CHLORPROMAZINE, HALOPERIDOL, METOCLOPRAMIDE AND DOMPERIDONE RELEASE PROLACTIN THROUGH DOPAMINE ANTAGONISM AT LOW CONCENTRATIONS BUT PARADOXICALLY INHIBIT PROLACTIN RELEASE AT HIGH CONCENTRATIONS

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Abstract
1 The effects of chlorpromazine, haloperidol, metoclopramide and domperidone on the release of prolactin from perfused columns of dispersed rat anterior pituitary cells were studied. 2 Chlorpromazine, haloperidol, metoclopramide and domperidone antagonized the dopamine-mediated inhibition of prolactin release at low concentrations. 3 Each dopamine antagonist displaced the dose-response curve for dopamine-induced suppression of prolactin release to the right in a parallel manner. 4 At higher concentrations, the four drugs became less effective as dopamine antagonists. 5 At high concentrations in the absence of dopamine, chlorpromazine, haloperidol, metoclopramide and domperidone paradoxically suppressed prolactin secretion by an unknown mechanism.