Conjoint radioenzymatic measurement of catecholamines, their catechol metabolites and DOPA in biological samples.

An assay is described for the simultaneous determination of dopamine, noradrenaline, adrenaline, dopa, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylethanol, 3,4-dihydroxymandelic acid and 3,4-dihydroxy-phenylglycol, capable of detecting amounts in the femtomol range. The assay is based on the O-methylation of the catechol moiety utilizing S-[3H-methyl]-adenosyl-L-methionine and a partially purified catechol-O-methyl transferase to form the various O-[3H-methyl]-catechol derivatives. The O-[3H-methyl]-catechol derivatives are purified by thin layer chromatography, solvent partitions and/or ion exchange chromatography. The assay was successfully applied to biological sample. It was possible for the first time, to detect free 3,4-dihydroxyphenylglycol, free 3,4-dihydroxyphenylethanol and 3,4-dihydroxymandelic acid in a small volume (25 microliter) of blood plasma of man, rat, dog and rabbit. The conjoint measurement of catecholamines and their catechol metabolites in minute amounts of biological samples may contribute to a more detailed understanding of catecholamine metabolism in the peripheral and central nervous system.