Effects of bromocriptine on dopamine turnover with or without levodopa.

Bromocriptine, a dopamine agonist, alleviates symptoms of Parkinson's disease, even when administered alone, and is used for its treatment. Better therapeutic effects are, however, achieved when bromocriptine is used in combination with levodopa. In this study, we examined the biochemical changes caused by bromocriptine administration with and without levodopa, and evaluated the effects of the treatments on dopamine turnover in the mouse striatum. Results show that dopamine turnover is suppressed by the administration of bromocriptine alone with a slight decrease in the amount of dopamine, and dopamine turnover is very strongly promoted by the administration of levodopa. When the two drugs are administered together, bromocriptine enhances the levodopa-induced increase in dopamine turnover in the striatum. These findings indicate that bromocriptine therapy in combination with levodopa enhances the dopaminergic function and suggest that the combination therapy of bromocriptine and levodopa shows good efficacy. The results of this study may, thus, provide a theoretical basis for the combination therapy of bromocriptine and levodopa.