A highly sensitive radioenzymatic assay for simultaneous estimation of norepinephrine, dopamine, and epinephrine

We have developed a radioenzymatic assay for simultaneous estimation of norepinephrine (NE), dopamine (DA), and epinephrine (E) that was the result of the integration of several unique features of previously described assay procedures. Catecholamines in sera or tissue homogenates were enzymatically O-methylated in the presence of partially purified catechol-O-methyltransferase with S-[methyl-3H] adenosyl methionine serving as the methyl donor. The O-methylated products were then separated by thin-layer chromatography, eluted from the gel, and their tritium content determined. The assay allows measurement of catecholamines with a sensitivity in the ranges of 15-20 pg. In addition, the assay is highly specific, reproducible, relatively rapid and simple, and inexpensive.