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

<p>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 (<em>Ursus arctos</em>), 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.</p>