Radioenzymatic assay

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. 

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. 

Kobayashi K, DeQuattro V, Kohoch R, Miano L. A radioenzymatic assay for plasma normetanephrine in man and patients with pheochromocytoma. Life Sci 1980 26 567-73,... 

N.D. Vlachakis and V. DeQuattro, A simple and specific radioenzymatic assay for measurement of urinary normetanephrine, Biochem. Med., 20, 107-114 (1978). 

K. Kobayashi, A. Foti, V. DeQuattro, R. Kolloch and L. Miano, A radioenzymatic assay for free and conjugated normetanephrine and octopamine excretion in man, Clin. Chim. Acta, 107, 163-173 (1980). 

Octopamine, (l-( -hydroxyphenyl)-2-aminoethanol), derives its name from the octopus in whose salivary glands it was first discovered (j.). As a biogenic amine, octopamine remained in relative obscurity until reports of its presence in the nervous tissue of a variety of invertebrates began to be published (2.3). These studies were made possible by the development of a sensitive and specific radioenzymatic assay (4-6). By means of this assay octopamine has now been found to be present in the nervous tissue of all invertebrates examined and, of vital importance, found within... 

Measurements of octopamine in insects have almost exclusively been made using the radioenzymatic assay. However, recent advances have now resulted in the availability of high performance liquid chromatography coupled with electrochemical detection for the measurements of catecholamines, monoamines and their metabolites (20,21 ). This technique affords the advantage of estimating several compounds simultaneously in a single sample. One may anticipate an increase in the use of this technique in the near future. 

Octopamine ( -hydroxyphenylethanolamine) was first discovered in the posterior salivary gland of the octopus over 30 years ago by Erspamer and Boretti (4). Although similar to norepinephrine in structure, octopamine was soon found to have very little activity as a sympathomimetic when injected into mammals (5). In addition, compared with norepinephrine, octopamine was found to be present in very low concentrations in vertebrate tissues (6) Because of these facts, relatively little attention was paid to octopamine until the early 1970 s, when Molinoff and Axelrod (7) developed a sensitive radioenzymatic assay for the compound and reported that octopamine was present in much higher concentrations in invertebrates, particularly in invertebrate nerve tissue ... 

A Broughton, JE Strong, LK Pickering, J Knight, GP Bodey. Radioimmunoassay and radioenzymatic assay of a new amino glycoside antibiotic netilmicin. Clin Chem 24 717, 1978. 

Benjonothan, N. and Porter, J. C., A sensitive radioenzymatic assay for dopamine, norepinephrine and epinephrine in plasma and tissue. Endocrinology, 98, 1497-1507, 1976. 

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). 

QUANTITATIVE TECHNIQUES Isotope dilution analysis Direct dilution analysis Reverse isotope dilution analysis Derivative analysis Double isotope dilution analysis Saturation analysis Radioenzymatic assays... 

One of the consequences of the explosion in scientific information over the past decade has been to obscure technical innovations contained in papers where the primary emphasis is not methodological. As Oldham has shown to be the case with radioenzymatic assays, this results in some laboratories using elaborate time consuming techniques unaware that simpler alternatives are available [310]. Radioisotopes have been a particularly significant factor in the simplification of metabolic studies as well as in elucidating other aspects of a drug profile. 

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