Abstract
Stressful disturbances activate the hypothalamic-pituitary-adrenal (HPA) axis and result in the release of glucocorticoid (GC) hormones. This characteristic stress response supports immediate energetic demands and subsequent recovery from disturbance. Increased baseline GC concentrations may indicate chronic stress and can impair HPA axis function during exposure to additional stressors. Levels of GCs, however, vary seasonally and with life-history stage, potentially confounding their interpretation. Our objective was to evaluate HPA axis function across variations in baseline GC levels. Northern elephant seals show substantial baseline variation in GC levels during their annual moulting period. We therefore conducted measurements early, in the middle and at the end of moulting; we simulated an acute stressor by administering adrenocorticotrophic hormone and evaluated the changes in circulating hormones and metabolites over the following 2 h. The stress response was characterized by increases in both cortisol and aldosterone (F 7,105 = 153 and 25.3, respectively; P < 0.001). These hormones increased in parallel and the slopes of their relationship varied by study group, suggesting they are regulated in a co--ordinated manner during acute stress in this species. There was no detectable difference in the total release of cortisol or aldosterone among study groups, indicating that the HPA axis remained sensitive to stimulation by adrenocorticotrophic hormone despite varying baseline levels of GCs. Acute stress influenced carbohydrate and fat metabolism in all study groups, but protein catabolism was affected to a far lesser degree. These findings suggest that elephant seals, and potentially other pinniped species, are resilient to moderate variations in baseline GC levels and remain capable of mounting a response to additional stressors.
Highlights
Numerous environmental conditions potentially disrupt homeostasis in free-ranging animals
The stress response was characterized by increases in both cortisol and aldosterone (F7,105 = 153 and 25.3, respectively; P < 0.001). These hormones increased in parallel and the slopes of their relationship varied by study group, suggesting they are regulated in a co-ordinated manner during acute stress in this species
To investigate the possibility that that increased GC concentrations influence the stress response, we examined the response to a simulated stressor—the administration of exogenous adrenocorticotrophic hormone—across the annual moult of juvenile seals when GC levels are anticipated to vary
Summary
Numerous environmental conditions potentially disrupt homeostasis in free-ranging animals. Sufficient disturbance will result in a stress response, characterized by activation of the hypothalamic–pituitary–adrenal (HPA) axis and the release of glucocorticoid (GC) hormones (e.g. cortisol; Fig. 1). Activation of the HPA axis and the release of GCs have wideranging consequences and influence several metabolic pathways; for example, at high concentrations GCs increase gluconeogenesis, lipolysis and protein catabolism (Sapolsky et al, 2000). Understanding how normal variation in baseline GC levels influences the capacity of animals to respond to subsequent stressors provides insight into how cumulative stressors may influence the resilience of animals to environmental disturbance and its potential fitness consequences
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
