Radioenzymatic determination of epinephrine, norepinephrine and dopamine in 0.1 ml plasma samples: plasma catecholamine response to submaximal and near maximal exercise.

A sensitive enzymatic isotope derivative method for simultaneous determination of epinephrine, norepinephrine, and dopamine in 0.1 ml plasma samples is described. The assay consists basically of 1. conversion of epinephrine, norepinephrine, and dopamine into their respective methyl-derivates in the presence of catechol-O-methyltransferase and S-adenosylmethionine-[3H]methyl, 2. extraction of the methylated 3H labelled amines with diethyl ether, 3. separation by thin-layer chromatography, 4. measurement in a beta radiation scintillation counter. The effect of standing upright and of submaximal and near-maximal steady state exercise on plasma epinephrine, norepinephrine, dopamine and plasma renin was studied in 16 young adults aged 22 to 34 years and 9 physically well trained boys 16-17 years old. Standing upright for 2 min did not results in significant changes in either epinephrine, norepinephrine, dopamine or plasma renin activity compared with supine (basal) values. During exercise, epinephrine, norepinephrine, dopamine and plasma renin activity increased exponentially with the work load, peak values being attained at the highest load or immediately after cessation of exercise. The respective maximal values for plasma renin activity and epinephrine and norepinephrine levels were approximately 3, 6 and 10 fold higher than basal values in the adults, and rose as high as 4, 10 and 20 fold in the boys. Peak dopamine values were only 2-3 times higher than the basal values in both adults and boys. It is concluded that the method described provides a suitable tool for a quantitative assessment of adreno-sympathetic tone during physiological and pathophysiological conditions.