Motor response to acute dopaminergic challenge with apomorphine and levodopa in Parkinson's disease: implications for the pathogenesis of the on-off phenomenon.

Abstract

The progressive shortening of motor response after both apomorphine and levodopa suggests that pharmacodynamic factors play an important part in determining the duration of motor response and argue against altered central pharmacokinetics of levodopa being principally responsible for the on-off effect. The widening response amplitude and increasing off phase disability occurring during disease progression are also critical factors in determining the appearance of motor fluctuations.