RICH, E.L.*; ROMERO, L.M.: Corticosterone response to variable doses of dexamethasone, CRF and ACTH in the European Starling (Sturnus vulgaris)

Captive European Starlings were used to determine dose-dependant responses of the Hypothalamus-Pituitary-Adrenal (HPA) axis to exogenous ACTH, CRF or dexamethasone (dex). Ten wild starlings were held in the laboratory on a short-day photoperiod (11L:13D). Between 10am and 12pm, basal blood samples were taken within 3min of disturbance, and birds were injected with hormone or lactated Ringers solution (control) within 10min. Subsequent blood samples were taken at 30min, 60min and 4h for all injections, and at 24h for dex injections. Corticosterone (cort) concentrations in all samples were measured. Hormones and doses tested were 50, 100 and 200 IU/kg ACTH; 3, 6 and 9µg/kg IV CRF; 0.5, 4 and 8µg subcutaneous CRF; 0.5, 2 and 5µg/kg dex. The control injection showed a cort peak at 30min in response to the stress of handling and restraint, which decreased to near basal levels at 60min and 4h. Both the 50 and 100 IU/kg ACTH doses elevated 30min and 60min concentrations of cort above control levels, with a return to basal levels by 4h. 200 IU/kg ACTH elevated cort at 30 and 60min, but to lower levels than the smaller doses, with a return to basal levels by 4h. None of the IV doses, nor the 0.5 or 4 µg subcutaneous doses of CRF had a significant effect on cort concentrations. 8µg subcutaneous CRF elevated cort only at 30min. By 60min, the 0.5 and 5µg/kg doses of dex had decreased cort concentrations below control levels, and at 4h the 2 and 5µg/kg doses continued to depress levels while the 0.5µg/kg dose returned to basal levels. All 24h samples were found to be at basal levels. These dose-response curves elucidate the function and sensitivity of the starling HPA axis and will aid future research.