Inhibition of L‐{18F}fluorodopa uptake into human brain by amino acids demonstrated by positron emission tomography

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Abstract
The brain uptake of L-{18F}fluorodopa was measured by positron emission tomography in a healthy male volunteer both under fasting conditions and during intravenous amino acid loading. A significant reduction of tracer uptake into the brain was demonstrated with amino acid loading. This finding represents the first direct evidence for competition between L-dopa and other amino acids for uptake across the blood–brain barrier obtained in vivo in a human subject. It underlines the possible importance of interference by dietary amino acids with the therapeutic actions of L-dopa in Parkinson's disease.