Abstract
After i.p. injection of l-3-14C-[3-methoxy-4-hydroxyphenyl]alanine (l-3-14C-O-methyldopa) to rats, small amounts of labeled catecholamines are found in the brain. In the urine, homovanillic acid, 3-methoxy-4-hydroxyphenyllactic acid, 3, 4-dihydroxvphenylacetic acid and O-methyldopa appear as the main radioactive compounds. In addition, minor amounts of labeled 3-methoxytyramine, 3, 4-dihydroxyphenylalanine and dopamine are excreted. Dopacetamide, an inhibitor of catechol-O-methyltransferase, enhances the urinary content of 14C-3, 4-dihydroxyphenylacetic acid and 14C-dopamine but decreases that of 14C-3-methoxytyramine. The major metabolite of 14C-3-methoxy-4-hydroxyphenyllactic acid in the urine of rats is 14C-homovanillic acid, but in addition some labeled O-methyldopa and catecholamines appear. The decarboxylation of l-1-14C-O-methyldopa (carboxyl-labeled) in vivo proceeds at a much slower rate than that of l-1-14C-3, 4-dihydroxyphenylalanine as judged by measurements of the expired 14CO2. In conclusion, l-O-methyldopa seems to be metabolized by transamination and demethylation. It is uncertain whether direct decarboxylation may also occur to some extent.
Footnotes
- Received November 2, 1971.
- Accepted May 12, 1972.
- © 1972, by The Williams & Wilkins Company
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