Habitat use and activity influence thermoregulation in a tropical lizard, Ameiva exsul

We examined the contributions of alterations in daily activity and behavioral selection of microhabitat to thermoregulation in a population of the lizard, Ameiva exsul (Teiidae), by combining data on lizard activity with data on the availability of sun-shade patches and operative temperatures (T_e). By comparing T_e distributions predicted by “no thermoregulation” and “only thermoregulation” hypotheses to those predicted by random use of thermal habitat, we assessed the relative contributions of microhabitat selection and daily activity to regulation of body temperature (T_b). Over the course of a day lizards maintained T_b very close to optimal temperature (T_sel) despite T_es that deviated substantially from T_sel. Data demonstrating a unimodal daily activity pattern reject the hypothesis of uniform activity throughout the day. Also, lizard activity was not positively correlated with the proportion of T_es within T_sel nor negatively correlated with the absolute deviation of available T_e from T_sel (d_e) (“only thermoregulation”). Microsite use by A. exsul deviated significantly from predictions of the “no thermoregulation” hypothesis, but our data could not reject predictions of the “only thermoregulation” hypothesis that lizards would use sun-shade patches relative to the proportion of microsites where T_e is within T_sel. Also, lizards appeared to actively select sunlit and partially shaded microsites at different times of day. Thus, despite thermal constraints imposed by the habitat, A. exsul maintained high and relatively constant T_bs throughout its daily activity period and thermoregulated effectively. This appears to be generally representative of West Indian species of Ameiva.     

Body temperature and thermoregulation of Komodo dragons in the field

Komodo dragons from hatchlings (≈0.1 kg) to adults (≤80 kg) express the full magnitude of varanid species size distributions. We found that all size groups of dragons regulated a similar preferred body temperature by exploiting a heterogeneous thermal environment within savanna, forest and mangrove habitats. All dragons studied, regardless of size, were able to regulate a daytime active body temperature within the range 34–35.6 °C for 5.1–5.6 h/day. The index of effectiveness of thermoregulation (a numerical rating of thermoregulatory activity) was not different among size groups of dragons. However, the index of closeness of thermoregulation, which rates the variability of body temperature, suggests a greater precision for regulating a preferred body temperature for medium compared to small and large dragons. Reference copper cylinders simulating small, medium and large Komodo dragons heated and cooled at the same rate, whereas actual dragons of all size groups heated faster than they cooled. Larger dragons heated and cooled more slowly than smaller ones. The mean operative environmental temperatures of copper cylinders representing medium sized dragons were 42.5, 32.0 and 29.4° C for savannah, forest and mangrove habitats, respectively. The index for average thermal quality of a habitat as measured by the absolute difference between operative environmental temperature and the dragon’s thermal range suggests the forest habitat offers the highest thermal quality to dragons and the savannah the lowest. The percent of total daytime that the operative environmental temperature was within the central 50% of the body temperatures selected by dragons in a thermal gradient (Phillips, 1984) was 45%, 15%, and 9% for forest, mangrove and savannah, respectively. Forest habitat offers the most suitable thermal environment and provides the greatest number of hours with conditions falling within the dragon’s thermal activity zone.     

Body temperature and thermoregulation in two species of yellowjackets,Vespula germanica and V. maculifrons

In spite of the abundance and broad distribution of social wasps, little information exists concerning thermoregulation by individuals. We measured body temperatures of the yellowjackets Vespula germanica and V. maculifrons and examined their thermoregulatory mechanisms. V. germanica demonstrated thermoregulation via a decreasing gradient between thorax temperature and ambient temperature as ambient temperature increased. V. maculifrons exhibited a constant gradient at lower ambient temperatures but thorax temperature was constant at high ambient temperatures. Head temperature exhibited similar patterns in both species. In spite of low thermal conductances, a simple heat budget model predicts substantial heat loads in warm conditions in the absence of thermoregulation. Both species regurgitated when heated on the head. A smaller volume of regurgitant was produced at lower head temperatures and a larger volume at higher head temperatures. Small regurgitations resulted in stabilization of head temperature, while large ones resulted in 4°C decreases in head temperature. Regurgitation was rare when wasps were heated upon the thorax. Abdomen temperature was 3–4°C above ambient temperature, and approached ambient temperature under the hottest conditions. No evidence was found for shunting of hot hemolymph from thorax to abdomen as a cooling mechanism. The frequency of regurgitation in workers returning to the nest increased with ambient temperature. Regurgitation may be an important thermoregulatory strategy during heat stress, but is probably not the only mechanism used in yellowjackets.Abbreviations M _b body mass - M _th thorax mass - T _a ambient temperature - T _ab abdomen temperature - T _b body temperature - T _h head temperature - T _th thorax temperature - C _t thermal conductance     

Effects of aerobic exercise on serum leptin levels in obese women

It has been demonstrated that leptin concentrations in obese patients may be altered by weight loss. We examined the effects of a 9-week aerobic exercise program on serum leptin concentrations in overweight women (20-50% above ideal body mass) under conditions of weight stability. Sixteen overweight women, mean (SE) age 42.75 (1.64) years, comprised the exercise group which adhered to a supervised aerobic exercise program. A graded exercise treadmill test was conducted before and after the exercise program to determine maximal oxygen uptake (VO2max) using open-circuit spirometry. The women demonstrated improved aerobic fitness (VO2max increased 12.29%), however, body fat and the body mass index did not change significantly [42.27 (1.35)-41.87 (1.33)%]. Fourteen women, age 40.57 (2.80) years, did not exercise over the same time period and served as a control group. Serum leptin levels were not significantly altered for either the exercise [28.00 (2.13)-31.04 (2.71) ng x ml(-1)] or the control group [33.24 (3.78)-34.69 (3.14) ng x mg(-1)]. The data indicate that 9 weeks of aerobic exercise improves aerobic fitness, but does not affect leptin concentrations in overweight women.     

Daily and annual patterns of thermoregulation in painted turtles (Chrysemys picta marginata) living in a thermally variable marsh in Northern Michigan

The capacity for an ectothermic reptile to thermoregulate has implications for many components of its life history. Over two years, we studied thermoregulation in a population of Midland painted turtles (Chrysemys picta marginata) in a shallow, thermally variable wetland during summer in Northern Michigan. Mean body temperature (T_b) of free-ranging turtles was greater in 2008 (25.8 °C) than in 2010 (19.7 °C). Laboratory determined thermoregulatory set point (T_set) ranged from 25 °C (T_set-min) to 31 °C (T_set-max) and was lower during the fall (17–26 °C). Deviations of T_b distributions from field measured operative temperatures (T_e) and indices of thermoregulation indicated that C. picta marginata were capable of a limited degree of thermoregulation. Operative temperatures and thermal quality (d_e=|T_set-min−T_e| and |T_e−T_set-max|) cycled daily with maximal thermal quality occurring during late morning and late afternoon. The accuracy of thermoregulation (d_b=|T_set-min−T_b| and |T_b−T_set-max|) was maximal (d_b values were minimal) as T_b declined and traversed T_set during the late afternoon–early evening hours and was higher on cloudy days than on sunny days because relatively low T_e values decreased the number of T_b values that were above T_set. Our index of thermal exploitation (E_x=frequency of T_b observations within T_set) was 36%, slightly lower than that reported for an Ontario population of C. picta marginata. Regression of d_b (thermal accuracy) on d_e (thermal quality) indicated that turtles invested more in thermoregulation when thermal quality was low and when water levels were high than when they were low. There were no intersexual differences in mean T_b throughout the year but females had relatively high laboratory determined T_b values in the fall, perhaps reflecting the importance of maintaining ovarian development prior to winter.     

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.     

The role of prostaglandins and the hypothalamus in thermoregulation in the lizard, Phrynocephalus przewalskii (Agamidae)

Typically, small lizards rely heavily on behavioral thermoregulation rather than physiological mechanisms to control their rates of warming and cooling. We tested the hypothesis that prostaglandins participate in mediating the cardiovascular response to heating and cooling and temperature regulating neurons in the hypothalamus of the small lizard Phrynocephalus przewalskii. In vivo and in vitro treatments, heart rates (HRs) were all found to be higher during heating than during cooling, hysteresis was distinct below 30 and 26°C, respectively. In vivo, as administration of COX inhibitor, there were no differences in HR between heating and cooling at any body temperature and administration of agonist prostaglandins only produced a significant effect on HR below 25°C. Single-unit activity was recorded extracellularly in vitro with microelectrodes, found the firing rate of the continuous unit increased 23% when the temperature of the artificial cerebrospinal fluid dropped from 30–20°C. We conclude that prostaglandins appear to play only a limited role in modulating heart activity in Phrynocephalus przewalskii and suggest that cold-sensitive neurons in the preoptic and anterior hypothalamus (PO/AH) are involved in thermoregulatory control during heating or cooling.     

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.     

Visualization of body thermoregulation by infrared imaging

This paper analyzes two mechanisms applied on the human body in order to study the thermoregulatory system according to heat generation and heat loss. Two approaches are presented. The first approach is based on plethysmography, where an armband is placed on the forearm in order to modulate the blood flow. The second approach uses a cold stimulation. The visualization is achieved using infrared imaging devices. The resulting images reveal a temperature balance between the stimulated and the non-stimulated hands. The thermal behavior and typical thermographic recordings on each subject are discussed and analyzed in response to different stimulations.     

Influence of the menstrual cycle and oral contraceptives on thermoregulatory responses to exercise in young women

Thermoregulatory responses to exercise in relation to the phase of the menstrual cycle were studied in ten women taking oral contraceptives (P) and in ten women not taking oral contraceptives (NP). Each subject was tested for maximal aerobic capacity ( ) and for 50% exercise in the follicular (F) and luteal (L) phases of the menstrual cycle. Since the oral contraceptives would have prevented ovulation a quasi-follicular phase (q-F) and a quasi-luteal phase (q-L) of the menstrual cycle were assumed for P subjects. Exercise was performed on a cycle ergometer at an ambient temperature of 24° C and relative air humidity of 50%. Rectal (T _re), mean skin ( ), mean body ( ) temperatures and heart rate (f _c) were measured. Sweat rate was estimated by the continuous measurement of relative humidity of air in a ventilated capsule placed on the chest, converted to absolute pressure (PH₂O_chest). Gain for sweating was calculated as a ratio of increase inPH₂O_chest to the appropriate increase inT _re for the whole period of sweating (G) and for unsteady-state (G_u) separately. The did not differ either between the groups of subjects or between the phases of the menstrual cycle. In P, rectal temperature threshold for sweating (T _{re, td}) was 37.85° C in q-L and 37.60° C in q-F (P < 0.01) and corresponded to a significant difference fromT _re at rest. TheT _re, andf _c increased similarly during exercise in q-F and q-L. No menstrual phase-related differences were observed either in the dynamics of sweating or in G. In NP,T _{re, td} was shorter in L than in F (37.70 vs 37.47° C,P<0.02) with a significantly greater value fromT _re at rest. The dynamics and G for sweating were also greater in L than in F. The G_u was 36.8 versus 16.6 kPa · ° C^–1 (P<0.01) while G was 6.4 versus 3.8 kPa · ° C^–1 (P<0.05), respectively. TheT _re, andf _c increased significantly more in phase F than in phase L. It was concluded that in these women performing moderate exercise, there was a greater temperature threshold and larger gains for sweating in phase L than in phase F. Intake of oral contraceptives reduced the differences in the gains for sweating making the thermoregulatory responses to exercise more uniform.     

Effect of pre-cooling, with and without thigh cooling, on strain and endurance exercise performance in the heat

Body cooling before exercise (i.e. pre-cooling) reduces physiological strain in humans during endurance exercise in temperate and warm environments, usually improving performance. This study examined the effectiveness of pre-cooling humans by ice-vest and cold (3 degrees C) air, with (LC) and without (LW) leg cooling, in reducing heat strain and improving endurance performance in the heat (35 degrees C, 60% RH). Nine habitually-active males completed three trials, involving pre-cooling (LC and LW) or no pre-cooling (CON: 34 degrees C air) before 35-min cycle exercise: 20 min at approximately 65% VO2peak then a 15-min work-performance trial. At exercise onset, mean core (Tc, from oesophagus and rectum) and skin temperatures, forearm blood flow (FBF), heart rate (HR), and ratings of exertion, body temperature and thermal discomfort were lower in LW and LC than CON (P<0.05). They remained lower at 20 min [e.g. Tc: CON 38.4+/-0.2 (+/-S.E.), LW 37.9+/-0.1, and LC 37.8+/-0.1 degrees C; HR: 177+/-3, 163+/-3 and 167+/-3 b.p.m.), except that FBF was equivalent (P=0.10) between CON (15.5+/-1.6) and LW (13.6+/-1.0 ml.100 ml tissue(-1) x min(-1)). Subsequent power output was higher in LW (2.95+/-0.24) and LC (2.91+/-0.25) than in CON (2.52+/-0.28 W kg(-1), P=0.00, N=8), yet final Tc remained lower. Pre-cooling by ice-vest and cold air effectively reduced physiological and psychophysical strain and improved endurance performance in the heat, irrespective of whether thighs were warmed or cooled.     

Effect of blood volume on plasma volume shift during exercise

To assess the relationship between blood volume (BV) and the reduction in plasma volume (PV) during exercise in individual variations, we measured BV and changes in PV in thirteen male volunteers during treadmill exercise until exhaustion. The lactate threshold (LT), as a predictor of aerobic exercise capacity, was calculated from the exercise intensity at the point of plasma lactate concentration buildup to 4 mmol. The relationship of peak VO₂ with BV indicated a significant positive correlation. The strong positive relation between the shifts in PV and total PV, and resulted in a maintenance of the circulating BV.     

Effects of airflow on body temperatures and sleep stages in a warm humid climate

Airflow is an effective way to increase heat loss—an ongoing process during sleep and wakefulness in daily life. However, it is unclear whether airflow stimulates cutaneous sensation and disturbs sleep or reduces the heat load and facilitates sleep. In this study, 17 male subjects wearing short pyjamas slept on a bed with a cotton blanket under two of the following conditions: (1) air temperature (Ta) 26°C, relative humidity (RH) 50%, and air velocity (V) 0.2 m s⁻¹; (2) Ta 32°C, RH 80%, V 1.7 m s⁻¹; (3) Ta 32°C; RH 80%, V 0.2 m s⁻¹ (hereafter referred to as 26/50, 32/80 with airflow, and 32/80 with still air, respectively). Electroencephalograms, electrooculograms, and mental electromyograms were obtained for all subjects. Rectal (Tre) and skin (Ts) temperatures were recorded continuously during the sleep session, and body-mass was measured before and after the sleep session. No significant differences were observed in the duration of sleep stages between subjects under the 26/50 and 32/80 with airflow conditions; however, the total duration of wakefulness decreased significantly in subjects under the 32/80 with airflow condition compared to that in subjects under the 32/80 with still air condition (P < 0.05). Tre, Tsk, Ts, and body-mass loss under the 32/80 with airflow condition were significantly higher compared to those under the 26/50 condition, and significantly lower than those under the 32/80 with still air condition (P < 0.05). An alleviated heat load due to increased airflow was considered to exist between the 32/80 with still air and the 26/50 conditions. Airflow reduces the duration of wakefulness by decreasing Tre, Tsk, Ts, and body-mass loss in a warm humid condition.     

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.     

Stability and reproducibility of simultaneously detected plasma and serum cytokine levels in asymptomatic subjects

Blood levels of cyto- and chemokines might reflect immune deregulations which might be related to lymphomagenesis. Potential utility of stored blood samples of a prospective cohort was evaluated by the effect of different blood sample types and freeze-thaw cycles on analyte levels. Bead-based immunoassays were performed on two fresh samples (serum, citrate and heparin plasma) of 10 asymptomatic adults collected 14 days apart and on aliquots of the first samples which were put through one to three freeze-thaw cycles to measure 11 cytokines, four chemokines and two adhesion molecules. Median coefficients of variation (CVs) of the measured analytes were 20%, 24% and 32% in serum, citrate and heparin plasma, respectively. Strong correlations (rank correlation coefficient 0.74–0.98) were observed between sample types, although small differences in analyte levels were observed for most analytes. Freeze-thaw cycles did not markedly change analyte levels. Our study supports the use of this assay among asymptomatic subjects in epidemiological studies.     

Influence of a low-carbohydrate diet on thermoregulatory responses to prolonged exercise in men

Tympanic temperature (T_ty), mean skin temperature (T_sk) and dynamics of sweating were measured in male subjects, performing prolonged, bicycle-exercise. The exercise was performed under thermoneutral environment after the normal-mixed (C) and low-carbohydrate (LCHO) diet. No difference in changes of T_ty was observed after the C and LCHO diets. Sweating was triggered much faster after the LCHO diet. The delay in onset and inertia time of sweating was shorter after the LCHO diet. It is concluded that LCHO diet affects the thermoregulatory responses to exercise by acceleration of sweating, without noticeable differences in body temperature.     

Plasma volume, osmolarity, total protein and electrolytes during treadmill running and cycle ergometer exercise

While haemoconcentration due to loss of plasma volume is well established during cycling, the existence of similar changes during running remains contentious. This study compared the changes in plasma volume and associated blood indices during 60 min of running and cycling at the same relative intensity (approximately 65% VO2max), with all changes referenced to blood indices obtained after 30 min seated at rest on a cycle ergometer. Plasma osmolarity increased similarly with both forms of exercise but was less than predicted for water loss alone, such that there was a net loss of sodium during exercise and of potassium postexercise, with essentially no loss of protein. Plasma volume decreased similarly (approximately 6.5%) in both exercise trials, but while that with cycling was initiated by exercise itself and was essentially maximal within 5 min, the reduction in plasma volume in the running trial was induced by adopting the upright posture and was complete before exercise began. These data would indicate that different mechanisms are responsible for the changes in plasma volume induced by running and cycling, while the similarity of change would suggest that there is a lower limit to any reduction in plasma volume, regardless of mechanism. Furthermore, the observation that the changes in plasma volume were complete before or early in exercise, would imply that oral water ingestion during prolonged exercise, which is essential for thermoregulation, may be more concerned with homeostasis of extravascular water rather than plasma volume.     

Hydration effects on thermoregulation and performance in the heat

During exercise, sweat output often exceeds water intake, producing a water deficit or hypohydration. The water deficit lowers both intracellular and extracellular fluid volumes, and causes a hypotonic-hypovolemia of the blood. Aerobic exercise tasks are likely to be adversely effected by hypohydration (even in the absence of heat strain), with the potential affect being greater in hot environments. Hypohydration increases heat storage by reducing sweating rate and skin blood flow responses for a given core temperature. Hypertonicity and hypovolemia both contribute to reduced heat loss and increased heat storage. In addition, hypovolemia and the displacement of blood to the skin make it difficult to maintain central venous pressure and thus cardiac output to simultaneously support metabolism and thermoregulation. Hyperhydration provides no advantages over euhydration regarding thermoregulation and exercise performance in the heat.