A radioenzymatic assay for femtomole determination of catecholamines using α-methyldopamine as an internal standard

Abstract

A radioenzymatic assay has been developed for the sensitive determination of plasma catecholamines in perchloric acid extracts using α-methyldopamine as an internal standard. With 25 μl of plasma extract in a total volume of 40 μl the assay gives blank values equivalent to approcximately 2 femtomoles (fmole) for epinephrine (E), norepinephrine (NE), 6 fmole for α-methyldopamine (MeDA) and approximately 15 femtomoles for dopamine (DA). Recoveries of 25 dpm/fmole NE, 40 dpm/fmole E, 56 dpm/fmole DA and 80 dpm/fmole MeDA have been obtained. The assay is linear to at least 1 picomole catecholamine (CA) and shows less than 0.5% crossover between E, NE and DA and a 4.7% crossover of αMeDA into DA. The interassay variability was ± 7% for DA, ± 4% for E and ±3% for NE.