PROLACTIN SECRETION IN SHEEP AFTER DEHYDRATION FOLLOWED BY RESTRAINT OR ADMINISTRATION OF OVINE CORTICOTROPIN-RELEASING FACTOR

Plasma concentrations of prolactin were measured in male sheep (wether s, n = 8) during 120 min exposure to mild physical stress (restraint), and also following i.v. injection of 30-mu-g ovine corticotrophin-rel easing factor (CRF), when the animals were water replete and when they had been deprived of water for 48 h. Restraint stress produced a smal l increase in prolactin secretion (n.s.) when the animals were euhydra ted and a large increase (P < 0.001) when they were dehydrated. Admini stration of CRF had no effect on prolactin concentrations in either ex perimental condition. In a further study in which euhydrated animals ( n = 6) were subjected to restraint while receiving infusions of vasopr essin (1-mu-g/h), there was no enhancement of basal or stress-induced prolactin secretion. Thus, dehydration enhances stress-induced prolact in release in sheep through a process that does not involve a pituitar y action of CRF or circulating vasopressin.