Pituitary adenylate cyclase-activating polypeptide maintains neonatal breathing but not metabolism during mild reductions in ambient temperature

Mild reductions in ambient temperature dramatically increase the mortality of neonatal mice deficient in pituitary adenylate cyclase-activating polypeptide (PACAP), with the majority of animals succumbing in the second postnatal week. During anesthesia-induced hypothermia, PACAP(-/-) mice at this age are also vulnerable to prolonged apneas and sudden death. From these observations, we hypothesized that before the onset of genotype-specific mortality and in the absence of anesthetic, the breathing of PACAP-deficient mice is more susceptible to mild reductions in ambient temperature than wild-type littermates. To test this hypothesis, we recorded breathing in one group of postnatal day 4 PACAP+/+, (+/-), and (-/-) neonates (using unrestrained, flow-through plethysmography) and metabolic rate in a separate group (using indirect calorimetry), both of which were exposed acutely to ambient temperatures slightly below (29 degrees C), slightly above (36 degrees C), or at thermoneutrality (32 degrees C). At 32 degrees C, the breathing frequency of PACAP(-/-) neonates was significantly less than PACAP+/+ littermates. Reducing the ambient temperature to 29 degrees C caused a significant suppression of tidal volume and ventilation in both PACAP+/- and (-/-) animals, while the tidal volume and ventilation of PACAP+/+ animals remained unchanged. Genotype had no effect on the ventilatory responses to ambient warming. At all three ambient temperatures, genotype had no influence on oxygen consumption or body temperature. These results suggest that during mild reductions in ambient temperature, PACAP is vital for the preservation of neonatal tidal volume and ventilation, but not for metabolic rate or body temperature.     

Heat exchange of the rat in thermoneutral zone temperature and comparison with heat exchange in ambient temperature over and under it

With the help of thermonetry and general calorimetry body temperature and heat production in ambient temperatures 20 degrees C, 28 degrees C, 33 degrees C were recorded. The experiments showed, that at the temperature 20 degrees C the rectal temperature was changing very little. But in ambient temperature 33 degrees C the rectal temperature was 40.5 +/- 0.1 degrees C.     

Metabolic rate and thermoregulation in two species of tuco-tuco, Ctenomys talarum and Ctenomys australis (Caviomorpha, Octodontidae)

1. Resting metabolic rate and body temperature in function of ambient temperature were determined for two species of Ctenomys. 2. Oxygen consumption was lowest between 25 and 30 degrees C and was 0.946 +/- 0.030 and 0.968 +/- 0.022 in Ctenomys talarum (from Mar de Cobo and Necochea, respectively). Resting metabolic rate was 0.343 +/- 0.053 at 30 C in C. australis. 3. Mean rectal temperature at thermoneutrality was 36.1 +/- 0.13 and 37.3 +/- 0.17 in C. talarum and C. australis, respectively. 4. Limited thermoregulation occurred in C. talarum down to 20 degrees C but C. australis maintained body temperature down to 10 degrees C. 5. Both species of tuco-tucos became hyperthermic at ambient temperatures above thermoneutrality.     

Thermoregulatory and nonthermoregulatory heat production in burned rat

Severely burned patients are hypermetabolic within their thermoneutral zone (TNZ), where there are no thermoregulatory demands on heat production. The rat has been used as a model of postburn hypermetabolism without clear evidence that it behaves in a similar way. Male rats (400-500 g; n = 34-39) were placed as a group in a respiration chamber and metabolic rates for the average rat were determined over 3-6 h at ambient temperatures between 9 and 36 degrees C. Colonic temperatures (Tco) and body weights were measured after each run. Animals were studied sequentially as normals (N), after clipping (C) and following 50% total body surface scald burns. Clipping increased the lower critical temperature (LCT) from 27.7 to 29.1 degrees C without affecting resting heat production (N = 42.6 +/- 0.5; C = 42.0 +/- 0.8 W/m2; mean +/- S.E.) or Tco (N = 36.6 +/- 0.1; C = 36.6 +/- 0.1 degrees C) in the TNZ. Injury increased LCT to 32.8 degrees C and the burned animals were hypermetabolic (47.2 +/- 0.6 W/m2; P less than 0.05 vs. N) and febrile (36.9 +/- 0.1 degrees C; P less than 0.05 vs. N) in the elevated TNZ. These metabolic and temperature responses of burned rats are limited in magnitude but are qualitatively similar to those of patients. The extra heat production in the TNZ reflects the basic metabolic cost of injury.     

Behavioral thermoregulation by hypoxic rats.

To address whether a shift in hypothalamic thermal setpoint might be a significant factor in induction of hypoxic hypothermia, behavioral thermoregulation was examined in 7 female Sprague-Dawley rats implanted with radiotelethermometers for deep body temperature (Tb) measurement in a thermocline during normoxia (PO2 = 125 torr) and hypoxia (PO2 = 60 torr). Normoxic rats (TNox) selected a mean ambient temperature of 19.7 +/- 1.4 (SE) degrees C and maintained Tb at 37.0 +/- 0.2 degrees C. Hypoxic rats selected a significantly higher ambient temperature (THox = 28.6 +/- 2.2 degrees C) but maintained Tb significantly lower at 35.5 +/- 0.3 degrees C. Without a thermal gradient (ambient temperature = 25 degrees C), Tb during hypoxia was 35.4 +/- 0.4 degrees C. The maintenance of a lower body temperature during hypoxia through behavioral thermoregulation despite having warmer temperatures available supports the hypothesis that the thermoregulatory setpoint of hypoxic rats is shifted to promote thermoregulation at a lower Tb, effectively reducing oxygen demand when oxygen supply is limited.     

Depression of sublingual temperature by cold saliva.

Sublingual and oesophageal temperatures were compared at various air temperatures in 16 subjects. In warm air (25-44 degrees C) sublingual temperatures stabilized within plus or minus 0-45 degrees C of oesophageal temperatures, but in air at room temperature (18-24 degrees C) they were sometimes as much as 1-1 degrees C below and in cold air (5-10 degrees C) as much as 4-4 degrees C below oesophageal readings. The sublingual-oesophageal temperature difference in cold air was greatly reduced by keeping the face warm, but it was not reduced in two patients breathing through tracheostomies and thereby eliminating cold air flow from the nose and pharynx. Parotid saliva temperature was low and saliva flow high during exposure, and cold saliva seemed to be mainly responsible for the erratic depression of sublingual temperature in the cold. These results indicate hazards in the casual use of sublingual temperatures, and indicate that external heat may have to be supplied to enable them to give reliable clinical assessments of body temperature.     

The effect of ambient temperature on beta-adrenergic responsiveness in rats.

The responses of tail skin and colonic temperatures of female rats to ambient temperatures of 20, 22, 24, 26, 28, and 30 degrees C were measured. Within this range, colonic temperature was stable while tail skin temperature increased linearly with increasing ambient temperature. Administration of the beta-adrenergic agonist, d,l-isoproterenol, at 10.0, 25.0, and 62.5 micrograms/kg, sc, at each ambient temperature was accompanied by increases in tail skin and colonic temperatures that were dependent on both the dose of isoproterenol administered and the ambient temperature. The integrated responses of tail skin temperature following administration of the three doses of isoproterenol were maximal at an ambient temperature of 26 degrees C while the integrated responses of colonic temperature were maximal at 30 degrees C. The results suggest that tests of beta-adrenergic responsiveness using this technique should be performed at an ambient temperature of 26 degrees C for maximal sensitivity.     

Hypothermia versus torpor in response to cold stress in the native Australian mouse Pseudomys hermannsburgensis and the introduced house mouse Mus musculus

This study compared torpor as a response to food deprivation and low ambient temperature for the introduced house mouse (Mus musculus) and the Australian endemic sandy inland mouse (Pseudomys hermannsburgensis). The house mouse (mass 13.0+/-0.48 g) had a normothermic body temperature of 34.0+/-0.20 degrees C at ambient temperatures from 5 degrees C to 30 degrees C and a basal metabolic rate at 30 degrees C of 2.29+/-0.07 mL O2 g(-1) h(-1). It used torpor with spontaneous arousal at low ambient temperatures; body temperature during torpor was 20.5+/-3.30 degrees C at 15 degrees C. The sandy inland mouse (mass 11.7+/-0.16 g) had a normothermic T(b) of 33.0+/-0.38 degrees C between T(a) of 5 degrees C to 30 degrees C, and a BMR of 1.45+/-0.26 mL O2 g(-1) h(-1) at 30 degrees C. They became hypothermic at low T(a) (T(b) about 17.3 degrees C at T(a)=15 degrees C), but did not spontaneously arouse. They did, however, survive and become normothermic if returned to room temperature (23 degrees C). We conclude that this is hypothermia, not torpor. Consequently, house mice (Subfamily Murinae) appear to use torpor as an energy conservation strategy whereas sandy inland mice (Subfamily Conilurinae) do not, but can survive hypothermia. This may reflect a general phylogenetic pattern of metabolic reduction in rodents. On the other hand, this may be related to differences in the social structure of house mice (solitary) and sandy inland mice (communal).     

An infrared thermographic study of surface temperature in the euthermic woodchuck (Marmota monax).

Surface temperatures were measured in euthermic woodchucks (Marmota monax) using infrared thermography across a range of ambient temperatures from -10 degrees C to 32 degrees C. The woodchuck keeps surface temperature of the peripalpebral region uniformly high, while head and body surfaces change proportionally with ambient temperature. When ambient temperature was below 0 degrees C, all surface temperatures increased which prevents freezing. At no point did the animals appear to be unable to regulate heat exchange. This species appears to be especially well adapted to the higher temperatures it encounters in its range. Vasomotion in the feet and to a lesser extent in the pinnae was used to regulate heat loss. At ambient temperature of 32 degrees C, mean temperatures of nose surfaces were 0.2 degrees C and 0.3 degrees C less than ambient temperature suggesting a type of counter current cooling mechanism may be present.     

Metabolic physiology of the numbat (Myrmecobius fasciatus)

The numbat (Myrmecobius fasciatus) is unique amongst marsupials as it is exclusively diurnal, feeds only on termites and is semi-fossorial. This study examines the thermal and metabolic physiology of the numbat to determine if its physiology reflects its phylogeny, diet and semi-fossorial habit. Numbats (mean adult body mass 552 g) were able to regulate body temperature at ambient temperatures of 15-30 degrees C, with a body temperature at thermoneutrality (30 degrees C) of 34.1 degrees C. The thermoneutral body temperature was not significantly different from that predicted for an equivalent-sized marsupial. Basal metabolic rate, measured at 30 degrees C, was 0.389 +/- 0.025 ml O(2) g(-1) h(-1), and was slightly but not significantly lower at 82.5% of that predicted for a typical marsupial of equivalent body mass. Metabolic rate increased with decreasing ambient temperatures below 30 degrees C. Patterns of metabolic cycling observed for completely inactive numbats at ambient temperatures below 30 degrees C are likely to be related to sleep phase. Wet thermal conductance of 1.94 J g(-1) h(-1) degrees C(-1) (at 30 degrees C) was 131% of that predicted for a marsupial. Evaporative water loss of the numbat remained constant below the thermoneutral zone (<30 degrees C) at approximately 0.6 ml g(-1) h(-1), only 47.4% of that predicted for a marsupial. It increased to 1.01 +/- 0.16 ml g(-1) h(-1) at an ambient temperature of 32.5 degrees C. The thermal and metabolic physiology of the numbat is generally similar to that expected for other marsupials, and is also comparable to that of termitivorous placental mammals. Thus the reduction in body temperature and basal metabolic rate of placental termitivores is a "marsupial-like" low energy turnover physiology, and the numbat being a marsupial already has an appropriate physiology to survive exclusively on a low energy diet of termites.     

Body temperature changes induced by huddling in breeding male emperor penguins

Huddling is the key energy-saving mechanism for emperor penguins to endure their 4-mo incubation fast during the Antarctic winter, but the underlying physiological mechanisms of this energy saving have remained elusive. The question is whether their deep body (core) temperature may drop in association with energy sparing, taking into account that successful egg incubation requires a temperature of about 36 degrees C and that ambient temperatures of up to 37.5 degrees C may be reached within tight huddles. Using data loggers implanted into five unrestrained breeding males, we present here the first data on body temperature changes throughout the breeding cycle of emperor penguins, with particular emphasis on huddling bouts. During the pairing period, core temperature decreased progressively from 37.5 +/- 0.4 degrees C to 36.5 +/- 0.3 degrees C, associated with a significant temperature drop of 0.5 +/- 0.3 degrees C during huddling. In case of egg loss, body temperature continued to decrease to 35.5 +/- 0.4 degrees C, with a further 0.9 degrees C decrease during huddling. By contrast, a constant core temperature of 36.9 +/- 0.2 degrees C was maintained during successful incubation, even during huddling, suggesting a trade-off between the demands for successful egg incubation and energy saving. However, such a limited drop in body temperature cannot explain the observed energy savings of breeding emperor penguins. Furthermore, we never observed any signs of hyperthermia in huddling birds that were exposed to ambient temperatures as high as above 35 degrees C. We suggest that the energy savings of huddling birds is due to a metabolic depression, the extent of which depends on a reduction of body surface areas exposed to cold.     

Role of nitric oxide in hypoxic hypometabolism in rats.

Because it has been recently suggested that nitric oxide (NO) may mediate the effects of hypoxia on body temperature and ventilation, the present study was designed to assess more completely the effects of a neuronal NO synthase inhibitor (7-nitroindazole, 25 mg/kg ip), at ambient temperature of 26 and 15 degrees C, on the ventilatory (V), metabolic (O(2) consumption), and thermal changes (colonic and tail temperatures) induced by ambient hypoxia (fractional inspired O(2) of 11%) or CO hypoxia (fractional inspired CO of 0.07%) in intact, unanesthetized adult rats. At both ambient temperatures, 7-nitroindazole decreased oxygen consumption, colonic temperature, and V in normoxia. The drug reduced ambient or CO hypoxia-induced hypometabolism and ventilatory response, but the hypothermia persisted. It is concluded that NO arising from neural NO synthase plays an important role in the control of metabolism and V in normoxia. As well, it mediates, in part, the hypometabolic and the ventilatory response to hypoxia. The results are consistent with the notion that central nervous system hypoxia resets the thermoregulatory set point by decreasing brain NO.     

The central efferent mechanism of brown adipose tissue thermogenesis induced by preoptic cooling

This study was performed to investigate central efferent mechanisms for brown adipose tissue thermogenesis. In unanesthetized rats, the effects of local anesthesia of the ventromedial hypothalamus, anterior hypothalamus, and lateral hypothalamus were observed on the brown adipose tissue thermogenesis induced by preoptic cooling. Rats had a thermode, thermocouple, and bilateral injection cannulae chronically implanted in the hypothalamus and a thermocouple beneath the interscapular brown adipose tissue. The experiments were done at an ambient temperature of 24-25 degrees C. Preoptic cooling increased brown adipose tissue and colonic temperatures without shivering. Injecting lidocaine bilaterally into the ventromedial hypothalamus during preoptic cooling reduced brown adipose tissue temperature (Tbat). The mean maximum decrease of Tbat was 0.51 +/- 0.26 degrees C and occurred 5-8 min after lidocaine injection. When lidocaine was injected into the anterior hypothalamus, Tbat increased. The mean maximum increase of Tbat was 0.85 +/- 0.29 degrees C and occurred 4-9 min after lidocaine injection. In the lateral hypothalamus, lidocaine had no effect on Tbat. Tbat was not influenced by injection of saline into the ventromedial, anterior, or lateral hypothalamus. The efferent pathway from preoptic to brown adipose tissue may thus traverse the medial part of hypothalamus. The ventromedial hypothalamus facilitates and anterior hypothalamus inhibits brown adipose tissue thermogenesis induced by preoptic cooling.     

Febrile response to infection in the American alligator (Alligator mississippiensis).

Temperature probes were inserted into the stomachs of juvenile American alligators (Alligator mississippiensis) maintained outdoors at ambient fluctuating temperatures. Internal body temperatures (T(b)) were measured every 15 min for two days, and then the alligators were injected with bacterial lipopolysaccharide (LPS), pyrogen-free saline, or left untreated. Alligators injected intraperitoneally with LPS exhibited maximum T(b)s 2.6+/-1.1 degrees C and 3.5+/-1.2 degrees C higher than untreated control animals on days one and two after treatment, respectively. T(b)s for these animals fell to within control ranges by day three postinjection. Similarly, mean preferred body temperatures (MPBTs) were significantly higher for LPS-injected alligators on days one (4.2+/-1.8 degrees C) and two (3.5+/-1.6 degrees C) after treatment. Intraperitoneal injection of heat-killed Aeromonas hydrophila, a gram-negative bacterium known to infect crocodilians, resulted in a fever while injection of Staphylococcus aureus (gram positive) did not elicit a febrile response. Injection of LPS in alligators maintained indoors in a constant temperature environment resulted in no increase in internal T(b). These results indicate that alligators did not exhibit a febrile response in the absence of a thermal gradient, and suggest that febrile responses observed are probably behavioral in nature.     

Cutaneous warming promotes sleep onset

Sleep occurs in close relation to changes in body temperature. Both the monophasic sleep period in humans and the polyphasic sleep periods in rodents tend to be initiated when core body temperature is declining. This decline is mainly due to an increase in skin blood flow and consequently skin warming and heat loss. We have proposed that these intrinsically occurring changes in core and skin temperatures could modulate neuronal activity in sleep-regulating brain areas (Van Someren EJW, Chronobiol Int 17: 313-54, 2000). We here provide results compatible with this hypothesis. We obtained 144 sleep-onset latencies while directly manipulating core and skin temperatures within the comfortable range in eight healthy subjects under controlled conditions. The induction of a proximal skin temperature difference of only 0.78 +/- 0.03 degrees C (mean +/- SE) around a mean of 35.13 +/- 0.11 degrees C changed sleep-onset latency by 26%, i.e., by 3.09 minutes [95% confidence interval (CI), 1.91 to 4.28] around a mean of 11.85 min (CI, 9.74 to 14.41), with faster sleep onsets when the proximal skin was warmed. The reduction in sleep-onset latency occurred despite a small but significant decrease in subjective comfort during proximal skin warming. The induction of changes in core temperature (delta = 0.20 +/- 0.02 degrees C) and distal skin temperature (delta = 0.74 +/- 0.05 degrees C) were ineffective. Previous studies have demonstrated correlations between skin temperature and sleep-onset latency. Also, sleep disruption by ambient temperatures that activate thermoregulatory defense mechanisms has been shown. The present study is the first to experimentally demonstrate a causal contribution to sleep-onset latency of skin temperature manipulations within the normal nocturnal fluctuation range. Circadian and sleep-appetitive behavior-induced variations in skin temperature might act as an input signal to sleep-regulating systems.     

Absence of selective brain cooling in pyrogen-induced fever in rabbits

In 9 rabbits the effect of intravenous administration of E. coli pyrogen 0.5 microgram/kg on the reaction of selective brain cooling was studied at ambient temperatures of 20, 30 and 40 degrees C. In the freely moving animals the temperatures of the brain, carotid artery and nuchal muscles were measured with an accuracy down to 0.05 degree C and the temperatures of the ear pinna and nasal mucosa were measured accurate to 0.5 degree C. The respiratory rate was measured as well. It was found that the spontaneous febrile reaction without the component of passive hyperthermia failed to cause selective brain cooling, even if its temperature reached higher values than in case of brain temperature rise caused only by high ambient temperature. On the other hand, when the high ambient temperature caused thermal panting, pyrogen administration at an ambient temperature of 30 degrees C could reduce panting, while at an ambient temperature of 40 degrees C intense panting initiated prior to the appearance of the febrile reaction and was associated with the fever and outlasted it.     

The heat-acclimated pigeon: an ideal physiological model for a desert bird

Acclimation of rock pigeon (Columba livia) to high ambient temperature (Ta) 50 degrees C from the time of hatching resulted in a well-developed cutaneous evaporative cooling mechanism (CECM), which became the dominant mechanism for heat dissipation. After the age of 15 days and in adults, acclimated pigeons exposed to 48-60 degrees C Ta could regulate normal body temperature (Tb) without employing either panting or gular fluttering. Respiration rate varied between 36 +/- 12 (SD) and 35 +/- 14 breaths/min at moderate and at extreme high Ta's, respectively. During thermal stress (42, 45, and 47 degrees C) imposed in a metabolic chamber, nonpanting pigeons' heat balance was achieved by adjusting low-level heat production (46.2 +/- 6.8 W/m2) and by use of an efficient CECM that dissipated 145% of the metabolic heat. Tb was regulated between 40.7 +/- 0.5 and 41.8 +/- 0.4 degrees C over a wide range of Ta's (20-56 degrees C). The respiratory evaporative cooling mechanism (RECM) was effective since hatching. The CECM developed approximately 24 h later during the ontogeny of the altricial nestling pigeon. This trait, which exists in many bird species and may be a recent development, possibly evolved as an adaptation to hot environments. In the present study we have brought evidence for a multitrait physiological adaptation that takes preeminence in adjusting the processes involved in maintaining heat balance. This integrative complex creates a powerful, efficient tool for contending with the most extreme thermal conditions.     

Temperature regulation in the unrestrained rabbit during exposure to 600 MHz radiofrequency radiation

Six male New Zealand white rabbits were individually exposed to 600 MHz radiofrequency (RF) radiation for 90 min in a waveguide exposure system at an ambient temperature (Ta) of 20 or 30 degrees C. Immediately after exposure, the rabbit was removed from the exposure chamber and its colonic and ear skin temperatures were quickly measured. The whole-body specific absorption rate (SAR) required to increase colonic and ear skin temperature was determined. At a Ta of 20 degrees C the threshold SAR for elevating colonic and ear skin temperature was 0.64 and 0.26 W/kg, respectively. At a Ta of 30 degrees C the threshold SARs were slightly less than at 20 degrees C, with values of 0.26 W/kg for elevating colonic temperature and 0.19 W/kg for elevating ear skin temperature. The relationship between heat load and elevation in deep body temperature shown in this study at 600 MHz is similar to past studies which employed much higher frequencies of RF radiation (2450-2884 MHz). On the other hand, comparison of these data with studies on exercise-induced heat production and thermoregulation in the rabbit suggest that the relationship between heat gain and elevation in body temperature in exercise and from exposure to RF radiation may differ considerably. When combined with other studies, it was shown that the logarithm of the SAR required for a 1.0 degree C elevation in deep body temperature of the rabbit, rat, hamster, and mouse was inversely related to the logarithm of body mass. The results of this study are consistent with the conclusion that body mass strongly influences thermoregulatory sensitivity of the aforementioned laboratory mammals during exposure to RF radiation.     

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 +/- 3 kg, means +/- SD). The animals, housed in a climatic chamber at 23 degrees C, were exposed for nine days to a cyclic protocol with daytime heat (40 degrees C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 +/- 4% of body mass, and plasma osmolality had increased from 290 +/- 8 to 323 +/- 9 mmol/kg (P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 +/- 0.18 degrees C) than in euhydration (-0.05 +/- 0.14 degrees C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27 degrees C) and dehydration (39.14 degrees C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 +/- 0.31) than in euhydrated animals (0.87 +/- 0.11, P = 0.003). Return of drinking water at 39 degrees C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.     

The effect of exercise in cool, control and hot environments on cardioprotective HSP70 induction

A number of environmental and metabolic stimuli rapidly induce the expression of several highly conserved proteins such as heat shock proteins (HSPs) or stress proteins. The purpose of this study was to investigate the effects of a single bout of submaximal exercise in varying ambient temperatures on cardiac and skeletal muscle. Adult male Sprague-Dawley rats were randomly placed in one of three ambient temperature groups; control (23 degrees C), hot (41 degrees C) and cool (11 degrees C). Each exercise bout consisted of treadmill running at 17 m/min and 0% grade. Tissue HSP70 levels for all groups were determined using analysis of variance in two factorial design (2 x 3). Baseline rectal temperature was similar for all three groups. In the control and hot temperature groups, final rectal temperatures differed from the baseline values (p<.05). The rectal temperature from the control/exercise group were 38.5+/-0.3 degrees C at rest and 39.8+/-0.3 degrees C at exhaustion, the hot/exercise group were 38.4+/-0.3 degrees C at rest and 41.2+/-0.9 degrees C at exhaustion and the cool/exercise group were 38.2+/-0.3 degrees C at rest and 38.5+/-0.2 degrees C at exhaustion. The running time was 102.0+/-39.5 min at the control/exercise group, 44.1+/-18.0 min at the hot/exercise group, and 55.4+/-11.9 min at the cool/exercise group. The level of soleus, cardiac and extensor digitorium longus (EDL) HSP70 in cool temperature does not change during a single bout of submaximal exercise. Whereas a single bout of submaximal exercise in hot and control ambient temperatures increases HSP70 accumulation in locomotor muscles, such as the soleus and cardiac, but not in the EDL tissue. This study shows that the changes of HSP70 level induced by a single bout of submaximal exercise at various ambient temperatures (control, hot and cool) depend on the rectal temperature.