Binding of (+)PHNO and other D2-dopamine agonists to D1-dopamine receptors labelled by [3H]SCH 23390.

The affinity of (+)PHNO for the D1-dopamine receptor subtype in striatal tissue was determined in a radioligand binding assay using the D1-selective compound, [3H]SCH 23390. The IC50 for (+)PHNO was 22 microM, a value considerably higher than obtained for reference agents (lisuride, apomorphine, pergolide, [-] EOE and bromocriptine). The low potency of (+)PHNO at the D1-receptor subtype contrasts with the compound's high potency at the D2-receptor subtype, as reported previously. (+)PHNO can, therefore, be classified as a very selective D2-receptor agonist.