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.     

Effect of heat stress and drinking water salt supplements on plasma electrolytes and aldosterone concentration in broiler chickens

An experiment was conducted to evaluate the effects of supplementing drinking water with isomolar (0.067 mol/l) KCl or NaCl on mass gain, food and water consumption, rectal temperature, and plasma concentrations of aldosterone, Na⁺, and K⁺ in broiler chickens reared in thermoneutral and cycling heat stressing environments. Heat stress decreased (P0.05) mass gain, food consumption, and plasma concentrations of Na⁺ and K⁺, while increases (P0.05) in plasma concentrations of aldosterone, rectal temperature, and water consumption were observed. Drinking water supplemented with either KCl or NaCl increased (P0.05) broiler mass gain and water consumption, but had no effect (P>0.1) on the other variables evaluated. The results of this study indicate that broiler chickens in a heat stress environment are under osmotic stress and supplementing drinking water with 0.067 mol/1 KCl or NaCl does not lessen this stress.     

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.     

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.     

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.     

Dopaminergic modulation of aldosterone secretion: effect of sodium balance and postural changes

The influence of an increased endogenous production of angiotensin II and of sodium homeostasis upon the response of plasma aldosterone to metoclopramide administration has been investigated in 5 normal volunteers. Our results show that the increase of plasma aldosterone after metoclopramide administration is independent of angiotensin II, ACTH and potassium, and that it increases even further due to the endogenous production of angiotensin II induced by postural changes. The state of sodium balance seems to influence the response of plasma aldosterone to metoclopramide administration as it occurs with other stimuli of aldosterone secretion.     

Effect of exercise-induced acidosis on aldosterone secretion in men

The present study was carried out to elucidate whether an exercise-induced increase in plasma hydrogen ion concentration influences aldosterone secretion. Six healthy men (aged 22–25 years) performed two intermittent exercise tests with and without drug administration. The intensities of these exercise tests were 40% maximal oxygen uptake (V˙O_2max) and 90% V˙O_2max, respectively. Administration of 2-mg Dexamethasone and 50-mg Captopril caused an almost complete suppression of adrenocorticotropic hormone (ACTH) and an enhancement of the elevation in renin concentration during exercise, indicating successful inhibition of ACTH release and angiotensin II production during exercise. While the magnitude of the increase in aldosterone in the drug experiment was depressed compared with the control experiment, a significant increase in aldosterone concentration was observed at the end of the 90% V˙O_2max exercise. Whilst the change in aldosterone concentration did not correlate with the change in plasma potassium concentration, there was a significant correlation between aldosterone and plasma hydrogen ion concentrations in the drug experiment. Since the correlation coefficient was low (r=0.455), the biological meaning of this correlation should be further investigated. These results would suggest that an elevation of plasma hydrogen ion concentration induced by exercise per se appears to be related, at least in part, with increased aldosterone secretion, independent of the pituitary-adrenal axis, and the renin-angiotensin system. Accepted: 23 September 1997     

Topiramate reduced sweat secretion and aquaporin-5 expression in sweat glands of mice

Decreased sweat secretion is a primary side effect of topiramate in pediatric patients, but the mechanism underlying this effect remains unclear. This study aimed to better understand how topiramate decreases sweat secretion by examining its effect on the expression of carbonic anhydrase (CA) II and aquaporin-5 (AQP5), total CA activity, as well as on tissue morphology of sweat glands in mice. Both developing and mature mice were treated with a low (20 mg/kg/day) and high dose (80 mg/kg/day) of topiramate for 4 weeks. Sweat secretion was investigated by an established technique of examining mold impressions of hind paws. CA II and AQP5 expression levels were determined by immunofluorescence and immunoblotting and CA activity by a colorimetric assay. In mature mice, topiramate treatment decreased the number of pilocarpine reactive sweat glands from baseline in both the low and high dose groups by 83% and 75%, respectively. A similar decrease was seen in developing mice. Mature mice with reactive sweat glands that declined more than 25% compared to baseline were defined as anhidrotic mice. These mice did not differ from controls in average secretory coil diameter, CA II expression and CA activity. In contrast, anhidrotic mice did show a reduction in membrane AQP5 expression in sweat glands after topiramate delivery. Thus, sweat secretion and membrane AQP5 expression in mouse sweat glands decreased following topiramate administration. These results suggest dysregulation of AQP5 may be involved in topiramate-induced hypohidrosis and topiramate may serve as a novel therapy for hyperhidrosis.     

The effect of high altitude on saliva aldosterone and glucocorticoid concentrations

Saliva was collected from six healthy young men at hourly intervals at sea level and after 1-2, 8-9 and 15-16 days at 4450 m on Mount Kenya for measurement of aldosterone (SA) and glucocorticoid (SGC, cortisol + cortisone) concentrations. Blood samples were collected simultaneously with some of the saliva samples and analysis of these showed that plasma and saliva concentrations of aldosterone and glucocorticoids were highly correlated (r = 0.91 and 0.75 respectively; p less than 0.01 for both hormones). Mean SA for the group was reduced to approximately 50% of the sea-level value (p less than 0.05) by the time the first saliva samples were collected at altitude, and remained at this depressed level throughout the 2-week period on Mount Kenya, although there was considerable inter-subject variation. SGC concentration also tended to be lower on Mount Kenya than at sea level. Though SA was lower throughout the day at altitude compared to sea level, the principal difference in the temporal pattern of SA was the reduction or complete absence of the marked rise in SA that normally occurs in the first few hours after rising. SA and SGC responses to exercise, which consisted of stepping on and off and 0.4-m high stool 60 times/min for 25 min, were assessed at sea level and after various periods at 4450 m.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pathophysiological roles of vascular 11beta-hydroxysteroid dehydrogenase and aldosterone

Mineralocorticoid receptor (MR) binding is tightly regulated by the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSDII) which selectively metabolizes glucocorticoids to inactive metabolites, thus allowing for MR activation by aldosterone. To examine whether this enzyme is involved in the pathophysiology of salt-sensitive hypertension, 11β-HSDII activity and messenger RNA (mRNA) levels were determined in blood vessels of Dahl Iwai salt-sensitive (DS) and salt-resistant (DR) rats. Decreased 11β-HSDII activity and mRNA levels in mesenteric arteries were observed in 8-week-old DS rats on a high-salt diet, indicating that 11β-HSDII may play a significant role in salt sensitivity and hypertension. It has been suggested that mineralocorticoids act on blood vessels, leading to increased vasoreactivity and peripheral resistance. We present direct evidence that blood vessels are aldosteronogenic. The production of aldosterone in blood vessels was compared between stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. Vascular aldosterone and CYP11B2 mRNA levels were significantly increased in 2-week-old SHRSP versus WKY rats. However, the vascular aldosterone levels in 4- and 9-week-old SHRSP and WKY rats were similar. High sodium intake further increased both blood pressure and vascular aldosterone synthesis in the SHRSPs. Both the local renin–angiotensin–aldosterone system (RAAS) and the vascular 11β-HSDII level are critically important in the pathophysiology of cardiovascular disorders.     

Effect of a low-carbohydrate diet on plasma and sweat ammonia concentrations during prolonged nonexhausting exercise

The purpose of this investigation was to examine the effect of low body glycogen stores on plasma ammonia concentration and sweat ammonia excretion during prolonged, nonexhausting exercise of moderate intensity. On two occasions seven healthy untrained men pedalled on a cycle ergometer for 60 min at 50% of their predetermined maximal O₂ uptakes ( _max) firstly, following 3 days on a normal mixed diet (N-diet) (60% carbohydrates, 25% fat and 15% protein) and secondly, following 3 days on a low-carbohydrate diet (LC-diet) (less than 5% carbohydrates, 50% fat and 45% protein) of equal energy content. Blood was collected from the antecubital vein immediately before, at 30th and at 60th min of exercise. Sweat was collected from the hypogastric region using gauze pads. It was shown that plasma ammonia concentrations after the LC-diet were higher than after the N-diet at both the 30th and 60th min of exercise. Sweat ammonia concentration and total ammonia loss through the sweat were also higher after the LC-diet. The higher ammonia concentrations in plasma and sweat after the LC-diet would seem to indicate an increased ammonia production, which may be related to reduced initial carbohydrate stores.     

Regional differences in sweat rate response of steers to short-term heat stress

Six Angus steers (319 ± 8.5 kg) were assigned to one of two groups (hot or cold exposure) of three steers each, and placed into two environmental chambers initially maintained at 16.5–18.8°C air temperature (T _a). Cold chamber T _a was lowered to 8.4°C, while T _a within the hot chamber was increased to 32.7°C over a 24-h time period. Measurements included respiration rate, and air and body (rectal and skin) temperatures. Skin temperature was measured at shoulder and rump locations, with determination of sweat rate using a calibrated moisture sensor. Rectal temperature did not change in cold or hot chambers. However, respiration rate nearly doubled in the heat (P < 0.05), increasing when T _a was above 24°C. Skin temperatures at the two locations were highly correlated (P < 0.05) with each other and with T _a. In contrast, sweat rate showed differences at rump and shoulder sites. Sweat rate of the rump exhibited only a small increase with T _a. However, sweat rate at the shoulder increased more than four-fold with increasing T _a. Increased sweat rate in this region is supported by an earlier report of a higher density of sweat glands in the shoulder compared to rump regions. Sweat rate was correlated with several thermal measurements to determine the best predictor. Fourth-order polynomial expressions of short-term rectal and skin temperature responses to hot and cold exposures produced r values of 0.60, 0.84, and 0.98, respectively. These results suggest that thermal inputs other than just rectal or skin temperature drive the sweat response in cattle.     

Paralysis and heart failure precede ion balance disruption in heat-stressed European green crabs

Acute exposure of ectotherms to critically high temperatures causes injury and death, and this mortality has been associated with a number of physiological perturbations including impaired oxygen transport, loss of ion and water homeostasis, and neuronal failure. It is difficult to discern which of these factors, if any, is the proximate cause of heat injury because, for example, loss of ion homeostasis can impair neuromuscular function (including cardiac function), and conversely impaired oxygen transport reduces ATP supply and can thus reduce ion transport capacity. In this study we investigated if heat stress causes a loss of ion homeostasis in marine crabs and examined if such loss is related to heart failure. We held crabs (Carcinus maenas) at temperatures just below their critical thermal maximum and measured extracellular (hemolymph) and intracellular (muscle) ion concentrations over time. Analysis of Arrhenius plots for heart rates during heating ramps revealed a breakpoint temperature below which heart rate increased with temperature, and above which heart rate declined until complete cardiac failure. As hypothesised, heat stress reduced the Nernst equilibrium potentials of both K⁺ and Na⁺, likely causing a depolarization of the membrane potential. To examine whether this loss of ion balance was likely to cause disruption of neuromuscular function, we exposed crabs to the same temperatures, but this time measured ion concentrations at the individual-specific times of complete paralysis (from which the crabs never recovered), and at the time of cardiac failure. Loss of ion balance was observed only after both paralysis and complete heart failure had occurred; indicating that the loss of neuromuscular function is not caused by a loss of ion homeostasis. Instead we suggest that the observed loss of ion balance may be linked to tissue damage related to heat death.     

Effect of prolonged physical exercise on intra-erythrocyte and plasma potassium

The intracellular concentrations of sodium [Na+] and potassium [K+] and the water content in human erythrocytes were investigated in 21 male runners before and after a marathon. From 2 to 5 min after the race, the intra-erythrocyte [K+] was significantly decreased (p less than 0.001) by 7% whereas the plasma [K+], intra-erythrocyte [Na+] and the erythrocyte water content were unchanged. The change in the intra-erythrocyte [K+] observed immediately after the marathon, was negatively correlated with the race time (r = -0.44; p less than 0.05). Furthermore, the change in the plasma [K+] (r = -0.64; p less than 0.001) and the amount of K+ excreted in the urine during the race (r = 0.54; p less than 0.05) were also, respectively, negatively and positively correlated with the race time. It is concluded that during prolonged physical exercise the erythrocytes could serve as a kind of K+ reservoir that is drained with increasing magnitude of body K+ loss. This might explain why in the faster marathon runners, in whom the urinary K+ loss is smaller and the K+ intake is greater than in the slower runners during race, the intra-erythrocyte [K+] is unchanged after a marathon whereas in the slower runners it is decreased.     

The effect of heat acclimation on maximal urine osmolality in humans

The purpose of the current study was to determine the effect of 9 days of active heat acclimation on maximal urine osmolality (MUO) in humans. Eight subjects completed 9 days of heat acclimation, which consisted of a daily 90 min exercise session in a heated environmental chamber. Before and following heat acclimation the subjects abstained from drinking fluids for 15 h, and urine samples were collected to measure MUO. The subjects successfully heat acclimated as evidenced by a significant (P<0.05) decrease in the mean±SD exercise core temperature (37.7±0.3 °C on day 1 to 37.4±0.3 °C on day 9) and heart rate (143±17 bpm on day 1 to 128±14 bpm on day 9). The mean pre- and post-heat acclimation MUOs were 868±117 and 846±89 mmol kg⁻¹, respectively, which were not significantly different (P>0.05). Previous studies have shown that prolonged dehydration can increase the MUO in various mammalian species, including humans. In contrast, the results of the current study suggest that 9 days of active heat acclimation, without significant dehydration, does not affect the MUO in humans.     

Circadian rhythm of water balance and aldosterone excretion in the whitebellied sunbird<Emphasis Type="Italic"> Nectarinia talatala</Emphasis>

Nectarivorous whitebellied sunbirds, Nectarinia talatala, demonstrate distinct circadian patterns in osmoregulatory parameters. We recorded intake of a 1 mol/l sucrose solution which enabled calculation of total water gain, and collected cloacal fluid for measurements of volume, osmolality and aldosterone concentration. These variables were assessed hourly over 12 h of photophase, and averaged over the 12-h scotophase period. Overnight, when sunbirds were in negative water balance, aldosterone concentrations and outputs were significantly higher than diurnal levels, reflecting a shut-down of cloacal fluid production. Early morning was marked by a high rate of osmotic excretion, disproportionate to water gain or cloacal fluid output, followed by steady intake and cloacal fluid output during the morning and early afternoon. Reduced water flux (decreased feeding and cloacal fluid output) during mid-afternoon was accompanied by a paradoxical decline in osmotic excretion, whilst a significant increase in the discrepancy between water intake and output was recorded as the birds effectively stored water before the scotophase. These patterns of intake and excretion may be informative in explaining drinking and foraging behaviour in the field.Abbreviations ALDO aldosterone - CF cloacal fluid - GFR glomerular filtration rate     

Steady-state sodium absorption and chloride secretion of colon and coprodeum,and plasma levels of osmoregulatory hormones in hens in relation to sodium intake

Summary The plasma levels of four osmoregulatory hormones and their target ion-transport systems in the lower intestines of the domestic fowl were determined in order to elucidate their interrelationship and their setpoints in relation to NaCl intake. White Plymouth Rock hens were adapted to six intake levels of NaCl (0.20±0.02–24.7±1.9 mmoles Na⁺·kg bw^–1·day^–1) for 6 weeks. The Na⁺ absorption and the Cl^– secretion of colon and coprodeum were characterized in vitro by the effects of hexoses, amino acids, amiloride, and theophylline on the short-circuit current (SCC) and electrical potential difference (PD). The NaCl-conserving system of the adult chicken is set at low intake levels of NaCl as the 80% range (quantitized by non-linear, logistic regression analyses) of the change in the plasma [ALDO], the amiloride-inhibitable Na⁺ absorption of coprodeum and colon ( SCC), occurred from 0.18 to 2.3, from 0.9 to 4.3, and from 1.2 to 7.3 mmoles Na⁺·kg bw^–1·day^–1, respectively. These results demonstrate that the amiloride-inhibitable Na⁺ absorption of coprodcum is more closely linked to plasma [ALDO] than that of colon. The aminoacid-Na⁺ coabsorption of colon increased over exactly the same range of Na⁺ intake as the colonic amiloride-inhibitable Na⁺ absorption decreased, whereas the hexose-Na⁺ coabsorption increased at higher levels of Na⁺ intake, from 2 to 11 mmoles Na⁺·kg bw^–1·day^–1. Both these Na⁺ absorption types had reached their maximums at 24.7 mmoles Na⁺·kg bw^–1·day^–1, whereas the plasma [AVT] and plasma [PRL], although significantly increased, apparently had not; their 80% range of change occurred from 9.9 to 99 mmoles Na⁺·kg bw^–1·day^–1, and the main changes in plasma osmolity were predicted to occur from 5.4 to 107 mmoles Na⁺·kg bw^–1·day^–1. These results suggest that these colonic and hormonal variables conserve osmotically-free water and operate at high NaCl intake. The theophylline-induced colonic Cl^– secretion did not change with NaCl intake, whereas the stimulation of SCC in coprodeum decreased with increasing NaCl intake: The main change occurred between 0 and 3.2 mmoles Na⁺·kg bw^–1·day^–1. Thus, all ion-transport capacity disappears in coprodeum with increased dietary NaCl intake, whereas colon maintains its ion-transport capacity (although the nature of the Na⁺ transport changes). It is suggested that hormones defending the extracellular volume and composition are regulated close to zero input and output of both NaCl and water, regardless of whether they are NaCl conserving or free-water conserving. Therefore, changes in their stable plasma concentrations occur at the extremes of tolerable range of NaCl intake.Abbreviation AA aminoacids - ALDO aldosterone - AMI amiloride - AVT arginine vasotocin - bw body weight - CS corticosterone - HEX hexoses - INDO indomethacin - PD potential difference - PRL prolactin - R resistance - SCC short-circuit current - SD standard deviation - SEM standard error of mean - THEO theophylline     

Circadian rhythm in plasma aldosterone concentration and its seasonal modulation in the camel (Camelus dromedarius) living in the Algerian Sahara desert

Five male camels dwelling in the Algerian Sahara were studied for circadian rhythmicity in plasma aldosterone concentration and its seasonal modulation. Blood was sampled at a frequency of 1 h or less for a span of 27 h during each season of the year. The mean plasma aldosterone concentration exhibited a significant circadian rhythmicity in every season of the year. Plasma aldosterone concentration was lowest in the morning, increased in the afternoon, and generally highest in the late evening. The peak of the circadian rhythm exhibited seasonal variation; it occurred at 20:04h in October, 16:41h in December, 20:40h in March, and 24:16h in June. The rhythm's 24h mean also exhibited seasonal variability, being significantly higher in March and June compared to October.