L-dopa reverses the elevated density of D2 dopamine receptors in Parkinson's diseased striatum

Striatal dopamine receptors were studied using [3H]-spiperone in postmortem tissues of thirty-six patients with Parkinson's Disease. Each tissue was analyzed by the receptor saturation method. In non-treated patients, the D2 dopamine receptor density was elevated in the caudate nucleus and putamen compared to controls. The dissociation constant for [3H]-spiperone was similar in all groups. The elevated density of D2 receptors in non-treated patients may indicate dopaminergic supersensitivity in this disease. The elevated density was reversed with dopamine agonist therapy, but the density was not lower than control tissues.