Differences in Salivary Alpha-Amylase and Cortisol Responsiveness following Exposure to Electrical Stimulation versus the Trier Social Stress Tests

Background

Cortisol is an essential hormone in the regulation of the stress response along the HPA axis, and salivary cortisol has been used as a measure of free circulating cortisol levels. Recently, salivary alpha-amylase (sAA) has also emerged as a novel biomarker for psychosocial stress responsiveness within the sympathetic adrenomedullary (SAM) system.

Principal Findings

We measured sAA and salivary cortisol in healthy volunteers after exposure to the Trier Social Stress Test (TSST) and electric stimulation stress. One hundred forty-nine healthy volunteers participated in this study. All subjects were exposed to both the TSST and electric stimulation stress on separate days. We measured sAA and salivary cortisol levels three times immediately before, immediately after, and 20 min after the stress challenge. The State (STAI-S) and Trait (STAI-T) versions of the Spielberger Anxiety Inventory test and the Profile of Mood State (POMS) tests were administered to participants before the electrical stimulation and TSST protocols. We also measured HF, LF and LF/HF Heart Rate Variability ratio immediately after electrical stimulation and TSST exposure. Following TSST exposure or electrical stimulation, sAA levels displayed a rapid increase and recovery, returning to baseline levels 20 min after the stress challenge. Salivary cortisol responses showed a delayed increase, which remained significantly elevated from baseline levels 20 min after the stress challenge. Analyses revealed no differences between men and women with regard to their sAA response to the challenges (TSST or electric stimulations), while we found significantly higher salivary cortisol responses to the TSST in females. We also found that younger subjects tended to display higher sAA activity. Salivary cortisol levels were significantly correlated with the strength of the applied electrical stimulation.

Conclusions

These preliminary results suggest that the HPA axis (but not the SAM system) may show differential response patterns to distinct kinds of stressors.     

Cortisol Response to Repeated Psychosocial Stress

Psychosocial stress plays a major role in the etiology and the course of mental disorders that often show an altered activation of the hypothalamus–pituitary–adrenal (HPA) axis. The Trier Social Stress Test (TSST) reliably activates the HPA axis and reflects real life stress exposure. However, habituation may confound the results of clinical trials that apply TSST. The present study investigates the cortisol response after repeated psychosocial stress induction with short-term and long-term intervals between repeated testing sessions. Forty-one healthy subjects were exposed to the TSST four times with an interval of 24 h between the first and the second testing session (t1 and t2). The 3rd and the 4th testing session (t3 and t4) were also separated by a 24-hour interval whereas there were 10 weeks between t2 and t3. A significant decrease in the salivary cortisol responses was noticed from testing session t1 to t2 as well as from testing session t3 to t4. By contrast, there were no differences in the HPA axis reactivity between testing session t2 and t3. Our results demonstrated the habituation of the HPA axis to a standardized psychosocial stress test when testing was repeated after 24 h. By contrast, a renewed challenge with a ten-week-interval in-between activated the HPA axis in a similar manner as before. It is suggested that studies designed to investigate the HPA axis activity under repeated psychosocial stress conditions should apply the TSST three times in order to separate habituation from intervention effects.     

The Reaction to Social Stress in Social Phobia: Discordance between Physiological and Subjective Parameters

Background

Research on the biopsychological background of social phobia (SP) is scarce and inconsistent. We investigated endocrine and autonomic markers along with subjective responses to a standardized stress situation (Trier Social Stress Test, TSST) in SP patients and healthy controls (HC).

Methods

We examined 88 patients with the primary diagnosis of SP as well as 78 age and sex comparable HCs with the TSST. Blood and saliva samples were obtained before and after the TSST for the assessment of salivary cortisol, plasma cortisol, salivary alpha-amylase (sAA), and prolactin. Heart rate (HR) and heart rate variability (HRV) were recorded continuously. Scalp-near hair samples were collected for the assessment of long-term cortisol secretion. The self-reported stress response was measured with different state and trait scales.

Results

While self-reported anxiety was elevated in SP before, during, immediately after, and one week after the TSST, no significant differences in biological stress responses were observed between SP and HC. There was a trend for SP to show higher baseline stress markers. Also long-term cortisol deposition in hair remained unaltered.

Conclusions

Our results suggest that the excessive self-reported stress in SP is not reflected by a respective biological stress response. Patients with SP apparently show neither an extreme form of focused fear reactivity nor excessive defensive impairment.     

Effects of affiliation arousal (hope of closeness) and affiliation stress (fear of rejection) on progesterone and cortisol

Our prior research has suggested a connection between progesterone (PROG) and implicit affiliation motivation, the non-conscious drive for positive social contact. In particular, experimental arousal of affiliation motivation led to relative PROG increase in women and men [Schultheiss, O.C., Wirth, M.M., Stanton, S.J., 2004. Effects of affiliation and power motivation arousal on salivary progesterone and testosterone. Horm. Behav. 46(5), 592-599]. The present study aimed to (1) replicate this effect, (2) simultaneously assess cortisol (CORT) levels in this paradigm in order to rule out non-specific adrenal effects induced by affiliation arousal, and (3) examine effects on PROG and CORT of approach (hope for closeness, HOC) versus avoidance (fear of rejection, FOR) affiliation arousal. These motivational states were experimentally aroused in participants using film segments containing approach- or avoidance-oriented affiliation-related themes; a neutral film segment was used as a control condition. The film segments affected participants' implicit affiliation motivation and self-reported mood, demonstrating effectiveness of the manipulation. In the FOR condition, participants' CORT and PROG were increased post-film, consistent with the idea that fear of rejection is stressful. We did not replicate our prior finding of PROG increase following the HOC manipulation. However, relationships between PROG and implicit affiliation motivation were apparent across conditions. In particular, PROG co-varied positively with affiliation motivation, and baseline affiliation motivation positively predicted PROG increase in the FOR condition. As prior research implicates PROG in down-regulation of stress, we speculate that PROG release during stress may encourage affiliation for stress reduction purposes.     

The combined dexamethasone/TSST paradigm--a new method for psychoneuroendocrinology

The two main physiological systems involved in the regulation of the stress response are the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). However, the interaction of these systems on the stress response remains poorly understood. To better understand the cross-regulatory effects of the different systems involved in stress regulation, we developed a new stress paradigm that keeps the activity of the HPA constant when exposing subjects to psychosocial stress. Thirty healthy male participants were recruited and randomly assigned to either a dexamethasone (DEX; n?=?15) or placebo (PLC; n?=?15) group. All subjects were instructed to take the Dexamethasone (2 mg) or Placebo pill the night before coming to the laboratory to undergo the Trier Social Stress Task (TSST). Salivary cortisol, salivary alpha amylase (sAA), heart rate, blood pressure and subjective stress were assessed throughout the protocol. As expected, the DEX group presented with suppressed cortisol levels. In comparison, their heart rate was elevated by approximately ten base points compared to the PLC group, with increases throughout the protocol and during the TSST. Neither sAA, nor systolic or diastolic blood pressures showed significant group differences. Subjective stress levels significantly increased from baseline, and were found to be higher before and after the TSST after DEX compared to placebo. These results demonstrate a significant interaction between the HPA and the SNS during acute stress. The SNS activity was found to be elevated in the presence of a suppressed HPA axis, with some further effects on subjective levels of stress. The method to suppress the HPA prior to inducing stress was found to completely reliable, without any adverse side effects. Therefore, we propose this paradigm as a new method to investigate the interaction of the two major stress systems in the regulation of the stress response.     

Implicit motives and gonadal steroid hormones: effects of menstrual cycle phase,oral contraceptive use,and relationship status

Implicit motives for power and affiliation, salivary levels of testosterone, estradiol, and progesterone, and relationship status were measured in 18 normally cycling (NC) women, 18 women using oral contraceptives (OC), and 18 men at three assessments, corresponding to the menstrual, midcycle, and premenstrual phases of women's menstrual cycle. NC and OC women had elevated levels of affiliation motivation and decreased levels of power motivation at midcycle. Power motive changes were particularly pronounced in NC women across cycle phases. OC women and participants not engaged in an intimate relationship had significantly heightened levels of affiliation motivation, averaged across all cycle phases. Testosterone and power motivation, both averaged across all cycle phases, were positively correlated in men and in single women, but not in women engaged in an intimate relationship. Averaged levels of estradiol and power motivation were positively correlated in engaged women, but not in single women or men. Averaged levels of progesterone and affiliation motivation were negatively correlated in men, and there was evidence for a positive association between luteal affiliation motivation and periovulatory and luteal progesterone in NC women. This study therefore provides evidence that implicit motivational states fluctuate across the menstrual cycle, that the power motive is associated with testosterone and, in women, with estradiol, and that the affiliation motive and progesterone are associated in different ways in men and NC women.     

Effects of affiliation and power motivation arousal on salivary progesterone and testosterone

Following up on earlier research suggesting a link between implicit affiliation motivation and progesterone (P) and implicit power motivation and testosterone [T; Schultheiss, O.C., Dargel, A., Rohde, W., 2003. Implicit motives and gonadal steroid hormones: Effects of menstrual cycle phase, oral contraceptive use, and relationship status. Horm. Behav. 43, 293-301.], we tested whether arousal of affiliation motivation increases P levels and whether arousal of power motivation increases T levels. Sixty subjects were randomly assigned to watch 30 min of either Bridges of Madison County (affiliation arousal) or The Godfather II (power arousal), or a documentary about the Amazon (control condition). Levels of P and T were assessed in saliva samples taken before (T1), immediately after (T2), and 45 min after the movie (T3). The efficacy of experimental conditions to differentially arouse motives was verified by assessment of changes in affiliation and power motive imagery expressed in imaginative stories written before and after the movie. After the movie, salivary P levels (T2 and T3) in the affiliation-arousal group were significantly higher than in the control group and marginally higher than in the power-arousal group. Subjects' postmovie T responses (T3) depended on premovie T levels: in men, higher premovie T levels predicted a greater likelihood of postmovie T increases in the Power Arousal condition but not in the other conditions, whereas in women, higher premovie T levels tended to be associated with postmovie T decreases in the Power Arousal condition but not in the other conditions. These findings suggest that aroused affiliation motivation has a specific stimulatory effect on P, whereas aroused power motivation has a specific stimulatory effect on T in men, but not in women, with high baseline T levels.     

Hippocampal damage abolishes the cortisol response to psychosocial stress in humans

The hippocampus (HC) is necessary for learning and memory, but it also plays a role in other behaviors such as those related to stress and anxiety. In support of the latter idea, we show here that bilateral HC damage abolishes the cortisol response to psychosocial stress. We collected salivary cortisol, heart rate, and affective responses to the Trier Social Stress Test (TSST) from 7 participants with bilateral HC lesions, 12 participants with damage outside the HC, and 28 healthy normal comparison participants matched to the HC participants on age and sex. HC participants showed elevated pre-stress cortisol, but no cortisol response to the TSST. Heart rate and affective responses in the HC group were similar to those of the comparison groups. Participants with brain damage outside the HC showed stress responses that were comparable to those of the healthy comparison group. These findings support the idea that the functions of the human HC extend beyond learning and memory, and suggest that the HC is necessary for producing the cortisol response to psychosocial stress.     

Immune responses to stress after stress management training in patients with rheumatoid arthritis

Introduction

Psychological stress may alter immune function by activating physiological stress pathways. Building on our previous study, in which we report that stress management training led to an altered self-reported and cortisol response to psychological stress in patients with rheumatoid arthritis (RA), we explored the effects of this stress management intervention on the immune response to a psychological stress task in patients with RA.

Methods

In this study, 74 patients with RA, who were randomly assigned to either a control group or a group that received short stress management training, performed the Trier Social Stress Test (TSST) 1 week after the intervention and at a 9-week follow-up. Stress-induced changes in levels of key cytokines involved in stress and inflammatory processes (for example, interleukin (IL)-6 and IL-8) were assessed.

Results

Basal and stress-induced cytokine levels were not significantly different in patients in the intervention and control groups one week after treatment, but stress-induced IL-8 levels were lower in patients in the intervention group than in the control group at the follow-up assessment.

Conclusions

In line with our previous findings of lower stress-induced cortisol levels at the follow-up of stress management intervention, this is the first study to show that relatively short stress management training might also alter stress-induced IL-8 levels in patients with RA. These results might help to determine the role of immunological mediators in stress and disease.

Trial registration

The Netherlands National Trial Register (NTR1193)     

The stress-response-dampening effects of placebo

This experiment used both biological and self-report measures to examine how alcohol modifies stress responses, and to test whether the interaction between these two factors alters risk-taking in healthy young adults. Participants were divided into stress or no-stress conditions and then further divided into one of three beverage groups. The alcohol group consumed a binge-drinking level of alcohol; the placebo group consumed soda, but believed they were consuming alcohol; the sober group was aware that they were not consuming alcohol. Following beverage consumption, the stress group was subjected to the Trier Social Stress Test (TSST) while the no-stress group completed crossword puzzles; all participants subsequently completed a computerized risk-taking task. Exposure to the TSST significantly increased salivary levels of the hormone cortisol and the enzyme alpha-amylase, as well as subjective self-ratings of anxiety and tension. In the stress condition, both placebo and intoxicated groups reported less tension and anxiety, and exhibited a smaller increase in cortisol, following the TSST than did the sober group. Thus, the expectation of receiving alcohol altered subjective and physiological responses to the stressor. Neither alcohol nor stress increased risk taking, however the sober group demonstrated lower risk-taking on the computer task on the second session. These findings clearly demonstrate that the expectation of alcohol (placebo) alters subsequent physiological responses to stress.     

No response of plasma substance P, but delayed increase of interleukin-1 receptor antagonist to acute psychosocial stress

Psychosocial stress has been shown to induce inflammatory reactions, followed by the release of immunosuppressive glucocorticoids. This may be mediated by catecholamines or other stress reactive substances such as neuropeptides or cytokines. We here set out to explore the effects of acute psychosocial stress on plasma levels of substance P (SP), a possible mediator of stress-induced inflammatory reactions, and interleukin-1 receptor antagonist (IL-1ra). Twelve healthy male subjects (mean age 27 yrs.) were subjected to the psychosocial stress test "Trier Social Stress Test" (TSST) and a resting control condition. Blood and saliva samples were taken before, as well as 1, 20, 45, and 90 min after TSST or rest, respectively. Salivary cortisol and plasma SP and IL-1ra were measured using immunoassays, salivary alpha-amylase (sAA) was measured by an enzyme kinetic method, and plasma epinephrine (E) and norepinephrine (NE) were measured by HPLC. The TSST induced immediate increases of E, NE, and sAA, and a delayed increase of free cortisol. Plasma IL-1ra showed an even further delayed peak at 90 min after stress. Plasma levels of SP did not respond to stress. No significant associations between changes of stress hormones and IL-1ra or SP were found. We conclude that substance P, epinephrine, and norepinephrine are probably not involved in mediating peripheral inflammation following psychosocial stress, at least with respect to IL-1ra. Further studies have to reveal the mechanisms involved in the stress-induced up regulation of IL-1ra.     

Psychosocial Stress Increases Salivary Alpha-Amylase Activity Independently from Plasma Noradrenaline Levels

Salivary alpha-amylase activity (sAA) and plasma noradrenaline (NA) concentrations are often considered to be surrogate markers of sympathetic activation in response to stress. However, despite accumulating evidence for a close association between sAA and noradrenaline and other indicators of sympathetic activity, reliability and generality of this relation remains unclear. We employed the Trier Social Stress Test (TSST) in order to directly compare the responses in sAA and NA to psychological stress in healthy volunteers (n = 23). The TSST significantly increased sAA and NA plasma levels with no significant differences in females and males. However, when subjects were divided according to their NA responses into low versus high responders, both groups did not significantly differ in their sAA before, during or after stress exposure. These data suggest that in response to acute psychological stress both plasma NA levels and sAA reflect sympathetic activity, however seemed to increase independently from each other.     

Prenatal exposure to maternal psychosocial stress and HPA axis regulation in young adults

Epidemiological studies have reported associations between measures of size and weight at birth and disease risk in later life. Alteration in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis in response to prenatal stress has been proposed as one underlying mechanism. The present study investigated in humans the association of prenatal psychosocial stress exposure with subsequent HPA axis regulation in adult life, with a focus on measures of response to challenge and feedback sensitivity. Healthy young adults whose mothers experienced severe stress during their pregnancy in form of major negative life events (e.g. death of someone close; prenatal stress (PS) group, n = 31) and an age-matched comparison group (CG, n = 30) underwent the Trier Social Stress Test (TSST) and a 1 μg ACTH_1-24 stimulation test. In addition, a diurnal cortisol profile was assessed. ACTH concentrations following a standardized behavioural challenge paradigm (TSST) were marginally significantly higher in PS subjects than in CG subjects (p = .06). Pre-TSST adrenocortical (cortisol) levels were lower (p = .007), whereas the increase in cortisol in response to the TSST was higher (p = .03) in PS subjects compared to CG subjects. Cortisol concentrations following a pharmacological stimulation test simulating pituitary activity (ACTH_1-24 test) were significantly lower in PS than in CG subjects (p = .006). No differences emerged between the two groups in basal diurnal cortisol levels. This study provides first evidence in humans of an association between prenatal psychosocial stress exposure and subsequent alterations in the regulation of the HPA axis.     

Psychosocial stressor effects on cortisol and ghrelin in emotional and non-emotional eaters: Influence of anger and shame

Food consumption in stressful situations vary as a function of individual difference factors (e.g., emotional vs. non-emotional eating), and may be related to hormonal responses elicited by the stressful event. These hormonal responses may be tied to specific emotions elicited by the stressful event. The present investigation examined the emotional and hormonal (cortisol, ghrelin) responses of high and low emotional eaters following a laboratory stressor (Trier Social Stress Test; TSST). Women (n = 48) either high or low in emotional eating status were tested in a TSST or served as controls during which blood samples were taken for analysis of cortisol and ghrelin, both of which have been implicated in eating and in response to stressors. The TSST promoted elevated cortisol levels, being somewhat more pronounced in emotional than in non-emotional eaters. Both shame and anger were provoked by the TSST, and although both these emotions were correlated with cortisol levels, only anger significantly mediated the relationship between the stressor and cortisol levels. As well, baseline ghrelin levels in low emotional eaters exceeded that of high emotional eaters, and increased moderately in response to the stressor situation, irrespective of emotional eating status. Interestingly, when provided with food, ghrelin levels declined in the non-emotional eaters, but not in emotional eaters. The possibility is offered that the lack of a decline of ghrelin in emotional eaters may sustain eating in these individuals.     

Effect of Rhinovirus Challenge on Antioxidant Enzymes in Respiratory Epithelial Cells

The host inflammatory response appears to be an important contributor to the pathogenesis of human viral respiratory illness. Virus-induced oxidative stress appears to mediate an early phase of elaboration of the proinflammatory cytokine interleukin-8 by respiratory epithelial cells. The purpose of these studies was to determine if virus-induced alterations in either the expression or function of antioxidant enzymes contributes to the cellular oxidative stress following rhinovirus challenge. The activities of Mn superoxide dismutase (MnSOD), catalase and glutathione peroxidase (GPX) were not significantly changed by rhinovirus challenge. CuZn superoxide dismutase (CuZnSOD) activity six hours after challenge was 2.55 &#45 0.56 U/mg protein in rhinovirus-challenged cells compared to 1.16 &#45 0.54 U/mg protein in control cells ( p =0.029). This increased activity was associated with a concomitant increase in CuZnSOD mRNA and protein concentration. These data suggest that rhinovirus-induced changes in the host cell redox state that result in the early elaboration of interleukin-8 are not mediated by inhibition of either the expression or function of these antioxidant enzymes.     

Bonobos Protect and Console Friends and Kin

Post-conflict third-party affiliation has been reported to have different functional meanings, one of them being consolation. Here, we tested the main hypotheses that have been put forth to explain the presence of this phenomenon at a functional level in the bonobo: Self-Protection Hypothesis, Victim-Protection Hypothesis, Relationship-Repair or Substitute for Reconciliation Hypothesis, and Consolation Hypothesis. By analyzing the data collected over 10 years, we investigated what factors affected the distribution of both spontaneous third party affiliation (initiated by the bystander) and solicited third party affiliation (initiated by the victim). We considered factors related to the individual features (sex, rank, age) of victim and bystander, their relationship quality (kinship, affiliation), and the effect that third party affiliation had on the victim (such as protection against further attacks and anxiety reduction). Both spontaneous and solicited third party affiliation reduced the probability of further aggression by group members on the victim (Victim-Protection Hypothesis supported). Yet, only spontaneous affiliation reduced victim anxiety (measured via self-scratching), thus suggesting that the spontaneous gesture – more than the protection itself – works in calming the distressed subject. The victim may perceive the motivational autonomy of the bystander, who does not require an invitation to provide post-conflict affiliative contact. Moreover, spontaneous - but not solicited - third party affiliation was affected by the bond between consoler and victim, being the relationship between consoler and aggressor irrelevant to the phenomenon distribution (Consolation Hypothesis supported). Spontaneous affiliation followed the empathic gradient described for humans, being mostly offered to kin, then friends, then acquaintances. Overall, our findings do not only indicate the consolatory function of spontaneous third-party affiliation but they also suggest that consolation in the bonobo may be an empathy-based phenomenon.     

Vasopressin needs an audience: neuropeptide elicited stress responses are contingent upon perceived social evaluative threats

The nonapeptide arginine vasopressin (AVP) plays an important role in hypothalamus-pituitary-adrenal axis regulation and also functions as a social hormone in a wide variety of species, from voles to humans. In the current report we use a variety of stress inducing tasks, including the Trier Social Stress Test (TSST) and intranasal administration of AVP to show that intranasal administration of this neuropeptide leads to a significant increase in salivary cortisol and pulse rate, specifically in conditions where subjects perform tasks in the presence of a social evaluative threat (task performance could be negatively judged by others). In contrast, in conditions without a social evaluative threat (no task condition, modified TSST without audience and bike ergometry), subjects receiving AVP did not differ from subjects receiving placebo. Thus exogenous AVP's influence is contingent upon a circumscribed set of initial conditions that constitute a direct threat to the maintenance of our social selves. Stress evoked by social threat is an integral part of social life and is related to self-esteem and in extreme forms, to poor mental health (e.g., social phobia). Our findings suggest that AVP is a key component in the circuit that interlaces stress and social threat and findings offer inroads to our understanding of individual differences in sociability and in stress response elicited in threatening social situations.     

Predicting cortisol stress responses in older individuals: influence of serotonin receptor 1A gene (HTR1A) and stressful life events

Considerable variability in the activity of the hypothalamus-pituitary-adrenal (HPA) axis in response to stress has been found in quantitative genetic studies investigating healthy individuals suggesting that at least part of this variance is due to genetic factors. Since the HPA axis is regulated by a neuronal network including amygdala, hippocampus, prefrontal cortex as well as brainstem circuits, the investigation of candidate genes that impact neurotransmitter systems related to these brain regions might further elucidate the genetic underpinnings of the stress response. However, aside from genetic risk factors, past stressful life events might also result in long-term adjustments of HPA axis reactivity. Here, we investigated the effects of the − 1019 G/C polymorphism in the HTR1A gene encoding the serotonin (5-HT) receptor 1A (5-HT_1A) and stressful life events experienced during childhood and adolescence on changes in cortisol levels in response to the Trier Social Stress Test (TSST) in a sample of healthy older adults (N = 97). Regression analyses revealed a significant effect of HTR1A genotype with the G allele being associated with a less pronounced stress response. In addition, an inverse relationship between past stressful life events and cortisol release but no gene × environment interaction was detected. The results further underscore the crucial role of functional serotonergic genetic variation as well as stressful events during critical stages of development on the acute stress response later in life.     

Glucose but not protein or fat load amplifies the cortisol response to psychosocial stress

We previously reported that glucose intake amplifies cortisol response to psychosocial stress and smoking in healthy young men, while low blood glucose levels prevented the stress-induced activation of the hypothalamus pituitary adrenal (HPA) axis. However, it remains unknown whether this modulation is specific for glucose load or a more common effect of energy availability. To elucidate this question, 37 healthy men, who fasted for at least 8 h before the experiment, were randomly assigned to four experimental groups, who received glucose (n = 8), protein (n = 10), fat (n = 10), and water (n = 9), one h before their exposure to the Trier Social Stress Test (TSST). Blood glucose levels were measured at baseline and following stress, while salivary cortisol was assessed repeatedly measured before after the TSST. The results show that both absolute cortisol levels and net cortisol increase were greater in the glucose group in comparison to the other groups (F(3,33) = 3.00, P < 0.05 and F(3,33) = 3.08, P < 0.05, respectively. No group differences were observed with respect to perceived stress and mood. Furthermore, the cortisol response was positively correlated with blood glucose changes (r = 0.49, P < 0.002). In conclusion, the results suggest a central mechanism responsible for regulation of energy balance and HPA axis activation, rather than peripheral mechanisms. We thus recommend controlling for blood glucose levels when studying HPA axis responsiveness.