The effect of carbidopa on plasma and muscle levels of L-dopa, dopamine, and their metabolites following L-dopa administration to rats

Authors

  • S. Rose,

    1. MRC Movement Disorder Research Group, University Department of Neurology and Parkinson's Disease Society Research Centre, Institute of Psychiatry and Kings College Hospital Medical School, London, England
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  • P. Jenner,

    1. MRC Movement Disorder Research Group, University Department of Neurology and Parkinson's Disease Society Research Centre, Institute of Psychiatry and Kings College Hospital Medical School, London, England
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  • Prof. C. D. Marsden

    Corresponding author
    1. MRC Movement Disorder Research Group, University Department of Neurology and Parkinson's Disease Society Research Centre, Institute of Psychiatry and Kings College Hospital Medical School, London, England
    • MRC Movement Disorder Research Group, University of Neurology and Parkinson's Disease Society Research Centre, Institute of Psychiatry and Kings College Medical School, Denmark Hill, London SE5, U.K.
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Abstract

Administration of L-dopa (L, 4-dihydroxyphenylalanine) (200mg/kg p.o.) to rats produced elevated plasma and muscle concentrations of both L-dopa and 3-O-methyldopa (3-OMD). This effect was potentiated by simultaneous administration of carbidopa (25 mg/kg p.o.) both L-dopa and 3-OMD accumulated in muscle after administration of L-dopa with or without carbidopa. Elevated dopamine levels were detected in both muscle and plasma after treatment with L-dopa alone. Concurrent administration of carbidopa only diminished dopamine levels in plasma, and the duration of raised dopamine levels in muscle was increased. Carbidopa administration had no effect on the elevated plasma concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) caused by L-dopa administration. In muscle, carbidopa treatment tended to prolong the duration of raised metabolite levels. Muscle appears to accumulate L-dopa at a site where decarboxylation is not totally prevented by concurrent carbidopa administration, and where dopamine is not degraded as actively as in other tissues. The muscle sink for L-dopa may influence the plasma profile of the amino acid, which has implications for the therapeutic response to L-dopa in Parkinson's disease.

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