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.     

The effect of rearing experience and TPH2 genotype on HPA axis function and aggression in rhesus monkeys: A retrospective analysis

Gene-environment (G × E) interactions contribute to the development of many neuropsychiatric disorders. Tryptophan hydroxylase-2 (TPH2) synthesizes neuronal serotonin and is closely related to the hypothalamic-pituitary-adrenal (HPA) axis, while early life experience is a critical environmental factor programming the HPA axis response to stress. This retrospective study investigated G × E interaction at the TPH2 locus in rhesus monkeys. Twenty-eight adult, male rhesus monkeys of Indian origin, either mother-reared or peer-reared as infants, were involved in this study. These monkeys have been previously genotyped for the functional A2051C polymorphism in rhTPH2, and had been physiologically and behaviorally characterized. rhTPH2 A2051C exerted a significant main effect (CC > AA&AC) on the cerebrospinal fluid (CSF) level of 5-hydroxyindole-3-acetic acid (5-HIAA; F_(1,14) = 6.42, p = 0.024), plasma cortisol level in the morning (F_(1,18) = 14.63, p = 0.002) and cortisol response to ACTH challenge (F_(1,17) = 6.87, p = 0.018), while the rearing experience showed a significant main effect (PR > MR) on CSF CRH (F_(1,20) = 11.66, p = 0.003) and cage shaking behavior (F_(1,27) = 4.45, p = 0.045). The effects of rhTPH2 A2051C on the afternoon cortisol level, plasma ACTH level, dexamethasone suppression of urinary cortisol excretion, and aggression were dependent upon the rearing experience. These results were not confounded by the functional C77G polymorphism in the mu-opioid receptor (MOR). The present study supports the hypothesis that rearing experience and rhTPH2 A2051C interact to influence central 5-HT metabolism, HPA axis function, and aggressive behaviors. Our findings strengthen the involvement of G × E interactions at the loci of serotonergic genes and the utility of the nonhuman primate to model G × E interactions in the development of human neuropsychiatric diseases.     

Alterations of postawakening cortisol parameters during a prolonged stress period: Results of a prospective controlled study

Though postawakening cortisol is considered to be altered under chronic stress prospective studies proving this assumption is missing, so far. Furthermore, there is some uncertainty which aspects of postawakening cortisol alterations are strongest related to stress. The present study thus analyzed the cortisol concentration at awakening itself (0 min), the cortisol awakening response (CAR; i.e. the increase within 30 min after awakening), the area under the curve of the first hour after awakening (AUC_G60) and the mean of samples taken 0 min and 30 min after awakening (AUC_G30) in 12 exam students, participating in a major exam and 12 matched control students not participating in any exam. Saliva samples were taken on two consecutive days at 0, 15, 30, 45, and 60 min after awakening, respectively, at four time points (T1-T4): on the verge of exams, when students anticipated and prepared the exam (T1), in the middle of exams (T2), and shortly after (T3). T4 (weeks after exams) represents a reference measure. Repeated measures analyses of covariance revealed a significantly higher AUC_G30 (p = 0.007) and AUC_G60 (p = 0.011) and higher cortisol concentrations at awakening (p = 0.016) in exam students and a significant time by group interaction for concentration at awakening (p = 0.031). No effects were found for the CAR. The results of this prospective controlled study support notions that chronic stress induces increases of overall postawakening cortisol. They further indicate that the CAR is not affected by chronic stress and that the awakening concentration responds later than the AUC_G to conditions of chronic stress as analyzed here.     

Negative relationships in the family-of-origin predict attenuated cortisol in emerging adults

Negative childhood family environments have been associated with stress-related physical and psychological health consequences across the lifespan. The present study examined the relation between adverse relationships in the family of origin and physiological stress response, as measured by salivary cortisol, in emerging adulthood. Seventy-six university students (age range = 18-22) selected from intact married families-of-origin characterized by either negative (n = 39) or positive (n = 37) relationship quality engaged in a challenging role play task. Results from multilevel models indicated that those from negative families exhibited significantly lower salivary cortisol across the task than those from positive families. This relation did not change in strength or direction after controlling for experiences with abuse or recent anxiety or depressive symptoms. These findings suggest the significance of early family relationships on the long-term activity of the HPA axis.     

Relationship between change in core temperature and change in cortisol and TNFα during exercise

The combined thermal load created by exercise and a hot environment is associated with an exaggerated core temperature response. The elevated core temperature is believed to increase the total stress of the exercise. Increased stress during exercise has been associated with increased levels of cortisol. The association of cortisol with increased inflammatory responses following exercise in the heat is equivocal. Thus, the purpose of the current investigation was to explore the relationship between increases in rectal temperature (T_re) and TNFα and cortisol. To induce T_re changes, 8 male subjects (mean±SD, age=23.6±2 yr, VO₂max=52.8±3.7 mL/kg/min, BMI=24.2±1.9) participated in two 40 min trials of cycle ergometry at 65% of VO₂peak immersed to chest level in cool (25 °C) and warm (38.5 °C) water. T_re was monitored throughout each trial, with blood samples taken immediately pre and post of each trial. Neither cortisol nor TNFα changed significantly during exercise in the cool water; however, in the warm trial, both cortisol and TNFα significantly increased (p<0.004). Concordance correlations (R_c) between Δ cortisol and Δ TNFα indicated a strong but non-significant correlation (R_c=0.833, p=0.135). In conclusion, changes in core temperature may be impacting the relationship between exercise induced changes in cortisol and TNFα. Therefore, acute moderate-intensity exercise (40 min or less) in warm water impacts the stress and inflammatory response. Understanding this is important because exercise load may need to be adjusted in warm and hot environments to avoid the negative effects of elevated stress and inflammation response.     

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.     

In utero cortisol and testosterone exposure and fear reactivity in infancy

Fetal programming is emerging as a major conceptual model for understanding developmental origins of health and disease, including behavioral outcomes. As part of a larger study of prenatal stress and child development, we examined the association between prenatal hormone exposure and fear reactivity, a temperament dimension that is a predictor of long-term behavioral adjustment. Amniotic fluid was collected from a sample of women undergoing clinically indicated amniocentesis for later analysis of cortisol and testosterone. Children with normal birth outcomes were recalled for follow-up assessment at 17 months, at which time we administered an observational assessment of temperament (lab-TAB; n = 108). Information on pregnancy and obstetric outcome was included as covariates. Results indicated that there was a significant association between prenatal testosterone and observed fear reactivity in boys (r(53) = 0.34, p = 0.01); no significant effect was found in girls (r(54) = − 0.07, ns); the effect remained when obstetric, psychosocial, and parental anxiety were controlled for. There was not a significant association between fetal cortisol exposure and fear reactivity. The prediction from in utero testosterone exposure to fear reactivity in boys extends prior research on prenatal testosterone and may represent an association with a general predisposition to greater arousal and reactivity.     

Increased urinary glucocorticoid metabolites are associated with metabolic syndrome, hypoadiponectinemia, insulin resistance and β cell dysfunction

Metabolic syndrome (MetS) may have increased cortisol (F) production caused by 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in liver and adipose tissue and/or by HPA axis dysregulation. F is then mainly metabolized by liver reductases into inactive tetrahydrometabolites (THMs). We measured THM levels in patients with or without MetS and evaluate the correlation between THMs and anthropometric and biochemical parameters. We recruited 221 subjects, of whom 130 had MetS by ATP III. We evaluated F, cortisone (E), adipokines, glucose, insulin and lipid profiles as well as urinary (24 h) F, E and THM levels. β Cell function was estimated by the HOMA Calculator. We observed that patients with MetS showed higher levels of THMs, HOMA-IR and leptin and lower levels of adiponectin and HOMA-β but no differences in F and E in plasma or urine. THM was associated with weight (r = +0.44, p < 0.001), waist circumference (r = +0.38, p < 0.01), glycemia (r = +0.37, p < 0.01), and triglycerides (r = +0.18, p = 0.06) and negatively correlated with adiponectin (r = −0.36, p < 0.001), HOMA-β (r = −0.21, p < 0.001) and HDL (r = −0.29, p < 0.01). In a logistic regression model, THM levels were associated with hypertension, hyperglycemia and dyslipidemia. We conclude that MetS is associated with increased urinary THMs but not with F and E levels in plasma or urine. Increased levels of THM, reflecting the daily cortisol production subsequently metabolized, are correlated with hypoadiponectinemia, hypertension, dyslipidemia, insulin resistance and β cell dysfunction. A subtle increased in glucocorticoid production may further account for the phenotypic and biochemical similarities observed in central obesity and Cushing’s syndrome.     

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.     

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.     

Abolished circadian rhythm of salivary cortisol in elite artistic gymnasts

Objective

The aim of this study was to evaluate the effects of intensive physical exercise and acute psychological stress during high level athletic competition as reflected on the levels of salivary cortisol in elite artistic gymnasts (AGs).

Design

The study included 239 AGs (142 females-97 males) who participated in the European Championship of Gymnastics in 2006 and 81 adolescents (40 females-41 males), matched for age, as controls. All athletes participated voluntarily in all or parts of the study, providing samples or data for each of the variables measured. Height, weight, body fat, lean body mass (LBM), bone age and Tanner stage of puberty were assessed and data concerning the time of thelarche, adrenarche and menarche as well as, the onset and the intensity (hours per week) of training were obtained.

Methods

Saliva samples were collected, the morning before training and in the afternoon shortly after the competition. From controls, the saliva samples were collected in the morning. Cortisol concentrations were measured using a chemiluminescence method. Acute stress was assessed using a questionnaire designed for the study.

Results

No difference was found between morning and afternoon salivary cortisol levels in both male and female AGs (females: AM: 15.45 ± 7.45 nmol/l vs PM: 15.73 ± 9.38 nmol/l; males: AM: 10.21 ± 5.52 nmol/l vs PM: 9.93 ± 13.8 nmol/l, p > 0.05).Female AGs presented higher levels of morning salivary cortisol than female controls (p < 0.05). Both male and female AGs had higher degree of psychological stress in comparison with controls (p < 0.001, p < 0.013, respectively). Female AGs had higher morning and afternoon salivary cortisol levels (p < 0.01, p < 0.01, respectively) and higher degree of stress (p < 0.003) than males.

Conclusions

In elite AGs the diurnal rhythm of salivary cortisol has been abolished, probably due to the strenuous training and competition conditions. Female AGs presented higher levels of morning salivary cortisol and psychological stress compared to both male AGs and female controls. The long term consequences of these modifications of the HPA axis remain to be elucidated.     

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.     

High Cardiorespiratory Fitness Is Negatively Associated with Daily Cortisol Output in Healthy Aging Men

Physical fitness has salutary psychological and physical effects in older adults by promoting neuroplasticity and adaptation to stress. In aging, however, the effects of fitness on the hypothalamic-pituitary-adrenal (HPA) axis are mixed. We investigated the association between cardiorespiratory fitness and HPA activity in healthy elderly men (n = 22, mean age 68 y; smokers, obese subjects, those taking drugs or reporting recent stressful events were excluded), by measuring in saliva: i) daily pattern of cortisol secretion (6 samples: 30’ post-awakening, and at 12.00, 15.00, 18.00, 21.00, 24.00 h); and ii) the cortisol response to a mental challenge. Cardiorespiratory fitness (VO_2max) was estimated using the Rockport Walking Test and the participants were assigned to high-fit (HF, ≥60°, n = 10) and low-fit (LF, ≤35°, n = 12) groups according to age-specific percentiles of VO_2max distribution in the general population. At all daytimes, basal cortisol levels were lower in the HF than the LF group, most notably in the evening and midnight samples, with a significant main effect of physical fitness for cortisol levels overall; the area-under-the-curve for total daily cortisol output was significantly smaller in the HF group. Among the subjects who responded to mental stress (baseline-to-peak increment >1.5 nmol/L; n = 13, 5 LF, 8 HF), the amplitude of cortisol response and the steepness of recovery decline displayed an increasing trend in the HF subjects, although between-group differences failed to reach the threshold for significance. In conclusion, cardiorespiratory fitness in healthy aging men is negatively correlated with daily cortisol output and contributes to buffering the HPA dysregulation that occurs with advancing age, thus possibly playing a beneficial role in contrasting age-related cognitive and physical decline.     

Combined effect of oxidative stress-related gene polymorphisms on atherosclerosis

It is well known that oxidative stress plays critical roles in the pathogenesis of atherosclerosis. In this study, we enrolled 1746 type 2 diabetic subjects, determined 4 common genetic variants related to oxidative stress (glutamate-cysteine ligase modifier subunit (GCLM) C-588T, myeloperoxidase G-463A, human paraoxonase 1 Gln192Arg and NAD(P)H oxidase p22phox C242T polymorphisms), and measured carotid intima-media thickness (IMT) as a surrogate marker for atherosclerosis. GCLM C-588T polymorphism was associated with average IMT (AveIMT) (r = 0.090, p = 0.0008), but the association between the other 3 polymorphisms and AveIMT did not reach the statistical significance. However, AveIMT was significantly greater as the total number of 4 concomitant “pro-oxidant alleles” in each subject was increased (r = 0.108, p < 0.0001). Furthermore, the number of “pro-oxidant alleles” was a risk factor for a high AveIMT independently of conventional risk factors (p = 0.0003). In conclusion, accumulation of oxidative stress-associated alleles was associated with carotid atherosclerosis in type 2 diabetic patients.     

Acculturation, childhood trauma and the cortisol awakening response in Mexican-American adults

Exposure to chronic and traumatic stress has been associated with the dysregulation of crucial stress response systems. Acculturation has been associated with unique forms of chronic psychosocial stress. The purpose of this study was to examine the effects of exposure to early traumatic stress and acculturation on dysregulation of the cortisol awakening response (CAR) in Mexican-American adults. Salivary cortisol samples were collected at awakening and 30, 45, and 60 min thereafter, on two consecutive weekdays from 59 healthy Mexican-American adult males (26) and females (33), ages 18-38 years. Participants were assessed for level of acculturation and exposure to early trauma. Data were analyzed using a mixed effects regression model with repeated measures at four time points. Mixed effects regression results indicated a significant Early Trauma × Time interaction (p = .0029) and a significant Acculturation × Time interaction (p = .0015), after controlling for age and sex. Subsequent analyses of the interaction of Trauma × Acculturation × Time showed that more than minimal exposure to either risk factor was associated with attenuation of the awakening cortisol response (p = .0002). Higher levels of acculturation with greater Anglo-orientation were associated with attenuation of the CAR in Mexican-American adults. Both moderate and higher levels of exposure to early trauma were associated with an attenuated CAR. However, greater exposure to both risk factors was only incrementally worse than exposure to either one.     

Urinary free cortisone, but not cortisol, is associated with urine volume in severe obesity

Background

High urine volume enhances urinary free cortisol (UFF) and cortisone (UFE) excretion rates in normal-weight adults and children. Renal excretion rates of glucocorticoids (GC) and their metabolites are frequently altered in obesity. The aim of the present study was to investigate whether UFF and UFE excretion is also affected by urine volume in severely obese subjects.

Experimental

In 24-h urine samples of 59 extremely obese subjects (mean BMI 45.3 ± 8.9 kg/m²) and 20 healthy lean subjects (BMI 22.1 ± 1.8 kg/m²), UFF and UFE, tetrahydrocortisol (THF), 5α-tetrahydrocortisol (5α-THF), and tetrahydrocortisone (THE) were quantified by RIA. The sum of THF, 5α-THF, and THE (GC3), the three major GC metabolites, reflects daily cortisol secretion. 11β-Hydroxysteroid dehydrogenase type 2 (11β-HSD2) activity was assessed by the ratio UFE/UFF. Daily GC excretion rates were corrected for urine creatinine and adjusted for gender and body weight.

Results

In extremely obese subjects, urine volume was significantly associated with creatinine-corrected UFE and 11β-HSD2 activity after adjustment for gender and BMI (r = 0.47, p = 0.0002 and r = 0.31, p = 0.02, respectively). However, urine volume was not associated with creatinine-corrected UFF and GC3 (p = 0.4 and p = 0.6, respectively). In lean controls, urine volume was significantly associated with creatinine-corrected UFE and UFF (r = 0.58, p = 0.01 and r = 0.55, p = 0.02, respectively), whereas urine volume was not associated with 11β-HSD2 activity after appropriate adjustment (p = 0.3).

Conclusions

In severe obesity, in contrast to normal weight, renal excretion of UFE, but not of UFF is affected by fluid intake. This discrepancy may be due to the increased renal 11β-HSD2 activity in obesity.     

Effects of Echinaforce treatment on ex vivo-stimulated blood cells

The herb Echinacea purpurea, also called purple coneflower, is regarded as an immune modulator. This study examined changes in cytokine production in blood samples from 30 volunteers before and during 8-day oral administration with an ethanolic extract of fresh Echinacea purpurea (Echinaforce^®). Daily blood samples were ex vivo stimulated by LPS/SEB or Zymosan and analysed for a series of cytokines and haematological and metabolic parameters. Treatment reduced the proinflammatory mediators TNF-α and IL-1β by up to 24% (p < 0.05) and increased anti-inflammatory IL-10 levels by 13% (p < 0.05) in comparison to baseline. This demonstrated a substantial overall anti-inflammatory effect of Echinaforce^® for the whole group (n = 28). Chemokines MCP-1 and IL-8 were upregulated by 15% in samples from subjects treated with Echinaforce^® (p < 0.05). An analysis of a subgroup of volunteers who showed low pre-treatment levels of the cytokines MCP-1, IL-8, IL-10 or IFN-γ (n = 8) showed significant stimulation of these factors upon Echinaforce^® treatment (30-49% increases; p < 0.05), whereas the levels in subjects with higher pre-treatment levels remained unaffected. We chose the term “adapted immune-modulation” to describe this observation. Volunteers who reported high stress levels (n = 7) and more than 2 colds per year experienced a significant transient increase in IFN-γ upon Echinaforce^® treatment (>50%). Subjects with low cortisol levels (n = 11) showed significant down-regulation of the acute-phase proteins IL1-β, IL-6, IL-12 and TNF-α by Echinaforce^® (range, 13-25%), while subjects with higher cortisol levels showed no such down-regulation. This is the first ex vivo study to demonstrate adapted immune-modulation by an Echinacea preparation. While Echinaforce^® did not affect leukocyte counts, we speculate that the underlying therapeutic mechanism is based on differential multi-level modulation of the responses of the different types of leukocytes. Echinaforce^® thus regulates the production of chemokines and cytokines according to current immune status, such as responsiveness to exogenous stimuli, susceptibility to viral infection and exposure to stress.     

Raft-like domain formation in large unilamellar vesicles probed by the fluorescent phospholipid analogue, C12NBD-PC

The liquid-ordered/disordered-phase domain co-existence in large unilamellar vesicle membranes consisting of phosphatidylcholine:sphingomyelin (2:1) with different amounts of cholesterol has been examined using a concentration-dependent self-quenching of a single reporter molecule, C12NBD-PC. A temperature-dependent decrease of fluorescence intensity was associated with the expected formation and increase of l_o-phase membrane fraction in the vesicles. The result is consistent with exclusion of the fluorescent probe from the liquid-ordered phase which partitions preferentially into the liquid-disordered phase membrane domains. This leads to an increase of the local concentration of fluorophore in the liquid-disordered phase and a decrease of the quantum yield. This effect was used to obtain a quantitative estimation of the fraction of the vesicle membrane occupied by the liquid-ordered phase, Φ_o, as a function of temperature and cholesterol content between 0 and 45 mol%. The value of Φ_o was related to the assumed partition coefficient k_p of probe between liquid-ordered/disordered phases. For large unilamellar vesicles containing 20 and 4 mol% cholesterol and probe, respectively, with k_p = 0 (probe completely excluded from liquid-ordered phase), Φ_o = 0.16 and with k_p = 0.2, Φ_o = 0.2. The results are relevant to the action of detergent in the fractionation of detergent-resistant membrane from living cells.     

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.     

The interface of hypothalamic–pituitary–adrenocortical axis and circulating brain natriuretic peptide in prediction of cardiopulmonary performance during physical stress

Brain natriuretic peptide (NT-pro-BNP) was implicated in the regulation of hypothalamic–pituitary–adrenocortical (HPA) responses to psychological stressors. However, HPA axis activation in different physical stress models and its interface with NT-pro-BNP in the prediction of cardiopulmonary performance is unclear. Cardiopulmonary test on a treadmill was used to assess cardiopulmonary parameters in 16 elite male wrestlers (W), 21 water polo player (WP) and 20 sedentary age-matched subjects (C). Plasma levels of NT-pro-BNP, cortisol and adrenocorticotropic hormone (ACTH) were measured using immunoassay sandwich technique, radioimmunoassay and radioimmunometric techniques, respectively, 10 min before test (1), at beginning (2), at maximal effort (3), at 3rd min of recovery (4). In all groups, NT-pro-BNP decreased between 1 and 2; increased from 2 to 3; and remained unchanged until 4. ACTH increased from 1 to 4, whereas cortisol increased from 1 to 3 and stayed elevated at 4. In all groups together, ΔNT-pro-BNP2/1 predicted peak oxygen consumption (B = 37.40, r = 0.38, p = 0.007); cortisol at 3 predicted heart rate increase between 2 and 3 (r = −0.38,B = −0.06, p = 0.005); cortisol at 2 predicted peak carbon-dioxide output (B = 2.27, r = 0.35, p < 0.001); ΔACTH3/2 predicted peak ventilatory equivalent for carbon-dioxide (B = 0.03, r = 0.33, p = 0.003). The relation of cortisol at 1 with NT-pro-BNP at 1 and 3 was demonstrated using logistic function in all the participants together (for 1/cortisol at 1 B = 63.40, 58.52; r = 0.41, 0.34; p = 0.003, 0.013, respectively). ΔNT-pro-BNP2/1 linearly correlated with ΔACTH4/3 in WP and W (r = −0.45, −0.48; p = 0.04, 0.04, respectively). These results demonstrate for the first time that HPA axis and NT-pro-BNP interface in physical stress probably contribute to integrative regulation of cardiopulmonary performance.