plasma catecholamines that is simpler than the existing radioenzymatic assays (Hallman et al, 1978 Fenn et al, 1978 Hjemdahl et al, 1979 Fig. 6). There are also reports discussing the measurement of serum 5-HT (Sasa et al, 1978). 

The value of electrochemical detection following high performance liquid chromatography is compared with that of the more widely used optical methods of detection. Its advantages are illustrated by its application to three areas of clinical chemistry that had previously posed analytical problems. Its sensitivity allowed its use for the measurement of plasma catecholamines. Its selectivity was employed to produce rapid methods for the determination of urinary levels of catecholamine and tryptophan metabolites. Finally, its value for the estimation of urinary oxalic acid is shown. Future developments such as increasing the range of detectable compounds by derivatization are briefly discussed. 

Stoddart, D. M. and Bradley, A. G. (1991). Measurement of short-term changes in heart rate and plasma concentration of cortisol and catecholamine in a small marsupial. Journal of ChemicalEcology 17,1333-1341. 

Plasma malondialdehyde-like material, an indicator of lipid peroxidation, is increased in conditions of ischaemia, such as stroke [83, 84] and myocardial infarction [85]. Mitochondria extracted from hearts of vitamin-E-deficient rabbits showed a decreased mitochondrial function and an increased formation of oxygen radicals associated with a reduced superoxide dismutase activity. This was partially reversed by addition of vitamin E in vitro [86]. Measurement of in vitro susceptibility to lipid peroxidation in cardiac muscle from vitamin-E-deficient mice showed a highly significant negative correlation between the concentration of vitamin E and in vitro lipid peroxidation. The results indicate that short-term vitamin E deficiency may expose cardiac muscle to peroxidation injuries [ 87 ]. In rats, treatment for 2 days with isoprenaline increased lipid peroxide activity, as measured by malondialdehyde levels, in the myocardium. Vitamin-E-deficient animals were even more sensitive to this effect, and pretreatment with a-tocopheryl acetate for 2 weeks prevented the effect induced by isoprenaline. The authors [88] propose that free-radical-mediated increases in lipid peroxide activity may have a role in catecholamine-induced heart disease. 

The determination of catecholamines requires a highly sensitive and selective assay procedure capable of measuring very low levels of catecholamines that may be present. In past years, a number of methods have been reported for measurement of catecholamines in both plasma and body tissues. A few of these papers have reported simultaneous measurement of more than two catecholamine analytes. One of them utilized Used UV for endpoint detection and the samples were chromatographed on a reversed-phase phenyl analytical column. The procedure was slow and cumbersome because ofdue to the use of a complicated liquid-liquid extraction and each chromatographic run lasted more than 25 min with a detection Umit of 5-10 ng on-column. Other sensitive HPLC methods reported in the literature use electrochemical detection with detection limits 12, 6, 12, 18, and 12 pg for noradrenaline, dopamine, serotonin, 5-hydroxyindoleace-tic acid, and homovanillic acid, respectively. The method used very a complicated mobile phase in terms of its composition while whilst the low pH of 3.1 used might jeopardize the chemical stability of the column. Analysis time was approximately 30 min. Recently reported HPLC methods utilize amperometric end-point detection. 

The basis for the high diagnostic efficacy of plasma free metanephrines is explained by several factors (1) plasma free metanephrines are produced by metabolism of catecholamines within pheochromocytomas, a process that occurs continuously and independently of variations in catecholamine release by tumors (2) normally only small amounts of metanephrines are produced in the body, and these are relatively unresponsive to sympathoadrenal activation compared with the parent amines and (3) VMA and the metanephrines commonly measured in urine are different metabofites from the free metanephrines measured in plasma, and are produced in different parts of the body by metabolic processes not directly related to the tumor itself." ... 

Additional markers of catecholamine overproduction have been employed to improve the biochemical detection of neuroblastomas. Free dopamine may be abnormal in urine from neuroblastoma patients with VMA and HVA excretion. Combined testing for VMA, HVA, and dopamine may therefore improve tumor detection, and in 1993 an international consensus report on neuroblastoma diagnosis added dopamine to the Hst of acceptable measurements to document the adrenergic nature of the tumor. Plasma measurements of dopamine and L-dopa, the amino acid precursor of dopamine, may also have clinical value and allow the alternate use of plasma. Measurement of methylated metabolites, especially normetanephrine, has also been explored. When urinary normetanephrine, metanephrine, methoxytyra-mine, dopamine, norepinephrine, VMA, and HVA were measured, clinical sensitivity for detection of neuroblastomas was 97% to 100% when results of normetanephrine testing were coupled either with VMA in the infants or with HVA in children greater than age 1. Even with an extended panel of catecholamines and metabolite measurements, a low incidence of nonsecreting tumors continues to be identified and should be considered in the interpretation of a negative test result. 

Dietary constituents or drugs can either cause direct analytical interference in assays or influence the physiological processes that determine plasma and urinary levels of catecholamines and catecholamine metabolites. In the former circumstances, the interference can be highly variable depending on the particular measurement method. In the latter circumstances, interference is usually of a more general nature and independent of the measurement method (Table 29-6). 

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