Decrease in blood histamine in drug-treated parkinsonian patients.

Blood histamine and serum histaminase activity were determined in a group of patients with Parkinson disease (PD) and in a group of healthy controls. Untreated PD patients present significantly higher blood histamine than normal controls. Therapy with L-dopa + cardidopa results in a significant decrease in blood histamine. This decrease becomes more accentuated when anticholinergics are added to this therapy. No significant changes were detected in plasma histaminase. The authors suggest, as a hypothesis, that the CNS contributes to blood histamine concentration and that its rise is the result of increased neuronal destruction.