Studies on Dopa Decarboxylase Inhibitors in vivo by Use of C 14 -Carboxyl-Labeled Dopa. ∗

Summary

A study has been made on the effects of some compounds on inhibition of decarboxylation of 3,4-dihydroxyphenylalanine (dopa) in vivo. A new rapid and simple method for determination of the inhibition has been developed which yields satisfactory results in intact unanesthetized mice. C¹⁴-carboxyl-labeled dopa is injected and the respiratory C¹⁴O₂ trapped in a phenethylamine solution containing fluorophore. Radioactivity is then counted directly in a liquid scintillation counter. The most active decarboxylase inhibitors of the compounds tested are dl-α-hydrazino-α-methyl,3,4-dihydroxyphenylbutyric acid and N(3-hydroxybenzyl)-N-methylhydrazine. Their inhibitory action is approximately 40 times higher than, e.g., that of l-α-methyldopa.