Effect of bilateral carotid cooling on thermal responses during cycling and arm cranking work due to identical oxygen consumption

1. During the control, tympanic temperature (T_ty), skin blood flow (SkBF), local sweating rate (LSR) and heart rate (HR) of the AC were markedly higher than those of the BE. No significant differences were finally observed in rectal (T_re) and mean skin (T_sk) temperatures or oxygen uptake (VO₂). In contrast, mechanical work efficiency (ME) was significantly higher in the BE than in the AC.

2. During ice cooling, T_ty and the increasing rate in T_ty began to be suppressed at 25–35 min after the beginning in both kinds of work. During the AC, SkBF, LSR, HR and mean T_sk in the ice cooling tended to be lower compared those in the control. There were no significant difference between the control and the ice cooling in ME, VO₂ or T_re in either kind of work.     

Muscle temperature and muscle metabolism during short-term exercise in the goat

1. 1.|External heat exchangers acting on lower aortal blood temperature were used to dissociate hindleg muscle temperature (T_hlm) from general internal temperature (T_int) during short-term exercise of moderate intensity.

2. 2.|In series 1 39°C T_hlm was combined with 40.6°C T_int, and in series II 42°C T_hlm was combined with 39.8°C T_int.

3. 3.|At constant work rates, the 3°C difference in muscle temperature did not result in significantly different concentrations of muscle metabolites.

4. 4.|It is concluded that high local muscle temperature without general hyperthermia does not influence muscle metabolism during short-term moderate excercise.

Thermoregulatory responses of old men to gradual changes in ambient temperature

1. 1. Thermoregulatory respones to gradual rise and fall in the ambient temperature (T_a) were compared between 8 old (68–78 years) and 8 younger (20–25 years) male subjects.

2. 2. Starting at T_a of 31.5°C (r.h. 40%), T_a was raised to 39.5°C, then lowered to 21.5°C, and raised back to 31.5°C at a constant rate of 0.3°C/min.

3. 3. Noticeable differences in responses between the age groups were as follows: decline of sweating rate and reduction of acral blood flow during room cooling were retarded in the aged group, with wider variations among individuals, compared with those in the younger group; the tympanic and oesophageal temperatures fell considerably during cooling in the elderly group, failing to return to the level at start during the rewarming of the room, in contrast to the younger group.

4. 4. Such sluggish responses may be attributed largely to reduced cutaneous thermal perception with advancing age.

Thermal gradients in the oesophagus of man during exercise and passive warming

1. 1.|Oesophageal temperature (T_es) has been recorded at four vertical levels in the oesophagus of human subjects during exercise and during passive body heating.

2. 2.|The temperature increased with depth.

3. 3.|The rate of increase in T_es during exercise was greatest at the level of the diaphragm.

4. 4.|During passive heating of the body T_es increased most rapidly, and with shortest latency time, at the level adjacent to the left atrium of the heart.

5. 5.|During exercise, when breathing is deeper than at rest, T_es should be measured at a deeper level than that which is used during passive heating.

Electrical skin resistance and rectal temperature changes in resting human subjects exposed to heat

1. 1.|Fourteen male volunteers were examined under passive heating.

2. 2.|Electrical skin resistance (ESR) and rectal temperature (T_re) were measured during the whole period of exposure.

3. 3.|It was found that:

• —|ESR decreases rapidly with increasing air temperature. Assuming an exponential curve yields a mean time constant of 14 min.

• —|There is a correlation between the individual ESR time constants and T_re increases (r = 0.695, P < 0.005).

• —|Additional changes of ESR were noted in 8 subjects at a constant air temperature of 42°C.

4. 4.|It is concluded that ESR may be a useful indicator of the sweating response of the human thermoregulatory system during exogenous heat load.

Exercise in the heat: Effects of dinitrophenol administration

1. 1.|Dinitrophenol (DNP) was administered to rats in two equal dosages (20 mg/kg, 30 min interval); the second injection was followed immediately by exercise (9.14 m/min) in the heat (30°C) or at room temperature (21°C).

2. 2.|At 21°C control (saline-treated) rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals.

3. 3.|At 30°C, control rats ran for 65 min (δT_re/min = 0.05°C) while DNP-treated animals had a mean endurance of only 12 min (δT_re/min = 0.22°C).

4. 4.|DNP-treated rats (30°C) manifested no decrements in tail-skin heat loss (δT_sk/min = 0.17°C vs 0.10°C) or saliva secretion (0.78 g/min, DNP vs. 0.19 g/min, control) for their brief treadmill duration.

5. 5.|The increased metabolic heat production of DNP severely reduced performance.

Influence of muscle glycogen availability on ERK1/2 and Akt signaling after resistance exercise in human skeletal muscle.

Two pathways that have been implicated for cellular growth and development in response to muscle contraction are the extracellular signal-regulated kinase (ERK1/2) and Akt signaling pathways. Although these pathways are readily stimulated after exercise, little is known about how nutritional status may affect stimulation of these pathways in response to resistance exercise in human skeletal muscle. To investigate this, experienced cyclists performed 30 repetitions of knee extension exercise at 70% of one repetition maximum after a low (2%) or high (77%) carbohydrate (LCHO or HCHO) diet, which resulted in low or high (approximately 174 or approximately 591 mmol/kg dry wt) preexercise muscle glycogen content. Muscle biopsies were taken from the vastus lateralis before, approximately 20 s after, and 10 min after exercise. ERK1/2 and p90 ribosomal S6 kinase phosphorylation increased (P < or = 0.05) 10 min after exercise, regardless of muscle glycogen availability. Akt phosphorylation was elevated (P < 0.05) 10 min after exercise in the HCHO trial but was unaffected after exercise in the LCHO trial. Mammalian target of rapamycin phosphorylation was similar to that of Akt during each trial; however, change or lack of change was not significant. In conclusion, the ERK1/2 pathway appears to be unaffected by muscle glycogen content. However, muscle glycogen availability appears to contribute to regulation of the Akt pathway, which may influence cellular growth and adaptation in response to resistance exercise in a low-glycogen state.     

Ambient temperature limits and stability of temperature regulation in telemetered male and female rats

Knowing the ambient temperature (T_a) limits of normothermia in laboratory rodents is important because their thermoregulatory responses are useful in studies of physiology, pharmacology and toxicology. The present study assessed the T_a limits of normothermia using radiotelemetry to monitor core temperature (T_c), heart rate (HR), and motor activity (MA) in unrestrained, male and female Long-Evans rats over a 24 h period. Rats were housed individually in acrylic cages with wire-screen tops and bottoms and maintained at T'_as ranging from 12 to 33.5°C for 24 h with food and water provided ad libitum on a 12:12 L:D photoperiod. The limits of normothermia (i.e. where there was no significant change in T_c) were <12–29.5°C for females and 14.5–29.5°C for males. T_c of males at T'_as of 12, 32, and 33.5°C increased significantly above the baseline T_c. Female rats had a lower T_c than males at the warmest and coldest T'_as. HR and MA were generally higher in females at all T'_as. Males appeared to be poorly adapted to thermoregulate at T'_as above 30°C as based on their excessively high T'_cs, low MA, and marked weight loss compared to that of the females. Within the limits of normothermia the stability of T_c regulation (i.e. [(ΔT_c/ΔT_a) × 100]/2) was ±1.3 and ± 0.9% for males and females, respectively, over a 24 h period. These data on the stability of T_c in the male and female rat provide a valuable framework to study the acute and chronic effects of drugs, chemicals and other agents that affect temperature regulation.     

Behavioural and autonomic thermoregulation in hamsters during microwave-induced heat exposure

1. 1.|Preferred ambient temperature (T_a) and ventilatory frequency were measured in free-moving hamsters exposed to 2450 MHz microwaves. A waveguide exposure system which permits continuous monitoring of the absorbed heat load accrued from microwave exposure was imposed with a longitudinal temperature gradient which allowed hamsters to select their preferred T_a. Ventillatory frequency was monitored remotely by analysing the rhythmic shifts in unabsorbed microwave energy passing down the waveguide.

2. 2.|Without microwave exposure hamsters selected an average T_a of 30.2°C. This preferred T_a did not change until the rate of heat absorption (SAR) from microwave exposure exceeded approx. 2 W kg⁻¹. In a separate experiment, a SAR of 2.0 W kg⁻¹ at a T_a of 30°C was shown to promote an average 0.5°C increase in colonic temperature. Hamsters maintained their ventilatory frequency at baseline levels by selecting a cooler T_a during microwave exposure. In contrast, hamsters maintained at a T_a of 30°C (without a temperature gradient) underwent a sharp increase in ventilatory frequency compared to animals allowed to select their own T_a.

3. 3.|These data support previous studies suggesting that during thermal stress behavioural thermoregulation (i.e. preferred T_a) takes prescedence over autonomic thermoregulation (i.e. ventilatory frequency). It is apparent that selecting a cooler T_a is a more efficient and/or effective than autonomic thermoregulation for dissipating a heat load accrued from microwave exposure.

Development of autonomic and behavioural thermoregulation in turkeys (Meleagris gallopavo)

1. 1.|Heat production (HP) and body temperature (T_b) measurements were conducted at ambient temperatures (T_a) between 10 and 40°C. In addition preference temperatures (PT) were determined in a temperature channel and T_b was measured at preferred T_a

2. 2.|The influence of age on T_b at constant, as well as at PT, was proved. Increasing age was accompanied by an elevation of T_b whereas HP remained constant in the mid-range of T_a

3. 3.|The lower T_b in the first days of life is suggested to result from a lower thermoregulatory set point during the postnatal period.

4. 4.|The PT were different for the observed types of behaviour. The PT at rest was higher than the PT during locomotion, food intake and drinking.

Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement.

In the present study, we tested the hypothesis that a carbohydrate-protein (CHO-Pro) supplement would be more effective in the replenishment of muscle glycogen after exercise compared with a carbohydrate supplement of equal carbohydrate content (LCHO) or caloric equivalency (HCHO). After 2.5 +/- 0.1 h of intense cycling to deplete the muscle glycogen stores, subjects (n = 7) received, using a rank-ordered design, a CHO-Pro (80 g CHO, 28 g Pro, 6 g fat), LCHO (80 g CHO, 6 g fat), or HCHO (108 g CHO, 6 g fat) supplement immediately after exercise (10 min) and 2 h postexercise. Before exercise and during 4 h of recovery, muscle glycogen of the vastus lateralis was determined periodically by nuclear magnetic resonance spectroscopy. Exercise significantly reduced the muscle glycogen stores (final concentrations: 40.9 +/- 5.9 mmol/l CHO-Pro, 41.9 +/- 5.7 mmol/l HCHO, 40.7 +/- 5.0 mmol/l LCHO). After 240 min of recovery, muscle glycogen was significantly greater for the CHO-Pro treatment (88.8 +/- 4.4 mmol/l) when compared with the LCHO (70.0 +/- 4.0 mmol/l; P = 0.004) and HCHO (75.5 +/- 2.8 mmol/l; P = 0.013) treatments. Glycogen storage did not differ significantly between the LCHO and HCHO treatments. There were no significant differences in the plasma insulin responses among treatments, although plasma glucose was significantly lower during the CHO-Pro treatment. These results suggest that a CHO-Pro supplement is more effective for the rapid replenishment of muscle glycogen after exercise than a CHO supplement of equal CHO or caloric content.     

Responses of core and peripheral temperatures to chronic cold stress in transiently goitrous goats

Thyroid hormones play a major role in controlling basal metabolic rate, body temperature and hemodynamics. Responses of core and peripheral body temperatures to transient use of thyreostatic drugs are seldom measured simultaneously under chronic experimental settings. We developed a technique to attain this goal. Eighteen Damascus goat kids (initial Avg. BW=44±0.7 kg) underwent a minor invasive surgical procedure to implant two miniature temperature data loggers, intraperitoneally and subcutaneously, to assess core (T_core) and subcutaneous (T_sq) temperature changes when subjected to chronic (47 days) cold (< 10 °C) environment along with or without oral administration of the reversible goitrogen 6-N-propyl-2-thiouracil (PTU; 20 mg/kg BW/day). Nine animals served as controls whereas the remaining nine were treated with PTU for 31 out of total 47-day trial period. The PTU treatment significantly (P<0.05) depressed circulating free thyroxine (FT4), followed by a rebound after termination. Prior to initiation of PTU treatment, all animals displayed similar daily means of T_core and T_sq. Subsequently, both temperatures precipitously declined (P<0.01) with the gradual drop in ambient temperature (T_a) overtime. However, PTU caused an immediate and further drop in T_sq, suggesting a reduction in cutaneous perfusion. Interestingly, on the other hand, a delayed downregulation of T_core by PTU occurred 14 days post-treatment, indicating a relatively slower depression in metabolic thermogenesis after suppression of circulating thyroxine. Upon termination of PTU, T_core but not T_sq, returned to simulate control levels. Results from the current study show the practicality of our technique to concurrently record core and peripheral temperatures in chronically-instrumented animals, and that PTU causes a marked depression in thermoregulatory ability during cold stress with no indication for a reduction in the temperature set-point.     

Day-night variation of thermoregulatory responses to intraperitoneal electric heating in rats

1. 1.Hypothalamic temperature (T_hy), nonevaporative heat loss (R + C + K), evaporative heat loss (E), thermal conductance (k), metabolic heat production (M) and heat storage (S) of rats were simultaneously measured by direct and indirect calorimetry during internal heat loading (2 W per rat) with an intraperitoneal electric heater.

2. 2.The tests were made twice a day; once during the day (1000–1200 h) and once at night (2200–2400 h) at an ambient temperature of 24°C.

3. 3.The resting values of T_hy, colonic temperature, (R + C + K), E, M and heart rate, and the T_hy threshold for tail skin vasodilation (T_th) during internal heat load were significantly higher at night than during the day.

4. 4.The slopes showing the relationshiop between (R + C + K), k or M and T_hy were significantly steeper during the day than at night after T_hy exceeded T_th.

5. 5.The slopes showing the relationship between E or S and T_hy were not different during the day and at night.

6. 6.These results indicate that the responses of nonevaporative heat loss and heat production to internal heat load vary with the time of day in rats.

Effect of repeated nicotine exposure on core temperature and motor activity in male and female rats

Comparatively little is known about the thermoregulatory effects of single and repeated administration of nicotine. Nicotine is a relatively fast acting drug that induces transient changes in core temperature (T_c) of rodents. The development of radio telemetry allows one to detect subtle and rapid changes in T_c that otherwise are difficult to measure with conventional colonic probe techniques. To this end, T_c and motor activity (MA) were monitored by radio telemetry in male and female Sprague-Dawley rats following five daily injections of saline or nicotine tartrate (0.5 mg/kg; sc). The first injection of saline led to a transient increase in T_c that was attributed to the handling and injection procedures. Rats dosed with nicotine for the first time were hypothermic for approximately 2 h after injection. The hypothermia was attributed to an impaired increase in T_c from handling and injection. A transient hyperthermic response began to develop with each successive injection of nicotine. After the fourth injection of nicotine, T_c of male rats increased by 0.5°C above controls; T_c of females increased by 0.25°C above controls after the fifth injection. MA also increased transiently with each injection of saline and nicotine. The MA response of females was significantly greater than the males for the second through fifth injections of nicotine. Overall, the thermoregulatory system develops sensitization with 4–5 repeated injections of nicotine. The mediation of a hyperthermic response to a systemically administered cholinergic agonist is a novel effect. It may aid in understanding the delayed hyperthermic response to organophosphate pesticides. The sensitization of the thermoregulatory system to nicotine may shed light on the neuropharmacological mechanisms of this drug.     

Stress hyperthermia in mice

1. 1.|Colonic temperature (T_c) of mice rose about 2°C in 20 min when the mice were taken out of their home cages and the T_c measured every 5 min.

2. 2.|The maximal rise in T_c diminished if the procedure was repeated daily for 43 days and increased abruptly again when the T_c measurements were taken, in one session, in the presence of a rat.

3. 3.|Salicylate diminished the maximal T_c but not the difference between the maximal and the initial T_c, i.e. the magnitude of the T_c rise.

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Thermal biology of the fossorial rodent Ctenomys fulvus from the Atacama desert, northern Chile

The Andean tuco-tuco, Ctenomys fulvus (Rodentia: Ctenomyidae) inhabits one of the most arid regions of the world, the Salar de Atacama, Northeast of Antofagasta, Chile (23°17′06″S, 68°05′43″W; 2.240 m.a.s.l). We found that a stable microclimate in burrows, a low evaporative water loss (EWL), and a diet of roots (59% water content) are the main factors that permit the survival of this fossorial species in harsh desert conditions. Large circadian variation in T_a was observed above ground. Daily ΔT_a (T_a max − T_a min) = 37.9±0.2°C in summer and in winter. In contrast, circadian variation of T_a inside the burrows was only 5.8±0.5°C in the same seasons. Relative humidity (RH) was 1.9–3.1% during the day, increasing to maximum values of 27% at night and early morning. Inside the burrows RH was higher and quite stable, ranging between 53.1 and 65%, independent of the time of day and season. EWL, measured between 10 and 25°C, was low (1.26 mg/g h), and a moderate increase of 13–20% was observed at higher temperatures. The low EWL may prevent dehydration. However, because of the low heat loss capability, animals became hyperthermic (0.8–1.6°C) in dry air at T_a=30–35°C. As T_a during afternoon normally exceeded 35°C, the microclimate of burrows provided the only way to avoid the lethal effects of hyperthermia.     

Influence of beta-adrenergic blockade on the control of sweating in humans

To evaluate the role of beta-adrenergic receptors in the control of human sweating, we studied six subjects during 40 min of cycle-ergometer exercise (60% maximal O2 consumption) at 22 degrees C 2 h after oral administration of placebo or nonselective beta-blockade (BB, 80 mg propranolol). Internal temperature (esophageal temperature, Tes), mean skin temperature (Tsk), local chest temperature (Tch), and local chest sweat rate (msw) were continuously recorded. The control of sweating was best described by the slope of the linear relationship between msw and Tes and the threshold Tes for the onset of sweating. The slope of the msw-Tes relationship decreased 27% (P less than 0.01), from 1.80 to 1.30 mg X cm-2 X min-1 X degree C-1 during BB. The Tes threshold for sweating (36.8 degrees C) was not altered as the result of BB. These data suggest that BB modified the control of sweating via some peripheral interaction. Since Tsk was significantly (P less than 0.05) reduced during BB exercise, from a control value of 32.8 to 32.2 degrees C, we evaluated the influence of the reduction in local skin temperature (Tsk) in the altered control of sweating. Reductions in Tch accounted for only 45% of the decrease in the slope of the msw-Tes relationship during BB. Since evaporative heat loss requirement during exercise with BB, as estimated from the energy balance equation, was also reduced 18%, compared with control exercise, we concluded that during BB the reduction in sweating at any Tes is the consequence of both a decrease in local Tsk and a direct effect on sweat gland.     

Development of thermoregulation in Hawaiian brown noddies (Anous stolidus pileatus)

1. 1.|Oxygen consumption ( ) and body temperture (T_b) of Hawaiian brown noddies (Anous stolidus pileatus [Aves: Laridae]) during late incubation and in the first 24 h after hatching were measured at ambient temperatures (T_a) between 28 and 38°C and between 15 and 43°C, respectively. Evaporative cooling by hatchings at T_a of 36–43°C was also measured.

2. 2.|Throughout the late incubation stages studied, and T_b both varied directly with T_a in an ectothermic pattern.

3. 3.|The hatchlings successfully regulated T_b at T_a between ca. 29 and 43°C.

4. 4.|The functional basis of the abrupt increase in thermoregulatory capacity with hatching is discussed.

Exercise thermoregulation after prolonged wakefulness

The effect of 33 h of wakefulness on the control of forearm cutaneous blood flow and forearm sweating during exercise was studied in three men and three women. Subjects exercised for 30 min at 60% peak O2 consumption while seated behind a cycle ergometer (Ta = 35 degrees C, Pw = 1.0 kPa). We measured esophageal temperature (Tes), mean skin temperature, and arm sweating continuously and forearm blood flow (FBF) as an index of skin blood flow, twice each minute by venous occlusion plethysmography. During steady-state exercise, Tes was unchanged by sleep loss. The sensitivity of FBF to Tes was depressed an average of 30% (P less than 0.05) after 33 h of wakefulness with a slight decrease (-0.15 degrees C, P less than 0.05) in the core temperature threshold for vasodilatory onset. Sleep loss did not alter the Tes at which the onset of sweating occurred; however, sensitivity of arm sweating to Tes tended to be lower but was not significant. Arm skin temperature was not different between control and sleep loss experiments. Reflex cutaneous vasodilation during exercise appeared to be reduced by both central and local factors after 33 h of wakefulness.