Radioenzymatic method

Radioenzymatic methods had also been used to quantify urinary NM." " Phenyletha-noleamine-A -rnethyltransferase and H iS -adenosylmethionine convert NM to its [ H]N-methylated derivative, The main advantages of this method were its high... 

Hjemdahl, P., Daleskog, M., and Kahan, T., 1979, Determination of plasma catecholamines by high-performance liquid chromatography with electrochemical detection Comparison with a radioenzymatic method. Life Sci. 25 131-138. 

A comparison between the chemiluminescence and the radioenzymatic assay methods that are used for the measurement of acetylcholine released from a rat phrenic nerve hemidiaphragm preparation was reported by Ehler et al. [57]. The comparison demonstrated quantitative equivalency and limits of detection for different analytes as 2 pmol. 

Eckernas and Aquilonius described a simple radioenzymatic procedure for the determination of choline and acetylcholine in brain regions of rats sacrificed by microwave irradiation [215]. The methods are based on acetylation (in phosphate buffer) of free choline with [14C]-acetylcholine using purified choline acetyltransferase. After ion-pair extraction of [14C]-acetylcholine with tertiary phenyl borate contained in toluene-based scintillation cocktail, the radioactivity was measured. 

Antibiotics may be assayed by a variety of methods (see Chapter 8, pages 166-188, in Pharmaceutical Microbiology, 5th edition, 1992). Only microbiological and radioenzymatic assays will be considered briefly here see Fig. 25.6 and sections 4.1.1 and 4.1.2. 

The free 0-methylated amine metabolites are present in plasma at picomolar concentrations that have made their accurate measurement technically difficult. Measurements of plasma metanephrines therefore represent relatively recent developments. The.first method enabling accurate measurement of plasma free normetanephrine involved a radioenzymatic assay in which normetanephrine was converted to H-iabeled metanephrine using preparations of the enzyme phenylethanolamine-N-methyltransferase, incubated with H-methyi-labeled S-adenosylmethionine. This method, however, did not allow measurements of metanephrine or methoxytyramine, and therefore had limited clinical utility. 

A variety of analytical methods have been used for the determination of serotonin in body fluids and tissue. The oldest assays involved the extraction of serotonin from interfering compounds and quantitation by spectrofluorometric procedures using the native fluorescence of serotonin (Xex = 300 nm, Aem - 340nm at neutral pH). Derivatization with Nin-hydrin or o-phthalaldehyde increased the sensitivity and selectivity of these fiuorometric methods. More specific and precise methods have subsequently been introduced, including radioenzymatic assay, RIA, EIA, gas chromatography, and HPLC. Reagent and/or test kits based on some of these techniques are available commercially. 

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). 

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