Investigating the relationship between corticosterone and glucose in a reptile

Abstract

The glucocorticoid hormone corticosterone (CORT) has classically been used in ecophysiological studies as a proxy for stress and energy mobilization, but rarely are CORT and the energy metabolites themselves concurrently measured. To examine CORT's role in mobilizing glucose in a wild reptile, we conducted two studies. The first study measured natural baseline and stress-induced blood-borne CORT and glucose levels in snakes during spring emergence and again when snakes return to the denning sites in fall. Our second study manipulated the hypothalamic pituitary adrenal axis in male snakes in the fall by taking a baseline blood sample, then subjecting individuals to one of five treatments (no injection, saline, CORT, adrenocorticotropin hormone, and metyrapone). Subsequent samples were taken at 30 minutes and 60 minutes. In both studies, we found that glucose levels do increase with the acute stress, but that the relationship was not directly related to CORT elevation. In the second study, we found that none of the HPA axis manipulations directly affected blood glucose levels, further indicating that CORT may play a complex, but not direct role in glucose mobilization in snakes. This study highlights the need for testing mechanisms in wild organisms by combining in situ observations with manipulative studies.