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.     

Shivering modulation in humans: Effects of rapid changes in environmental temperature

During cold exposure, increase in heat production is produced via the activation of shivering thermogenesis and nonshivering thermogenesis, the former being the main contributor to compensatory heat production in non-acclimatized humans. In rats, it has been demonstrated that shivering thermogenesis is modulated solely by skin thermoreceptors but this modulation has yet to be investigated in humans. The aim of this study was to determine if cold-induced shivering in humans can be modulated by cutaneous thermoreceptors in conditions where increases in heat loss can be adequately compensated by increases in thermogenic rate. Using a liquid-conditioned suit, six non-acclimatized men were exposed to cold (6 °C) for four 30 min periods, each of them separated by 15 min of heat exposure (33 °C). Core temperature remained stable throughout exposures whereas skin temperatures significantly decreased by 12% in average during the sequential cold/heat exposures compared to baseline (p<0.0001). Shivering intensity and metabolic rate increased significantly during 6 °C exposures (3.3±0.7% MVC, 0.40±0.0 L O₂/min, respectively) and were significantly reduced during 33 °C exposure (0.5±0.1% MVC, 0.25±0.0 L O₂/min; p<0.005 for both). Most importantly, shivering could be quickly and strongly inhibited during 33 °C exposure although skin temperature often remained below baseline values. In conclusion, under compensatory conditions, cutaneous thermoreceptors appear to be a major modulator of the shivering response in humans and seem to react rapidly to changes in the microclimate right next to the skin and to skin temperature.     

Effects of acute exercise on serum interleukin-17 concentrations in hot and neutral environments in trained males

The purpose of this study was to determine the effects of acute exercise on IL-17 concentrations in hot and neutral environments in trained males. Ten trained, non-heat acclimated males performed two 1 h run on treadmill at 60% VO2max in neutral (22±1 °C, 50±5RH) and hot (35±1 °C, 50±5) temperature conditions. Samples of the venous blood were taken (Pre, post, 2 h post) for determination of serum IL-17, cortisol concentrations and numbers of leukocytes and neutrophils. In addition, body temperature, RPE and PVC during exercise were measured. The collected data were analyzed using the Repeated-Measures analyses of variance and Bonferroni post hoc and Paird T tests (p<0.05). The concentration of cortisol and total number of leukocytes increased significantly after exercise, in both conditions (p<0.0001) and were significantly higher in hot than neutral (p=0.016, p=0.002). During the rest period (2 h post) the number of neutrophils increased significantly in hot environment (p=0.018). The concentrations of IL-17 increased significantly only after exercise in hot (p<0.0001) and were significantly higher during hot than neutral (p=0.002). The results suggest that exercise in hot environment cause increase in body temperature, perceived exertion and cardiac-vascular changes which are sufficient to elicit immune, hormonal and inflammatory responses. The present results confirm the additive effect of heat stress on the IL-17 response during exercise.     

Human plasma inflammatory response during 5 days of exercise training in the heat

The aim of the present investigation was to examine the response of 80 plasma inflammatory analytes during five days of exercise in a hot (38 °C, 40% relative humidity) environment. 15 male participants (25±4yrs, 54±6 ml kg⁻¹ min⁻¹ VO₂ max), with no heat exposure within the previous 3 weeks, were asked to cycle in a hot environment at 70% of their VO₂ max workload until their terminal temperature was obtained, for 5 consecutive days. Terminal temperature was determined as the core temperature at volitional exhaustion or a core temperature of 39.5 °C, whichever came first. Blood samples were collected pre- and post-exercise on day 1 and day 5. Pre-trial urine specific gravity and body weight was not different on day 1 and day 5. Exercise time and heart rate at terminal temperature did not change during the five days. Of the 52 plasma analytes that increased in concentration on day 1, only 30 demonstrated increased concentrations at terminal temperature on day 5. Resting concentrations of 18, both pro- (IL-12p40, IL-15) and anti-inflammatory (IL-1ra, IL-10, IL-13) analytes were elevated on day 5 compared to day 1. We conclude that individuals completing consecutive days of exercise in the heat, but not definitively attaining heat acclimation, have increased resting levels of many inflammatory analytes associated with heat illness, but also demonstrate a reduced inflammatory response to a subsequent bout of exercise in the heat.     

Effects of heat acclimatisation on work tolerance and thermoregulation in trained tropical natives

This study aimed to investigate the effects of heat acclimatisation on thermoregulatory responses and work tolerance in trained individuals residing in the tropics. Eighteen male trained soldiers, who are native to a warm and humid climate, performed a total of four heat stress tests donning the Skeletal Battle Order (SBO, 20.5 kg) and Full Battle Order (FBO, 24.7 kg) before (PRE) and after (POST) a 10-day heat acclimatisation programme. The trials were conducted in an environmental chamber (dry bulb temperature: 32 °C, relative humidity: 70%, solar radiation: 400 W/m²). Excluding the data sets of which participants fully completed the heat stress tests (210 min) before and after heat acclimatisation, work tolerance was improved from 173±30 to 201±18 min (∼21%, p<0.05, n=9) following heat acclimatisation. Following heat acclimatisation, chest skin temperature during exercise was lowered in SBO (PRE=36.7±0.3 vs. POST=36.5±0.3 °C, p<0.01) and FBO (PRE=36.8±0.4 vs. POST=36.6±0.3 °C, p<0.01). Ratings of perceived exertion were decreased with SBO and FBO (PRE=11±2; POST=10±2; p<0.05) after heat acclimatisation. Heat acclimatisation had no effects on baseline body core temperature, heart rate and sweat rate across trials (p>0.05). A heat acclimatisation programme improves work tolerance with minimal effects on thermoregulation in trained tropical natives.     

Metabolic and hormonal responses during exercise at 20°, 0° and −20°C

This study was designed to clarify the effects of cold air exposure on metabolic and hormonal responses during progressive incremental exercise. Eight healthy males volunteered for the study. Informed consent was obtained from every participant. The following protocol was administered to each subject on three occasions in a climatic chamber in which the temperature was 20°, 0° or –20°C with relative humidity at 60%±1%. Exercise tests were conducted on an electrically braked ergocycle, and consisted of a propressive incremental maximal exercise. Respiratory parameters were continuously monitored by an automated open-circuit sampling system Exercise blood lactate (LA), free fatty acids (FFA), glucose levels, bicarbonate concentration (HCO ₃ ^– ), acidbase balance, plasma epinephrine (E) and norepinephrine (NE) were determined from venous blood samples obtained through an indwelling brachial catheter. Maximal oxygen uptake was significantly different between conditions: 72.0±5.4 ml kg^–1 min^–1 at 20°C; 68.9±5.1 ml kg^–1 min^–1 at 0°C and 68.5±4.6 ml kg^–1 min^–1 at –20°C. Workload, time to exhaustion, glucose levels and rectal Catecholamines and lactate values were not significantly altered by thermal conditions after maximal exercise but the catecholamines were decreased during rest. Bicarbonate, respiratory quotient, lactate and ventilatory thresholds increased significantly at –20°C. The data support the contention that metabolic and hormonal responses following progressive incremental exercise are altered by cold exposure and they indicate a marked decrease in maximal oxygen uptake, time to exhaustion and workload.This study was supported by grants from CSR, Univesité du Québec; FIR, Université du Québec à Trois-Rivières and NATO no, 86.0435.     

The effect of exercise induced hyperthermia on muscle fibre conduction velocity during sustained isometric contraction

This study investigated the effect of dynamic exercise in a hot environment on muscle fibre conduction velocity (MFCV) of the knee extensors during a sustained isometric contraction. Seven trained male cyclists (mean [±SD], age, and were 35 ± 9.9 and 57.4 ± 6.6 ml kg⁻¹ min⁻¹) cycled for 50 min at 60% of peak power output in either: (1) 40 °C (HOT); or (2) 19 °C (NEUTRO); and (3) remained passive in 40 °C (PASS). Post-intervention a 100 s maximal sustained isometric contraction (SMC) of the knee extensors was performed. Rectal temperature increased (p < 0.01) for both HOT and NEUTRO with PASS unchanged and with HOT rising higher (p < 0.01) than NEUTRO (38.6 ± 0.4 vs. 37.6 ± 0.4 °C). Muscle temperature increased (p < 0.01) for all three conditions with HOT rising the highest (p < 0.01) (40.3 ± 0.5 vs. 38.3 ± 0.3 and 37.6 ± 1.3 °C for NEUTRO and PASS, respectively). Lactate showed higher accumulation (p < 0.01) for HOT than NEUTRO (6.9 ± 2.3 vs. 4.2 ± 2.1 mmol l⁻¹). During SMC the torque, electromyography root mean squared (RMS) and MFCV all significantly (p < 0.01) declined. Only in HOT did MFCV decline significantly (p < 0.01) less than torque and RMS (9.9 ± 6.2% vs. 37.5 ± 17.8% and 37.6 ± 21.4%, respectively). In conclusion, during exercise induced hyperthermia, reduced motor unit recruitment as opposed to slower conducting properties of the muscle fibre appears to be responsible for the greater reduction in torque output.     

Hormonal growth-promotant effects on grain-fed cattle maintained under different environments

Six steers (3/4 Charolais×1/4 Brahman) (mean body weight 314±27 kg) and six spayed heifers (3/5 Shorthorn×2/5 Red Angus) (mean body weight 478±30 kg) were used to determine the effects of climatic conditions and hormone growth promotants (HGP) on respiration rate (RR; breaths/min), pulse rate (beats/min), rectal temperature (RT; °C), and heat production (HP; kJ). Cattle were exposed to the following climatic conditions prior to implantation with a HGP and then again 12 days after implantation: 2 days of thermoneutral conditions (TNL) [21.9±0.9°C ambient temperature (T_A) and 61.7±22.1% relative humidity (RH)] then 2 days of hot conditions [HOT; 29.2±4°C (T_A) and 78.3±13.2% (RH)], then TNL for 3 days and then 2 days of cold conditions [COLD; 17.6±0.9°C (T_A) and 63.4±1.8% (RH); cattle were wet during this treatment]. The HGP implants used were: estrogenic implant (E), trenbolone acetate implant (TBA), or both (ET). Both prior to and following administration of HGP, RRs were lower (P<0.05) on cold days and greater (P<0.05) on hot days compared to TNL. On hot days, RTs, were 0.62°C higher after compared to before implanting. Across all conditions, RTs were >0.5°C greater (P<0.05) for E cattle than for TBA or ET cattle. On cold days, RTs of steers were >0.8°C higher than for the heifers, while under TNL and HOT, RTs of steers were 0.2–0.35°C higher than those of heifers. Prior to implantation, HP per hour and per unit of metabolic body weight was higher (P<0.05) for cattle exposed to hot conditions, when compared to HP on cold days. After implantation, HP was greater (P<0.05) on hot days than on cold days. Under TNL, ET cattle had the lowest HP and greatest feed intake. On hot days, E cattle had the lowest HP, and the highest RT; therefore, if the potential exists for cattle death from heat episodes, the use of either TBA or ET may be preferred. Under cold conditions HP was similar among implant groups.     

Effect of hydration,photoperiod and temperature on diapause termination in eggs ofPetrobia (Tetranychina) harti (Acari: Tetranychidae)

Petrobia harti (Ewing) displays a facultative summer diapause in the egg stage. An adult female will lay only either diapause or non-diapause eggs throughout her life. In the laboratory, diapause eggs are laid by females which develop on detachedOxalis articulata leaves under long-day photoperiods and a relatively low temperature of 19±1°C.Diapause occurs in a stage of advanced embryonic development, in which the embryo appears U-shaped when observed from the egg's ventral side. Embryonic development ceased at this stage, and no further growth occurred when the eggs were kept under a relative humidity of about 70% in various photoperiod and temperature conditions. However, when the eggs were hydrated by placing them on wet cotton wool, development in some embryos (apparently in those which had completed their diapause development) proceeded beyond the U-stage at a rate similar to that in non-diapause embryos and the eggs hatched.Under LD 168 and 19±1°C or 26±1°C, the later from oviposition the period of egg hydration started, the higher the percentage of diapause termination. Under LD 168 and 26±1°C, diapause termination occurred mostly during the first week of hydration, while at 19±1°C mostly during the second and third week.At 26±1°C, in eggs hydrated 15 days but not 30 days from oviposition, the percentage of diapause termination was higher under a long-day than under a short-day photoperiod.Under LD 168, when the eggs were hydrated continuously from oviposition or starting 15, 30 and 45 days from it, the percentage of diapause termination was higher at 26±1°C than at 19±1°C.The percentage of diapause-laying adult females and the intensity of egg diapause were higher when the pre-imaginal mites grew at LD 1212 and 19±1°C, than when they grew at LD 168 and 26±1°C. This maternal effect on egg diapause intensity was expressed when the eggs were maintained at LD 1212 and 19±1°C but not at LD 168 and 26±1°C.     

Validity of a model of cultured myocardial cells for assessment of cardioplegia

Myocardial protection is usually studied in vitro on perfused heart preparations, but never directly on cultured cardiomyocytes. We evaluated a model of cultured newborn rat cardiomyocytes to study both the cytotoxicity and the protective effect against chemical hypoxia of three cardioplegic solutions (St Thomas' I, Bretschneider, St Thomas' II) under normothermic (37°C) and hypothermic (4°C) conditions. Cytotoxicity was evaluated in 50% and 100% concentrations of the cardioplegic solutions with incubation times from 90 to 360 min. Myocardial protection was studied in 50% cardioplegic solution with metabolic inhibitors. Immediate and late viabilities, after 24 h of recovery in the medium, were evaluated by simultaneous staining with fluorescein diacetate and propidium iodide.At 37°C, the 50% concentration of the three cardioplegic solutions did not modify cell viability. At 37°C, with 360 min of incubation, the 100% concentration of the St Thomas' I and Bretschneider solutions diminished immediate viability (mean ± SD: medium 87% ± 2%; St Thomas' I 58% ± 5%; Bretschneider 37% ± 8%; St Thomas' II 89% ± 3%) as well as late viability (medium 69% ± 2%; St Thomas' I 32% ± 3%; Bretschneider 24% ± 7%; St Thomas' II 65% ± 4%). At 4°C, immediate and late viabilities were unaffected by cardioplegic solutions.At 37°C, after 360 min incubation time, metabolic inhibitors diminished immediate viability to 29% ± 1% and late viability to zero. None of the three cardioplegic solutions used at 50% concentration prevented this effect.At 4°C, immediate viability was not significantly affected by metabolic inhibitors (73% ± 10%), but the use of Bretschneider cardioplegic solution seemed to be detrimental (53% ± 9%). On the other hand, recovery phase after pretreatment with metabolic inhibitors with or without cardioplegic solutions for 360 min significantly diminished late viability (medium 63% ± 7%; metabolic inhibitors 17% ± 8%; St Thomas' I 17% ± 6%; Bretschneider 8% ± 6%; St Thomas' II 15% ± 3%) and again cardioplegia was inefficient. In conclusion, in this in vitro model for the study of cardioplegic solutions, only pure concentrations of the St Thomas' I and Bretschneider solutions under normothermic conditions were cytotoxic. The well-known protective effects of hypothermia against ischemia and reperfusion injury were both reproduced. Therefore, and even though cardioplegia failed to have any protective effect, probably owing to a severe metabolic inhibition, this model may be useful for studying myocardial protection.     

Force variability depends on core and muscle temperature

The aim of this study was to investigate if voluntary activation and force variability during maximal voluntary contraction (MVC) depends more on muscle (local) or body (core) temperature. Ten volunteers performed a 2-min MVC of the knee extensors under the control (CON) conditions (ambient temperature (21 °C), relative humidity (30%), and air velocity (∼0.1 m/s)) as well as after heating (HT) and cooling (CL) of the lower body. During water manipulation procedure lower body was immersed up to the waist in a water bath at ∼44 °C for 45 min for HT experiment, and ∼15 °C for 30 min for CL experiment. Peak torque, torque variability, muscle voluntary activation and half-relaxation time were assessed during the exercise. HT increased muscle (2.8±0.2 °C) and rectal (1.9±0.1 °C) temperatures while CL lowered muscle (2.2±0.2 °C) temperature, but did not affect rectal temperature. During 2-min MVC, peak torque decreased (P<0.05; SP>90%) and to a lower level in HT compared to CON and CL experiments (52.6±2.3% versus 69.0±2.3% and 65.6±1.9% MVC, respectively, P<0.05; SP>90%). Torque variability increased significantly during exercise and was significantly larger in HT and lower in CL compared to CON experiment. Voluntary activation of exercising muscle was more depressed in HT (i.e. greater central fatigue) and the smallest effect was found in CL compared to CON. In conclusion increased core and muscle temperature impairs voluntary activation and increases force variability of the exercising muscles while a local muscle cooling decrease force variability but has a small effect on central fatigue.     

A non-invasive device to continuously determine heat strain in humans

Heat stroke remains a very dangerous, potentially lethal illness in humans. The Physiological Strain Index (PSI), originally based on heart rate and rectal temperature recordings in humans, describes heat strain in quantitative terms. The objective of our study was to establish whether the rectal temperature recordings serving to determine the PSI could be replaced by a non-invasive skin temperature sensor combined with a heat flux sensor (Double Sensor) attached to the inside of a helmet. We assumed (i) that the difference between the recordings by the device under test and the rectal temperature should be less than ±1.0 °C for ±2 S.D. at 10, 25, and 40 °C ambient temperature, and (ii) that the temperature predictions based on the Double Sensor temperature should differ by less than 1 PSI score from the calculations based on recordings of the rectal temperature. Twenty male subjects participated in the study. Rectal, nasopharyngeal, and skin temperatures, heat flux, and cardiovascular data were collected continuously during different experimental setups at ambient temperatures of 10, 25, and 40 °C. Depending on the protocols, the exercise intensities varied from 25% to 55% of the individual VO_2max. A comparison of the recordings obtained from the device under test with those of the rectal temperature revealed that (i) the recordings of the Double Sensor differed by −0.16 to 0.1 °C from the mean rectal temperature, (ii) the concordance correlation coefficients (CCC) during all work and rest periods rose with rising ambient temperatures (all work periods: 10 °C: 0.49; 25 °C: 0.69; 40 °C: 0.75; all rest periods: 10 °C: 0.39; 25 °C: 0.81; 40 °C: 0.74), and that (iii) the Double Sensor in the helmet showed that during all rest periods and in all ambient conditions, the temperature dropped much more quickly than what was recorded when taking the rectal temperature (p<0.01). When we compared the PSI values based on the rectal temperature recordings to those determined by the Double Sensor, it was found that (i) the PSI based on the Double Sensor recordings differed by −0.27 to 0.17 from the mean PSI established by rectal temperature recordings. Furthermore, the CCC for the PSI rose during all work periods (10 °C: 0.81, 25 °C: 0.93, 40 °C: 0.87) and rest periods (10 °C: 0.68; 25 °C: 0.93; 40 °C: 0.79). In conclusion, under warm/hot environmental conditions the device under test provided a reliable method of assessing the PSI in operational environments to improve physiological situational awareness and safety in action. However, there are some limitations that reduce the device's performance in cold environments; these need to be investigated further.     

Core temperature response to cycling exercise: Effect of time of day and measurement site

This study evaluated the effect of time of day and temperature measurement site on core temperature response to exercise. Six trained cyclists performed a 1 h cycling exercise at a fixed power-output of 160 W in a controlled environment (ambient temperature of 21.5±1.6 °C and relative humidity of 31±6%) at batyphase +2 h (08:00 h) and acrophase +2 h (20:00 h) of their estimated circadian temperature rhythm; corresponding respectively to the heat gain and heat loss mode phases. Throughout the exercise, rectal and gastro-intestinal temperature data were collected. A two-way ANOVA was applied and a common nonlinear logistic-type function dependant on three parameters (asymptote, xmid and scale) was used to fit collected data. ANOVA only indicated a time of day effect without interaction with exercise duration. A nonlinear mixed-effect model allowed further analysis of temperature kinetics. The model indicated a higher theoretical increase in temperature at the end of morning exercise compared to the evening session. However, the circadian difference observed at rest persists throughout the exercise. Theoretical asymptotic temperature values at the end of the exercise and scale values (inversely proportional to the slope) are higher for the rectal measurement site than for the gastro-intestinal measurement. The model proposed offers a solution for refining the study of individual core temperature response to prolonged exercise. The main advantage is that it takes into consideration intra- and inter-individual variability in temperature kinetics.     

Sperm viability, motility and morphology in emus (Dromaius novaehollandiae) are independent of the ambient collection temperature but are influenced by storage temperature

A protocol for storage of emu semen >6 h has not yet been optimized. The objective was to determine: a) whether sperm quality was adversely affected by sudden exposure to low temperatures (5, 10 and 20 °C) during collection; and b) the effects of three storage temperatures (5, 10 and 20 °C) on survival of emu sperm. In two experiments, each repeated three times on alternate days, ejaculates were diluted 1:1 with precooled (5, 10, or 20°C) UWA-E3 diluent and stored for up to 48 h. Collection temperature, or interaction with either the storage time or storage temperature, had no significant effect on sperm viability, motility, or morphology. Mass Motility Score (2.91-3.27 ± 0.26, mean ± SEM), and percentages of live (72.4-76.2 ± 2.4) and morphologically normal sperm (63.3-64.5 ± 2.3) were comparable among collection temperatures. Conversely, storage temperature and storage time affected (P < 0.05) sperm viability, motility, and morphology. After storage for 48 h, percentages of viable, normal, and motile sperm were higher (P < 0.001) at 5 °C (58.7% ± 1.1, 44.7% ± 1.3, and 50.7% ± 4.9, respectively) and 10 °C (62.6% ± 1.1, 54.1% ± 1.3, and 60.4% ± 4.9) than at 20 °C (27.6% ± 1.1, 20.1% ± 1.3, and 25.9% ± 4.9). Beyond 6 h of storage, the percentage of abnormal sperm was higher (P < 0.001) for storage at 5 °C compared to 10 and 20 °C. After 48 h, bacterial counts were considerably higher at 20 °C compared to 5 and 10 °C (P < 0.001). The pH of stored sperm suspension remained unaffected at 5 and 10 °C, but at 20 °C declined to 6.5 ± 0.03 after 24 h (P < 0.05) and to 6.0 ± 0.03 after 48 h (P < 0.001). We concluded that emu semen could be collected at low ambient temperatures (5-20 °C) without compromising its in vitro storage duration and that semen quality during storage for 48 h was better if it was stored at 10 °C than at 5 or 20 °C.     

Effects of mild heat exposure on sleep stages and body temperature in older men

The purpose of this study was to examine the effects of mild heat exposure on sleep stages and body temperature in older men. Ten healthy male volunteers with a mean age of 69.2 ± 1.35 years served as subjects. The experiments were carried out under two different sets of conditions: 26 °C 50% relative humidity (RH) and 32 °C 50% RH. The subjects slept from 2200 hours to 0600 hours with a cotton blanket and wearing short-sleeve pajamas and shorts on a bed covered by a sheet. Electroencephalogram, electro-occulogram and mental electromyogram recordings were made through the night. Rectal and skin temperatures were measured continuously. No significant differences were observed in sleep onset latency. In time spent in each sleep stage, wakefulness was significantly increased at 32 °C than at 26 °C. The total amount of wakefulness increased and rapid eye movement sleep (REM) decreased at 32 °C compared to 26 °C. The fall in rectal temperature was significantly suppressed and the mean skin temperature was significantly higher at 32 °C than at 26 °C. These results suggest that, for older men, even mild heat exposure during the nighttime sleep period may increase thermal load, suppress the decrease of rectal temperature, decrease REM, and increase wakefulness and whole-body sweat loss.     

用傅里叶变换红外光谱技术研究HIV-1融合肽的插膜深度与角度

为探讨HIV－1gp41N端融合肽诱导膜融合的机理,利用傅里叶变换红外光谱技术研究了化学方法合成的代表HIV－1gp41N末端的23肽（HIV     

Effect of primary hypohydration on physical work capacity

Physical work capacity (PWC₁₈₀) was assessed with different levels of hypohydration in 25 heat-acclimatized male volunteers in hot dry (45°C DB, 30% RH) and hot humid (39°C DB, 60% RH) conditions equated to a heat stress level of 34°C on the WBGT scale. Heat acclimatization was carried out by exposing the subjects for 8 consecutive days in a climatic chamber with moderate work for two 50 min work cycles and 10 min intervening rest pauses. Acclimatization resulted in significant decreases in heart rate (27 bpm), oral temperature (0.8°C), mean skin temperature (1.2°C) and a significant increase in sweating rate (120 g h^–1 m^–2). Day-to-day variations in body hypohydration levels during heat acclimatization were not significantly different, although water intake was found to increase significantly from day 3 onwards when the subjects were in ad lib water intake state. The heat acclimatized subjects were then hypohydrated to varying degrees, viz. 1%, 2% and 3% body weight deficit, with moderate work in heat in the climatic chamber and after successful recovery from the effects of thermal stress and exercise; their physical work capacity was assessed individually. Physical work capacity was found to decrease significantly with hypohydration as compared to controls. The decrease was of the order of 9%, 11% and 22% in the hot dry condition and 6%, 8% and 20% in the hot humid condition with hypohydration levels of 1%, 2% and 3% respectively. The decrease was more pronounced during 3% hypohydration level under both heat stress conditions. This decrease was in spite of significant increases in maximal ventilation. However, the PWC₁₈₀ under the two heat stress conditions, when compared, did not reveal any significant difference. It was concluded that the heat stress vehicle did not adversely affect the physical work capacity. On the other hand, the decreases in physical work capacity were found to be closely related to the primary hypohydration level in heat-acclimatized tropical subjects.Abbreviations WBGT wet bulb globe temperature - bam beats per minute - YSI Yellow Springs Instrument - EKG electrocardiogram     

Biology of the shore fly Scatella stagnalis in rockwool under greenhouse conditions

The development times and survival of immature stages in rockwool and the fecundity and longevity of adult Scatella stagnalis were determined and stage-specific life-tables constructed for the species at constant 20 and 25 °C and at a fluctuating temperature (23–34 °C, mean 28.5 °C). Development time from egg to adult decreased with temperature, being 15.9±0.1 days at 20 °C, 11.4±0.1 days at 25 °C and 10.1±0.2 days at fluctuating temperature with mean of 28.5 °C. The lower threshold for egg-to-adult development was 6.4±2.7 °C and the total quantity of thermal energy required to complete development was 212.8±.0 °C. The proportion of females in two populations studied was 0.521. High temperature increased the mortality of pupae from 7% (20 °C) and 10% (25 °C) to 29% at 28.5 °C. At 25 °C, female longevity was 15.5±0.7 days and fecundity 315±19 eggs/female (20.4 eggs/female/day). Males lived for 22.0±1.1 days. At constant 25 °C, the net reproductive rate was 126.1 female eggs/female, generation time was 18.4 days, the doubling time of the population 5.3 days, and the intrinsic rate of increase (r _m) 0.263 day^–1.     

Ambient temperature modulates the magnitude of LPS-induced fevers in Pekin ducks

The consequences of variations in environmental temperature on innate immune responses in birds are by and large not known. We investigated the influence of ambient temperature on the febrile response in female Pekin ducks (Anas platyrhynchos). Ducks, implanted with temperature data loggers to measure body temperature, were injected with lipopolysaccharide (100 μg kg⁻¹) to evoke febrile responses and kept at ambient temperatures higher, within, and lower than their thermoneutral zone (n=10), and in conditions that simulated one day of a heat wave (n=6). Compared to the febrile response at thermoneutrality, at low temperatures, febrile responses were significantly attenuated; fevers reached lower magnitudes (from basal body temperature of 41.2±0.3 °C to a peak of 42.0±0.3 °C). In contrast, at high ambient temperatures, ducks rapidly developed significantly enhanced fevers, which reached markedly higher febrile peaks (from basal body temperature of 41.6 °C to a peak of 44.0 °C in a simulated heat wave when ambient temperature reached 40 °C). These results indicate that ambient temperature affects the febrile response in female Pekin ducks. Our findings reveal a key difference in febrile mediation between ducks and mammals, and have implications for avian survival because high environmental temperatures during febrile mediation could lead to febrile responses becoming physiologically deleterious.     

Factors affecting low temperature preservation of the marine rotifer Brachionus rotundiformis Tschugunoff

Experiments were performed to determine suitable conditions for low temperature preservation of small S (Fukuoka) and ultra-small SS (Thai) strains of B. rotundiformis. For this, single rotifers (an adult bearing one egg or a 4-h neonate) were incubated for 10 days in 1 ml seawater (22 ppt salinity). The highest survival was achieved at 10 and 12 °C for S-strain and 12 °C for SS-strain. The effect of salinity, change of culture medium and feeding regime were further tested on rotifers (300 ind. ml^–1) cultured in vials containing 10 ml seawater and microalgae at 12 °C. Survival of S-strain was highest (55.5±0.8%) at 35 ppt, while SS-strain survived best (43.1±2.6%) at 17 ppt. Survival was suppressed by changing the culture medium every 4 days. Feeding rotifers every 2 days yielded better survival (66.2±6.6%: S-strains, cultured at 35 ppt and 81.8±5.2%, SS-strains cultured at 17 ppt) than feeding them only at the beginning of the experiment or at 4-day intervals. An acclimation at 20 °C for 24 h before transferring them from their usual culture temperature (28 °C) to 12 °C resulted in higher survival of SS-strain. For S-strain, however, no significant improvement resulted from acclimation. SS-strain was more susceptible to lower temperature and higher salinity than S-strain.