³H-haloperidol binding to dopamine receptors in rat corpus striatum: Influence of chlorpromazine metabolites and derivatives

A series of chlorpromazine metabolites and derivatives have been assayed for their ability to compete with ³H-haloperidol binding to dopamine receptors in membranes of rat corpus striatum. 3-Hydroxylation of chlorpromazine doubles affinity for receptor sites, while 7-hydroxychlorpromazine has a potency similar to that of chlorpromazine itself. Other patterns of hydroxylation reduce affinity. Side chain demethylation lowers affinity for binding sites. Several metabolites which lack neuroleptic activity in vivo, such as chlorpromazine-5-oxide, also are inactive in competing for ³H-haloperidol binding. Since blood levels of 7-hydroxychlorpromazine tend to be similar to those of chlorpromazine itself in patients, these observations indicate that 7-hydroxychlorpromazine may account for a major portion of the antischizophrenic efficacy of chlorpromazine. The structure-activity relationship observed in the present study support a model in which chlorpromazine interacts with dopamine receptors by assuming a conformation with its side chain tilted toward ring A.