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An in Vivo Test for Measuring Monoamine Oxidase Inhibition in Human Subjects

AMA Arch Gen Psychiatry. 1960;2(4):459-461. doi:10.1001/archpsyc.1960.03590100099011.
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Previous work in this laboratory1-5 has shown that when epinephrine labeled with C14 in the N-methyl group of the side-chain was infused, approximately one-third of the radioactivity was recovered in the urine. These data suggested the following conclusions: (1) Approximately two-thirds of the infused epinephrine lose the N-methyl group of the side-chain via the monoamine oxidase enzyme system (MAO), and (2) approximately one-third of the infused epinephrine retains the N-methyl group, of which 1%-5% represents epinephrine and its conjugate and the remainder represents metanephrine and its conjugate.

If a patient under therapy with a MAO inhibitor is infused with N-methyl-labeled epinephrine, more than one-third of the infused radioactivity should be recovered in the urine if the MAO is inhibited. The following information is thus obtained: 1. One may determine whether or not the compound is entering the blood stream in amounts sufficient


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