Remage-Healey, L.; Romero, L.M.: Corticosterone and insulin interact to regulate glucose and lipid concentrations during stress in starlings undergoing molt.
Captive starlings ( Sturnus vulgaris ) undergoing a prebasic molt (the costly replacement of body feathers) were given exogenous insulin and corticosterone (CORT) to determine how counterregulatory hormones alter glucose and triglycerides during stress. Experiments were conducted at both morning (11:00) and night (23:00) to monitor daily variation in responses. Concentrations of CORT, glucose and triglycerides were measured in blood plasma at <3 min (basal) and at three time points over 2.5 hours thereafter (stress-induced) to monitor the effect of injected saline, insulin or CORT. Birds were exposed to handling and restraint stress, which caused an increase in CORT concentrations, a decrease in triglycerides, but had no effect on circulating glucose. Circadiel (daily) variation was not evident in CORT or glucose, but concentrations of triglycerides were higher at night than during the day. Insulin markedly suppressed glucose concentrations, and had no effect on plasma CORT or triglycerides. Injected CORT hastened the recovery of glucose concentrations from insulin-induced hypoglycemia, while CORT had no effect on plasma triglycerides. Exogenous CORT also produced considerable hyperglycemia in the absence of injected insulin, and this effect was demonstrated at both times-of-day. Basal concentrations of CORT, glucose and triglycerides exhibited circannual (seasonal) variation when combined with data from an earlier study of starlings held on short and long days. During the energetically-costly prebasic molt, all three indicators were at lower basal concentrations than during simulated winter (short days) or summer (long days). These results further demonstrate the substantial alteration of metabolism and stress physiology in birds undergoing molt, and present evidence for a permissive role of glucocorticoids during stress.