The binding of [3H]N-(chloroethyl)-norapomorphine to rat striatal membranes.

N-(chloroethyl)-norapomorphine (NCA) irreversibly inhibits striatal dopamine function, the binding of dopamine agonist ligands and dopamine-stimulated adenylate cyclase. A selective interaction of [3H]NCA with dopamine receptor sites would be of use in the characterisation and isolation of brain dopamine receptors. In this study the binding of [3H]NCA to homogenates of rat striatum was investigated. Binding of [3H]NCA to striatal preparations was saturable and irreversible and prevented with high affinity by dopamine agonist drugs with a catechol moiety. However, binding was not prevented in a stereoselective manner by the isomers of butaclamol, flupenthixol or sultopride. Nor was [3H]NCA binding specific to brain areas containing dopamine receptors. We conclude that [3H]NCA binding is not selective for dopamine receptors, although NCA inhibited both [3H]N,n-propylnorapomorphine (NPA) and [3H]spiperone binding in a non-competitive manner.