Abstract
A sensitive double-isotope derivative technique for the determination of dopamine is described. It is based on the formation of the 3-O-methyl derivative of dopamine in the presence of a 14C-labelled methyldonor and the enzyme catechol-O-methyl-transferase. The recovery in each sample is calculated from 3H-labelled dopamine. The dopamine concentration averaged 0.20 ng/ml ± 0.06 (± S.D.) in venous blood obtained from 6 normal subjects who rested in the supine position. 24-hour urinary excretion of dopamine was 207 and 297 μg in two normal subjects. The present technique may also be suitable for measurement of dopamine in spinal fluid.