Technical note: effect of corticotropin-releasing hormone on adrenocorticotropic hormone and cortisol in steers.
The objective of this study was to determine an appropriate exogenous dose of bovine corticotropin-releasing hormone (bCRH) to stimulate the physiological effects of the hypothalamic-pituitary-adrenal axis in steers as a method to test the sensitivity of the pituitary and adrenal gland. Twenty 14-mo-old Holstein-Friesian steers were blocked by weight (443.7+/-2.5 kg) and randomly allotted to receive either saline (control) or bCRH (0.1, 0.3, 1.0, or 1.5 microg/kg BW). Animals were housed in a slatted-floor facility (n = 5 per pen). Indwelling jugular catheters, for both the administration of bCRH and blood collection, were fitted on d -1 of the experiment. Saline and bCRH were administered i.v. at time 0. Serial blood samples were collected at -15, 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, and 180 min relative to time 0. Following administration of 0.1 microg of bCRH/kg BW, the peak ACTH response was not significantly different from pretreatment baseline concentrations (mean concentrations as measured at -15 and 0 min before bCRH administration). Mean ACTH concentrations from 0 to 180 min following 0.1 microg of bCRH/kg BW were not significantly different (P = 0.177) from controls. Administration of 0.3, 1.0, and 1.5 microg of bCRH/kg BW increased (P < 0.05) peak ACTH above pretreatment concentrations, and mean ACTH from 0 to 180 min for these treatments were greater (P < 0.05) than for controls. Peak cortisol responses to all bCRH treatments were greater (P < 0.05) than those to pretreatment concentrations. Mean cortisol concentrations from 0 to 180 min were greater (P < 0.05) in all bCRH-treated steers than in controls, but there were no significant differences among the bCRH treatments. The ratio of mean cortisol to mean ACTH for all bCRH doses tested differed (P < 0.05) from control values, indicating reactivity of the adrenals. In conclusion, bCRH challenge may be a useful method for testing the sensitivity of the hypothalamic-pituitary-adrenal axis in steers subjected to stressful husbandry conditions, and a minimum dose of 0.3 microg of bCRH/kg BW is required to stimulate physiological effects of stressor hormones.
Teagasc, Grange Research Centre, Dunsany, Co. Meath, Ireland.
S
S
Gupta
B
B
Earley
S T L
ST
Ting
N
N
Leonard
M A
MA
Crowe
D000324:Adrenocorticotropic Hormone / Q000097:blood* / Q000187:drug effects; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000097:blood / Q000502:physiology*; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006854:Hydrocortisone / Q000097:blood*; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000502:physiology*; D011897:Random Allocation
D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D006854:Hydrocortisone