The effects of fur on the thermal regulation of mice (Mus musculus)

In order to ascertain the thermal insulation function of fur in mice, food and water intakes and rectal and skin temperatures were observed in Jcl: ICR mice and a group of the same species with their fur clipped, as well as BALB/C nu/+ and nu/nu mice. Food and water intakes increased as the ambient temperature dropped. The rectal temperature remained almost unchanged at ambient temperatures of from 18 to 30 degrees C. Skin temperatures were highest at side of the abdomen, lower at the neck, and lowest at the head. There was a tendency for skin temperatures to increase as the ambient temperature rose. The skin temperatures of mice with fur were higher than those of mice without fur. The thermal insulation of fur was 0.25, 0.14 and -0.06 clo at 18, 22, 26 and 30 degrees C in ICR mice, and 0.36, 0.01, 0.01 and -0.03 clo at 18, 22, 26 and 30 degrees C in BALB/C mice, respectively. These results confirm that heat loss from the skin at low temperatures could be prevented by the presence of fur. It also appeared that the hairless mice mutant had a lower metabolic rate than the animals with their fur clipped.     

Effects of high temperature on body temperature and hormonal adjustments in piglets

Effects of a high (33 degrees C) or thermoneutral (23 degrees C) temperature on body temperature and endocrine parameters were studied in weaned piglets. Rectal and skin temperatures were measured in four ad libitum fed animals per temperature during three weeks. After this acclimation period, 11 blood samples were withdrawn on a 24-h period. Over the acclimation period, rectal and skin temperatures were 0.6 and 2.9 degrees C higher, respectively, at 33 degrees C than at 23 degrees C (P < 0.01), this change occurring from the 1st day at 23 or 33 degrees C. A tendency of serum leptin concentrations to be lower after meals at 33 degrees C than at 23 degrees C was also displayed (P = 0.09). Plasmatic concentrations in Insulin-like growth factor I and thyroxine were decreased at 33 degrees C relative to 23 degrees C (P < 0.01 and P < 0.06, respectively), and triiodothyronine concentrations tended to be lower at 33 degrees C than at 23 degrees C (P = 0.1), which could account for the lower heat production and growth observed in pigs exposed to high temperatures.     

Evaluation of miniature data loggers for body temperature measurement during sporting activities

We recorded body temperatures in four runners, two squash players and one swimmer at 1-min intervals using miniature data loggers. These single-channel loggers are small and light (25 g), and were easily carried by the athletes during their sporting activities. Wide-range loggers (-37 degrees C to +46 degrees C), which had a temperature resolution of 0.4 degrees C, were used to measure thigh skin temperature. Auditory canal temperature and rectal temperature were measured with narrow-range loggers (+34 degrees C to + 46 degrees C) which had a considerably higher resolution (0.04 degrees C). With the aid of visual analogue scales subjects reported that the thermometric equipment caused very little discomfort or impairment of exercise performance. Loggers connected to uncoated bead thermistors (used for skin and auditory canal temperatures) had a thermal time constant of 0.4 s, and that of the coated thermistors (rectal probes) was 6 s. We were able to waterproof the equipment and measure rectal temperature in a swimmer. Hot (35 degrees C) or cold (5 degrees C) ambient temperatures had an insignificant effect on the intrinsic accuracy of the data loggers, even when used without recalibration at those temperatures. We believe that miniature temperature loggers are convenient and accurate thermometers for use during sporting activities and may provide new insights into thermoregulation during exercise.     

Effects of increase in body temperature on the breathing pattern in premature infants

This study was designed to determine the effects of a mild increase in body temperature within the physiological range (0.8 degrees C) in healthy premature infants. Seven unsedated premature infants (38.4 wk +/- 1.5 postconceptional age) were monitored polygraphically during "morning naps" in an incubator under two different environmental temperatures: (1) normothermia with the incubator temperature set at 25 degrees C and the rectal temperature equal to 36.9 degrees C +/- 0.1; (2) hyperthermia with the incubator temperature set at 35 degrees C and the rectal temperature equal to 37.7 degrees C +/- 0.15. Respiratory frequency and heart rate, respiratory events, i.e., central and obstructive apnea, and periodic breathing with and without apneic oscillations were tabulated. Results for respiratory events were expressed as (1) indices of the total number of respiratory events, and of specific respiratory events per hour of total, quiet and active sleep times; (2) duration of total and specific respiratory events expressed as a percentage of total sleep, quiet and active sleep times. Respiratory frequency and heart rate were significantly increased by hyperthermia (P less than 0.05). Hyperthermia did not significantly modify the indices or the duration of central and obstructive apnea. But the indices and the duration of periodic breathing with and without apneic oscillations were significantly increased by hyperthermia during active sleep (P less than 0.05) but not during quiet sleep. The present study shows that a mild increase in body temperature within the physiological range in premature infants enhances the instability of the breathing pattern during active sleep.     

Influence of thermal and nutritional acclimatization on body temperatures and metabolic rate

1. An investigation of the influence of previous thermal and nutritional experience on body temperatures and metabolic rate has been carried out with growing piglets. Littermates were kept, from shortly after birth, at either 10 or 35 degrees C and fed either a high (H) or a low (L) energy intake. At 8 weeks of age the animals were exposed to a series of environmental temperatures of 10, 20, 27 and 35 degrees C for 1.5 hr and their rates of oxygen consumption were determined over the last 45 min. At the end of the session body temperatures were measured. 2. Rectal temperatures measured 24 hr after the start of the last meal were higher at each test temperature in piglets which had been living at 35 degrees C than in those at 10 degrees C. Also, rectal temperatures were higher in those on the H intake for animals which had been living in either the hot or the cold environment. 3. Skin temperature on the back was similar in all groups at any given test temperature although there was a tendency for those on an H intake to have the higher temperatures. Skin temperatures of the legs and ears were higher in the 10H and 10L groups than in the 35H or 35L groups at all the test environmental temperatures; energy intake had little effect. 4. Metabolic rate was greater for the animals on the H than the L intake, for those which had been living at either 10 or 35 degrees C at all the test environmental temperatures. The analysis did not reveal any significant difference related to the overall effect of living temperature, which was independent of energy intake. 5. At thermal neutrality (27 degrees C) there was a significant interaction, between energy intake and normal living temperature, on metabolic rate. Living temperature was found to modify the effect of intake: the difference between the two intakes was greater in those from the cold environment than from the hot.     

Body temperature changes in dogs exposed to varying effective temperatures

Adult male and female Beagle dogs (eight total) were exposed individually, in series, to each of 23 effective temperatures for a period of 2 hours or until rectal temperature increased 1.1 degrees C. Rectal temperature was measured to the nearest 0.1 degree C by thermistor probes in the pre-test condition (basal temperature) and at each 5-minute interval during the test conditions (effective temperatures between 21.1 degrees C and 34.7 degrees C). The frequency at which dogs displayed a 1.1 degree C rise in rectal temperature was related to the magnitude of the effective temperature. At an effective temperature of 32.6 degrees C or greater, 100% of the dogs displayed a 1.1 degree C rise in rectal temperature. Between an effective temperature of 29.3 degrees C and 31.4 degrees C, some animals displayed a 1.1 degree C rise while others did not. At an effective temperature of 28.4 degrees C or below no animals displayed a 1.1 degree C rise. The mean time necessary for a 1.1 degree C rise was negatively correlated (P less than 0.01) to the magnitude of the effective temperature. The minimum effective temperature necessary to increase rectal temperature by 1.1 degree C in male Beagles (29.6 +/- 1.0 degree C) was not significantly different from females (30.8 +/- 0.4 degrees C).     

A test of biochemical symmorphosis in a heterothermic tissue: bluefin tuna white muscle

Selective brain cooling (SBC) is defined as a brain temperature cooler than the temperature of arterial blood from the trunk. Surrogate measures of arterial blood temperature have been used in many published studies on SBC. The use of a surrogate for arterial blood temperature has the potential to confound proper identification of SBC. We have measured brain, carotid blood, and rectal temperatures in conscious sheep exposed to 40, 22, and 5 degrees C. Rectal temperature was consistently higher than arterial blood temperature. Brain temperature was consistently cooler than rectal temperature during all exposures. Brain temperature only fell below carotid blood temperature during the final few hours of 40 degrees C exposure and not at all during the 5 degrees C exposure. Consequently, using rectal temperature as a surrogate for arterial blood temperature does not provide a reliable indication of the status of the SBC effector. We also show that rapid suppression of SBC can result if the animals are disturbed.     

Sweating response in man during transient rises of air temperature

Nude men were exposed to neutral environments (Ta = 28 degrees C, Pw = 20 mbar) changing to warm environments (Ta = 50 degrees C, Pw = 20 mbar). The transient period from neutral to warm environment lasted 4 min (dTA/DT = 5.50 degrees C/min) or 20 min (DTa/dt = 1.10 degrees C/min) or 40 min (dTa/dt = 0.55 degrees C/min) or 60 min (dTa/dt = 0.37 degrees C/min). Continuous measurements were made of rectal and mean skin temperatures and of body weigth loss. Sweating started before appreciable variation in rectal temperature. Onset of sweating could be explained by a peripheral proportional and rate control. Unsteady-state sweating can be predicted by summated stimulation of skin and rectal temperatures. This stimulation could be increased for some subjects by a multiplicative effect due to differences in local skin temperatures. This multiplicative effect occurred during the first transient period.     

The Sickle-cell and Altitude

High altitude seemed to be responsible for seven recent cases of sickling crisis. People with sickle-cell trait are at risk if they fly in unpressurized aircraft, which are used for many local air services. Those with sickle-cell haemoglobin C disease should avoid air travel even in pressurized aircraft. Possibly as a result of “autosplenectomy,” patients with sickle-cell anaemia seem to be able to fly in pressurized aircraft with little risk. All passengers and aircrew who might have some form of sickle-cell disease should be screened before flight.     

Observations on normal body temperatures in Vietnamese and Japanese in Vietnam

The observations described in this paper were made during a study of the effects of tropical climate upon Vietnamese and Japanese. We measured rectal and skin temperatures every 10 min for 26 hrs in 6 Vietnamese and 6 Japanese. The experiments have been conducted for 2 hot months, June and July 1999 and 2000 in Hanoi, Vietnam. The ambient temperatures ranged from 33 to 36 degrees C. The results obtained are summarized as follows: 1) Skin temperatures at thigh, forearm and hand during the daytime were significantly higher in the Vietnamese subjects than in the Japanese ones. It would be physiological reactions to warm ambient temperatures, which is advantageous for dissipation of body heat. 2) The average rectal temperature during the daytime is significantly higher in the Vietnamese than in the Japanese, while significantly lower at night. 3) Average range of oscillation of rectal temperature was 1.26 degrees C in the Vietnamese, which was clearly greater than in the Japanese. The higher core temperature, which was actively regulated under warm temperature, seemed of adaptive significance, resulting in the reduction of water consumption like camels in the desert. A greater range of oscillation in tropical Vietnamese people might have ecological significance for efficient acclimatization in the warm environment, suggesting that the setpoint of core temperature could show a greater range of oscillation.     

Effect of thermal history on the rat's response to varying environmental temperature

After acclimating individually housed male rats to temperatures of either 24.5 +/- 0.1 or 29.2 +/- 0.1 degrees C for 14 days, randomly paired animals from each group were acutely exposed (3 h) in series to experimental temperatures between 18.0 and 34.5 degrees C in a controlled environment room. Relative humidity of 50 +/- 0.3% and a 12-h light-dark photoperiod (light from 0900 to 2100 h) were maintained. Metabolic rate (MR) and evaporative water loss (EWL) were-measured using an open-flow system; thermistors were used to measure the rectal (Tre) and tail skin (Tts) temperatures. MR was relatively constant over a temperature range of 22.2 to 27.0 degrees C for rats acclimated to 24.5 degrees C and 20.0 to 29.2 degrees C for rats acclimated to 29.2 degrees C. Above and below these ranges, MR for both groups was significantly (P less than 0.05) elevated. At their respective acclimation temperatures, the absolute Tre and Tts of 29.2 degrees C rats were maintained at an elevated level compared with 24.5 degrees C rats. Although EWL for both groups was relatively constant between 18.0 and 27.0 degrees C, 24.5 degrees C rats displayed higher EWL changes at most environmental temperatures above 27.0 degrees C. At 34.5 degrees C, 29.2 degrees C rats dissipated 26% more metabolic heat by evaporation compared with 24.5 degrees C rats. These data suggest that acclimation temperatures of rats affected the thermoneutral zone and alter the set-point temperature around which thermal responses are regulated.     

Effects of color temperature of fluorescent lamps on body temperature regulation in a moderately cold environment

A study on the effects of different color temperatures of fluorescent lamps on skin and rectal temperatures in a moderately cold environment involving (i) changes in skin temperature of 7 male subjects exposed to an ambient temperature ranging from 28 degrees C to 18 degrees C (experiment I) and (ii) changes in skin and rectal temperatures and metabolic heat production of 11 male subjects exposed to ambient temperature of 15 degrees C for 90 min (Experiment II) was conducted. In Experiment I, the reduction of mean skin temperature from the control value was significantly greater under 3000 K than under 5000 K or 7500 K lighting. In Experiment II, the reductions in mean skin temperature and rectal temperature were respectively greater and smaller under 3000 K than those under 5000 K or 7500 K lighting. However, metabolic heat production was not affected by color temperature conditions. The relationships between morphological and physiological parameters revealed that no significant relation of rectal temperature to body surface area per unit body weight was found only under 3000 K. Furthermore, while the mean skin temperature was independent on the mean skinfold thickness under 3000 K, a significant negative correlation between the rectal and mean skin temperatures was observed. Therefore, body heat loss might be suppressed effectively by increasing the vasoconstrictor tone under a color temperature of 3000 K, and the body shell was dependent only on morphological factors under 5000 K and 7500 K lighting.     

Thermoregulatory responses of diabetic rats

1. Thermal responses and skin microcirculation were measured in streptozotocin-induced diabetic (SD) rats during acute and chronic exposure to ambient (Ta) temperatures ranging from about 5 to 35 degrees C. 2. At 28 degrees C, SD rats had higher rate of oxygen consumptions (VO2), tail skin blood flow (SKBF), but lower rectal temperatures (Tre) than saline-injected controls. 3. Chronic exposure of the SD rats to 35 and 5 degrees C caused a sharp rise and decline in Tre, respectively. 4. At 35 degrees C, hyperthermia in the SD rats was associated with greater increase in VO2 than controls, but changes in SKBF were similar in both groups. 5. At 5 degrees C, VO2 changed similarly in both the SD and control rats, but vasoconstriction was greater in the controls. 6. The data suggest that hypothermia in SD rats may be associated with impairment of vasoconstriction and hyperthermia may be related to an increase VO2 not accompanied by greater vasodilation.     

Thermoregulatory responses of dystrophic hamsters to changes in ambient temperatures

The ability of dystrophic hamsters to maintain their body temperature despite abnormal muscle and brown adipose tissue, two organs involved in thermoregulation, was evaluated. Dystrophic hamsters (CHF 146) between the ages of 30 and 160 days kept at 21 degrees C had core (rectal) temperatures (TR) that were 0.5-1.5 degrees C lower than Golden Syrian controls. The reduced core temperatures of dystrophic hamsters were unlikely the result of an incapacity to generate heat since the dystrophic hamsters were able to maintain their TRs during 3 h of acute cold stress (4 degrees C) and to adapt to prolonged cold exposure. However, TRs of cold-acclimated dystrophic hamsters were still 1 degree C below TRs of cold-acclimated control animals. By contrast, increasing the ambient temperature raised TRs of both normal and dystrophic hamsters. When kept at 32 degrees C overnight, the TRs of dystrophic hamsters remained significantly below those of control animals. When heat-exposed dystrophic hamsters were returned to 21 degrees C, their TRs returned to values significantly lower than those of control hamsters. Thus, dystrophic hamsters showed a capacity to thermoregulate, like control hamsters, but appeared to do so at a lower temperature. The reduced core temperatures of dystrophic hamsters kept at 21 degrees C cannot be explained by a reduction in metabolic activity since newborns and 30- and 140-day-old dystrophic hamsters had rates of oxygen consumption (VO2) and carbon dioxide production (VCO2) that were similar to those of controls. These results suggest that the thermoregulatory set point may be altered in dystrophic hamsters.     

Size-dependent pigmentation-pattern formation in embryos of Alligator mississippiensis: time of initiation of pattern generation mechanism

The pigmentation pattern of Alligator mississippiensis was examined. The number of white stripes on the dorsal side of embryos (stages 21-28) and hatchlings from eggs incubated at 30 degrees C (100% females) and 33 degrees C (100% males) was recorded. Total length, nape-rump length and tail length were recorded for each embryo and hatchling. The number of white stripes was affected by incubation temperature but not sex; hatchlings incubated at 33 degrees C had two more white stripes than those at 30 degrees C, despite being the same length. Five female hatchlings produced at 33 degrees C by manipulation of the temperature, had the same number of stripes as males that developed under the same incubation temperatures. The appearance of the pigmentation was accelerated in embryos incubated at 33 degrees C, occurring eight days earlier than at 30 degrees C. At the time just before the first signs of pigment deposition, embryos from 33 degrees C were longer than those at 30 degrees C. If the stripe formation is size dependent this explains why hatchlings at 33 degrees C have more stripes than hatchlings from 30 degrees C. The mechanism that produces the stripe patterns is unknown. We describe key elements a pattern formation mechanism must possess to produce such stripes and suggest a possible mechanism, based on cell movement driven by chemotaxis. We apply the mathematical model to dorsal patterning on A. mississippiensis. We show how length at pattern formation is the prime factor in determining stripe number and how the pattern can be formed in the observed anterior-posterior sequence. We present numerical simulations and show that the qualitative behaviour is consistent with the experimental results.     

Resuscitation from cardiopulmonary arrest during accidental hypothermia due to exhaustion and exposure.

A 16-year-old boy with accidental hypothermia and cardiopulmonary arrest due to exhaustion and exposure was resuscitated after warming measures -- hot wet towels, hot water bottles, and hot water enemas and gastric lavage -- had increased his rectal temperature from 25.2 to 28.0 degrees C. Despite prolonged cardiopulmonary arrest, recovery was almost complete, with no evident cerebral damage. Cardiopulmonary resuscitation procedures should not be abandoned until the body temperature is more than 30 degrees C, because the prognosis in cases of accidental hypothermia without associated disease is excellent if cardiac function can be re-established.     

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.     

Effect of cold and hot ambient temperatures on plasma progesterone concentrations in ewes with intact and denervated ovaries containing experimentally maintained corpora lutea

Twenty ewes in which maintained corpora lutea had been established were subject to 1 of 3 treatments: denervation of the ovaries by freezing, denervation of the ovaries using the chemical 6-hydroxydopamine, or control. The animals were exposed sequentially to normal (24.5 degrees C), cold (10.7 degrees C), normal (23.8 degrees C), hot (39.4 degrees C) and normal (24.6 degrees C) temperatures, each for 1 week. On the final 3 days of exposure rectal temperatures and heart rates were measured, and on the final day the body weights, respiratory rates, and blood glucose concentrations were measured and a series of 5 blood samples was collected from each ewe for determination of the progesterone concentrations. The progesterone concentration was greatest during the hot period in 8 of the 12 animals, particularly in the ewes with denervated ovaries (6 of the 7 animals). This suggests that high ambient temperatures increase progesterone concentrations non-specifically, and that denervated ovaries are more sensitive to the circulating catecholamines that presumably mediate this effect. The progesterone concentrations were lower (P less than 0.001) in the groups with freezing or chemically denervated ovaries (2.86 and 2.73 ng/ml respectively) than in the control group (3.38 ng/ml), suggesting that the ovarian innervation plays a physiological role in regulating progesterone secretion.     

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.     

The effect of liposomes on thermotropic membrane phase transitions of bovine spermatozoa and oocytes: implications for reducing chilling sensitivity

We have examined the effects of combinations between egg-phosphatidylcholine (EPC) or dipalmitoylphosphatidylcholine (DPPC) liposomes with either bovine spermatozoa or oocytes on cellular chilling sensitivity, lipid phase transition temperature (T(m)), and the ability of the oocytes to develop to the blastocyst stage. Spermatozoa and oocytes were exposed to EPC and DPPC liposomes at various temperatures (spermatozoa: 4, 12, 16, and 25 degrees C; oocytes: 4, 16, and 32 degrees C). The membrane integrity of the spermatozoa-control group decreased significantly following exposure to 16 or 12 degrees C, compared to ambient temperature (25 degrees C). In contrast, the EPC-sperm group had a greater resistance to chilling at each temperature and showed a decline in membrane integrity only at the lowest temperatures investigated. However, the DPPC-sperm group was injured significantly at all temperatures tested. Similar to the sperm, oocytes from the control group that were exposed to 16 degrees C were injured more severely than oocytes that were electrofused with EPC or DPPC liposomes. The membrane integrity of the oocytes at 16 degrees C that were electrofused with either EPC or DPPC liposomes was approximately the same as the control group held at 32 degrees C (normalized to 100%), compared to 46% in the control group at 16 degrees C (P<0.01). The transition temperatures of the sperm and oocyte membranes revealed different T(m) for the different liposome treatments. All groups had a significantly higher cleavage rate, as well as increased blastocyst formation when oocytes were exposed to temperatures above or below their T(m). We suggest that the T(m) of spermatozoa or oocytes can be changed by spontaneous association or electrofusion of liposomes with cellular membranes and, consequently, the chilling sensitivity can be altered. The resulting possibility is that embryo development after cryopreservation could be improved with such a method.