Summary
The magnitude of the decarboxylation of L-Dopa in the intestinal organs was determined by a method based on oral and intravenous administration of L-3′,4′-dihydroxyphenylalanine-1-14C (carboxyl labelled L-Dopa) and analysis of the radioactivity in urine.
In 11 parkinsonian patients studied under standardized conditions 74% of L-Dopa given orally as a 0.5 g tablet was decarboxylated in the intestinal organs. Thus less than 26% of the ingested L-Dopa reached the general circulation.
The possibility that individual variations in the magnitude of intestinal decarboxylation might be at least partly responsible for the individual variations in the dose requirement of parkinsonian patients was tested. There was neither any correlation between dose requirement of L-Dopa and the intestinal decarboxylation nor between that dose and the plasma disappearance rate of L-Dopa.
It is concluded that other factors than those responsible for the peripheral metabolism of L-Dopa determine the individual dose requirement.
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Granerus, AK., Jagenburg, R. & Svanborg, A. Intestinal decarboxylation of L-Dopa in relation to dose requirement in Parkinson's disease. Naunyn-Schmiedeberg's Arch. Pharmacol. 280, 429–439 (1973). https://doi.org/10.1007/BF00506633
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DOI: https://doi.org/10.1007/BF00506633