Receptor affinities of aporphine enantiomers in rat brain tissue.

ABSTRACT

R(-) and S(+) enantiomers of apomorphine, N-n-propylnorapomorphine and 11-hydroxy-N-n-propylnorapomorphine were screened for affinity at over 40 representative sites in rat brain tissue that included amine, purine, amino acid and peptide receptors, transporters, ion channels, and effector components; only dopamine receptors and alpha-adrenoceptors showed appreciable affinity that was quantified further. The aporphines showed R(-) > S(+) isomeric selectivity as well as D2 > D1 selectivity at dopamine receptors. While R(-) isomers preferred alpha 2-adrenoceptors, S(+)-aporphines were alpha 1-selective, with similar affinity at alpha 1-adrenoceptors and dopamine D2 receptors. Interactions of S(+)-aporphines at alpha 1-adrenoceptors as well as dopamine D2 receptors may contribute to their unusual behavioral properties.