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PubMed2000

Physiological responses of pre-ruminant kid goats and lambs to different environmental temperatures.

The purpose of this study was to establish the metabolic behaviour of both preruminant kid goats and lambs, when they are kept at different environmental temperatures (12, 24 and 30 degrees C). The animals were fed ad libitum with a milk replacer for the first two months of life. Blood samples were taken from all the animals on days 30, 40, 50 and 60 post partum, to determine serum levels of glucose, insulin, free fatty acids, triiodothyronine (T3) and thyroxine (T4), both when fasting and 4 hours after starting feeding. The high sensitivity of both kinds of animal to the lowest of the environmental temperatures used, particularly for the first periods of life here considered, was established from the glucose/insulin and T3/T4 molar ratios and from the concentrations of free fatty acids. The results obtained by species were also evidence of metabolic behaviour typical of leanner animals in kids.

Adaptation, Physiological↗
PubMed1982

Cold acclimation and resistance to ethanol-induced hypothermia.

The fall in core temperature induced by a fixed dose of ethanol (1 g x kg-1 i.p.) was an exponential function of the ambient temperature over the range 0-18 degrees C. In rats acclimated to 4 degrees C for 7 days the dose response curve relating the fall in body temperature to ethanol was markedly attenuated. The hypothermic effect of ethanol declined exponentially over 20 days of exposure to 4 degrees C and by the 20th day the fall was no greater than in saline injected controls. Blood ethanol concentrations were similar in acclimated and non-acclimated rats indicating that pharmacokinetic factors do not account for the altered responses. Although the time course of the development of resistance to the hypothermic effect of ethanol parallels that of cold acclimation to 4 degrees C, and the development of non-shivering thermogenesis, the attenuated drug effect does not appear to be due to the altered metabolic activity of brown adipose tissue. It is suggested that the modulation of the effect of ethanol in lowering the thermoregulatory set point results from central nervous system adaptation to the environmental thermal stress.

Acclimatization↗
PubMed1986

Cold-rearing normalizes capacity for norepinephrine-stimulated thermogenesis but not body temperature in 16-day-old fatty Zucker rats.

The effects of a lowered rearing temperature on body weight, core temperature (Tc) and norepinephrine(NE)-stimulated thermogenesis were investigated in 16- to 17-day-old Zucker rat pups. 16-day-old fatty pups were significantly heavier (9%) than lean littermates in litters reared at 18 degrees C ("cold-reared") but not in litters reared at 25 degrees C ("normally-reared"). After 2 h isolation at 25 degrees C, Tc of lean pups was slightly higher (37.1 degrees C) in cold-reared litters than in normally-reared litters (36.4 degrees C), while fatty pups reared at either temperature were severely hypothermic (Tc = 33 - 34 degrees C). At an ambient temperature of 25 degrees C Tc in fatty and lean cold-reared pups increased to 39.5 degrees C after subcutaneous injection of 800 micrograms/kg NE. Normally-reared lean pups reached the same peak Tc after NE injection, while their fatty littermates reached a significantly lower peak Tc of 38.4 degrees C. The hypothermia associated with the onset of excess fat deposition in suckling fatty Zucker rats is not caused by a reduced capacity for NE-stimulated thermogenesis.

Adipose Tissue, Brown↗
PubMed1984

Cold acclimation of obese (ob/ob) mice: effects of energy balance.

Obese (ob/ob) and lean mice at 4 weeks of age were housed at 23 degrees C or 14 degrees C for 4 to 8 weeks to examine effects of acclimation to mild cold on energy balance. Energy intake of young lean mice increased by about 50% when housed at 14 degrees C, but energy intake of cold-acclimated obese mice increased by only 8%. Efficiency of energy retention (ratio of energy gain to energy intake) in obese mice declined from 22% +/- 1.2% at 23 degrees C to 10% +/- 1.8% after 4 weeks at 14 degrees C. Lean mice exhibited a less pronounced response to temperature; their efficiency of energy retention declined from 7% +/- 1.3% at 23 degrees C to 4% +/- 2.2% after 4 weeks at 14 degrees C. After 8 weeks of cold exposure, body weights and efficiency of energy retention became equal in obese and lean mice. Calculated heat production of cold-acclimated obese and lean mice was 40% higher than that of respective controls. Obese mice reacclimated to 23 degrees C after being kept for 4 weeks at 14 degrees C consumed the same amount of energy and were 16% more efficient than obese maintained at 23 degrees C; reacclimated lean mice consumed 12% more energy but were 53% less efficient than lean mice maintained at 23 degrees C. The results indicate that obese mice are able to increase heat production and markedly reduce their efficiency of energy retention when acclimated to mild cold but that they, unlike lean mice, rapidly revert to a high efficiency of energy retention after 4 weeks of reacclimation to 23 degrees C.

Acclimatization↗
PubMed1985

Defective thermoregulatory thermogenesis in monosodium glutamate-induced obesity in mice.

We have studied thermoregulatory thermogenesis in mice rendered obese by neonatal administration of monosodium glutamate (MSG) and in saline treated controls. At 12 weeks of age MSG-treated mice maintained on a chow diet and housed at 24 degrees C, exhibited hypertrophy of brown adipose tissue (BAT) compared to controls (65% increase in wet weight and lipid content, no difference in DNA content). Acute cold exposure (4 degrees C for two hours) resulted in a significantly greater fall in core temperature in MSG-treated than control mice. After cold exposure to 4 degrees C for six hours, control animals mobilized BAT lipid whereas MSG-treated animals did not. Both groups showed comparable increments in oxygen consumption in response to exogenous norepinephrine. The above changes were qualitatively the same for both male and female animals. The following conclusions were reached: (1) MSG-treated mice have defective cold induced thermogenesis, indirect evidence suggests this results from impaired activation of thermogenic mechanisms in BAT; (2) the defect responsible for this lies extrinsic to BAT; and (3) the quantitative significance of defective thermoregulatory thermogenesis for the development of obesity in these mice is uncertain.

Adipose Tissue↗
PubMed1982

Effects of early cold adaptation on food efficiency and dietary-induced thermogenesis in the adult rat.

The food intakes of male and female rats (Harvard strain) adapted to cold (5 degrees C) starting at weaning were studied in the cold and during reacclimation to 25 degrees C. Following 24 hr food deprivation, the male rats regained the weight they had lost without making up for the food they had missed (increased food efficiency), while the female rats ate 75% more food than they had missed in regaining their body weights (decreased food efficiency), independent of the temperature at which the animals were housed. On a high fat diet, both cold groups gained less weight than did the two control groups. However, each female group gained significantly less weight than its same temperature male group. Dietary-induced thermogenesis was significantly enhanced in male cold adapted rats 3 months after reacclimation to the zone of thermal neutrality but not in cold adapted female rats. Sex and strain differences are discussed. These data indicate that early chronic cold exposure results in both immediate and long-term changes in food efficiency and metabolism in adult rats, but the effects vary with the sex of the animal.

Acclimatization↗
PubMed1984

Alleviation in the rat of a GABA-induced reduction in food intake and growth.

Cold exposure and diet dilution which stimulate food intake of normal rats lessened depressions of food intake and growth induced by dietary GABA. During a 3-day adaptation to the cold, rats fed a diet containing 4.5% GABA lost weight; thereafter, food intake and growth rate differed little from those of cold control rats and were usually greater than those of normal rats fed GABA. Hepatic GABA-aminotransferase activity of cold-exposed rats fed the GABA diet increased to about twice that of normal control rats. Rats fed a control diet diluted by half with cellulose ate 50% more of this diet than of the undiluted diet but gained only 20% less weight. Rats ate twice as much of a diluted, 9% GABA diet as of an undiluted, 4.5% GABA diet (thus doubling their GABA intake) and gained three times as much weight. A novel food (condensed milk) barely lessened the adverse responses to GABA. These results show that conditions requiring rats to increase their food intake in order to maintain body weight can also increase their acceptance of a diet high in GABA.

4-Aminobutyrate Transaminase↗
PubMed1984

Effect of a cold ambient temperature on the rat's food hoarding behavior.

In a first experiment, the amount of food hoarded in three hour sessions (HB) by eight food deprived rats, was measured at three ambient temperatures: 30, 17.5 and 5 degrees C. At the three temperatures, the mass of food pellets hoarded by the rats was linearly related to the rats' body weight (BW) with a negative slope. The slope of the regression lines was significantly higher at 5 and 17.5 degrees C than at 30 degrees C. In a second experiment, BW and HB of ten non-deprived rats were measured every day, first at 30, then at 10 degrees C, then at 30 degrees C again (70 days). In the cold environment, HB immediately increased without BW loss. This effect was immediately reversible by the adjunction of an insulating styrofoam mattress. HB of non deprived rats in the cold was therefore more a thermoregulatory behavior than an alimentary response. In a third experiment, ad lib fed or deprived rats could hoard either food pellets or styrofoam lumps at 30 degrees C or at 5 degrees C. In the cold environment, when non-deprived, the rats hoarded styrofoam rather than food. However, as soon as they were food deprived, they reversed their choice and hoarded food rather than styrofoam. It is concluded that food can be hoarded as a thermal insulator in a cold environment but HB is mainly an alimentary response increased by a cold stress.

Animals↗
PubMed1987

Decrease in body temperature and locomotor activity as an adaptational response in piglets exposed to cold on restricted feeding.

Littermate piglets weaned at 14 days of age were acclimated at 10 degrees C. During six weeks of the experiment half the littermates, OP, were able to make an operant response for heat, the control half, CP, could obtain only light. The piglets were fed in such a way that CP gained weight very slowly. OP maintained a high ambient temperature, and increased body weight by 134%, while CP by 40% (p less than 0.001); food efficiency (weight gain/food intake) was 0.66 for OP and 0.25 for CP (p less than 0.001). Rectal temperature, Tre, of OP was maintained at 38.3 degrees C, and that of CP at 36.7 degrees C (p less than 0.001). Locomotor activity of OP was 137% higher (p less than 0.001) than that of CP. During a one-day access to an operant heater, or a one-day period of unrestricted feeding, CP increased Tre and locomotor activity to values observed in OP. By the end of the experiment CP had shorter bodies, tails, snouts and smaller ears than OP. The proportion of skin with attached fat was higher in OP than CP. It is concluded that restrictions imposed on thermoregulatory behaviour and on thermogenic capabilities of the autonomic system resulted in a lowered body temperature and locomotor activity as cold defence responses in young pigs.

Acclimatization↗
PubMed1986

Age comparisons of body temperature and cold tolerance among different strains of Mus musculus.

The age-related declines in colonic temperature (Tco) and cold tolerance (ability to maintain Tco when exposed to 10 degrees C for 3 h) described for C57BL/6J mice are compared to other mouse strains. Assessment of young and aged male mice of the C57BL/6J and A/J inbred strains and their F1 hybrid, B6AF1/J, as well as a pen-bred strain of Mus musculus captured from the wild revealed an aged-related decline in thermoregulation among all these strains. The degree of decline in thermoregulation was roughly correlated to differences in strain-specific lifespan. Aged mice of the relatively short-lived genotype, A/J (mean lifespan of 22 months), had the lowest Tco and poorest cold tolerance. The long-lived hybrids, B6AF1/J (mean lifespan of 29 months), demonstrated the highest Tco and the best cold tolerance among aged mice. C57BL/6J (mean lifespan of 26 months) showed an intermediate level of thermoregulation. Aged pen-bred mice demonstrated a significant decline in cold tolerance, but not a significant decline in Tco. The thermoregulatory responses of the pen-bred mice were superior to those observed among the domesticated strains. These data suggest that the age-related impairment in thermoregulation is a general phenomenon of aging in Mus musculus that is correlated with strain-specific lifespan but is possibly affected by the level of hybridization and domestication.

Aging↗