title: Paradoxical effect of neuroleptic drugs on prolactin secretion by rat pituitary cell cultures.
abstract: Several antipsychotic drugs reverse the dopamine-induced inhibition of prolactin release by rat pituitary cell cultures. Paradoxically, at high doses and without dopamine, antipsychotic drugs can also inhibit prolactin secretion. The mechanism underlying this phenomenon is unclear. Some evidence suggests that these drugs have an agonistic action. We sought to verify whether clozapine and fluphenazine, at doses higher than those reversing dopamine-induced inhibition of prolactin secretion in vitro, show this paradoxical effect and eventually a partial agonistic action. Both antipsychotics inhibited prolactin secretion, clozapine at doses starting from 10(-6) M and fluphenazine from 10(-7) M. Haloperidol reversed clozapine-induced prolactin inhibition but left fluphenazine-induced inhibition unchanged. These in vitro findings suggest that clozapine has a partial agonistic action on dopaminergic receptors but fluphenazine does not.
authors.affiliation: Institute of Pharmacology and Pharmacognosy, University of Rome La Sapienza, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Braghiroli
authors.forename: A
authors.initials: A
authors.lastname: Ponzianelli
authors.forename: G
authors.initials: G
authors.lastname: Mazzanti
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003024:Clozapine / Q000494:pharmacology; D005260:Female; D005476:Fluphenazine / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012636:Secretory Rate / Q000187:drug effects
chemical_list: D014150:Antipsychotic Agents; D011388:Prolactin; D003024:Clozapine; D005476:Fluphenazine