A ROLE FOR VASOPRESSIN IN THE STRESS-INDUCED INHIBITION OF GONADOTROPIN-SECRETION - STUDIES IN THE BRATTLEBORO RAT

The effects of stress on the secretion of adrenocorticotrophin, corticosterone and luteinizing hormone (LH) in rats congenitally lacking hypothalamic vasopressin (Brattleboro rats) and in normal controls of the parent strain (Long Evans) have been compared in an attempt to examine the role of vasopressin in the stress-induced depression of gonadotrophin secretion. In the Long Evans rats, stress (0.6 mg/100 g histamine, ip) initiated, within 5 and 20 min respectively, significant (P < 0.01, Student's t-test) increases in the plasma adrenocorticotrophin and corticosterone concentrations. It also caused a reduction in the serum LH concentration which was maximal at 5 min. By contrast, in the vasopressin deficient Brattleboro rats, stress had no effect on the serum LH concentration and produced only modest increases in pituitary adrenocortical activity compared with those in Long Evans controls. Pretreatment of both Long Evans and Brattleboro rats with dexamethasone (20-mu-g/100 g ip, daily for 3 days) effectively abolished the pituitary-adrenal response to stress. The steroid treatment also prevented the stress-induced suppression of LH in the Long Evans rats; indeed, these animals, unlike the vehicle-treated controls, exhibited a rise in serum LH concentration within 5 min of exposure to stress. Stress did not affect the serum LH concentrations in steroid-treated Brattleboro rats. The results confirm previous reports that vasopressin is required for the full expression of the pituitary-adrenocortical response stress. They also provide novel evidence which suggests that vasopressin released in stress contributes to the impairment of gonadotrophin secretion.