concept

glucocorticoid levels

Also known as: glucocorticoid concentrations, circulating glucocorticoid levels, blood glucocorticoid levels, glucocorticoid concentration

Facts (33)

Sources

Allostasis revisited: A perception, variation, and risk framework frontiersin.org Frontiers Sep 28, 2022 32 facts

referenceWhen an animal relies on cues indicating a threat to Potential Reproductive Potential (PRP) and responds with anticipatory elevation in glucocorticoid levels, it can lead to Emergency Life History Stage (ELHS) activation and/or homeostatic overload as described in the Reactive Scope model.

claimMcEwen and Wingfield (2003) established the allostatic load framework, but research assessing the relationship between animal energetics and hallmarks of allostatic load, such as circulating glucocorticoid levels, remains limited.

claimGlucocorticoid concentrations rise from level A (homeostatic level) to level B (reactive scope) as conditions deteriorate, and to level C (allostatic overload) when conditions become extreme, which triggers facultative responses such as the Emergency Life History Stage (ELHS).

claimCirculating glucocorticoid levels are likely regulated in part based on an individual’s proximity to energetic crisis, which is identified as the perturbation resistance potential (PRP).

claimChronically elevated glucocorticoid levels in allostatic overload Type 2 may cause imbalances in sympathetic and parasympathetic tone, as well as in other hormones associated with homeostasis, food intake, and reproduction, potentially leading to conditions like hypertension and insulin resistance.

referenceSchoenle et al. (2021) conducted a phylogenetic meta-analysis titled 'Does variation in glucocorticoid concentrations predict fitness?' published in General and Comparative Endocrinology.

claimThe basal regulatory level of glucocorticoid concentration is rarely observed.

claimBruce McEwen (1998) suggests that chronically elevated glucocorticoid levels may cause imbalances in sympathetic and parasympathetic tone, as well as hormones associated with homeostasis, food intake, and reproduction, which may manifest as conditions like hypertension and insulin resistance.

claimELHS activation, referred to as 'physiological state level C,' occurs when glucocorticoid concentrations are consistently elevated above the seasonal norm for the life-history stage, known as 'physiological state level B'.

claimThe decision to elevate glucocorticoid levels to engage the Emergency Life-History Stage (ELHS) resembles the decision prey animals make regarding flight-initiation-distance in response to a perceived predation threat.

claimResearch assessing the relationship between animal energetics and hallmarks of allostatic load, such as circulating glucocorticoid levels, is limited according to McEwen and Wingfield (2003).

referenceThe hypothesis that variation in allostatic load is correlated with mediators such as plasma glucocorticoid levels was tested in birds and tentatively rejected by Word et al. (2022).

claimThe original model of allostasis predicted that blood glucocorticoid levels should change in correlation with allostatic load.

claimPerturbation resistance potential (PRP) is defined as an individual's proximity to energetic crisis, which helps regulate circulating glucocorticoid levels.

claimNuclear mineralocorticoid receptors (MR) have high affinity but low capacity and become quickly saturated at lower glucocorticoid concentrations, whereas nuclear glucocorticoid receptors (GR) have a binding affinity an order of magnitude lower or more than MR and remain minimally occupied until hormone levels are elevated.

claimThe Perceived Resource Potential (PRP) describes the gap between allostatic load (Eload) and resource availability (Ecr), and is proposed to correlate with glucocorticoid levels rather than allostatic load itself.

claimArctic-breeding songbirds often display muted or no elevation in glucocorticoid levels in response to stressors during the nesting phase.

claimElevated glucocorticoid levels indicate a perception of perturbation and systemic activation of the ELHS, and are considered more reliable in less-responsive individuals favoring Type 2 error.

claimIn most species, glucocorticoid levels are elevated during Phase I and Phase III of starvation, but many species exhibit low glucocorticoid levels during Phase II, according to Cherel et al. (1988).

claimIn Strategy 2 of endocrine response, an animal maintains glucocorticoid levels near a seasonal baseline until Potential Resource Predictability (PRP) is critically low, at which point only a negative energy balance triggers the Emergency Life History Stage (ELHS).

claimResearchers can investigate how animals use environmental cues to determine when to elevate glucocorticoid levels by asking qualitative questions about which cues are ignored or responded to, and whether these cues change seasonally.

claimThe PRP describes the gap between allostatic load and resource availability, and is proposed to correlate with glucocorticoid levels rather than allostatic load itself.

referenceWord et al. (2022) suggest that the absence of a clear correlation between allostatic load and glucocorticoid levels in previous studies may be explained by cases where energetic requirements (Eg) are very high, causing changes in allostatic load to constitute only proportionally minor changes in the Potential Resource Pool (PRP).

claimElevated glucocorticoid levels indicate a perception of perturbation and systemic activation of the Emergency Life History Stage (ELHS). These levels are more reliable as an indicator in less-responsive individuals favoring Type 2 error, though Type 1 error in hormone response is propagated to the outcome.

referenceLandys et al. (2006) propose a model where basal glucocorticoid concentrations at which mineralocorticoid receptor (MR) occupancy occurs constitute 'level A', a state where glucocorticoid levels are low and MR binding occurs at an exponential rate.

claimArctic-breeding songbirds often display muted or no elevation in glucocorticoid levels in response to a stressor when nesting, as observed by Wingfield and Romero (2001) and Krause et al. (2018).

claimActivation of the 'emergency life-history stage' (ELHS), referred to as 'physiological state level C', occurs when glucocorticoid concentrations are consistently elevated above the seasonal norm for the life-history stage, which is referred to as 'physiological state level B'.

claimElevated glucocorticoid levels indicate a perception of perturbation and systemic activation of the Emergency Life History Stage (ELHS).

claimChronically elevated glucocorticoid levels in allostatic overload Type 2 are suggested to occur at the interface of physiological state levels B and C.

claimElevated glucocorticoid levels increase the probability that additional perturbations will lead to Emergency Life History Stage (ELHS) activation.

claimUnder Strategy 2, there is typically no observed correlation between Potential Resource Availability (PRP) and glucocorticoid levels under most conditions.

claimReplacing Eg with Ecr in the allostatic load model delays the occurrence of allostatic overload until Phase III starvation, which satisfies the requirement that overload occurs concurrently with elevated glucocorticoid levels.

Sleep Across the Lifespan: A Neurobehavioral Perspective link.springer.com Springer Feb 5, 2025 1 fact

claimLoneliness is linked to increased physiological arousal, specifically through the activation of the HPA axis, which regulates glucocorticoid levels and modulates the sleep-wake cycle.