Basal serum concentrations of prolactin (PRL) and the elevation of serum PRL concentrations induced by the serotonergic agents, quipazine and 5-hydroxytryptophan (5-HTP) were suppressed in rats treated acutely with dexamethasone. Acute dexamethasone treatment did not alter the stimulation of PRL release produced by the dopamine antagonist haloperidol. In contrast, chronic treatment of rats with dexamethasone resulted in a potentiation of the PRL response to quipazine, 5-hydroxytryptophan and haloperidol. It is concluded that dexamethasone can exert differential effects on the secretion of PRL, and that these effects are dependent upon the duration of dexamethasone treatment.
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