We show that octopamine is detectable in plasma of all subjects, the mean levels of which are significantly lower in PD patients, including de novo patients, when compared to controls (p < 0.001). Unlike this, no changes in plasmatic noradrenaline levels were found in the de novo patients, but only in plasma of fluctuating and non-fluctuating PD patients. These findings raise the possibility that Parkinson’s disease is firstly characterized by abnormalities of tyrosine decarboxylase, rather than tyrosine hydroxylase, enzyme activity.
