EFFECT OF CHRONIC ACTIVE IMMUNIZATION ANTICORTICOTROPIN-RELEASING FACTOR ON THE PITUITARY-ADRENAL-FUNCTION IN THE SHEEP

ACTH and cortisol diurnal variations and responses to two types of str ess (insulin-induced hypoglycemia and isolation-restraint stress) or t o an acute injection of lysinevasopressin were studied in intact and a nti-corticotropin-releasing factor (CRF) actively immunized rams. Immu nization was obtained by the injection of synthetic ovine CRF coupled to BSA with carbodiimide. All animals developed antibodies anti-CRF an d displayed an alteration of their general condition and a body weight reduction. The mean basal ACTH and cortisol secretion as well as the number and mean amplitude of diurnal pulses of these hormones was sign ificantly reduced in the group of anti-CRF immunized rams. However, th e reduction in all three parameters was much more pronounced for corti sol than for ACTH. No ACTH and cortisol response to insulin-induced hy poglycemia and isolation-restraint stress was observed. The stimulatin g action of lysine-vasopressin on ACTH release was significantly reduc ed as compared to controls. These results indicate that CRF is a major physiological component of the ovine hypothalamo-hypophysial-adrenal axis and participates in the events that regulate ACTH and cortisol di urnal variations and response to stress.