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.
Diamine oxidase (DAO) or histaminase is an enzyme which deaminates histamine and several aliphatic amines to their corresponding aldehydes. Hydrogen peroxide and ammonia are side products of this reaction. The purpose of the present work was to evaluate if determination of produced hydrogen peroxide reflects DAO activity or if intermediate formation of the superoxide radical could be a reason for lack of correspondence between oxygen uptake and hydrogen peroxide production at different pH. Superoxide radical formation was determined by cytochrome c reduction in the presence and absence of superoxide dismutase (SOD). Oxygen uptake was measured with an oxygen electrode and hydrogen peroxide production by a spectrophotometric method. At pH 6.6 there was no superoxide production, but at pH 7.4 there was some, and it increased markedly at pH 9.5. Oxygen uptake also increased with increasing pH, especially with histamine as substrate. These results lead us to suggest that the mechanism of action of DAO involves the intermediate generation of superoxide radicals.
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