Determination of noradrenaline and adrenaline in plasma by a radioenzymatic assay using high pressure liquid chromatography for the separation of the radiochemical products.

Plasma catecholamines are determined by a radioenzymatic assay using high pressure liquid chromatography for the separation of the labelled radiochemical products. Noradrenaline and adrenaline are converted to their O-methylated analogues, normethanephrine and metanephrine, by the enzyme catechol O-methyltransferase in the presence of tritiated S-adenosyl-L-methionine. Non-radioactive carriers are added, whereupon the metanephrines are extracted in an organic phase and re-extracted in an aqueous phase. The aqueous phase is dried, the residue taken up in a phosphate solution and chromatographed. The normetanephrine and metanephrine peaks are collected, converted to vanillin and assayed for radioactivity. The detection limit for noradrenaline is 32 ng/l plasma and for adrenaline 16 ng/l plasma. Intra- and interassay variables are respectively 6.2 and 10% for noradrenaline and 5.3 and 8.8% for adrenaline. The mean supine levels of noradrenaline and adrenaline in normal subjects are 355 and 61 ng/l plasma, respectively. This highly specific procedure takes two days for one person to assay 45 blood samples and can be reduced to one day if the chromatography step is automated.