The effect of TRH on the release of TSH, PRL and GH in man under basal conditions and following methysergide.

Pretreatment with methysergide, a blocker of serotoninergic receptors, significantly reduced the TSH response to TRH in six male volunteers. The TRH-induced PRL release was also slightly decreased, while plasma GH levels were not significantly modified by TRH either during the control period or after methysergide. These results indicate that alterations of central nervous system monoaminergic pathways may modify the hypophysiotropic effects of TRH.