Abstract
These studies characterise the pharmacology of ropinirole, a selective D-2 agonist. High-affinity human caudate binding revealed a K i for D 2 receptors of 2.9 × 10 −8 M with no affinity for D 1 at 10 −4 M in the rat. Ropinirole was weakly active at α 2-adrenoceptors and 5-HT 2 receptors but inactive at 5-HT 1, benzodiazepine and gamma-aminobu acid receptors or α 1 and β-adrenoceptors. In rodents, ropinirole, like apomorphine, caused biphasic spontaneous locomotor activity and contralateral circling in 6-OHDA-lesioned mice with no tolerance to the latter after 14 days treatment. Amphetamine caused ipsilateral responses in the lesioned mice. Ropinirole did not cause marked stereotypies. In marmosets ropinirole (0.05–1.0 mg/kg SC or 0.1 mg/kg OPO) reversed all motor and behavioral deficits induced by MPTP. This response started 10–20 minutes after dosing, and exceeded 2 hours. No tolerance was seen following chronic b.i.d. treatment. Similar results were obtained with 1-dopa plus benserazide; however, 1-dopa always caused emesis, whereas beneficial effects were shown with ropinirole in the absence of this side effect. These results support the continued clinical assessment of ropinirole for the treatment of Parkinson's disease.
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