Brain temperatures in the rat during exposure to low environmental temperatures

1964 ◽  
Vol 207 (3) ◽  
pp. 736-739 ◽  
Author(s):  
Peter Lomax ◽  
E. Malveaux ◽  
R. E. Smith
Keyword(s):  
Metabolic Rate ◽  
Rectal Temperature ◽  
Heat Production ◽  
Low Temperatures ◽  
Hypothalamic Temperature ◽  
Temperature Changes ◽  
Metabolic Heat ◽  
Environmental Temperatures ◽  
Thalamic Region

Exposure to cold is known to elicit a rise in metabolic rate in various tissues of homeothermic animals. The role of the hypothalamus in this response was investigated by exposing normal and cold-acclimated rats to environmental temperatures of 26 C, 6 C, and –8 C and comparing the temperature changes in the thalamus, hypothalamus, and rectum using chronically implanted thermocouples. At all environmental temperatures the cold-acclimated rats had lower hypothalamic temperatures than did the normal animals. Apart from this, pattern of response was similar in all animals; the hypothalamic temperature tends to increase on exposure of the animal to cold while the adjacent thalamic region shows a marked fall in temperature, the rectal temperature staying fairly constant. This difference in response suggests increased metabolic heat production in the hypothalamus on exposure of the rat to low temperatures.

scholarly journals Human thermoregulatory responses during serial cold-water immersions

1998 ◽  
Vol 85 (1) ◽  
pp. 204-209 ◽  
Author(s):  
John W. Castellani ◽  
Andrew J. Young ◽  
Michael N. Sawka ◽  
Kent B. Pandolf
Keyword(s):  
Body Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Alternative Explanation ◽  
Cold Water ◽  
Metabolic Heat Production ◽  
Normal Body Temperature ◽  
Repeat Trial ◽  
Metabolic Heat ◽  
Made In

This study examined whether serial cold-water immersions over a 10-h period would lead to fatigue of shivering and vasoconstriction. Eight men were immersed (2 h) in 20°C water three times (0700, 1100, and 1500) in 1 day (Repeat). This trial was compared with single immersions (Control) conducted at the same times of day. Before Repeat exposures at 1100 and 1500, rewarming was employed to standardize initial rectal temperature. The following observations were made in the Repeat relative to the Control trial: 1) rectal temperature was lower and heat debt was higher ( P < 0.05) at 1100; 2) metabolic heat production was lower ( P < 0.05) at 1100 and 1500; 3) subjects perceived the Repeat trial as warmer at 1100. These data suggest that repeated cold exposures may impair the ability to maintain normal body temperature because of a blunting of metabolic heat production, perhaps reflecting a fatigue mechanism. An alternative explanation is that shivering habituation develops rapidly during serially repeated cold exposures.

Acclimatization of calves to a hot dry environment

1959 ◽  
Vol 52 (3) ◽  
pp. 296-304 ◽  
Author(s):  
W. Bianca
Keyword(s):  
Heart Rate ◽  
Respiratory Rate ◽  
Rectal Temperature ◽  
Heat Production ◽  
Metabolic Heat Production ◽  
Metabolic Heat ◽  
Physiological Reactions

1. Three calves were individually exposed in a climatic room to an environment of 45° C. dry-bulb and 28° C. wet-bulb temperature for 21 successive days up to 5 hr. each day.2. In the 21-day period, mostly during the first half of it, the following changes in the physiological reactions of the animals were observed: progressive reductions in rectal temperature, in heart rate and in respiratory rate with a change of breathing from a laboured to a less laboured type.3. It was suggested that a decrease in metabolic heat production might play a part in the observed acclimatization.

Metabolic Factors in the Development of Homeothermy in Dogs

1958 ◽  
Vol 194 (2) ◽  
pp. 293-296 ◽  
Author(s):  
Donald G. McIntyre ◽  
H. E. Ederstrom
Keyword(s):  
Oxygen Consumption ◽  
Metabolic Rate ◽  
Rectal Temperature ◽  
Heat Production ◽  
Cold Exposure ◽  
Metabolic Factors ◽  
Air Temperatures ◽  
Heat Conservation

Dogs from 1 to 25 days of age were exposed to air temperatures of 5, 23 and 30°C and their oxygen consumption measured in a closed calorimeter. Animals 1–5 days old had a rise of 20–25% in metabolic rate, but rectal temperature fell, when they were exposed to 5 or 23°C. At 11–21 days of age dogs exposed to 5°C had a rise of about 75% in metabolic rate, but rectal temperature fell several degrees in 1 hour. In dogs 21–25 days of age metabolic rate increased about 75% at air temperatures of 5°C and rectal temperature fell only about 1°C. Under the same conditions a trained adult dog had a rise of 80% in metabolic rate, and no fall in rectal temperature. Since heat production in 2- to 3-week-old dogs was increased to about the same extent as in the adult on cold exposure, it was assumed that heat conservation lagged behind heat production in the development of homeothermy.

Poly I:C-induced fever elevates threshold for shivering but reduces thermosensitivity in rabbits

1995 ◽  
Vol 268 (5) ◽  
pp. R1266-R1272 ◽  
Author(s):  
O. Toien ◽  
J. B. Mercer
Keyword(s):  
Heat Exchanger ◽  
Ambient Temperature ◽  
Heat Production ◽  
Metabolic Heat Production ◽  
Poly I:C ◽  
Saline Injection ◽  
Hypothalamic Temperature ◽  
Square Wave ◽  
Metabolic Heat ◽  
Fever Response

Shivering threshold and thermosensitivity were determined in six conscious rabbits at ambient temperature (Ta) 20 and 10 degrees C before and at six different times after saline injection (0.15 ml iv) and polyriboinosinic-polyribocytidylic acid (poly I:C)-induced fever (5 micrograms/kg iv). Thermosensitivity was calculated by regression of metabolic heat production (M) and hypothalamic temperature (Thypo) during short periods (5-10 min) of square-wave cooling. Heat was extracted with a chronically implanted intravascular heat exchanger. Shivering threshold was calculated as the Thypo at which the thermosensitivity line crossed resting M as measured in afebrile animals at Ta 20 degrees C. There were negligible changes in shivering threshold and thermosensitivity in saline-injected rabbits. In the febrile animals, shivering threshold generally followed the shape of the biphasic fever response. At Ta 20 degrees C, shivering threshold was higher than regulated Thypo during the initial rising phase of fever and was lower during recovery. At Ta 10 degrees C the shivering thresholds were always higher than regulated Thypo except during recovery. Thermosensitivity was reduced by 30-41% during fever.

Effects of altered ambient temperature on metabolic rate during CO2 inhalation

1985 ◽  
Vol 58 (5) ◽  
pp. 1592-1596 ◽  
Author(s):  
R. P. Kaminski ◽  
H. V. Forster ◽  
G. E. Bisgard ◽  
L. G. Pan ◽  
S. M. Dorsey ◽  
...  
Keyword(s):  
Metabolic Rate ◽  
Heat Production ◽  
Pulmonary Ventilation ◽  
O2 Consumption ◽  
Breathing Frequency ◽  
Ambient Temperatures ◽  
Metabolic Heat ◽  
Respiratory Heat Loss ◽  
Unit Increase ◽  
Stimulation Of

The purpose of this study was to determine if the changes in O2 consumption (VO2) during CO2 inhalation could in part be due to stimulation of thermogenesis for homeothermy. Twelve ponies were exposed for 30-min periods to inspired CO2 (PIco2) levels of less than 0.7, 14, 28, and 42 Torr during the winter at 5 (neutral) and 23 degrees C ambient temperatures (TA) and during the summer at 21 (neutral TA), 30, and 12 degrees C. Elevating TA in both seasons resulted in an increased pulmonary ventilation (VE) and breathing frequency (f) (P less than 0.01) but no significant increase in VO2 (P greater than 0.05). Decreasing TA in the summer resulted in a decrease in VE and f (P less than 0.01) but no significant change in VO2 (P greater than 0.05). At neutral TA in both seasons, VO2 increased progressively (P less than 0.05) as PIco2 was increased from 14 to 28 and 42 Torr. The increases in VO2 during CO2 inhalation were attenuated (P less than 0.05) at elevated TA and accentuated at the relatively cold TA in the summer (P less than 0.05). Respiratory heat loss (RHL) during CO2 inhalation was inversely related to TA. Above a threshold RHL of 2 cal X min-1 X m-2, metabolic heat production (MHP) increased 0.3 cal X min-1 X m-2 for each unit increase in RHL during CO2 inhalation at the neutral and elevated TA. However, during cold stress in the summer, the slope of the MHP-RHL relationship was 1.6, indicating an increased MHP response to RHL.

Effect of water restriction and environmental temperatures on metabolic rate and physiological parameters in sheep

2000 ◽  
Vol 80 (1) ◽  
pp. 97-104 ◽  
Author(s):  
B. T. Li ◽  
R. J. Christopherson ◽  
S. J. Cosgrove
Keyword(s):  
Metabolic Rate ◽  
Heat Production ◽  
Plasma Osmolality ◽  
Blood Parameters ◽  
Water Restriction ◽  
Creatinine Concentration ◽  
Warm Environment ◽  
Plasma Creatinine Concentration ◽  
Hb Concentration ◽  
Environmental Temperatures

The hypothesis that water restriction reduces metabolic rate and contributes to energy conservation of sheep, and induces changes in blood parameters was tested. Four of eight adult sheep were housed in either a warm (24.8 ± 1.5 °C) or cold (0.4 ± 1.2 °C) environment and fed a diet of alfalfa pellets at 1.2 × maintenance. Each sheep was fasted with or without water according to a crossover design. Average heat production (HP) and rectal temperature (Tr) were higher (P < 0.05) in the cold than in the warm. Fasting decreased HP and Tr (P < 0.05). Water restriction had no additional effect on HP and Tr. Fasting and fasting plus water restriction influenced plasma osmolality and creatinine concentration. Plasma creatinine concentration was lower (P < 0.01) and haemoglobin (Hb) concentration higher in the cold than in the warm environment. Hb concentration was increased with water restriction (P < 0.01) in the warm environment. Plasma cortisol concentration was altered by fasting. Packed cell volume (PCV) in blood, plasma volume and plasma aldosterone were not affected by treatments. The results suggest that water restriction, per se, for 3 d does not suppress metabolic rate in sheep below that resulting from fasting alone. Key words: Heat production, sheep, temperature, water restriction

Observations on the effect of salicylate in fever and the regulation of body temperature against cold

1976 ◽  
Vol 54 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Q. J. Pittman ◽  
W. L. Veale ◽  
K. E. Cooper
Keyword(s):  
Body Temperature ◽  
Skin Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Intravenous Infusion ◽  
Sodium Salicylate ◽  
Single Injection ◽  
Continuous Intravenous Infusion ◽  
Skin Temperatures

Prostaglandins appear to be mediators, within the hypothalamus, of heat production and conservation during fever. We have investigated a possible role of prostaglandins in the nonfebrile rabbit during thermoregulation in the cold. Shorn rabbits were placed in an environment of 20 °C, and rectal and ear skin temperatures, shivering and respiratory rates were measured. A continuous intravenous infusion of leucocyte pyrogen was given to establish a constant fever of approximately 1 °C, and after observation of a stable febrile temperature for 90 min, a single injection of 300 mg of sodium salicylate, followed by a 1.5 mg/min infusion was then given. After the salicylate infusion was begun, rectal temperature began to fall, and reached nonfebrile levels within 90 min. Shivering activity ceased, respiratory rates increased, and in two animals, ear skin temperature increased. When these same rabbits were placed in an environment of 10 °C, at a time they were not febrile, and an identical amount of salicylate was given, rectal and ear skin temperatures, shivering and respiratory rates did not change. These results indicate that prostaglandins do not appear to be involved in heat production and conservation in the nonfebrile rabbit.

Acclimatization of calves to a hot humid environment

1959 ◽  
Vol 52 (3) ◽  
pp. 305-312 ◽  
Author(s):  
W. Bianca
Keyword(s):  
Heart Rate ◽  
Body Temperature ◽  
Respiratory Rate ◽  
Skin Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Metabolic Heat ◽  
Hot Environment ◽  
Humid Environment ◽  
Physiological Reactions

1. Three calves were exposed in a climatic room to an environment of 40° C. dry-bulb and 38° C. wet-bulb temperature for up to 110 min. each day for 1-2 weeks.2. These exposures produced progressive changes in the physiological reactions of the animals to heat:(a) Rectal temperature and skin temperature (for a given time of exposure) declined. In consequence there was a marked increase in the tolerance time, i.e. in the time for which the animals could withstand the hot environment before reaching a rectal temperature of 42° C.(b) Respiratory rate rose earlier and assumed higher levels (for given levels of body temperature).(c) Heart rate decreased markedly.3. These changes are discussed in relation to heat loss and heat production and have been interpreted as reflecting chiefly a reduction in the metabolic heat production of the animals.

Effects of phentolamine on thermoregulatory functions of rats to different ambient temperatures

1979 ◽  
Vol 57 (12) ◽  
pp. 1401-1406 ◽  
Author(s):  
M. T. Lin ◽  
Andi Chandra ◽  
T. C. Fung
Keyword(s):  
Heat Loss ◽  
Rectal Temperature ◽  
Heat Production ◽  
Room Temperature ◽  
Metabolic Heat Production ◽  
Central Component ◽  
Evaporative Heat Loss ◽  
Central Administration ◽  
Ambient Temperatures ◽  
Metabolic Heat

The effects of both systemic and central administration of phentolamine on the thermoregulatory functions of conscious rats to various ambient temperatures were assessed. Injection of phentolamine intraperitoneally or into a lateral cerebral ventricle both produced a dose-dependent fall in rectal temperature at room temperature and below it. At a cold environmental temperature (8 °C) the hypothermia in response to phentolamine was due to a decrease in metabolic heat production, but at room temperature (22 °C) the hypothermia was due to cutaneous vasodilatation (as indicated by an increase in foot and tail skin temperatures) and decreased metabolic heat production. There were no changes in respiratory evaporative heat loss. However, in the hot environment (30 °C), phentolamine administration produced no changes in rectal temperature or other thermoregulatory responses. A central component of action is indicated by the fact that a much smaller intraventricular dose of phentolamine was required to exert the same effect as intraperitoneal injection. The data indicate that phentolamine decreases heat production and (or) increases heat loss which leads to hypothermia, probably via central nervous system actions.

Role of α-Adrenoceptors in the Maintenance of Core Temperature in Humans

1995 ◽  
Vol 89 (3) ◽  
pp. 219-225
Author(s):  
Steven M. Frank ◽  
Nader El-Gamal ◽  
Srinivasa N. Raja ◽  
Peter K. Wu ◽  
Osama Afifi
Keyword(s):  
Blood Flow ◽  
Surface Temperature ◽  
Core Temperature ◽  
Heat Production ◽  
Skin Surface ◽  
High Dose ◽  
Skin Surface Temperature ◽  
Metabolic Heat ◽  
Males And Females

1. Although α-adrenoceptor antagonists have been shown to induce core hypothermia in animals, it is unclear whether the primary mechanism is increased heat loss or decreased heat production. Furthermore, studies have not been performed in humans to determine the role of α-adrenoceptors in the maintenance of core temperature. 2. α-Adrenoceptor blockade was achieved with three doses of phentolamine given by random assignment on three different study days in five male and five female healthy subjects. Core temperature, mean skin-surface temperature, fingertip capillary blood flow and metabolic heat production were measured. Dose—response curves were plotted for all measured variables, and males and females were compared to identify potential gender differences. 3. Core temperature decreased with all doses of phentolamine. At the completion of the phentolamine infusion, the decrease in core temperature was more significant with high-dose (0.3 ± 0.1°C, P = 0.03) and with medium-dose (0.2 ± 0.0deg;C, P = 0.05) phentolamine than with low-dose phentolamine (0.1 ± 0.0deg;C). The maximum core temperature decrease during the study was more significant with high dose (0.6 ± 1°C) than with medium (0.3 ± 1deg;C, P = 0.04) or low (0.3 ± 1°C, P = 0.005) doses. Mean skin-surface temperature was increased with all doses. Fingertip blood flow was increased (approximately 60% above baseline) with the medium and high doses, but was unchanged with the low dose. Total body oxygen consumption was unchanged regardless of dose. Although females had a higher core temperature at baseline, changes in core temperature, skin-surface temperature and fingertip blood flow were similar in males and females. 4. These findings suggest that α-adrenergic-antagonist-induced hypothermia results from a dose-dependent redistribution of heat from the core to the periphery, and not from a decrease in metabolic heat production. This leads us to conclude that baseline α-adrenergic ‘tone’ serves to maintain core temperature by constraining heat to the core thermal compartment.

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