A sensitive radioenzymatic assay for adrenaline and noradrenaline in plasma.

1 An existing radioenzymatic assay for plasma catecholamines using catechol-o-methyl transferase and [3H]-S-adenosyl-methionine has been modified resulting in a more sensitive assay for the measurement of plasma adrenaline and noradrenaline. 2 The lower limit of sensitivity for this method is 25 pg for adrenaline and 30 pg for noradrenaline/ml of plasma. 3 Resting supine (60 min) plasma adrenaline concentration was (mean +/- s.d.) 124 +/- 76 pg/ml(n=11) in males and 130 +/- 71 pg/ml (n=7) in females; plasma noradrenaline concentrations were respectively 444 +/- 129 pg/ml and 550 +/- 87 pg/ml. 4 The changes in plasma catecholamine concentrations in response to 40 degrees head-up tilt have been determined in a group of healthy normal subjects and have been shown to be related to changes in blood pressure and heart rate.