Dopamine (3-Hydroxytyramine) metabolism in parkinsonism

Abstract

Three patients with idiopathic parkinsonism and six normal subjects were infused over a 4 hr period with 104.6 μc of dopamine-2-¹⁴C (3,4-dihydroxyphenylethylamine, 3-hydroxytyramine),¹ the immediate precursor in the synthesis of the sympathetic neurohormone, noradrenaline (norepinephrine). Urine was collected during the infusion period, 0-2 hr, 2-4 hr, 4-8 hr, 8-24 hr, and thereafter for 4 additional days. Using a technique herein described, the various metabolic and biosynthetic products of dopamine, including noradrenaline and its metabolic products, were separated, identified, and their radioactivity measured. The metabolic pattern of dopamine in the normal subject was compared to that of the three parkinsonism patients. The results indicate that in idiopathic parkinsonism there is a decrease in the recovery of free radioactive noradrenaline in the urine following an infusion of dopamine-2-¹⁴C and a slight shift toward dopamine metabolism. The latter is reflected by an increase in the following metabolites of dopamine: 3,4-dihydroxyphenylacetic acid and the conjugates of 3-methoxy-4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylethanol and dopamine.