3H-Spiroperidol binding to dopamine receptors in rat striatal membranes: influence of loxapine and its hydroxylated metabolites.

The effects of loxapine and its hydroxylated metabolites 7-hydroxyloxapine and 8-hydroxyloxapine on 3H-spiroperidol binding to rat striatal membranes were investigated. Whereas 7-hydroxyloxapine and loxapine displayed strong affinities for 3H-spiroperidol binding sites, 8-hydroxyloxapine was essentially inactive. The potency of 7-hydroxyloxapine to displace 3H-spiroperidol is 1.5 times and 8 times those of haloperidol and chlorpromazine, respectively. These results suggest that the combined effects of loxapine and 7-hydroxyloxapine on the postsynaptic dopamine receptors in the brain may explain the clinical efficacy of loxapine in the treatment of schizophrenia.