Modification of dopamine D2 receptor activity by pergolide in Parkinson's disease: an in vivo study by PET

It is well known that chronic administration of pergolide and other dopamine agonists may induce a downregulation of dopamine D2 receptors in the rat model of Parkinson's disease (PD). To our knowledge, this effect has not been demonstrated in vivo in patients with PD. At present, the status of striatal dopamine D2 receptors can be studied with use of positron emission tomographic (PET) technology. Five patients with PD chronically treated with levodopa were studied with use of PET and [11C]-raclopride before and after 6 months of pergolide treatment (dose range = 4.5-7.5 mg/d). We found a slight reduction in the specific striatal [11C]-raclopride uptake index (mean reduction 14% in putamen and 9% in caudate) after pergolide treatment. This reduction appears to be related to downregulation of the receptor, although competitive binding of pergolide at the D2 receptor cannot be excluded.