Thermoregulatory responses to acute body heating in rats acclimated to continuous heat exposure

1990 ◽  
Vol 68 (1) ◽  
pp. 59-65 ◽  
Author(s):  
O. Shido ◽  
T. Nagasaka
Keyword(s):  
Heat Load ◽  
Heat Exposure ◽  
Thermal Conductance ◽  
The Other ◽  
Electric Heater ◽  
Acclimation Temperature ◽  
Metabolic Heat ◽  
Thermoregulatory Responses ◽  
Colonic Temperature ◽  
Continuous Heat

Thermoregulatory responses to an acute heat load with intraperitoneal heating (IH) or indirect external warming (EW) by increasing ambient temperature (Ta) were investigated with direct and indirect calorimetry in rats acclimated to environments of 24.0 degrees C (Cn), 29.4 degrees C (H1), and 32.8 degrees C (H2) for greater than 15 days. The rats were placed in a direct calorimeter where the air temperature was maintained at 24 degrees C for the initial 3 h. IH was then made for 30 min through an electric heater implanted chronically (6.5 W.kg-1) in the peritoneal cavity, and EW was performed by raising the jacket water temperature surrounding the calorimeter from 24 to 39 degrees C (0.19 degrees C.min-1). Hypothalamic (Thy) and colonic temperature immediately before the start of the heat load tended to be higher as the acclimation temperature increased. During IH, the threshold Thy for the tail skin vasodilation (Tth) was significantly higher in H2 than in Cn rats. During EW, however, there was no difference in Tth between the groups. Metabolic heat production (M) was slightly suppressed during IH and significantly depressed only in H2 rats. During EW, M was suppressed in all the groups. The magnitude and duration of suppression were greater in H2 rats than in the other two groups. The responses in nonevaporative heat loss and thermal conductance (C) to the rise in Thy did not differ among the three groups during IH. According to the rise in Thy, however, there was a greater C increase in H2 than in Cn and H1 rats during EW.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature regulation during acute heat loads in rats after short-term heat exposure

1991 ◽  
Vol 71 (6) ◽  
pp. 2107-2113 ◽  
Author(s):  
O. Shido ◽  
S. Sakurada ◽  
M. Tanabe ◽  
T. Nagasaka
Keyword(s):  
Heat Loss ◽  
Thermal Equilibrium ◽  
Heat Load ◽  
Heat Exposure ◽  
Heat Losses ◽  
Electric Heater ◽  
Internal Heating ◽  
Short Term ◽  
Metabolic Heat ◽  
Heat Loads

Eleven rats were kept at an ambient temperature of 33.5 degrees C (HC) for 4–5 consecutive days, 9 additional rats were subjected to 33.5 degrees C for approximately 5 h daily (HI) for the same period, and 12 controls (Cn) were kept at 24 degrees C. After the exposure, the rats were placed in a direct calorimeter, where the wall temperature was set at 24 degrees C, and subjected to direct internal heating (6.2 W.kg-1, 30 min) through an intraperitoneal electric heater. After the first heat load and when thermal equilibrium had been attained again, the rats were subjected to indirect external warming by raising the jacket water temperature surrounding the calorimeter from 24.0 to 38.8 degrees C in 90 min. Hypothalamic (Thy) and colonic temperatures (Tco), evaporative and nonevaporative heat loss, and metabolic heat production (M) before the acute heat loads did not differ among the groups. During heat loads, the latent times for the onsets of the rises in tail skin temperature and evaporation were significantly longer, and Thy and Tco at the start of increases in heat losses tended to be higher, in the HC than in the Cn. M significantly decreased in all groups, but the magnitude and duration of reduction in M were significantly greater in the HC than in the Cn. There were no differences between the thermoregulatory responses to heat loads of the HI and Cn. These results suggest that in HC the threshold core temperature for heat loss response and the upper critical temperature have already shifted to a higher level and that HC respond to heat stress more strongly with the reduction of M than Cn. Short-term intermittent heat exposure had little effect on the thermoregulatory mechanisms in rats.

Thermoregulatory responses of rats acclimated to heat given daily at a fixed time

1995 ◽  
Vol 78 (5) ◽  
pp. 1720-1724 ◽  
Author(s):  
N. Sugimoto ◽  
O. Shido ◽  
S. Sakurada
Keyword(s):  
Core Temperature ◽  
Exposure Time ◽  
Heat Exposure ◽  
Fixed Time ◽  
Body Core Temperature ◽  
Electric Heater ◽  
Dark Phase ◽  
Thermoregulatory Responses ◽  
Body Core ◽  
Pronounced Reduction

Body core temperature of rats acclimated to heat given daily at a fixed time falls during the previous heat exposure time. In the present study, thermoregulatory responses of heat-acclimated rats were examined during the specific period. Heat-acclimated rats were subjected to an ambient temperature of 32 degrees C for approximately 5 h in the first half or last half of the dark phase for 14 days while control rats were kept at 24 degrees C. Then the rats were placed in a direct calorimeter and were warmed for 30 min with an intraperitoneal electric heater. Measurements were made twice in the first and last halves of the dark phase. Body warming significantly increased body core temperature in all rats. In the heat-acclimated rats, heat production (M) was significantly depressed during the previous heat exposure time but not during the other period. Body warming had little effect on M in the control rats during either period. The results suggest that rats acclimated to heat given at a fixed time daily respond to an acute heat load with a pronounced reduction of M. However, such a response was observed only during the period when the rats had been previously exposed to heat.

Effects of modafinil on heat thermoregulatory responses in humans at rest

2002 ◽  
Vol 80 (8) ◽  
pp. 796-803 ◽  
Author(s):  
Jean-Claude Launay ◽  
Yves Besnard ◽  
Angélique Guinet ◽  
Germain Bessard ◽  
Christian Raphel ◽  
...  
Keyword(s):  
Heat Storage ◽  
Sweat Rate ◽  
Heat Exposure ◽  
Body Temperatures ◽  
Metabolic Heat ◽  
Thermoregulatory Responses ◽  
The Central Nervous System ◽  
Male Subjects ◽  
Skin Temperatures ◽  
Body Heat

The effects of modafinil on heat thermoregulatory responses were studied in 10 male subjects submitted to a sweating test after taking 200 mg of modafinil or placebo. Sweating tests were performed in a hot climatic chamber (45°C, relative humidity <15%, wind speed = 0.8 m·s–1, duration 1.5 h). Body temperatures (rectal (Tre) and 10 skin temperatures (Tsk)), sweat rate, and metabolic heat production (Mdot) were studied as well as heart rate (HR). Results showed that modafinil induced at the end of the sweating test higher body temperatures increases (0.50 ± 0.04 versus 0.24 ± 0.05°C (P < 0.01) for deltaTre and 3.64 ± 0.16 versus 3.32 ± 0.16°C (P < 0.05) for deltaTbarsk (mean skin temperature)) and a decrease in sweating rate throughout the heat exposure (P < 0.05) without change in Mdot, leading to a higher body heat storage (P < 0.05). DeltaHR was also increased, especially at the end of the sweating test (17.95 ± 1.49 versus 12.52 ± 1.24 beats/min (P < 0.01)). In conclusion, modafinil induced a slight hyperthermic effect during passive dry heat exposure related to a lower sweat rate, probably by its action on the central nervous system, and this could impair heat tolerance. Key words: modafinil, heat, human, thermoregulation.

scholarly journals Working Productivity Analysis on the Process of Drying Fish Using Solar Dryers

2021 ◽  
Vol 12 (1) ◽  
pp. 70-73
Author(s):  
I Gede Santosa ◽  
◽  
I Gede Bawa Susana ◽  
Keyword(s):  
Solar Collector ◽  
Heat Exposure ◽  
Sun Exposure ◽  
Weather Conditions ◽  
The Other ◽  
Productivity Analysis ◽  
Drying Process ◽  
Worker Productivity ◽  
Continuous Heat ◽  
Drying Chamber

The process of drying fish using solar energy is strongly influenced by weather conditions. Sunlight is needed by household scale workers because it is cheap. On the other hand, sun drying creates additional workload for workers. Workers are exposed to hot sun during drying. Continuous heat exposure results in an increased work pulse. This affects the level of worker productivity. To anticipate this, a solar dryer is used by utilizing a solar collector as an absorber of sunlight and a drying chamber for the drying process of fish. The use of solar dryers has been shown to increase drying temperatures and reduce workers' sun exposure. This decreases the workload of workers, so that it has an impact on increasing productivity. Worker productivity increased by 133.94%.

Decreased thermal conductance during the luteal phase of the menstrual cycle in women

1990 ◽  
Vol 69 (6) ◽  
pp. 2029-2033 ◽  
Author(s):  
P. Frascarolo ◽  
Y. Schutz ◽  
E. Jequier
Keyword(s):  
Menstrual Cycle ◽  
Thermal Equilibrium ◽  
Luteal Phase ◽  
Thermal Conductance ◽  
Heat Losses ◽  
Tympanic Temperature ◽  
Whole Body ◽  
Direct Calorimetry ◽  
Plasma Progesterone ◽  
Metabolic Heat

To study the influence of the menstrual cycle on whole body thermal balance and on thermoregulatory mechanisms, metabolic heat production (M) was measured by indirect calorimetry and total heat losses (H) were measured by direct calorimetry in nine women during the follicular (F) and the luteal (L) phases of the menstrual cycle. The subjects were studied while exposed for 90 min to neutral environmental conditions (ambient temperature 28 degrees C, relative humidity 40%) in a direct calorimeter. The values of M and H were not modified by the phase of the menstrual cycle. Furthermore, in both phases the subjects were in thermal equilibrium because M was similar to H (69.7 +/- 1.8 and 72.1 +/- 1.8 W in F and 70.4 +/- 1.9 and 71.4 +/- 1.7 W in L phases, respectively). Tympanic temperature (Tty) was 0.24 +/- 0.07 degrees C higher in the L than in the F phase (P less than 0.05), whereas mean skin temperature (Tsk) was unchanged. Calculated skin thermal conductance (Ksk) was lower in the L (17.9 +/- 0.6 W.m-2.degrees C-1) than in the F phase (20.1 +/- 1.1 W.m-2.degrees C-1; P less than 0.05). Calculated skin blood flow (Fsk) was also lower in the L (0.101 +/- 0.008 l.min-1.m-2) than in the F phase (0.131 +/- 0.015 l.min-1.m-2; P less than 0.05). Differences in Tty, Ksk, and Fsk were not correlated with changes in plasma progesterone concentration. It is concluded that, during the L phase, a decreased thermal conductance in women exposed to a neutral environment allows the maintenance of a higher internal temperature.

Effect of pressure on thermal insulation in humans wearing wet suits

1988 ◽  
Vol 64 (5) ◽  
pp. 1916-1922 ◽  
Author(s):  
Y. H. Park ◽  
J. Iwamoto ◽  
F. Tajima ◽  
K. Miki ◽  
Y. S. Park ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Water Temperature ◽  
Heat Loss ◽  
Thermal Insulation ◽  
Heat Production ◽  
Water Immersion ◽  
The Other ◽  
Body Parts ◽  
Metabolic Heat ◽  
Healthy Males

The present work was undertaken to determine the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 3 h without shivering, of wet-suited subjects during water immersion at different ambient pressures. Nine healthy males wearing neoprene wet suits (5 mm thick) were subjected to immersion to the neck in water at 1, 2, and 2.5 ATA while resting for 3 h. Continuous measurements of esophageal (T(es)) and skin (Tsk) temperatures and heat loss from the skin (Htissue) and wet suits (Hsuit) were recorded. Insulation of the tissue (Itissue), wet suits (Isuit), and overall total (Itotal) were calculated from the temperature gradient and the heat loss. The Tcw increased curvilinearly as the pressure increased, whereas the metabolic heat production during rest and immersion was identical over the range of pressure tested. During the 3rd h of immersion, Tes was identical under all atmospheric pressures; however, Tsk was significantly higher (P less than 0.05) at 2 and 2.5 ATA compared with 1 ATA. A 42 (P less than 0.001) and 50% (P less than 0.001), reduction in Isuit from the 1 ATA value was detected at 2 and 2.5 ATA, respectively. However, overall mean Itissue was maximal and independent of the pressure during immersion at Tcw. The Itotal was also significantly smaller in 2 and 2.5 ATA compared with 1 ATA. The Itissue provided most insulation in the extremities, such as the hand and foot, and the contribution of Isuit in these body parts was relatively small. On the other hand, Itissue of the trunk areas, such as the chest, back, and thigh, was not high compared with the extremities, and Isuit played a major role in the protection of heat drain from these body parts.

Relationship between preferred ambient temperature and autonomic thermoregulatory function in rat

1987 ◽  
Vol 252 (6) ◽  
pp. R1130-R1137 ◽  
Author(s):  
C. J. Gordon
Keyword(s):  
Ambient Temperature ◽  
Thermal Conductance ◽  
Sprague Dawley ◽  
Adult Rats ◽  
Evaporative Water ◽  
Longitudinal Temperature Gradient ◽  
Longitudinal Temperature ◽  
Thermoregulatory Function ◽  
Colonic Temperature ◽  
Experiment Individual

This study was designed to elucidate the relationships between behavioral and autonomic thermoregulation in three common strains of the laboratory rat. In one experiment eight adult rats of the Sprague-Dawley (SD), Long-Evans (LE), and Fischer (FCH) strains were repeatedly placed in a longitudinal temperature gradient while their preferred ambient temperature (Ta) was recorded. The mean preferred Ta's (+/- SE) for the SD, LE, and FCH strains were 24.9 +/- 0.4, 19.8 +/- 0.3, and 23.4 +/- 0.3 degrees C, respectively. In another experiment, individual adult rats of the same strains were placed in an environmental chamber thermostabilized at 2 degrees C intervals from 14 to 36 degrees C for 90 min while metabolic rate (MR), evaporative water loss (EWL), thermal conductance (C), and colonic temperature (Tcol) were determined. All three strains exhibited a minimal MR at a Ta of 30 degrees C. As Ta decreased below 30 degrees C, MR increased in a nonlinear fashion. EWL and C were minimal at cool Ta's and increased gradually with an elevation in Ta. All three strains maintained a normal Tcol between Ta's of 14 to 30 degrees C. The FCH strain exhibited the best control of Tcol at Ta's above 30 degrees C. Generally, one would predict that the preferred Ta would be associated with minimal thermoregulatory effort. However, the rat is unusual from other rodents (e.g., mouse, hamster, and guinea pig) in that the preferred Ta is well below the lower critical Ta for elevating MR.

Effects of hypoxia on thermal polypnea in intact and carotid body-denervated conscious cats

1989 ◽  
Vol 67 (2) ◽  
pp. 578-583 ◽  
Author(s):  
M. Bonora ◽  
H. Gautier
Keyword(s):  
Body Temperature ◽  
Carotid Body ◽  
Heat Load ◽  
Heat Exposure ◽  
Ambient Air ◽  
Severe Hypoxia ◽  
Central Action ◽  
Lower Body ◽  
Respiratory Response ◽  
Mild Hypoxia

The effects of the level of oxygenation on the respiratory response to heat exposure have been studied in conscious cats during normoxia, severe or mild hypocapnic hypoxia [inspired O2 fraction (FIO2) = 0.11 or 0.13], or hyperoxia. Several cats were also studied during severe normocapnic hypoxia. Experiments were repeated while the same animals were chronically carotid body denervated (CBD). The increase in respiratory frequency (f) leading to thermal tachypnea occurred at a lower body temperature (Tb) in severe hypocapnic hypoxia than in ambient air, but this effect was less pronounced when hypocapnia was corrected. No significant changes were observed during mild hypoxia or hyperoxia compared with normoxia in intact animals. After CBD, thermal tachypnea occurred at lower Tb in air than it did with intact animals in three of five cats, and it also occurred at lower Tb in mild hypocapnic hypoxia compared with air. It appears, therefore, that in conscious cats exposed to heat load 1) severe hypoxia enhances thermal tachypnea, 2) this effect persists after CBD, which suggests that it originates from a central action of hypoxia, and 3) the chemoreceptor afferents, to some degree, inhibit the onset of thermal tachypnea, as was previously observed for hypoxic tachypnea, which appears only in CBD cats (J. Appl. Physiol. 49: 769–777, 1980). Therefore, triggering of thermal and hypoxic tachypnea may involve common central mechanisms, probably located in the diencephalic structures under the control of afferents from arterial chemoreceptors.

Effect of prolonged exposure to continuous heat and humidity similar to long haul live export voyages in Merino wethers

2011 ◽  
Vol 51 (2) ◽  
pp. 135 ◽  
Author(s):  
C. A. Stockman ◽  
A. L. Barnes ◽  
S. K. Maloney ◽  
E. Taylor ◽  
M. McCarthy ◽  
...  
Keyword(s):  
Prolonged Exposure ◽  
Physiological Responses ◽  
Heat Exposure ◽  
High Heat ◽  
Controlled Environment ◽  
Physiological Changes ◽  
Bicarbonate Concentration ◽  
The Core ◽  
Continuous Heat ◽  
Live Export

This experiment investigated the physiological responses of Merino wethers (n = 12) to prolonged high heat and humidity similar to that experienced during long haul, live export voyages from Australia to the Middle East. Merino wethers were randomly assigned to individual pens in rooms with a controlled environment, and exposed to gradually increasing temperatures, and two exposures of 3–4 days of sustained high heat and humidity, up to a maximum of 31°C wet bulb temperature (37°C dry bulb and 67% relative humidity). There was 1 day at thermoneutral temperatures separating the heat exposures. The core temperatures and respiratory rates of Merino wethers increased during both heat exposures, with open-mouthed panting observed during both exposures. Plasma partial pressure carbon dioxide (pCO2) and bicarbonate concentration (HCO3–) decreased, and plasma pH increased during the second heat exposure. Both pCO2 and HCO3– returned to normal immediately following the heat exposures. Feed intake was maintained during the heat exposures. There were no large alterations in blood electrolyte concentrations attributable to the effects of the heat. The results show that Merino wethers experienced significant physiological changes during exposure to prolonged and continuous high heat and humidity, but maintained most aspects of homeostasis despite being hyperthermic and recovered quickly when conditions returned to thermoneutral.

Effects of acceleration on thermoregulatory responses of unanesthetized rats

1977 ◽  
Vol 42 (1) ◽  
pp. 74-79 ◽  
Author(s):  
C. A. Fuller ◽  
J. M. Horowitz ◽  
B. A. Horwitz
Keyword(s):  
Rapid Decrease ◽  
Mechanical Forces ◽  
Slow Recovery ◽  
Environmental Conditioning ◽  
Thermoregulatory Responses ◽  
Initial Drop ◽  
Thermoregulatory System ◽  
Colonic Temperature ◽  
Induced Changes ◽  
The Brain

Upon exposure of rats to 2 G environments (achieved by centrifugation), there occurred a rapid decrease in colonic temperature (Tco) followed, after about 50 min, by a slow recovery toward precentrifugation levels. The initial drop in Tco was accompanied by decreases in hypothalamic and spinal cord temperatures and increases in tail temperature (Tta). In contrast to this anomalous response (i.e., increased heat loss (manifested by increased Tta) despite decreasing temperature at spinal and hypothalamic thermoreceptor areas) the return toward normal Tco appeared to involve appropriate thermoregulatory responses. The initial fall in Tco was decreased in magnitude by inverting the rat during acceleration, thereby suggesting that mechanical forces acting on the brain may underlie this temperature decrease. Exposure to cold during centrifugation allowed further examination of the thermoregulatory system. Unlike the initial acceleration-induced changes, the cold-evoked fall in Tco was not accompanied by increasing Tta and was modified by the environmental conditioning of the rats. These results are consistent with the view that exposure to 2 G adversely affects the thermoregulatory ability of rats challenged by cold.

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