Evidence that Serotonin Stimulates a Prolactin-Releasing Factor in the Rat

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Abstract
Methanol extracts of rat plasma resulted in release of prolactin (PRL) from rat hemipituitaries in vitro with a linear log-dose relationship. This prolactin-releasing factor (PRF)-like activity was not altered in plasma from rats treated with bromocryptine or chlorpromazine despite significant suppression and stimulation of plasma PRL levels, respectively. Fluoxetine, a serotonin reuptake inhibitor, plus 5-hydroxytryptophan, the immediate precursor of serotonin, markedly stimulated both plasma PRL and plasma PRF-like activity. Neither fluoxetine, 5-hydroxytryptophan, nor the combination directly stimulated PRL release from rat pituitary tissue in vitro. We conclude that serotonergic stimulation augments PRL release via a PRF.