An integrative appraisal of the hormonal and metabolic changes induced by acute stress using king penguins as a model

Abstract

A large number of studies have focused on the reactivity of the hypothalamic-pituitaryadrenal (HPA) axis and the consequences of glucocorticoids (GC) in mediating life-history trade-offs. Although short-term increases in GCs are viewed as adaptive, mobilizing energy substrates allowing animals to deal with impending threats (e.g. stimulating hepatic gluconeogenesis, stimulating lipolysis, mobilizing amino acids), few studies have actually measured the exact time-course of substrate mobilisation in response to acute stress in natural conditions. We evaluated the hormonal and metabolic components of the stress response to acute stress in 32 free-living king penguins (Aptenodytes patagonicus). We monitored changes in blood GCs (corticosterone, CORT), glucose, lactate, ketone bodies (b-hydroxybutyrate), non-esterified fatty acids, and uric acid in response to a standardized capture-restraint protocol lasting for up to 90 min. Furthermore, we tested whether the vigilance status of the animal (alert or asleep) affected its perception of the capture, thereby modulating the hormonal and metabolic stress responses. The time course of energy mobilisation followed the characteristic pattern expected from laboratory and theoretical models, with a rapid depletion of those energy stores linked to rapid adrenergic responses (i.e. glucose and ketone bodies), followed by a mobilisation of energy stores associated with the sustained longer-term GC response (i.e. fats and protein stores). HPA reactivity was generally slower than reported in other birds, and there was high inter-individual variability. Sleeping birds had higher GC and glucose responses to acute stress, suggesting a more rapid mobilization of energy stores. Our results highlight the importance of considering HPA and metabolic responses to acute stress against species-specific life history and ecological relevant backgrounds.

Oxidative stress and mitochondrial responses to stress exposure suggest that king penguins are naturally equipped to resist stress

“…1 mL) was taken from the flipper vein using a heparinized syringe. In the king penguin, no detectable increase in baseline GC levels occurs within the first 5 minutes of capture 40 . Thus, corticosterone levels measured in this first blood sample represent bird’s baseline levels under natural conditions.…”

“…Here, we subjected 24 free-living incubating king penguins to an acute restraint-stress for 30 minutes. We collected blood samples both before (baseline <4 min post-capture 40 ) and at the end of the 30 minutes of restraint-stress. We used these samples to measure baseline and stress-induced plasma total CORT levels and oxidative stress markers measured both in plasma and red blood cells (RBCs).…”

Beyond corticosterone: The acute stress response increases DNA damage in house sparrows

“…Individuals were either restrained in an opaque breathable cloth bag for 30 ( n = 5 females, 5 males) or 120 min ( n = 5 females, 5 males); we chose to test two different restraint times to more clearly understand whether the responses we observed in DNA damage, Cort, and uric acid were regulated by the length of the stressor. In addition, these restraint times represent a traditional protocol used in lab and field studies (e.g., Deviche et al, 2014; Viblanc et al, 2018) and a more recent version that holds animals for 120 min to measure negative feedback (e.g., Hau et al, 2015; Love et al, 2017; Vera et al, 2019). In each of these cases, blood samples (<60 μl) from the alar vein were taken at 0, 30, 60, and 120 min and collected in heparinized capillary tubes (Fisherbrand, Pittsburg, PA); birds that were restrained for 30 min were returned to their cages for the 60 and 120‐min samples, while birds in the 120‐min restraint treatment remained in the cloth bag for the entirety of the sampling period.…”

“…We tested two different restraint times (30 and 120 min) to help assess whether changes in the measured parameters are tuned to stressor length. We chose these two times based on the popular assessment of the acute stress response using a 30‐min restraint (e.g., Deviche et al, 2014; Viblanc et al, 2018) and the more recent addition of assessing negative feedback, which requires handling of the animal for up to 120 min (e.g., Hau et al, 2015; Love, Lovern, & DuRant, 2017; Vera, Antenucci, & Zenuto, 2019). If DNA damage is affected by stressor length, we would expect a gradated response with birds restrained for 30 min to exhibit reduced responses relative to those restrained for 120 min.…”

The human stress response

“…The rapid rise in CORT seen under conditions of stress increases availability of supplemental energy stores by promotion of gluconeogenesis and inhibition of insulin production combined with vasoconstriction, which aids delivery of blood to muscles and the brain 97 . Centrally, CORT promotes decision making and alertness and stimulates cognitive functioning.…”