title: Adrenocorticotropin responses to endogenous and exogenous secretagogues in the sheep: specificity of glucocorticoid action.
abstract: Glucocorticoids act upon the hypothalamus and pituitary to regulate both corticotropin-releasing factors and adrenocorticotropin (ACTH) in a classical negative feedback loop. There are two distinct receptor systems in the central nervous system for glucocorticoids: type I corticosterone/cortisol-preferring, predominantly hippocampal receptors, and type II dexamethasone-binding receptors with a much broader distribution. To determine the relative roles played by these two receptors in determining basal and stress-induced ACTH/cortisol levels in the sheep, we have conducted two series of experiments. In the first, we infused 4 sheep with cortisol (50 micrograms/h), or dexamethasone (20 micrograms/h) for 17 h, collected 10-min blood samples for 3 h for basal hormone levels, and then subjected the sheep to an audiovisual stress (barking dog), 10 micrograms of ovine corticotropin-releasing factor (oCRF) 1 h later, and 100 U of insulin another 2 h later. Dexamethasone reduced ACTH and cortisol levels, both basal and in response to stress; cortisol infusion had no effect on any parameters; oCRF did not raise ACTH levels. In the second experiment, cortisol (100 micrograms/h) alone was infused into 4 sheep for 17 h, and blood samples were collected for 3 h for basal hormone levels; this was followed by the injection of 10 micrograms oCRF, and 2 h later a barking dog was introduced into the sheep shed. Again, cortisol infusion did not affect basal ACTH or cortisol levels, though both cortisol-infused and control animals had ACTH responses to oCRF when it was not preceded by the audiovisual stress. ACTH and cortisol levels were higher in the 2 h following oCRF injection.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Medical Research Centre, Prince Henry's Hospital, Melbourne, Australia.
authors.forename: B J
authors.initials: BJ
authors.lastname: Canny
authors.forename: I J
authors.initials: IJ
authors.lastname: Clarke
authors.forename: J W
authors.initials: JW
authors.lastname: Funder
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood / Q000378:metabolism*; D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology*; D005246:Feedback / Q000502:physiology; D005260:Female; D006854:Hydrocortisone / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology*; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects*; D007262:Infusions, Intravenous; D011965:Receptors, Glucocorticoid / Q000187:drug effects*; D012756:Sheep / Q000502:physiology*; D013312:Stress, Physiological / Q000097:blood / Q000503:physiopathology*
chemical_list: D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D006854:Hydrocortisone