CENTRALLY ADMINISTERED VASOPRESSIN MODIFIES STRESS HORMONE (CORTISOL,PROLACTIN) SECRETION IN SHEEP UNDER BASAL CONDITIONS, DURING RESTRAINT AND FOLLOWING INTRAVENOUS CORTICOTROPIN-RELEASING HORMONE

The effects of central (lateral ventricle) injections of vasopressin ( 2.5, 25 or 250 ng) on cortisol and prolactin release were investigated in castrated male sheep (N = 6) under basal (non-stress) conditions, during 120 min of physical restraint and following peripheral injectio n of ovine corticotrophin-releasing hormone (oCRH). Cortisol and prola ctin concentrations in non-stressed sheep were raised significantly (p < 0.05) in the 120 min following administration of 250 ng of vasopres sin. The prolactin response to restraint stress was decreased (p < 0.0 5) in the 30-min period following central injection of 250 ng of vasop ressin. The stimulatory effect of oCRH on cortisol release was enhance d (p < 0.05) by vasopressin (25 and 250 ng), whereas prolactin levels decreased (p < 0.02) in the 30-min period following injection of the h ighest dose of vasopressin. None of the central doses of vasopressin s ignificantly altered plasma levels of this hormone, although vasopress in secretion was increased during restraint.