Functional potencies of new antiparkinsonian drugs at recombinant human dopamine D1, D2 and D3 receptors.

We measured the affinities of bromocriptine, pramipexole, pergolide and ropinirole at human recombinant dopamine D1, D2 and D3 receptors in binding and functional tests. All four compounds bound with high affinity at the dopamine D3 receptor; bromocriptine and pergolide also had high affinity for the dopamine D2 receptor, while only pergolide had significant, although moderate, affinity for the dopamine D1 receptor. Only pergolide had high potency and intrinsic activity at the dopamine D1 receptor for stimulating cyclic AMP accumulation. In addition, the potencies and efficacies of pergolide and bromocriptine, as well as that of dopamine, at the dopamine D1 receptor were increased in the presence of forskolin, an adenylate cyclase activator. All four compounds were highly potent agonists at dopamine D2 and D3 receptors, as measured in a mitogenesis assay. Bromocriptine was ten times more potent and pramipexole and ropinirole ten times less potent at the dopamine D2 than at the dopamine D3 receptor, whereas pergolide was equipotent at the two receptors. These results suggest that the activity of recently developed antiparkinsonian drugs at either the dopamine D1 or the dopamine D3 and not only the dopamine D2 receptors should be taken into account in analyses of their mechanisms of action in therapeutics.