Abstract
Comparisons of circulating and excreted corticosteroid profiles during a biological stress response could provide more data concerning the timing and magnitude of acute hormone changes in different sample matrices. A stress test was performed in 13 zoo-based killer whales (Orcinus orca) whereby animals were elevated out of the water on a rising lift-bottom platform for 20 min. Paired blood and feces were tested for cortisol, corticosterone, aldosterone, and their metabolites and hematological and serum chemistry parameters. Circulating corticosteroids significantly increased during the stress test and returned to pre-treatment concentrations within 24 h, indicating hypothalamic-pituitary-adrenal-axis activation. Concentrations of fecal corticosteroid metabolites did not change significantly during the stress test. Significant differences between pre-test levels and the stress test stage were observed for counts of white blood cells and absolute neutrophils, consistent with a stress leukogram. For serum chemistry, significant deviations from baseline levels were seen for the majority (20/37) of measured parameters. This study provides a direct measurement of the physiologic response of clinically healthy killer whales to a stress event. However, due to the lack of significant changes in fecal hormone metabolite profiles, further investigation of the excretory dynamics of corticosteroids during acute and chronic stress is warranted.
Highlights
Maintenance of physiological homeostasis in response to rapid or long-term environmental, cognitive or physical changes requires corticosteroids, which include both glucocorticoids (GCs), such as cortisol or corticosterone, and mineralocorticoids (MCs), such as aldosterone
Our objectives were to: (1) Determine if previously validated GC antibodies for killer whale sera were appropriate for measuring fecal glucocorticoid metabolites (FGCMs); (2) Determine the suitability of an aldosterone enzyme immunoassay (EIA) for use in killer whale sera and feces; (3) Quantify corticosteroid measures in blood and feces prior to and after an induced acute stress event; and (4) Determine if any correlation exists between changes in serum hormones and serum chemistry and hematological parameters
Analysis of High performance liquid chromatography (HPLC) fractions using the cortisol EIA showed that the largest immunoreactive peak for both female and male fecal extract pools coincided with the elution time point for the known cortisol standard (Figure 1A)
Summary
Maintenance of physiological homeostasis in response to rapid (acute) or long-term (chronic) environmental, cognitive or physical changes requires corticosteroids, which include both glucocorticoids (GCs), such as cortisol or corticosterone, and mineralocorticoids (MCs), such as aldosterone. Glucocorticoid measurements are rapidly becoming the preferred method in wildlife species for detecting animals or populations of animals experiencing increased or atypical stressors in their environment (Wasser et al, 2000; Touma and Palme, 2005; Palme, 2019). These hormonal indices represent potential markers of animal health and welfare under a variety of conditions and stakeholders can use this information when drafting and implementing environmental and animal management policies (Ayres et al, 2012). It follows that inferences based on GC measures and their relationship to stress and the environment should be based on a sound understanding of the natural patterns and fluctuations of these hormones
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