Sweat rate and sweat composition during heat acclimation

The purpose of this study was to determine local sweat rate (LSR) and sweat composition during heat acclimation (HA). For ten consecutive days of HA, eight participants cycled in 33 °C and 65% relative humidity at an intensity such that a rectal temperature of 38.5 °C was reached within ~40 min, followed by a 60-min clamp of this rectal temperature (i.e., controlled hyperthermia). Four participants extended HA by a 28-day decay period and five consecutive days of heat re-acclimation (HRA) using controlled hyperthermia. Sweat from the upper arm and upper back was collected three times during each heat exposure session. LSR and sweat sodium, chloride, lactate, and potassium concentrations were determined. Relative to HA day 1, LSR was increased at the final day of HA (day 10) (arm: +58%, P < 0.001; back: +36%, P < 0.05). Concentrations of sodium, chloride, and lactate significantly (P < 0.05) decreased to ~60% at HA day 10 compared to day 1 on the arm and back. Potassium concentration did not significantly differ on HA day 10 compared to day 1 (arm: +11%, P > 0.05; back: +8%, P > 0.05). The induction patterns of the sudomotor adaptations were different. Whilst LSR increased from HA day 8 on the arm and from HA day 7 on the back, sodium and chloride conservation already occurred from HA day 3 on both skin sites. Lastly, the sweat lactate reduction occurred from HA day 6 on the arm and back. Initial evidence is provided that adaptations were partly conserved after decay (28 days) and that a 5-day HRA may be sufficient to restore HA adaptations. In conclusion, ten days of exercise-induced HA using controlled hyperthermia led to increases in LSR and concomitant reductions of sweat sodium, chloride, and lactate concentrations, whilst potassium concentrations remained relatively constant.     

Validity of a wearable sweat rate monitor and routine sweat analysis techniques using heat acclimation

Introductionthe aim of this study was to assess the validity of a novel wearable sweat rate monitor against an array of sweat analysis techniques which determine sudomotor function when exercising moderately under heat stress. Construct validity was determined utilising a 5-day short-term heat acclimation (STHA) intervention.MethodsNineteen healthy individuals (age: 41 ± 23 years, body mass: 74.0 ± 12.2 kg, height: 174.9 ± 6.9 cm) [male; n = 15, female; n = 4] completed nine trials over a three-week period, in a controlled chamber set to 35 °C, 50% relative humidity for all sessions. The pre and post-trials were separated by five consecutive controlled hyperthermia HA sessions. Sweat analysis was compared from pre and post-trial, whereby whole body sweat rate (WBSR) was assessed via pre and post nude body mass. Local sweat rate (LSR) was determined via technical absorbent patches (TA) (weighed pre and post) and a novel wearable KuduSmart® (SMART) monitor which was placed on the left arm during the 30-min of exercise. Tegaderm patches, used to measure sweat sodium chloride conductivity (SC), and TA patches were placed on the back, chest and forearm for the 30-min cycling.ResultsSudomotor function significantly adapted via STHA (p < 0.05); demonstrated by a WBSR increase of 24%, LSR increase via the TA method (back: 26%, chest: 45% and arm: 48%) and LSR increase by the SMART monitor (35%). Finally, SC decreased (back: -21%, chest: -25% and arm: -24%, p < 0.05).ConclusionAll sweat techniques were sensitive to sudomotor function adaptation following STHA, reinforcing their validity. The real time data given by the wearable KuduSmart® monitor provides coaches and athletes instant comparable sudomotor function feedback to traditional routinely used sweat analysis techniques.     

Dynamic changes in blood immune cell composition and function in Holstein and Jersey steers in response to heat stress

Heat stress has detrimental effects on livestock via diverse immune and physiological changes; heat-stressed animals are rendered susceptible to diverse diseases. However, there is relatively little information available regarding the altered immune responses of domestic animals in heat stress environments, particularly in cattle steers. This study aimed to determine the changes in the immune responses of Holstein and Jersey steers under heat stress. We assessed blood immune cells and their functions in the steers of two breeds under normal and heat stress conditions and found that immune cell proportions and functions were altered in response to different environmental conditions. Heat stress notably reduced the proportions of CD21⁺MHCII⁺ B cell populations in both breeds. We also observed breed-specific differences. Under heat stress, in Holstein steers, the expression of myeloperoxidase was reduced in the polymorphonuclear cells, whereas heat stress reduced the WC1⁺ γδ T cell populations in Jersey steers. Breed-specific changes were also detected based on gene expression. In response to heat stress, the expression of IL-10 and IL-17A increased in Holstein steers alone, whereas that of IL-6 increased in Jersey steers. Moreover, the mRNA expression pattern of heat shock protein genes such as Hsp70 and Hsp90 was significantly increased in only Holstein steers. Collectively, these results indicate that altered blood immunological profiles may provide a potential explanation for the enhanced susceptibility of heat-stressed steers to disease. The findings of this study provide important information that will contribute to developing new strategies to alleviate the detrimental effects of heat stress on steers.     

Individual differences in the diurnal cortisol response to stress

The objectives of this study were to explore individual differences associated with diverse reactions in cortisol secretion under different stress levels. This study was part of a larger project concerning working hours and health. Thirty-four white-collar workers participated under two different conditions; one work week with a high stress level (H) and one with a lower stress level (L) as measured through self-rated stress during workdays. Based on the morning cortisol concentration during a workday subjects were divided into two groups. One group consisted of subjects whose morning level of cortisol increased in response to the high-stress week, compared to their morning levels in the low-stress condition (Group 1). The other group consisted of subjects whose morning cortisol response was the opposite, with a lower level under the high stress condition (Group 2). Subjects wore actiwatches, completed a sleep diary, and rated their sleepiness and stress for one work week in each condition, i.e., high and low stress. Saliva samples for measures of cortisol were collected on a Wednesday. Group 2 reported higher workload, fatigue, and exhaustion during both weeks. Since there were no differences in perceived stress, neither within nor between groups, the data indicate that there are other factors influencing morning cortisol. The results suggest that one component modulating the cortisol response might be the level of exhaustion, probably related to work overload. Higher levels of stress in exhausted individuals might suppress morning cortisol levels.     

Rapid regulation of electrolyte absorption in sweat duct

Even though the same Cl channel (CFTR) is common to certain fluid transport functions that are oppositely directed, i.e., secretion and absorption, only fluid secretion has clearly been shown to be acutely regulated. It is now clear that fluid secretion activated by -adrenergic stimulation is controlled by cAMP-mediated opening and closing of CFTR-Cl channels. Since the conductance of the human sweat duct is almost wholly due to CFTR-Cl conductance (CFTR-G_Cl), we sought to determine whether salt absorption via CFTR-Cl channels could also be subject to acute regulation in this purely absorptive epithelium. After -toxin permeabilization, we found that addition of cAMP resulted in a large increase in Cl diffusion potentials across the apical membrane and a more than twofold increase in the average membrane conductance. Since the cAMP effects were dependent on Cl alone, not on Na, and since apical Cl conductance appears to be almost exclusively comprised of CFTR-G_Cl, we surmise that this form of electrolyte absorption like secretion is also subject to acute control through CFTR-G_Cl. Acute regulation of absorption involves both activation by phosphorylation (PKA) and inactivation by dephosphorylation (unknown endogenous phosphatase) of CFTR. Phosphorylation of CFTR was shown by the facts that CFTR-G_Cl could be activated by cAMP and inhibited by the kinase antagonist staurosporine, or by removal of either substrate ATP or Mg²⁺ cofactor. Inactivation of CFTR-G_Cl by endogenous phosphatase(s) was indicated by a spontaneous but reversible loss of CFTR-G_Cl upon removal of cAMP. Such loss of CFTR-G_Cl activity could be prevented either by application of phosphatase inhibitors or by using phosphatase-resistant ATP--S as substrate to phosphorylate CFTR. We surmise that absorptive function is subject to rapid regulation which can be switched on and off acutely by a control system that is common to both absorptive and secretory processes and that this control is crucial to switching between conductive and nonconductive transport mechanisms during salt absorption.The authors are grateful to Mr. Kirk Taylor for expert technical assistance, and to numerous volunteer human subjects for participating in the experiments with informed consent. Supported by grants from the National Institutes of Health, DK-41329-04 and the National Cystic Fibrosis Foundation, Z 439.     

The effect of sodium balance on sweat sodium secretion and plasma aldosterone concentration

The effect of manipulating sodium intake upon sweat sodium secretion was investigated during heat acclimation. Twenty-five male subjects were confined to an environmental chamber at a temperature of 25°C for 3 days, and then acclimated to heat by a further 5 days at 40°C. The subjects' daily sodium intake was controlled throughout as follows: high (HNa), 348.4 (0.8) mmol · day⁻¹, n = 7; moderate (MNa), 174.1 (0.6) mmol · day⁻¹, n = 9; or low (LNa), 66.3 mmol · day⁻¹, n = 9. Sodium losses were estimated from urinary, faecal and sweat collections using a whole-body washdown method. Plasma aldosterone concentration was also measured from venous blood sampled each morning. Measurements of body temperature and heart rate during the heat exposure phase indicated a degree of heat acclimation. During this heat phase there was a reduction (P < 0.01) in sweat sodium secretion for all three conditions which was greatest for the LNa condition, although this finding was not significant (P < 0.1). In the LNa condition, plasma aldosterone concentration increased (P < 0.05) prior to heat exposure, and the secretion of aldosterone was potentiated (P < 0.01) during the heat exposure in comparison with the MNa condition. In contrast, the HNa diet produced a fall (P < 0.05) in plasma aldosterone concentration prior to heat exposure and an attenuation of aldosterone secretion thereafter. These findings are inconsistent with the hypothesis that retention of sweat sodium is dependent upon a net body sodium deficit, but demonstrate that aldosterone secretion is potentiated under such conditions. Accepted: 22 May 1988     

Transition duration of ingested deuterium oxide to eccrine sweat during exercise in the heat

The time necessary for the initial appearance of ingested water as sweat during exercise in the heat remains unknown. Based on the current literature, we estimated fluid transition through the body, from ingestion to appearance as sweat, to have a minimum time duration of approximately three minutes. The purpose of this study was to test this prediction and identify the time necessary for the initial enrichment of deuterium oxide (D₂O) in sweat following ingestion during exercise in the heat. Eight participants performed moderate intensity (40% of maximal oxygen uptake) treadmill exercise in an environmental chamber (40 °C, 40% rH) to induce active sweating. After fifteen minutes, while continuing to walk, participants consumed D₂O (0.15 ml kg⁻¹) in a final volume of 50 ml water. Scapular sweat samples were collected one minute prior to and ten minutes post-ingestion. Samples were analyzed for sweat D₂O concentration using isotope ratio mass spectrometry and compared to baseline. Mean±SD ∆ sweat D₂O concentration at minutes one and two post-ingestion were not significantly higher than baseline (0 min). Minutes three (9±3 ppm) through ten (23±11 ppm) post-ingestion had ∆ sweat D₂O concentrations significantly (P<0.05) higher than baseline. Such results suggest that ingested water rapidly transports across the mucosal membrane of the alimentary canal into the vasculature space, enters the extravascular fluid, and is actively secreted by the eccrine sweat glands onto the surface of the skin for potential evaporation in as little as three minutes during exercise in the heat.     

Effects of exposure to high temperatures on serum,urine and sweat concentrations of iron and copper

The objective of this research was to determine the acute effect of a maximum test until exhaustion in normothermia and hyperthermia, and after repeated exposure to heat at high temperatures on the homeostasis of Fe and Cu.The sample was composed of twenty-nine male university students. The participants were divided into a control group (CG) and an experimental group (EG). All of them underwent an incremental test until exhaustion in normothermia and hyperthermia before and after the repeated exposure of EG to heat at high temperatures, consisting of 9 heat acclimatisation sessions in the sauna. Samples of urine and blood were taken before and after each test. Additionally, sweat samples were collected in the hyperthermia test. The samples were frozen at −80 °C for further analysis by ICP-MS.None of the metal concentrations in serum were affected by hyperthermia or exposure to heat. Urinary Fe increased in CG in the hyperthermia test before Heat exposure at High Temperature (HEHT)(p < 0.05) and in both groups after HEHT (p < 0.05). In EG there was an increase in the urinary excretion of Cu after HEHT (p < 0.01) in both trials. Fe suffered a decrease in sweat in EG after exposure to heat (p < 0.05).The concentrations of Fe and Cu in serum were not affected by acute exercise and exposure to high temperatures. However, there was a decrease in excretion of Fe in sweat due to HEHT, and an increase in urinary excretion in both. Therefore, we think that in conditions of high temperatures for long periods of time, attention should be paid to the body levels of these metals.     

Peripheral sweat gland function,but not whole-body sweat rate,increases in women following humid heat acclimation

The purpose of this study was to compare both the whole-body and pharmacological-induced sweat rates of men and women following humid heat acclimation.     

Effects of exposure to short-term heat stress on male reproductive fitness in a soil arthropod

Ambient temperature is a key environmental factor influencing a variety of aspects of the ecology and evolution of ectotherms. Reproductive traits have been suggested to be more sensitive to thermal stress than other life history traits. This study investigated the direct and indirect effects of heat shock on male reproductive success in the widespread springtail Orchesella cincta. Male springtails were exposed to four temperature treatments: heat hardening (35.2 °C for 1 h), heat shock (37.2 °C for 1 h), heat hardening + heat shock (35.2 °C for 1 h, followed 15 h later by 37.2 °C for 1 h), and control (20 °C). The heat shock gene Hsp70 showed high expression in all the heat treatments, indicating that the treatments indeed induced thermal stress. Significant mortality was only found in the treatment with heat shock, both with and without heat hardening. A direct effect of heat treatment was found on time to first reproduction, which was significantly longer after heat shock (with or without heat hardening) than in the control treatment. There was no difference among treatments in the number of spermatophores produced in the first reproductive instar. Heat treatment also had indirect effects on male reproductive success. Females chose significantly more spermatophores from control males than from males that received heat shock, heat hardening or both. A high percentage of spermatophores produced by heat shocked males caused reproductive failure in females, but no significant differences among treatments were found.Our results suggest that not all traits were equally affected by the heat stress. Heat hardening did not protect reproductive traits against the negative effects of heat shock. The indirect effects of heat shock on reproduction may be equally important as the direct effects.     

Sex differences impact the pancreatic response to chronic immobilization stress in rats

Chronic stress has been related to multiple diseases. Inflammation is proposed strongly to link stress to stress-related diseases in different organs, such as small intestine, colon, and brain. However, stress cellular effect on the pancreatic tissue, especially the exocrine one, had received relatively little attention. This work aimed to evaluate the cellular effect of chronic immobilization stress on the pancreatic tissue function and structure along with evaluating the sex role in this type of pancreatic injury. Thirty rats were equally divided into 5 groups: control male, control female, stressed male, stressed female, and stressed female with bilateral ovariectomy. Stressed rats were exposed to immobilization for 1 h/day, 6 days/week, for 3 weeks. Rats were then decapitated for further biochemical, histological, histo-morphometric, and immunohistochemical study. The results showed that, in male and female rats, chronic immobilization stress produced hypoinsulinemia and hyperglycemia, with increasing exocrine pancreatic injury markers by increasing oxidative and inflammatory status of the pancreatic tissue, and exhibited a degenerative effect on the pancreatic tissue. However, the stress-induced pancreatic effects were more obvious in male rats and female rats with bilateral ovariectomy than that in female rats. It could be concluded that male animals were more susceptible to stress-induced pancreatic damage than females. The ovarian hormones are responsible, at least partly, for pancreatic tissue protection since the stress-induced pancreatic injury in females was exacerbated by ovariectomy. In this study, inflammatory and oxidative stress differences in both sexes could provide a plausible explanation for sex differences.     

戊糖片球菌热胁迫应答机制探究

目的 以发酵柚子皮中分离到的戊糖片球菌WPPE03、WPPE04作为研究对象,用标准株CGMCC1.2695作为对照,探索其热胁迫相关机制。方法 通过平板计数法,确定戊糖片球菌的热适应条件和热致死条件;采用扫描电子显微镜观察细胞热应激前后形态学变化;应用RT-qPCR分析热休克蛋白及细胞膜脂肪酸合成相关基因转录水平变化,阐明热胁迫机制。结果 确定了三株戊糖片球菌热适应条件（47℃,60 min）和热致死评价条件（62℃,15 min）;发现了热致死条件处理菌体,膜表面会出现凹陷、皱褶,部分菌体出现破裂、胞内物质外溢等现象,而热致死条件处理前先经过热适应处理,菌体破裂现象明显减少;同时,证明了热应激处理过程中,相关热休克蛋白基因表达显著上调（P<0.05）,脂肪酸合成相关基因表达发生了变化。结论 研究戊糖片球菌的热应答相关机制,可为合理开发、利用具有发酵性能的戊糖片球菌提供借鉴。     

Aerobic fitness and sympatho-adrenal response to short-term psycho-emotional stress under field conditions

A possible relationship between aerobic fitness (AF), measured by maximal cycle ergometry (CE) and sympatho-adrenal response to acute, short lasting psycho-emotional stress was investigated by monitoring heart rate (f _c) and excretion of catecholamines. The activation of the sympatho-adrenal system was characterised by the noradrenaline : adrenaline ratio. A group of 11 healthy men [22.8 (SD 2.52) years] lived under identical environmental conditions; their mean maximal oxygen uptake ( ) was 47.1 (SD 3.9) ml · min^–1 · kg^–1. After the physiological and psychological laboratory tests had been completed thef _c of the subjects was monitored continuously during the guerilla slide and parachute jump by night, two emotionally stressful military tasks. Maximalf _c (f _{c, max}) attained during these events was 84.5% and 83% off _{c, max} during CE (f _{c, max, CE}), respectively. A significant relationship (r=–0.92,P<0.0002) betweenf _{c, max} reached during the stressful tasks and was found only for the guerilla slide, which was preceded by physical strain, sleep deprivation and energy deficit. One subject with some prior experience in parachuting showed the lowestf _c response and the lowest sympatho-adrenal activation in both events, independent of the degree of AF. In conclusion, AF was found to influence the sympatho-adrenal and fc response to acute, short-lasting emotional stress when the stressful event was aggravated by preceding physical strain, the magnitude of the stress response depending largely on individual experience and effective mechanisms for coping with specific stimuli.     

Influence of a high-temperature programme on serum,urinary and sweat levels of selenium and zinc

IntroductionThe effect of hyperthermia on the antioxidant system in the human organism is well known.AimThe objective of this study was to observe the effects of heat on the concentration of Se and Zn, elements related to antioxidant systems.MethodsTwenty-nine subjects voluntarily participated in this study. They were divided into a control group (CG; n = 14) and an experimental group (EG; n = 15). All of them underwent two incremental tests until exhaustion in normothermia (22 °C, 20–40%RH) and hyperthermia (42 °C, 20–40%RH). EG experienced nine sessions of repeated heat exposure at high temperatures (100 °C, 20%RH) for three weeks (HEHT). After the intervention, the initial measurements were repeated. Urine and blood samples were collected before and after each test. Additionally, sweat samples were collected after tests in hyperthermia.ResultsThere were no significant changes in serum. An increase in the elimination of Zn and Se in EG was observed in urine after HEHT (p < .05). The elimination of Zn by sweating decreased after HEHT in EG (p < .05).ConclusionsExposure to heat at high temperatures increases the urinary excretion of Se and Zn.     

An overview of heat stress in tomato (Solanum lycopersicum L.)

Heat stress has been defined as the rise of temperature for a period of time higher than a threshold level, thereby permanently affecting the plant growth and development. Day or night temperature is considered as the major limiting factor for plant growth. Earlier studies reported that night temperature is an important factor in the heat reaction of the plants. Tomato cultivars capable of setting viable fruits under night temperatures above 21 °C are considered as heat-tolerant cultivars. The development of breeding objectives is generally summarized in four points: (a) cultivars with higher yield, (b) disease resistant varieties in the 1970s, (c) long shelf-life in 1980s, and (d) nutritive and taste quality during 1990s. Some unique varieties like the dwarf “Micro-Tom”, and the first transgenic tomato (FlavrSavr) were developed through breeding; they were distributed late in the 1980s.High temperature significantly affects seed, pollen viability and root expansion. Researchers have employed different parameters to evaluate the tolerance to heat stress, including membrane thermo stability, floral characteristics (Stigma exertion and antheridia cone splitting), flower number, and fruit yield per plant. Reports on pollen viability and fruit set/plant under heat stress by comparing the pollen growth and tube development in heat-treated and non-heat-stressed conditions are available in literature. The electrical conductivity (EC) have been used to evaluate the tolerance of some tomato cultivars in vitro under heat stress conditions as an indication of cell damage due to electrolyte leakage; they classified the cultivars into three groups: (a) heat tolerant, (b) moderately heat tolerant, and (c) heat sensitive.It is important to determine the range in genetic diversity for heat tolerance in tomatoes. Heat stress experiments under field conditions offer breeders information to identify the potentially heat tolerant germplasm.     

Caffeine and heat have additive but not interactive effects on physiologic strain: A factorial experiment

This study tested the interactive effects of heat and caffeine on exercise-induced physiological strain by using a 2x2 within-subjects factorial design. Thirty-five physically fit Caucasians underwent a bout of exercise under four conditions wherein ambient conditions (heat vs no heat) and caffeine (placebo vs caffeine; double-blinded) were manipulated. Exercise consisted of a 60-min walk and 5-min step/squat test while wearing weighted backpack. Primary outcomes include measures of physiologic strain (Core temperature [T_r] and heart rate [HR]). Secondary measures included blood pressure, markers of sweat loss, and creatine kinase (CK). Repeated measures models were created to evaluate the individual and combined effects of heat and caffeine. Key results indicated that heat and caffeine significantly increased T_r and HR after walking and stair-stepping. No significant heat by caffeine interactions were detected, and caffeine's main effects were relatively low (≤0.17 °C for T_r and ≤6.6 bpm for HR). Of note, heat and caffeine exhibited opposite effects on blood pressure: caffeine increased both systolic and diastolic blood pressure (by 6–7 mmHg) and heat decreased them (by 4–6 mm Hg; ps < 0.05). In summary, heat and caffeine affected physiologic strain during exercise but exhibited no synergistic effects. In contrast, neither factor affected muscle damage. Clinical implications for heat illness risk in the military are discussed.     

Proteomic study of Carissa spinarum in response to combined heat and drought stress

Carissa spinarum is one of the secondary advantage plants grown in dry‐hot valleys in China, which can survive under stress conditions of high temperature and extreme low humidity. Here, we studied the physiological and proteomic changes of C. spinarum in response to 42°C heat stress treatment in combination with drought stress. Dynamic changes in the leaf proteome were analyzed at four time points during the stress treatment and recovery stages. Approximately, 650 protein spots were reproducibly detected in each gel. Forty‐nine spots changed their expression levels upon heat and drought treatment, and 30 proteins were identified by MS and 2‐D Western blot. These proteins were classified into several categories including HSP, photosynthesis‐related protein, RNA‐processing protein and proteins involved in metabolism and energy production. The potential roles of these stress‐responsive proteins are discussed.