Blood-brain transfer and metabolism of 6-( sup 18 F)fluoro-L-dopa in rat

Journal Article · Sat Sep 01 00:00:00 EDT 1990 · Journal of Cerebral Blood Flow and Metabolism; (USA)

DOI:https://doi.org/10.1038/jcbfm.1990.124· OSTI ID:6525821

Reith, J; Dyve, S; Kuwabara, H; Guttman, M; Diksic, M; Gjedde, A ^[1]

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1. Montreal Neurological Institute, Quebec (Canada)

In a study designed to reveal the rates of blood-brain transfer and decarboxylation of fluoro-L-3,4-dihydroxyphenylalanine (FDOPA), we discovered a major discrepancy between the DOPA decarboxylase activity reported in the literature and the rate of FDOPA decarboxylation measured in the study. Donor rats received intravenous injections of 6 mCi fluorine-18-labeled FDOPA. The donor rats synthesized methyl-FDOPA. Arterial plasma, containing both FDOPA and methyl-FDOPA, was sampled from the donor rats at different times and reinjected into recipient rats in which it circulated for 20 s. The blood-brain clearance of the mixture of labeled tracers in the plasma was determined by an integral method. The individual permeabilities were determined by linear regression analysis, according to which the average methyl-FDOPA permeability in the blood-brain barrier was twice that of FDOPA, which averaged 0.037 ml g-1 min-1. The permeability ratio was used to determine the fractional clearance from the brain of FDOPA (and hence of methyl-FDOPA), which averaged 0.081 min-1. In the striatum, the measured average FDOPA decarboxylation rate constant (kD3) was 0.010 min-1, or no more than 1% of the rate of striatal decarboxylation of DOPA measured in vitro and in vivo. We interpreted this finding as further evidence in favor of the hypothesis that striatum has two dopamine (DA) pools, of which only DA in the large pool is protected from metabolism. Hence, no more than 1% of the quantity of fluoro-DA theoretically synthesized was actually retained in striatum.

• OSTI ID: 6525821
• Journal Information: Journal of Cerebral Blood Flow and Metabolism; (USA), Vol. 10:5; ISSN 0271-678X
• Country of Publication: United States
• Language: English

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62 RADIOLOGY AND NUCLEAR MEDICINE
BLOOD-BRAIN BARRIER
PERMEABILITY
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RADIOPHARMACEUTICALS
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BRAIN
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DOPAMINE
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RATS
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CARBON-CARBON LYASES
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CARDIOTONICS
CARDIOVASCULAR AGENTS
CENTRAL NERVOUS SYSTEM
CHEMICAL REACTIONS
DRUGS
ENZYMES
FLUORINE ISOTOPES
HOURS LIVING RADIOISOTOPES
HYDROXY COMPOUNDS
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
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MAMMALS
MATHEMATICS
NERVOUS SYSTEM
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NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PHENOLS
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RADIOISOTOPES
RODENTS
STATISTICS
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