The influence of vasopressin on hypothalamic corticotrophin releasing activity in rats with inherited diabetes insipidus.

1. The corticotrophin releasing activity of hypothalamic extracts from rats congenitally lacking vasopressin (Brattleboro strain) has been studied in the presence and absence of arginine vasopressin and its antiserum. 2. Hypothalamic extracts from Brattleboro rats stimulated the production of corticotrophin by pituitary segments in vitro but both their potency and the slopes of their dose-response lines were significantly less than those of controls. Arginine vasopressin also stimulated pituitary-adrenocorticotrophic activity in vitro but only in concentrations considerably greater than those present in hypothalamic extracts from normal rats. 3. In low, physiological concentrations arginine vasopressin did not affect the corticotrophin releasing activity of hypothalamic extracts from controls but potentiated markedly the activity of extracts from Brattleboro rats and rendered the slopes of their dose-response lines parallel with those of the controls. 4. The antiserum to arginine vasopressin did not affect the corticotrophin releasing activity of Brattleboro extracts but reduced the activity of control extracts and rendered the slopes of their dose-response lines parallel with those of Brattleboro extracts. 5. The results suggest that vasopressin acts synergistically with the corticotrophin releasing factor and is essential for the full expression of pituitary-adrenocorticotrophic activity.