title: Glucocorticoids regulate ovine hypophysial portal levels of corticotropin-releasing factor and arginine vasopressin in a stress-specific manner.
abstract: Hypophysial portal circulation levels of immunoreactive (ir) CRF, immunoreactive arginine vasopressin (ir-AVP), and systemic ir-ACTH and cortisol were determined in dexamethasone-infused (20 micrograms/h) ewes, both under basal conditions and in response to audiovisual and hypoglycemic stress. Glucocorticoid infusion lowered mean basal levels of ir-CRF (P less than 0.05), ir-ACTH (P less than 0.05), and cortisol (P less than 0.05), but not of ir-AVP. Audiovisual stress led to coordinate release of ir-AVP and ir-CRF, and although the hypothalamic response to this stress was not altered in dexamethasone (DEX)-infused sheep, the pituitary-adrenal response was blocked, suggesting that glucocorticoids act on the pituitary rather than on higher centers to inhibit this response. In contrast, hypoglycemia led to preferential release of ir-AVP over ir-CRF, and DEX infusion delayed and inhibited both hypothalamic and pituitary responses. Ketamine injection also led to preferential release of ir-AVP, but neither the hypothalamic nor pituitary-adrenal responses were affected by DEX infusion. These results suggest that different stressors evoke different patterns of hypothalamic secretagogue release, and that glucocorticoids act in a site-specific fashion to regulate the hypothalamo-pituitary-adrenal responses to stress.
authors.affiliation: Medical Research Centre, Prince Henry's Hospital, Melbourne, Australia.
authors.forename: B J
authors.initials: BJ
authors.lastname: Canny
authors.forename: J W
authors.initials: JW
authors.lastname: Funder
authors.forename: I J
authors.initials: IJ
authors.lastname: Clarke
mesh_terms: D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood / Q000378:metabolism*; D003346:Corticotropin-Releasing Hormone / Q000097:blood / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D007003:Hypoglycemia / Q000503:physiopathology; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000503:physiopathology*; D007044:Hysterectomy; D007328:Insulin / Q000494:pharmacology; D007649:Ketamine / Q000494:pharmacology; D010052:Ovariectomy; D012756:Sheep; D013312:Stress, Physiological / Q000097:blood / Q000503:physiopathology*; D013315:Stress, Psychological / Q000097:blood / Q000503:physiopathology*
chemical_list: D007328:Insulin; D001127:Arginine Vasopressin; D007649:Ketamine; D003907:Dexamethasone; D003346:Corticotropin-Releasing Hormone