[Dynamics of plasma catecholamines and beta-adrenoreceptor functions. Use of a new radio-enzymatic micro-method]

The new method for simultaneous determination of noradrenaline (NA), adrenaline (A) and dopamine in 50 mul plasma has proved specific, sensitive and readily reproducible. In 6 healthy volunteers NA was 190 pg/ml and A 63 pg/ml in the supine position and rose during graded upright exercise to NA 819 pg/ml and A 161 pg/ml (150 watts; p less than 0.001 and less than 0.05 respectively). NA and A paralleled exercise tachycardia (r = 0.894; p less than 0.001) and renin stimulation (r = 0.620; p less than 0.001). 21 patients with essential hypertension exhibited relatively higher NA concentrations both at rest and during graded exercise (p less than 0.05 for both). Exercise-stimulated NA and A further rose following 0.15 mg/kg propranolol i.v. (p less than 0.01 and p less than 0.05 respectively). With increasing age and blood pressure, plasma catecholamine concentrations rise while the reactivity of heart rate and renin secretion decreases. Acute pharmacological blockade of beta-adrenoreceptors increases catecholamine overflow in similar fashion to the physiological dissociation of plasma catecholamines and adrenoceptor responsiveness.