Meeting Abstract
In developing birds, costs of elevated glucocorticoids have been repeatedly demonstrated while benefits – reallocation of endogenous resources – are often assumed. Although mobilization of glucose in response to elevated glucocorticoids occurs in mammals, some studies suggest that in birds, lipid rather than glucose mobilization may be the primary resource reallocation pathway. However, most of the evidence about relationships between glucocorticoids and glucose in birds is either conducted in captivity or correlational, based on concurrent increases in corticosterone (cort) and glucose during capture-and-handling protocols. We tested the hypothesis that in free-living birds, cort has a larger effect on the acute mobilization of lipid-based energy substrates than on glucose. We administered a single oral dose of cort in oil to black-legged kittiwake (Rissa tridactyla) chicks; total handling time averaged 20 sec. We collected blood 15, 30, or 60 min after cort administration and compared circulating glucose, triglycerides, and cholesterol in cort-treated chicks to those in oil-only controls and unhandled controls. At 30 min, both groups of handled chicks had elevated glucose compared to unhandled controls, but cort and oil treatments did not differ.. Triglycerides were not responsive to treatments, however, cholesterol was elevated in cort chicks 15 min after administration, suggesting non-genomic effects of corticosterone on cholesterol mobilization. Disentangling the roles of catecholamines and glucocorticoids will require additional experimental manipulations and attention to very short time scales.
