Catecholamine plasma assays

Baumgartner, H., Ridl, W., Klein, G., and Preindl, S., Improved radioenzymic assay for the determination of catecholamines in plasma, Clin. Chim. Acta, 132, 111, 1983 Chem. Abs., 99, 99459k, 1983. 

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. 

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-... 

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). 

Highly sensitive, specific, and reliable assay methods are required for measuring the normally very low concentrations of epinephrine, norepinephrine, and dopamine in plasma. Both unconjugated (free) and sulfoconjugated catecholamines circulate in human plasma and are increased in plasma from patients with pheochromocytomas. Clinical... 

Only a few methods for urinary catecholamines have been published that do not require preextraction prior to analysis." " These methods minimized sample preparation by making use of different precolumn derivatization procedures. The selection of a suitable method for sample preparation prior to analysis by HPLC depends on a number of factors, such as the biological source, the type of column used and the selectivity of the detection method. In cases where the analyte concentration is very low and the analyte is present in a complex matrix (urine or plasma) with interfering compounds, an exhaustive pretreatment may be unavoidable. Sample pretreatment is also essential to ensure the sensitivity and specificity of the assay and protect the analytical column from contamination. 

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). 

A Gas Chromatographic-Mass Spectro-metric Assay of Human Plasma Catecholamines... 

Female rats kept under controlled environmental conditions were given a single intraperitoneal injection of saline solutions of isoproterenol (80 pg), epinephrine (80 or I60 pg), norepinephrine (80 or 160 p.g), dopamine (l mg), vasopressin (500 mU), histamine (300 jig), or 0.9 normal saline (0.2 ml). Throughout this paper all doses are expressed as weight units of free base. Ten minutes after the injection they were decapitated and the plasma separated ffom the pooled heparinized blood, was frozen and stored at -12 C until assayed for its ACTH content. The results as shown in Table 1, indicate that norepinephrine is more potent than epinephrine which is in turn more potent than isoproterenol in stimulating ACTH secretion, and that dopamine, histamine, and vasopressin in larger amounts have a similar effect. Since the potency of the catecholamines in this respect appeared to be... 

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