Modes of thermal protection in polar bear cubs--at birth and on emergence from the den

1979 ◽  
Vol 236 (1) ◽  
pp. R67-R74 ◽  
Author(s):  
A. S. Blix ◽  
J. W. Lentfer
Keyword(s):  
Rectal Temperature ◽  
Heat Production ◽  
Polar Bear ◽  
Thermal Protection ◽  
Resting Metabolic Rate ◽  
Subcutaneous Fat ◽  
Metabolic Heat Production ◽  
Metabolic Heat ◽  
Lower Critical Temperature ◽  
Ice Water

At birth in late December the polar bear is small (700 g), uninsulated, and helpless. It probably has a modest capacity for metabolic heat production and depends on the female and a snow den in which it is born for thermal protection. The microclimate of an artificial polar bear den was investigated at Point Barrow, AK, and the temperature therein found to stay around 0 degrees C provided a heat source (200 W) equivalent to an adult polar bear was introduced. When the bears desert the den in early April the cub has grown to about 10 kg and has a well-developed fur insulation, but almost no subcutaneous fat. The cub has a high resting metabolic rate (4.6 W.kg-1), which is supported by the fat polar bear milk. Its lower critical temperature is about -30 degrees C, and an ambient temperature of -45 degrees C results in only a 33% increase in metabolism. The cub can tolerate a wind chill of 2.3 kW.m2 without apparent stress of drop in rectal temperature. If the cub is immersed in ice water rectal temperature drops 11 degrees C in 30 min. It is concluded that the cub can tolerate extremely low temperatures in air due to fur insulation and high metabolic heat production, but is unable to cope with the chill of ice water for any prolonged period of time.

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.

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.

EFFECT OF FEED TEMPERATURE ON COLD SUSCEPTIBILITY OF CATTLE AND SHEEP

1990 ◽  
Vol 70 (1) ◽  
pp. 191-197 ◽  
Author(s):  
A. M. NICOL ◽  
B. A. YOUNG
Keyword(s):  
Critical Temperature ◽  
Heat Production ◽  
Metabolic Heat Production ◽  
Ambient Temperatures ◽  
Metabolic Heat ◽  
Lower Critical Temperature ◽  
Temperature Heat ◽  
Feed Temperature ◽  
Key Words Cold ◽  
Cattle And Sheep

The metabolic heat production of steers was measured at ambient temperatures of +10, −8 and −20 °C following their consumption of 15-kg turnip bulbs (Brassica napus) with a temperature of 27, 2 or −8 °C, or 10-kg turnips with a temperature of 2 °C followed by 1 kg hay. Metabolic heat production was elevated 13–80% after eating the cold and frozen turnips when steers were exposed to −8 °C and 35–80% when exposed to −20 °C. Sheep fed 20, 35, 55, 80 and 110 g pelleted ration per kg−0.75 d−1, accompanied by a ruminal infusion of water at 38 or 2 °C at a volume required to simulate a 10% dry matter feed had their metabolic heat production measured at +10 and −20 °C. Heat production was significantly increased at −20 °C for only the 2 °C infusion although with the 38 °C infusion at the lower feed intake levels, metabolic heat production was higher by up to 37% at an ambient temperature of −20 °C than at +10 °C. The lower critical temperature of the steers after ingestion of the turnips was estimated to be −4.5, −2.4, +3.2 and +13.9 °C forthe27, 2 + hay, 2 and −8 °C turnips, respectively. The lower critical temperature of sheep was raised by 1, 11, 31, 25 and > 22 °C by the ruminal infusion of water at 2 °C compared to water at 38 °C in sheep fed 20, 35, 55, 80 and 110 g feed kg−0.75 d−1, respectively. Key words: Cold, temperature, heat production, cattle, sheep

Rate of metabolic heat production and rectal temperature of steers exposed to simulated mud and rain conditions

1993 ◽  
Vol 73 (1) ◽  
pp. 207-210 ◽  
Author(s):  
A. Allan Degen ◽  
Bruce A. Young
Keyword(s):  
Key Words ◽  
Air Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Metabolic Heat Production ◽  
Metabolic Heat ◽  
Air Temperatures ◽  
Significant Difference

Rate of metabolic heat production and rectal temperature were measured in steers (n = 4) standing in 0 (control), 10, 25 and 50 cm of water and in steers standing in 50 cm of water that were also showered. The measurements were done at air temperatures of 0 and 15 °C. There was no significant difference in the rate of metabolic heat production of the steers due to the two air temperatures. However, there was an increase in the rate of metabolic heat production of steers that stood in 50 cm water and were showered; by 39–56% over control steers. Rectal temperature was not affected by either air temperature or treatment. Key words: Steers, mud, rain, heat production, rectal temperature

Effect of ketamine on thermoregulation in rats

1978 ◽  
Vol 56 (6) ◽  
pp. 963-967 ◽  
Author(s):  
M. T. Lin ◽  
C. F. Chen ◽  
I. H. Pang
Keyword(s):  
Drug Treatment ◽  
Skin Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Intraperitoneal Administration ◽  
Metabolic Heat Production ◽  
Ambient Temperatures ◽  
Metabolic Heat ◽  
Dose Dependent ◽  
Skin Temperatures

Intraperitoneal administration of ketamine produced dose-dependent hypothermia at the ambient temperatures (Ta) of both 8 and 23 °C in unanesthetized rats. At a Ta of 8 °C, the hypothermia was brought about solely by a decrease in metabolic heat production. There were no changes in either the tail skin temperature (Ttail) or the sole skin temperature (Tsole). At a Ta of 23 °C, the hypothermia was due to an increase in Ttail, an increase in Tsole, and a decrease in metabolic heat production. However, at a Ta of 31 °C, there were no changes in rectal temperature in response to ketamine application, since neither heat production nor skin temperatures (e.g., Ttail and Tsole) was affected by ketamine at this Ta. The data indicate that the effect of the drug treatment may be to decrease heat production and (or) increase heat loss.

Physical fitness and thermoregulatory reactions in a cold environment in men

1988 ◽  
Vol 65 (5) ◽  
pp. 1984-1989 ◽  
Author(s):  
J. H. Bittel ◽  
C. Nonotte-Varly ◽  
G. H. Livecchi-Gonnot ◽  
G. L. Savourey ◽  
A. M. Hanniquet
Keyword(s):  
Physical Fitness ◽  
Cold Stress ◽  
Heat Production ◽  
Ambient Air ◽  
Metabolic Heat Production ◽  
Adult Males ◽  
Fitness Level ◽  
Metabolic Heat ◽  
Air Temperatures ◽  
Thermoregulatory Reactions

The relationship between the physical fitness level (maximal O2 consumption, VO2max) and thermoregulatory reactions was studied in 17 adult males submitted to an acute cold exposure. Standard cold tests were performed in nude subjects, lying for 2 h in a climatic chamber at three ambient air temperatures (10, 5, and 1 degrees C). The level of physical fitness conditioned the intensity of thermoregulatory reactions to cold. For all subjects, there was a direct relationship between physical fitness and 1) metabolic heat production, 2) level of mean skin temperature (Tsk), 3) level of skin conductance, and 4) level of Tsk at the onset of shivering. The predominance of thermogenic or insulative reactions depended on the intensity of the cold stress: insulative reactions were preferential at 10 degrees C, or even at 5 degrees C, whereas colder ambient temperature (1 degree C) triggered metabolic heat production abilities, which were closely related to the subject's physical fitness level. Fit subjects have more efficient thermoregulatory abilities against cold stress than unfit subjects, certainly because of an improved sensitivity of the thermoregulatory system.

Sign in / Sign up

Export Citation Format

Share Document