Effect of two serotonin antagonists on prolactin and thyrotrophin secretion in man

The effects of serotoninergic blockade on prolactin and thyrotrophin secretion in man was evaluated by determining the basal and TRH-stimulated serum prolactin and TSH concentrations in normal volunteers before and after a 3 days course of cyproheptadine or methergoline administration. Cyproheptadine, a serotonin antagonist with antihistaminic, anticholinergic and antidopaminergic properties as well, did not affect prolactin secretion, while it reduced the serum TSH response to TRH; methergoline, a specific blocker of central serotonin receptors, decreased basal and TRH-induced serum prolactin levels, without affecting TSH secretion. These results support the existence of serotoninergic stimulatory influences on human prolactin release, while suggesting that human TSH secretion is not modulated by serotoninergic inputs.