Document Type

Thesis

Publication details

Mulder, AM 2011, 'An exploration of the acute stress response to psychological and physical stressors, utilising biomarkers of the cardiovascular, HPA, SAM and secretory immune systems', PhD thesis, Southern Cross University, Lismore, NSW.

Copyright AM Mulder 2011

Abstract

Current understanding of the biochemical changes associated with acute ‘stress’ is equivocal and unresolved. Whilst it has been hypothesised (Selye, 1976) that both psychological and physical stressors produce a non-specific stress response, it has also been suggested that psychological stress is common to a diversity of stressors, and that it is the psychological component that elicits the stress response (Mason, 1975b). To date, there appears no conclusive evidence to accept or refute either hypothesis. Therefore, the aim of this study was, by application of psychological and physical stressors to a single group of participants, and measurement of a variety of stress response biomarkers, to add further weight to either an acceptance or rejection of a non-specific stress response and the importance of emotional arousal.

Using a repeated measures design, 21 healthy young men (18-35 years) undertook one psychological stressor (the Trier Social Stress Test (TSST)), and two physical stressors (resistance exercise (RE) and the cold pressor (CP) task); each stressor condition separated by 7-14 days. The TSST consisted of a 5 minute speech and 5 minutes of mental arithmetic in front of an evaluative panel, the RE task consisted of 4 sets of 10 repetition maximum back squats performed on a Smith machine (10 minutes), while the CP consisted of the immersion of hands in 10oC water for 8 minutes. Multiple saliva samples were collected before and after each stressor task to assess stages of the response including the impact of anticipatory stress. Cortisol and dehydroepiandrosterone (DHEA) (markers of the hypothalamic-pituitary-adrenal (HPA) axis), secretory-IgA (S-IgA) and lactoferrin (the secretory immune system), cardiovascular activity and a- amylase (the sympathetic-adrenal-medullary (SAM) system) and state anxiety were measured at various times before and after the stressor task. State anxiety was determined using the Spielberger State Trait Anxiety Inventory, cortisol and DHEA were determined by commercial enzyme-linked immuno-sorbent assays (ELISA), whilst _-amylase was measured by an enzyme assay. Lactoferrin and S-IgA were measured by in-house purpose developed ELISAs, based on a direct sandwich ELISA incorporating a biotin-streptavidin labelled detecting antibody.

One-way ANOVA (*time), revealed significant increases in the psychological measure of state anxiety, and the biochemical measures of salivary cortisol and DHEA concentrations, and a-amylase, S-IgA and lactoferrin secretion rates, in response to all three stressors. These increases occurred, depending on the biomarker, before (anticipatory stress), during and after the stressor task. Significant increases in both heart rate and systolic BP occurred during the TSST and RE tasks but not the CP, whilst increases in diastolic BP occurred only in response to the TSST. In addition, significant decreases in salivary flow rate occurred in response to both the TSST and RE tasks but not the CP task.

Analysis by two-way ANOVA (stressor*time) and evaluation of the area-under-the-curve to increase (AUCi) revealed a statistically significant increase in the magnitude of the state anxiety response to the psychological stressor (TSST) compared to both the physical stressor (RE and CP) responses. In contrast, no significant differences were found between all three stressors in either the pattern or magnitude of the stress response for cortisol and DHEA concentrations, S-IgA and lactoferrin secretion rates, and salivary flow rates during the anticipatory, task or recovery phases; however a significant increase in the magnitude of the _-amylase secretion rate response to both the TSST and RE, compared to the CP, was found.

In conclusion, results show that the biochemical responses to the TSST, RE and CP were of the same pattern despite isolated differences in magnitude, suggesting that Selye’s hypothesis of a non-specific stress response is valid. Further, the significant impact of anticipatory stress and the measure of a significant psychological component to physical stressors, suggests that the psychological component of a stressor produces a major impact, implying that Mason’s observations were also accurate. Therefore this work proposes that the psychological component of stress is a major contributor to the stress response but remains far from being the only contributor to the common acute biochemical response to stress.

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