REMAGE-HEALEY, L.; ROMERO, L.M.*: Effects of Insulin and Corticosterone on Stress in Captive Starlings: Daily and Seasonal Variations in Metabolite Responses.

Captive starlings (Sturnus vulgaris) were used to examine the effects of exogenous insulin and corticosterone administration on plasma metabolite levels in response to stress, and how these responses varied over the course of the day and season. Starlings were captured from the wild during the winter, held on short days (11L:13D – mimicking winter), and then shifted to long days (19L:5D – mimicking summer). Levels of corticosterone (CORT), glucose, and triglycerides were measured in blood plasma. Basal samples were taken within 3 min of disturbance and subsequent concentrations were measured 40, 70, and 150 min following handling stress and injection of exogenous saline, insulin or CORT. Both triglyceride and CORT concentrations responded to handling and restraint stress in control (saline-injected) birds when monitored at both morning and night, while control birds only exhibited stress-induced hyperglycemia at night (23:00) and not during the day (11:00). Basal CORT levels were higher at night than during the day, opposite of the circadiel variation in basal glucose concentrations, and triglycerides showed no daily variation. Injected insulin did not affect circulating CORT or triglyceride concentrations but significantly lowered plasma glucose (hypoglycemia). Injected insulin + injected CORT did not affect triglyceride concentrations but CORT appeared to hasten plasma glucose recovery from insulin-induced hypoglycemia. These findings provide evidence of a possible permissive role of glucocorticoids in the stress response in birds.