In vivo Inhibition of Monoamine Oxidase Studied with Radioactive Tyramine

Summary1. Tyramine, labeled with C14 in the a-position of the side chain, has been synthesized for use as a substrate in studies of the in vivo inhibition of monoamine oxidase. 2. With the exception of a small degree of conjugation, no metabolic route for tyramine could be detected in intact rats and mice other than that due to monoamine oxidase action. 3. A technic for evaluating in vivo inhibitory effect on monoamine oxidase has been devised and a number of substances tested. Only 2 active compounds were found; the common sympathomimetic amines were inactive.