Evidence that Melatonin Acts in the Pituitary Gland through a Dopamine‐independent Mechanism to Mediate Effects of Daylength on the Secretion of Prolactin in the Ram

Abstract

A previous study provided evidence that melatonin acts in the pituitary gland to mediate the effects of daylength on the secretion of prolactin in sheep. This was based on the observation that hypothalamo‐pituitary disconnected (HPD) Soay rams showed normal patterns in the changes in the peripheral blood concentrations of prolactin in response to alterations in photoperiod (10‐fold higher concentrations under long than short days), and in response to exogenous melatonin (rapid decline following the administration of a constant‐release implant of melatonin). The purpose of this study was to establish whether dopamine (DA) might be involved in mediating the effects of melatonin on the secretio..