Therapeutic Implications in Parkinsonism of m-Tyramine Formation from L-Dopa in Man

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THE urinary output of m-hydroxyphenylacetic acid is increased during treatment of Parkinsonian patients with L-dopa1 and decreases significantly after administration of neomycin to reduce gut flora2. Thus, it seems that p-dehydroxylation of this type is achieved by intestinal microorganisms3. Whereas earlier animal experiments had suggested that 3,4-dihydroxy-phenylacetic acid is the immediate precursor of m-hydroxy-phenylacetic acid4, we now have evidence of increased m-tyramine formation, indicating that some degree of microbial dehydroxylation of dopamine or of L-dopa itself takes place.

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