Abstract
Rats with unilateral lesions of the substantia nigra were treated with L-dopa 25 mg/kg subcutaneously 30 minutes after treatment with carbidopa 25 mg/kg intraperitoneally. In the ipsilateral striatum, dopamine levels achieved a peak of 1.57 ± 0.63 pg/g (control 0.19 ± 0.05 pg/g)at 20 minutes and did not differ from controls by 90 minutes after L-dopa administration. Dopamine levels peaked in the contralateral striatum at 45 minutes (11.96 ± 0.14 pg/g, where control levels were 7.74 ± 0.22 pg/g) and returned to control values by 180 minutes. These data suggest that in patients with advanced Parkinson's disease, L-dopa administration results in a smaller increase and a shorter duration of elevation in striatal dopamine concentration than in controls. These observations support the hypothesis that the “wearing-off” phenomenon that occurs during the treatment of patients with Parkinson's disease occurs as a consequence of a reduction in the rate of conversion of L-dopa to dopamine and perhaps diminished capacity for the storage of dopamine.
- © 1984 by the American Academy of Neurology
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