During both ovine and human pregnancy plasma cortisol is increased. In human pregnancy the placenta secretes corticotropin-releasing factor (CRF), but pituitary responses to CRF are decreased. However, in ovine pregnancy there is no measurable placental secretion of CRF. This study tests for changes in pituitary responsiveness to CRF or AVP. Pregnant and nonpregnant ewes were infused with saline or CRF at three doses (3, 9, 45 microg/h), with or without coinfusion of AVP (9 microg/h). AVP infusion increased plasma AVP to approximately 250 pg/ml. CRF infusions increased plasma CRF from approximately 25 to 50, 150, and 850 pg/ml. ACTH was significantly increased by the infusion of AVP and by all infusions of CRF. Within-animal comparisons revealed a potentiation of the ACTH response to CRF in the presence of AVP. The ACTH responses to AVP and/or CRF were During both ovine and human pregnancy plasma cortisol is increased. In human pregnancy the placenta secretes corticotropin-releasing factor (CRF), but pituitary responses to CRF are decreased. However, in ovine pregnancy there is no measurable placental secretion of CRF. This study tests for changes in pituitary responsiveness to CRF or AVP. Pregnant and nonpregnant ewes were infused with saline or CRF at three doses (3, 9, 45 microg/h), with or without coinfusion of AVP (9 microg/h). AVP infusion increased plasma AVP to approximately 250 pg/ml. CRF infusions increased plasma CRF from approximately 25 to 50, 150, and 850 pg/ml. ACTH was significantly increased by the infusion of AVP and by all infusions of CRF. Within-animal comparisons revealed a potentiation of the ACTH response to CRF in the presence of AVP. The ACTH responses to AVP and/or CRF were