Blood cortisol and fecal cortisol metabolite concentrations following an ACTH challenge in unanesthetized brown bears (Ursus arctos)

Fecal cortisol metabolites (FCMs) are increasingly used to index
physiological stress in wildlife. Cortisol and other stress
hormones act to mobilize glucose, providing energy for the organism
to respond to environmental perturbations. Cortisol, the
predominant glucocorticoid (GC) in most mammals, is metabolized
by the liver and excreted as FCMs. For FCMs to serve as a
meaningful physiological index of stress in brown bears (Ursus
arctos), we sought to quantify the relationship between blood
cortisol and FCM concentrations. Consequently, we conducted
an adrenocorticotropic hormone (ACTH) challenge on nine
unanesthetized captive brown bears at the Washington State
University Bear Research, Education, and Conservation Center.
We collected 10mL of blood at 0, 3, 6, 24, 48, and 72 hours
post-injection to measure changes in blood cortisol concentrations. Fecal
samples were collected between 7:00 am to 8:00 pm from 24 hours prior to
injection through 72 hours post-ACTH challenge. We found that the peak
blood cortisol concentrations occurred between 3 to 6 hours following an
ACTH challenge whereas FCMs peaked between 10 and 27 hours after
injection.