Regional cerebral blood flow in patients with Parkinson's disease under chronic levodopa therapy: measurements during "on" and "off" response fluctuations.

In ten Parkinsonians who developed dose-related response fluctuations under long-term levodopa therapy, regional cerebral blood flow (rCBF) and plasma levodopa levels were measured simultaneously, once during an "off" phase and again at an "on" stage of clinical benefit induced by a single oral dose of levodopa. Although plasma levodopa increased threefold during the "on" period, rCBF and the degree of its reduction from normal age-matched control values remained unchanged and similar to those in the "off" phase. Study suggests that the rCBF decreases in Parkinson's disease are unaffected by levodopa and are not due to deficient dopaminergic neurotransmission in the brain.