Thermotherapy as an alternative to exercise for metabolic health in obese postmenopausal women: focus on circulating irisin level.

Irisin is a myokine caused by exercise that improves insulin resistance and weight loss. However, under unfavorable conditions such as air pollution, and during the pandemic, outdoor activities are uncomfortable. Therefore, in this study, the effect of heat therapy (half bath 42 ± 0.5°C for 30 min) on irisin circulation levels as an exercise alternative for middle-aged obese women after menopause was investigated. Subjects were 33 women aged 49.54 ± 6.04 years, with parameters of height, 160.12 ± 4.33 cm, weight, 69.71 ± 7.52 kg, body surface area 1.73 ± 0.13 m2, body mass index, 27.19 ± 3.40 kg/m2. The results suggest that circulating irisin levels showed a significant increase after one-time thermotherapy (TH-1). However, the increase in circulating irisin levels after 15 treatments (TH-15, 5 days/week, 3 weeks) was significantly varied. The level of adiponectin, which increases fatty oxidation to reduce fatty deposition, increased significantly at TH-1, but further increased at TH-15, which was significantly different from the level of TH-1. In addition, the basic serum free fatty acid (FFA) level was significantly increased at TH-15 compared to TH-1. Significant differences were also found in the lipid profile (body mass index, waist circumference, and % body fat). Thermotherapy can significantly increase the tympanic temperature and induce changes in circulating irisin and adiponectin levels. Thus, it resulted in positive changes in FFA and lipid profiles. Therefore, repeated thermotherapy is effective in increasing circulating irisin levels in postmenopausal obese women.

The effect of listening to SMT music made using musical expectancy violations on brain concentration and activation.

This study investigated the effect of listening to self-music therapy training (SMT) music, which was specially developed using musical expectancy violations, on improving brain concentration and activation. It was performed with a sample of 12 adults. Electroencephalograms (EEG) were obtained and analyzed after allowing the participants to listen to SMT music. An EEG device with eight channels was used to measure the brain waves. The changes in the EEGs were recorded when listening to SMT music in three states (stable, basic, and stimulated) after attaching the electrodes to the prefrontal cortex (Fp1 and Fp2), and the frontal (F3 and F4), temporal (T3 and T4), and parietal lobes (P3 and P4) according to the International 10/20 system. The EEG data were analyzed to determine the m-ß wave appearance rate and absolute total power (ATP) for the three conditions, and a t-test was performed. The results showed that the rate of m-ß wave appearance was higher in the stimulated and basic states than in the stable state (Fp1, Fp2, F4, T3, T4, P3, and P4) and higher in the stimulated state than in the basic state (Fp1, Fp2, T3, T4, and P4). The ATP was lower in the basic state than in the stable state (Fp2, F3, F4, and T3), but the ATP in the stimulated state was higher than in the basic or stable state in all areas excluding the left and right parietal lobes (Fp1, Fp2, F3, F4, T3, and T4). These results demonstrated that listening to SMT music by normal adults could increase brain concentration and activation.

Mealworm (Tenebrio molitor)-derived protein supplementation attenuates skeletal muscle atrophy in hindlimb casting immobilized rats.

This study aimed to investigate the effect of mealworm (Tenebrio molitor) derived protein supplementation on skeletal muscle atrophy of hindlimb casted immobilized rats. Twenty-four six-week-old male Sprague-Dawley rats were randomly divided into three groups: control sedentary group (CD, n = 8), control diet casting group (CDC, n = 8), and the mealworm-derived protein supplemented casting group (MDC, n = 8). CD and CDC group was supplemented AIN-76G diet and mealworm-derived protein supplemented diet for MDC group was substituted as 5% casein protein to 5% mealworm protein for 5 weeks and left hindlimb casting immobilization using casting tape for CDC and MDC group was done 1 week before sacrifice. After 5 weeks of mealworm supplementation, the soleus muscle weight of the MDC group was significantly higher compared to the CDC group. In addition, the level of muscle protein synthesis factors p-Akt/Akt, p-4EBP1/4EBP1, and p-S6K/S6K significantly increased in the MDC group compared to the CDC group. On contrary, the level of muscle protein degradation factors (MuRF1 and atrogin-1) was significantly lower in the MDC group than that of the CDC group. These results suggest that mealworm-derived protein supplementation may have a significant role in the prevention of skeletal muscle atrophy via stimulation of muscle protein synthesis factors and inhibition of muscle protein degradation factors, and therefore a promising intervention in sarcopenia.

Sex-related differences in sudomotor function in healthy early twenties focused on activated sweat gland density.

The purpose of this study was to quantitatively assess the difference in sudomotor function between healthy males and females in their early twenties by measuring skin surface area and activated sweat gland density (ASGD). The quantitative sudomotor axon reflex test (QSART), a method for evaluating autonomic nervous system activity, was used for quantification. In QSART, the sweat glands are activated directly or indirectly by the subcutaneous application of neurotransmitters, such as acetylcholine, through iontophoresis. This series of mechanisms is called the sudomotor axon reflex. After recording age, height, weight, and several measurements of the forearm, QSART was performed on 101 healthy controls aged 21-26 years to measure ASGD. The mean temperature and humidity on the measurement days were 11.4°C and 58.1% on May 3, 2018, and 14.7°C and 70.3% on May 10, 2018. The result of independent sample t-test showed higher ASGD in women (P < 0.05). The body surface area and the surface area of the forearms were higher in men (P < 0.001), but the number of activated sweat glands was not significantly different according to sex. The activated sweat gland counts of the body and forearms were analyzed through linear regression by age for males and females. Except for the activated sweat gland count of the male body, the analysis showed a tendency to decrease with increasing age but was not statistically significant in any case (P > 0.05). Showing insufficient coefficient of determination (R2), multiple regression analyses with sex and ages did not correct this insignificance between age and activated sweat gland count.

Blood dopamine level enhanced by caffeine in men after treadmill running.

The aim of this study was to investigate the plasma dopamine and serum serotonin levels in humans with and without caffeine (CAFF) ingestion during treadmill running exercise. Thirty male volunteers participated in the randomized experiment involving two groups: CON (n = 15, 200 mL of tap water) versus CAFF (n = 15, 3 mg/kg CAFF and 200 mL tap water). After treadmill running, the dopamine level was significantly increased in the CAFF group (P < 0.01) and was significantly higher than in the CON group (P < 0.01). Serotonin was significantly increased in both groups after treadmill running (P < 0.05). However, serotonin levels showed no significant statistical difference between the groups. Prolactin and cortisol were significantly increased in both groups after treadmill running (P < 0.01). However, there was no significant statistical difference between groups. ß-endorphin level was significantly increased in the CAFF group at after treadmill running (P < 0.01) and was significantly higher than in CON after treadmill running (P < 0.01). In conclusion, 3 mg/kg CAFF ingestion before treadmill running stimulated dopamine release without inhibiting serotonin, which may reduce central fatigue.

Sweating distribution and active sweat glands on the scalp of young males in hot-dry and hot-humid environments.

PURPOSE: We investigated the effects of humidity on regional sweating secretion and active sweat gland density on the scalp during passive heating in hot environments. METHODS: Eight male subjects shaved their heads prior to expose to dry (30%RH; H30%) and humid (85%RH; H85%) conditions at an air temperature of 32 °C. Total sweat rate, local sweat rates (frontal, vertex, temporal, and occipital regions), active sweat glands on the scalp (2 frontal, 2 parietal, 2 temporal, 1 occipital, and 1 vertex), and rectal and skin temperatures were measured during leg immersion in 42 °C water for 60 min. RESULTS: (1) Total sweat rates were greater for H30% (179.4 ± 35.6 g h-1) than for H85% (148.1 ± 27.2 g h-1) (P < 0.05). (2) Scalp sweat secretion tended to be greater in the H85% than the H30%. (3) Head sweat rates were greater on the frontal than on the vertex for both humidity conditions (P < 0.05). (4) Active sweat gland density on the scalp was greater for H85% (82 ± 13 glands cm-2) than for H30% (62 ± 17 glands cm-2) (P < 0.05). (5) No significant difference was found in rectal temperature between H30% and H85%, whereas mean skin temperature was significantly lower for H30% (34.8 ± 0.7 °C) than for the H85% condition (36.0 ± 0.3 °C) (P < 0.05). CONCLUSIONS: These results indicate that the thermoregulatory sweating responses for the scalp region were significantly increased in the hot-humid condition compared to the hot-dry condition. Among the regions on the scalp surface, the vertex was the least sensitive to the change in humidity.

Seasonal acclimation in sudomotor function evaluated by QSART in healthy humans.

The quantitative sudomotor axon reflex testing (QSART) is a classic test of routine postganglionic sudomotor function. We investigated sudomotor function by QSART after summer (July 2012) and winter (January 2013) seasonal acclimation (SA) in the Republic of Korea. QSART with acetylcholine (ACh) iontophoresis were performed to determine directly activated (DIR) and axon reflex-mediated (AXR1, 2) sweating rate. Onset time of axon reflex, activated sweat gland density (ASGD), activated sweat gland output (ASGO), tympanic and skin temperatures (Tty, Tsk), basal metabolic rate (BMR), and evaporative loss volume changes were measured. Tympanic and mean body temperature (Tb; calculated from Tty, Tsk) were significantly lower after summer-SA than that of winter-SA. Sweat onset time was delayed during winter-SA compared to that after summer-SA. BMR, AXR(1), AXR(2), and DIR sweat rates, ASGD and ASGO, and evaporative loss volume were significantly diminished after winter-SA relative to after summer-SA. In conclusion, changes in sweating activity measured by QSART confirmed the involvement of the peripheral nervous system in variation of sudomotor activity in seasonal acclimation.

Seasonal Acclimatization in Summer versus Winter to Changes in the Sweating Response during Passive Heating in Korean Young Adult Men.

We investigated the sweating response during passive heating (partial submersion up to the umbilical line in 42±0.5℃ water, 30 min) after summer and winter seasonal acclimatization (SA). Testing was performed in July during the summer, 2011 [summer-SA; temp, 25.6±1.8℃; relative humidity (RH), 82.1±8.2%] and in January during the winter, 2012 (winter-SA; temp, -2.7±2.9℃; RH, 65.0±13.1%) in Cheonan (126°52'N, 33.38'E), Republic of Korea. All experiments were carried out in an automated climatic chamber (temp, 25.0±0.5℃: RH, 60.0±3.0%). Fifteen healthy men (age, 23.4±2.5 years; height, 175.0±5.9 cm; weight, 65.3±6.1 kg) participated in the study. Local sweat onset time was delayed during winter-SA compared to that after summer-SA (p< 0.001). Local sweat volume, whole body sweat volume, and evaporative loss volume decreased significantly after winter-SA compared to those after summer-SA (p<0.001). Changes in basal metabolic rate increased significantly after winter-SA (p< 0.001), and tympanic temperature and mean body temperature were significantly lower after summer-SA (p<0.05). In conclusion, central sudomotor acitivity becomes sensitive to summer-SA and blunt to winter-SA in Rebubic of Korea. These results suggest that the body adjusts its temperature by economically controlling the sweating rate but does not lower the thermal dissipation rate through a more effective evaporation scheme after summer-SA than that after winter-SA.

Passive heat loading links lipolysis and regulation of fibroblast growth factor-21 in humans.

There is relativley little information on the serum biomarkers of heat stress. Therefore, the goal of this study was to verify the effect of passive heat loading (PHL) on the expression of fibroblast growth factor-21 (FGF21) and free fatty acids (FFAs). Four PHL protocols based on intensity (39 °C vs. 43 °C, leg immersion, 30 min) and type (leg vs. half immersion, 42 °C, 30 min) were used. Each protocol was applied on a 2 day cycle to 12 healthy adult males (age, 22.4 ± 2.9 years; height, 174.1 ± 4.6 cm; weight, 71.3 ± 5.6 kg; body mass index, 23.1 ± 3.0). The subjects were categorized into two groups according to the study design (randomized, with a parallel trial). Body temperature, FGF21 and FFAs were determined prior to PH L, immediately and 60 min after PHL. Body temperature was significant higher (43 °C) than the 39 °C measured under identical PHL type (leg immersion). PHL was effective for the expression of FGF21 and for lipolysis. The quantitative levels of FGF21 and FFA increased with increasing temperature (39 °C<42 °C<43 °C). A significant difference in the quantitative levels of FGF21 and FFAs was also evident based on the type of PHL (leg

Decreased sudomotor function is involved in the formation of atopic eczema in the cubital fossa.

BACKGROUND: Eczema in the cubital fossa, which is susceptible to sweat, is frequently observed in atopic dermatitis (AD). However, there has been no direct evidence that sweating causes eczema in the cubital fossa. METHODS: To investigate this issue, axon reflex-mediated sweating volume (AXR) and skin barrier function in the cubital fossa were measured in subjects with AD and in healthy volunteers, and were applied to clinical feature of the cubital fossa. RESULTS: AXR in the cubital fossa decreased in AD subjects; it positively correlated only with water-holding capacity in healthy subjects but not in patients with in AD. Furthermore, AD subjects with lichenoid eczema and either prurigo or papules over the cubital fossa showed extremely decreased AXR. CONCLUSIONS: These results suggest that decreased sweating is a major source of water in the stratum corneum, and decreased sudomotor function may be involved in both the cause and aggravation of representative atopic eczema in the cubital fossa.

Effects of music therapy as an alternative treatment on depression in children and adolescents with ADHD by activating serotonin and improving stress coping ability.

OBJECTIVE: The objective of this study was to determine the effect of music therapy as an alternative treatment on depression in children and adolescents with attention-deficit hyperactivity disorder (ADHD) by activating serotonin (5-HT) and improving stress coping ability. METHODS: This study is designed based on randomization method. A total of 36 subjects participated in the experiment, consisting of an ADHD control group (n = 18) and ADHD music therapy group (n = 18). The ADHD control group received standard care, while the ADHD music therapy group received music therapy and standard care. The ADHD music therapy group received both active music therapy (improvisation) and receptive music therapy (music listening) for 50 minutes, twice a week, for 3 months: a total of 24 times. From a neurophysiological perspective, changes in depression and stress were tracked by measuring 5-HT secretion, cortisol expression, blood pressure (BP), heart rate (HR), and CDI and DHQ psychological scales. RESULTS: The ADHD music therapy group's 5-HT secretion increased (p < 0.001), whereas cortisol expression (p < 0.001), BP (p < 0.001) and HR (p < 0.001) decreased. The CDI and DHQ psychological scales also showed positive changes (p < 0.01 and p < 0.001, respectively). However, the ADHD Con G's (who did not receive music therapy) 5-HT secretion did not increase, whereas cortisol expression, BP, and HR did not decrease. In addition, the CDI and DHQ psychological scales did not display positive changes. CONCLUSIONS: In conclusion, the application of music therapy as an alternative treatment for ADHD children and adolescents showed positive neurophysiological and psychological effects. Therefore, this study would like to propose a new alternative to medicine for preventing and treating depression through various uses of music therapy.

Abnormal axon reflex-mediated sweating correlates with high state of anxiety in atopic dermatitis.

BACKGROUND: Sweating plays a key role in skin homeostasis, including antimicrobial and moisturizing effects, and regulation of skin surface pH. Impaired axon reflex-mediated (AXR) sweating has been observed in patients with atopic dermatitis (AD). However, the mechanism of such abnormal sudomotor axon reflex remains to be revealed. METHODS: To investigate this mechanism, sudomotor function was analyzed using a quantitative sudomotor axon reflex test (acetylcholine iontophoresis) in patients with AD (n = 26) and healthy volunteers (n = 12). Correlation between sudomotor function and certain background factors, including Spielberger State Trait Anxiety Inventory score, Severity Scoring of Atopic Dermatitis (SCORAD) score, number of circulating eosinophils, and serum concentrations of thymus and activation-regulated chemokine and immunoglobulin E radioimmunosorbent test, was validated. RESULTS: Latency time was significantly prolonged in AD (p = 0.0352), and AXR sweating volume (mg/0-5 min) was significantly lower in AD patients than in healthy controls (p = 0.0441). Direct sweating volume (mg/0-5 min) was comparable in AD patients and healthy controls. A significant correlation between the evaluation results of quantitative sudomotor axon reflex tests and certain background factors was not observed. The latency time in non-lesioned and lesioned areas for AD patients versus continuous anxiety value in the Spielberger State Trait Anxiety Inventory and the AXR versus SCORAD showed significant correlations (p = 0.0424, p = 0.0169, and p = 0.0523, respectively). CONCLUSIONS: Although the number of study subjects was little, abnormal AXR sweating in patients with AD was observed. Correlative analysis suggests possible involvement of continuous anxiety and the immune system in such abnormal sudomotor function.

Coffee intake may promote sudomotor function activation via the contribution of caffeine.

Objectives: To determine whether drinking coffee with caffeine accelerates the sympathetic response to acetylcholine (ACh). Methods: Tests were performed twice at 1-week intervals following the intake of coffee. Subjects were randomly divided into two groups: Group A was administered 16 fluid oz of water (CON), while Group B was given 16 fluid oz of coffee (Coffee). After 1 week, Group A was administered 16 fluid oz of coffee (Coffee), while Group B was given 16 fluid oz of water (CON). The quantitative sudomotor axon reflex test (QSART) was performed after intake of coffee and water and a 40 min break. QSART with iontophoresis and 10% ACh was performed to determine axon reflex (AXR) mediated with and without iontophoresis [AXR (1) and AXR (2), respectively], and directly activated sweating (DIR). Results: The sweat onset time of the AXR was shorter in the Coffee compared with the CON (p < 0.05). The sweat rates in AXR (1) AXR (2) and DIR were significantly higher in the Coffee than in the CON (p < 0.05, p < 0.05, p < 0.01, respectively). In addition, the Coffee showed significantly higher density of activated sweat glands and activated sweat gland output than the CON (p < 0.05, p < 0.01, respectively). The overall results of this study showed that coffee intake could stimulate higher activation in both AXR and DIR sweat responses. Conclusion: Coffee intake can improve sweating sensitivity in both the AXR and DIR by the contribution of caffeine contained in coffee. This suggests that other compounds in coffee may not inhibit the sympathetic response to ACh. Therefore, coffee may be clinically worth considering as a supplement for the activation of the cholinergic and sudomotor function.

Effects of caffeine ingestion and thermotherapy on blood orexin circulation in humans.

Caffeine and orexin can affect awakening, neuroendocrine, and sympathetic nerve function. Our previous study has reported that caffeine intake can increase human body temperature. However, little is known about the combined effects of thermotherapy and caffeine intake on human serum orexin concentrations. Forty-two healthy male subjects with age of 26.72 ± 5.05 years, height of 174.10 ± 7.09 cm, and body weight of 74.68 ± 8.91 kg participated in this study. They were randomly assigned to a control (CON) group (n = 21) and a caffeine (CAFF) group (n = 21). After thermotherapy (half-body immersion in a hot water bath at 42 ± 0.5 °C, circulating orexin level increased more (p < 0.05) in the CAFF group than in the CON group. Positive relationships between mean body temperature and orexin were observed before and after heat stimulation (p < 0.001). Caffeine intake boosted the upregulation of serum orexin concentrations in subjects undergoing thermotherapy.

The acclimatization of Haenyeo to a cold environment and occupational characteristics evaluated by orexin and irisin levels.

Background: Haenyeo is a woman who has the job of collecting seafood in the Jeju Sea at an average temperature of 13°C-14°C. The purpose of this study was to examine the cold acclimatization and occupational characteristics of Haenyeo through biomarkers such as orexin and irisin related to heat generation in the body. Methods: Twenty-one Haenyeo and 25 people with similar age, body type, and body mass index were selected as the control group (Control G). In the cold exposure experiment, a climate chamber was set to 5°C and both feet were immersed in a 15°C water tank for 30 minutes. Tympanic temperature (Tty) and skin temperature (Tsk) were measured, and the mean body temperature (mTb) was calculated. Blood samples were collected before and immediately after the examination. Orexin and irisin levels were analyzed. Results: Orexin levels were elevated after cold stimulation from 12.17 ± 4.44 to 12.95 ± 4.53 ng/mL (Haenyeo group [Haenyeo G], p < 0.01) and 10.37 ± 3.84 to 11.25 ± 4.02 ng/mL (Control G, p < 0.001). Irisin levels were elevated after cold stimulation from 4.83 ± 2.28 to 5.36 ± 2.23 ng/mL (Haenyeo G, p < 0.001) and 3.73 ± 1.59 to 4.18 ± 2.04 ng/mL (Control G, p < 0.001). The difference between Haenyeo G and Control G values in orexin and irisin appears not only in pre-exposure but also in post-exposure (p < 0.05). Conclusions: Our experimental results suggest that Haenyeo G were relatively superior in cold tolerance to Control G under cold exposure conditions. Haenyeo's cold acclimatization is due to the basic differences in pyrogens regarding body temperature control such as orexin and irisin. This means that Haenyeo are advantageous for cold survival.

Effect of Heat Stimulation on Circulating Irisin in Humans.

High temperatures lead to oxidative stress. The aim of the study was to determine whether heat stimulation-induced hyperthermia can increase the level of circulating irisin. Twenty-one healthy female subjects (age, 26.3 ± 2.71 years; height, 162.1 ± 3.15 cm; weight, 54.2 ± 3.86 kg; and body surface area, 1.57 ± 0.11 m2) not taking contraceptives participated in this study. All experiments were performed individually for each participant when they were in the early proliferative menstrual phase. In an automated climate chamber (25 ± 0.5°C), the heat load was applied via half-body immersion into a hot water bath (42 ± 0.5°C). Five-minutes break was provided every after 5 min of immersion and the total passive heating time was 30 min. Tympanic temperature (Tt y) and skin temperature (Ts) were measured. Mean body temperature (mTb) was calculated. Blood samples were collected before and immediately after immersion. Levels of irisin, cortisol, creatine kinase (CK), and lactate dehydrogenase (LDH) were analyzed. Tty, mTb and serum irisin levels increased after hot water immersion. The blood levels of cortisol, CK, and LDH were also elevated after hot water immersion. Heat stimulation might increase the levels of circulating irisin in humans in response to oxidative stress.

Increase effect of transforming growth factor on eotaxin production by normal cultured dermal fibroblasts stimulated with interleukin-4: inhibitory effect of suplatast tosilate on eotaxin production.

Eotaxin plays a central role in the development of allergic disease, including atopic dermatitis, asthma, and nasal allergy. Interleukin (IL)-4 induces eotaxin production in normal human dermal fibroblasts. On the other hands, Transforming growth factor-beta (TGF-beta), a multifunctional regulatory cytokine, affects many biological functions, including fibroblast growth and differentiation and Th2 cytokine regulation. In this study, we investigated the effect of TGF-beta on IL-4-induced eotaxin production by normal human fibroblasts, as well as the effect of suplatast tosilate, an antiallergic drug that selectively inhibits Th2 cytokine production. Dermal fibroblast treatment with IL-4 and TGF-beta for 24 h increased eotaxin production and expression of eotaxin mRNA, as measured by enzyme-linked immunosorbent assay (ELISA) and reverse-transcriptase polymerase chain reaction (RT-PCR), respectively. TGF-beta synergistically up-regulated eotaxin production and eotaxin mRNA expression when stimulated with IL-4. Suplatast tosilate dose-dependently inhibited eotaxin production induced by IL-4 or IL-4 plus TGF-beta. These results suggest that TGF-beta may regulate skin allergic inflammation by up-regulating eotaxin production in dermal fibroblasts. Suplatast tosilate might suppress this inflammation by inhibiting eotaxin production.

Depression, symptoms and the quality of life in patients on hemodialysis for end-stage renal disease.

BACKGROUND: End-stage renal disease (ESRD) is a progressive, debilitating, chronic illness requiring nursing and medical interventions. The goal of this study was to explore the level of depression experienced by patients receiving hemodialysis (n = 146), and to compare the symptoms with the quality of life (QoL) between patients that were depressed and those that were not depressed. METHODS: For this descriptive, cross-sectional survey, participants aged 18 and above were recruited from three different regions in the Republic of Korea. The level of depression, symptoms and QoL of the participants were measured by questionnaires from October to December 2006. The data was analyzed with descriptive statistics, the chi(2) and t test using the SPSS WIN 14.0 program. RESULTS: The prevalence of depression (PHQ-9) among the participants was 25.34%. There were more symptoms reported in the depressed group of patients than in those that were not depressed. In addition, the QoL was not as good in the depressed group when compared to patients that were not depressed. CONCLUSION: Therefore, the evaluation for depression may be an important part of the management of patients with ESRD. Further research is needed to understand the causal relationship between depression and health outcomes.

Tropical Malaysians and temperate Koreans exhibit significant differences in sweating sensitivity in response to iontophoretically administered acetylcholine.

Natives of the tropics are able to tolerate high ambient temperatures. This results from their long-term residence in hot and often humid tropical climates. This study was designed to compare the peripheral mechanisms of thermal sweating in tropical natives with that of their temperate counterparts. Fifty-five healthy male subjects including 20 native Koreans who live in the temperate Korean climate (Temperate-N) and 35 native tropical Malaysian men that have lived all of their lives in Malaysia (Tropical-N) were enrolled in this study after providing written informed consent to participate. Quantitative sudomotor axon reflex testing after iontophoresis (2 mA for 5 min) with 10% acetylcholine (ACh) was used to determine directly activated (DIR) and axon reflex-mediated (AXR) sweating during ACh iontophoresis. The sweat rate, activated sweat gland density, sweat gland output per single gland activated, and oral and skin temperature changes were measured. The sweat onset time of AXR (nicotinic-receptor-mediated) was 56 s shorter in the Temperate-N than in the Tropical-N subjects (P < 0.0001). The nicotinic-receptor-mediated sweating activity AXR (1), and the muscarinic-receptor-mediated sweating activity DIR, in terms of sweat volume, were 103% and 59% higher in the Temperate-N compared to the Tropical-N subjects (P < 0.0001). The Temperate-N group also had a 17.8% (P < 0.0001) higher active sweat gland density, 35.4% higher sweat output per gland, 0.24 degrees C higher resting oral temperature, and 0.62 degrees C higher resting forearm skin temperature compared to the Tropical-N subjects (P < 0.01). ACh iontophoresis did not influence oral temperature, but increased skin temperature near where the ACh was administered, in both groups. These results suggest that suppressed thermal sweating in the Tropical-N subjects was, at least in part, due to suppressed sweat gland sensitivity to ACh through both recruitment of active sweat glands and the sweat gland output per each gland. This physiological trait guarantees a more economical use of body fluids, thus ensuring more efficient protection against heat stress.