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PubMed1993

Fetal alcohol exposure attenuates lipopolysaccharide-induced fever in rats.

Exposure to alcohol in utero can lead to long-lasting impairments of immune functions and to decreased resistance to infectious agents. We studied the effects of fetal alcohol exposure (FAE) in rats on the core body temperature response to an exogenous challenge of the immune system with lipopolysaccharide (LPS). We report that FAE rats show markedly decreased LPS-induced fever [i.e., they require a higher dose than control rats to show any LPS-induced hyperthermia (50 micrograms/kg vs. 10 micrograms/kg)], and even with the higher LPS dose they manifest a weaker hyperthermia, which declines faster than in control animals. These results suggest that FAE produces an impairment in the release of endogenous pyrogens and/or in the neural substrate for body temperature regulation. This impairment may account for at least some of the decreased resistance to infections observed in FAE animals and humans.

Animals↗
PubMed1986

Regulation of the cutaneous circulation.

In this symposium, a diversity of perspectives was focused on how blood flow to the skin is controlled. Thus, control of the cutaneous circulation by reflexes aimed at body temperature regulation, blood pressure regulation, and the reflexes attending muscular exercise was discussed in detail, as were the similarities and differences between control of cutaneous arterioles and arteriovenous anastomoses. A mechanistic treatment of interaction between adrenergic control of cutaneous blood vessels and their temperature brought physical factors and pharmacological approaches to the consideration of reflex control. Finally, the more slowly developing changes in the control of the skin circulation that accompany circadian rhythms, changes in blood volume or its distribution, physical training, and acclimatization were discussed. Because the cutaneous circulation has potentially large vascular conductance, blood flow, and blood volume, control of the resistance and compliance vessels within the skin has an importance well beyond that of tissue nutrition. Indeed, overall hemodynamics are dependent on how much blood flow and how much blood volume are distributed to skin. Consequently, reflex factors, physical factors, and their interaction all have roles of importance with respect to exchange of heat with environment as well as maintenance of blood pressure, cardiac output, and blood flow to other tissues.

Adrenergic Fibers↗
PubMed2000

Local cutaneous water barrier in cold- and heat-acclimated pigeons (Columba livia) in relation to cutaneous water evaporation.

The thermoregulatory function of the skin differs in adult cold-acclimated and heat-acclimated rock pigeons (Columba livia). In general, the cutaneous evaporative cooling mechanism is not activated by appropriate stimuli in cold-acclimated pigeons in contrast to heat-acclimated pigeons. We studied with electron microscopy whether the differences in the function of the skin are reflected in the structure of the epidermal water barrier of these two extreme acclimation states. The epidermis of cold-acclimated pigeons is attenuated, and the underlying dermis lacks any intimate vascularization. Both the extracellular and the intracellular domains in the stratum corneum contain organized lamellar lipids. At the stratum transitivum-stratum corneum interface, multigranular body secretion is indicated by the highly convoluted cell membranes and membraneous sacculae enclosing the multigranular bodies. Alternatively, multigranular bodies retain in the corneocytes, and the lipoid material originated from them is reprocessed to broad lamellae. The keratohyalin (KH) granules are spotlike and oriented as cortical bands beneath the plasma membrane. In heat-acclimated pigeons, the epidermis displays modified patches side by side with basic structural type of epidermis. The modified areas are characterized by hypertrophy and abundance of dermal capillaries adjacent to the hypertrophied patch. No lamellar lipids are discerned in the dilated extracellular space. The structure of multigranular bodies is abnormal, and the numbers of lipid droplets in the outer viable epidermis and stratum corneum are decreased. The transitional cells contain stellate KH granules, which form a network throughout the cell. It is concluded that cold-acclimated pigeons have a lamellar, extracellular water barrier, the cutaneous water evaporation is minimized, and heat is stored in the body core. Acclimation to heat leads to formation of structurally heterogeneous skin. The structurally modified skin patches show disruption of the barrier-forming machinery in the multigranular bodies and marked reorganization of fibrillar proteins and electron-dense KH masses in the transitional layer. Thus water barrier adjustments in cold- and heat-acclimated pigeons manifest the dynamic function of avian skin as a thermoregulatory organ.

Acclimatization↗
PubMed1981

The role of body mass in thermoregulation.

Inbred Fisher and Buffalo rats were raised in small and in large litters and by such litter manipulation, large- and small-bodied animals were obtained within the same strain. When the rats were exposed to extreme cold and heat, it appeared that large-bodied rats in both strains survived longer in cold and small-bodied rats survived longer in heat. The two trends were clearly evident, and individual correlations between survival time and body mass were generally significant. However, there were also irregularities in such correlations. It is concluded that this is due to the fact that body mass is only one factor determining temperature tolerance in addition to hypothalamic, endocrine, and possibly neurochemical factors not known to be correlated to body mass.

Animals↗
PubMed1986

The effect of melatonin administration and short exposures to cold on body temperature of the blind subterranean mole rat (Rodentia, Spalax ehrenberghi, Nehring).

Improvement of the cold resistance capacity of the mole rat (Spalax ehrenbergi, Nehring), a blind subterranean rodent, was achieved following subcutaneous melatonin administration. Melatonin-treated mole rats exhibited reduction both in initial body temperature (Tbo) and in the decrease of body temperature (delta Tb) after 6 hours of exposure to cold. The tested mole rats were acclimated to and kept during the experiment, under long (16L/8D) photoperiod schedule while the effects of melatonin administration on body temperature simulated the effects of short photoperiod conditions. These results suggest that in mole rats, melatonin biochemically mediates photoperiodic information into body temperature physiological response. As a byproduct of the original experiment, it was found that frequently repeated short (6 hours) exposure to cold (Ta = 5 +/- 1 degrees C) can in itself initiate an improvement of cold resistance capacity similar to the effect of melatonin administration. This supports the idea that mole rats may improve their cold resistance in response to either photoperiodic or climatic changes.

Animals↗
PubMed1993

Effects of body morphology and mass on thermal responses to cold water: revisited.

Seven male volunteers were divided into two groups based on body morphology and mass. The large body mass (LM) group (n = 4) was 21.2 kg heavier and 0.32 m2.kg-1 smaller in surface area-to-mass ratio (P < 0.05) than the small body mass (SM) group (n = 3). Both groups were similar in total body fat and regional skinfold thicknesses. All subjects were immersed to the first thoracic vertebrae for 120 min in stirred water at 18 degrees C. Overall, tissue insulation was similar (P > 0.05) between the SM and LM groups across time. Perceptual ratings of thermal sensation increased (P < 0.05) across time. Therefore, as cold water immersion progressed, tissue insulation was similar and thermal sensation increased (P < 0.05) in males matched for subcutaneous fat and total fat but differing in body mass and morphology.

Analysis of Variance↗
PubMed1990

Inactivation of brown adipose tissue thermogenesis by oestradiol treatment in cold-acclimated rats.

Both cold-acclimated female rats and rats at thermoneutrality received 0.15-0.20 mg daily of 17 beta-oestradiol over 15 days via a Silastic capsule implanted subcutaneously. Controls received empty implants. Comparison between the oestradiol-treated animals and the untreated controls revealed that at thermoneutrality, oestradiol treatment decreased food intake and body weight gain, but did not affect brown adipose tissue (BAT) thermogenesis and composition. By contrast, in cold-acclimated rats, oestradiol treatment did not modify food intake or body weight gain, but it decreased BAT thermogenesis. It is concluded that the effects of oestradiol treatment on BAT depend on the activity of the tissue, i.e. it has no effect on BAT when the tissue is thermogenically inactive, but it decreases cold-induced BAT thermogenesis. It is suggested that oestradiol could be the hormonal factor responsible for the previously observed inactivation of BAT thermogenesis during pregnancy in cold-acclimated rats.

Adipose Tissue↗
PubMed1996

Longitudinal effects of age on heat-activated sweat gland density and output in healthy active older men.

To investigate longitudinal effects of age on heat-activated sweat gland density and output, eight healthy active men (mean age 65-70 years) were retested after 5-years using 60-min passive heating [by placing the lower legs and feet in a 42 degrees C water bath while sitting in a warm chamber (35 degrees C and 45% relative humidity)]. Their height, body mass, surface area-to-mass ratio, mean skinfold thickness, resting systolic and diastolic blood pressures, pedometer readings and estimated maximal oxygen uptake did not differ over the 5-years. During the 60-min exposure the increase of rectal temperature was significantly greater in the second test than in the initial test (P < 0.05), although mean skin temperature, metabolic heat production and heart rate did not differ. Total body sweating rate was significantly less in the second test than in the initial test [210 (SEM 13) vs 253 (SEM 16) g.m-2.h-1, P < 0.02]. The mean body temperature at the onset of sweating on the thigh was significantly higher in the second test (P < 0.04), but not on the back. Local sweat rate (msw) had decreased significantly on the back in the second test (P < 0.001), but had not changed on the thigh where it had been smaller (compared to younger men) in the initial test. The decreased msw on the back was due to a lower sweat gland output (SGO) per gland, but not from the recruitment of fewer glands. In contrast, the sweat gland density on the thigh was less in the second test than in the initial test [72 (SEM 4) vs 86 (SEM 7) glands.cm-2, P < 0.03], but the SGO which had shown considerably smaller values in the initial test remained unchanged. These results would suggest that sweat gland function decreased over 5 years in healthy active men in their sixth and seventh decades, despite their having similar physical characteristics and exercise habits. Furthermore, the decline did not occur uniformly over the body surface and it is suggested that it may well extend from the lower limbs to the trunk.

Aged↗
PubMed1996

Regional differences in age-related decrements of the cutaneous vascular and sweating responses to passive heating.

Ten older (aged 64-76 years) and ten younger (aged 20-24 years) healthy men were exposed to a standard heat stress [by placing the lower legs and feet in a water bath at 42 degrees C while sitting in a controlled environment (ambient temperature 35 degrees C and 45% relative humidity) for 60 min]. During passive heating, the rectal temperature of the older men was significantly greater (P < 0.05) and mean skin temperature was lower (P < 0.001), compared to the younger men. Skin blood flow by laser Doppler flowmetry (LDF) was significantly lower on the chest and thigh for the older men (P < 0.001), but forehead LDF did not differ between the groups. The percentages of total LDF in the older men to total LDF in the younger men for the last 30 min were 99%, 58% and 50% on the forehead, chest and thigh, respectively. The age-related differences in LDF responses mirrored cutaneous vascular conductances (CVC), since no group and time effects were observed in mean arterial blood pressure during the test. During the last 30 min the local sweat rates (msw) on the back and thigh were significantly lower for the older men (P < 0.02), but not on forehead, chest and forearm, although the older men had lower msw during the first 30 min exposure regardless of site (P < 0.03). The percentages of total msw in the older men to total msw in the younger men during the last 30 min were 105%, 99%, 63%, 106% and 88% on the forehead, chest, thigh, forearm, and back, respectively. During the latter half of the exposure, the older men had similar LDF, CVC and msw on the forehead, lower LDF and CVC and a similar msw on the chest, and lower LDF, CVC and msw on the thigh, compared to the younger men. These results suggest firstly that regional differences exist in the age-related decrement of cutaneous vasodilatation as well as sweat gland function, secondly that the age-related decrement in cutaneous vascular function may precede a decrement in sweat gland function, and thirdly that the successive decrements may develop sequentially from the lower limbs to the upper body, and head.

Adult↗
PubMed1987

Inhibition of diet-induced thermogenesis during pregnancy in the rat.

Both virgin and pregnant rats were maintained at two different ambient temperatures (28 degrees C and 10 degrees C) for 19 days. Virgin rats maintained their daily food intake and body weight at both temperatures. At 28 degrees C pregnant rats showed a greater daily food intake and body weight than virgin ones and their brown adipose tissue suffered regressive changes in composition when compared with brown fat of virgin rats. At 10 degrees C the increases in daily food intake and body weight of pregnant rats took place from day 15-16 of pregnancy onward and foetuses taken from these pregnant rats were smaller than those taken from pregnant rats at 28 degrees C. It is concluded that pregnant rats at thermoneutrality, although hyperphagic, do not show diet-induced thermogenesis. However, it is proposed that pregnant rats in the cold may show BAT cold-induced thermogenesis.

Adipose Tissue, Brown↗
PubMed1975

The influence of the social thermoregulation on the cold-adaptive growth of BAT in hairless and furred mice.

When mice were living in groups they developed less brown adipose tissue (BAT) during cold adaptation as compared with single mice. This effect of social aggregation was more pronounced in genetically hairless mice than in furred mice. In both races of mice the most significant difference in BAT growth was found between single mice and pairs of mice, indicating that the formation of pairs causes the relatively most effective improvement of thermal balance.

Adaptation, Physiological↗
PubMed1992

Thermoregulatory responses of young and older men to cold exposure.

Nine young (20-25 years) and ten older (60-71 years) men, matched for body fatness and surface area:mass ratio, underwent cold tests in summer and winter. The cold tests consisted of a 60-min exposure, wearing only swimming trunks, to an air temperature of 17 degrees C (both seasons) and 12 degrees C (winter only). Rectal (Tre) and mean skin (Tsk) temperatures, metabolic heat production (M), systolic (BPs) and diastolic (BPd) blood pressures and heart rate (fc) were measured. During the equilibrium period (28 degrees C air temperature) there were no age-related differences in Tre, Tsk, BPs, BPd, or fc regardless of season, although M of the older men was significantly lower (P < 0.003). The decrease in Tre and Tsk (due to the marked decrease in six of the older men) and the increase in BPs and BPd were significantly greater (P < 0.004) for the older men during all the cold exposures. The rate of increase in M was significantly greater (P < 0.01) for the older group when exposed to 12 degrees C in winter and 17 degrees C in summer (due to the marked increase in four of the older men). This trend was not apparent during the 17 degrees C exposure in winter. There was no age-related difference in fc during the exposures. Significant decreases in Tre and Tsk and increases in M, BPs and BPd during the 12 degrees C exposure were observed for the older group (P < 0.003) compared to their responses during the 17 degrees C exposure in winter. In contrast, Tre, M, BPs in the young group were not affected as much by the colder environment. It was concluded that older men have more variable responses and some appear more or less responsive to mild and moderate cold air than young men.

Adipose Tissue↗
PubMed1986

Effects of cold, short day and melatonin on thermogenesis, body weight and reproductive organs in Alaskan red-backed voles.

This study examined whether cold, short day or melatonin causes reproductive regression and stimulates nonshivering thermogenesis in a subarctic rodent Clethrionomys rutilus. Red-backed voles born and raised at 23 degrees C and 22 h light per day (LD 22:2) at Fairbanks, Alaska (65 degrees N) were exposed in one of six groups to: 1) long day (LD 22:2), 23 degrees C, injected daily with melatonin or saline 2 h before lights out, 2) long day, 3 degrees C, injected daily with melatonin or saline, 3) short day (LD 8:16), 23 degrees C or 3 degrees C. Voles were tested for nonshivering thermogenesis (NST) prior to and after 8 wk exposure. Body weight, testes weight and female reproductive tract weight were assessed after 8 wk in long day and 12 wk in short day. NST was not altered by short day or melatonin but cold (3 degrees C) caused an increase in NST which was similar in long day and short day. Body weight of males and females was not affected by short day but was decreased by melatonin. Short day did not alter mean testes weight (about 20% voles regressed) but reduced mean female reproductive tract weight (more than 40% voles regressed). Melatonin reduced testes weight and female reproductive tract weight (more than 50% of voles of both sexes regressed). The results suggest that in northern red-backed voles: the pineal does not mediate seasonal changes in thermogenic capacity, the pineal may mediate reduction of body weight and regression of reproductive organs but, in addition to day-length, other cues or factors may be important, populations may exhibit variability in sensitivity of reproduction to photoperiod which could allow for opportunistic breeding.

Animals↗
PubMed1985

Increased contribution of brown adipose tissue to nonshivering thermogenesis in the Djungarian hamster during cold-adaptation.

The effect of cold-adaptation was investigated on the brown adipose tissue of Djungarian hamsters. Animals maintained at 23 degrees C and 16 hours light per day (controls) were exposed to 5 degrees C. The wet weight of the total brown fat is reduced by some 40% within 4 days of cold-exposure, as a result of extensive triacylglycerol depletion of the tissue with no reduction in DNA; the tissue mass remains constant under persistent cold influence. The total amount of tissue mitochondria is doubled by 24 h and increases by a factor of 3 under persistent cold-stimulus, the specific respiratory capacity of the organelles remaining unchanged. The amount of 32 kDa regulatory protein per mg mitochondrial protein quantified from high-affinity GDP-binding, is increased by a factor of 2.7 after 21 days of cold-adaptation; a 9-fold increment is found of the total mitochondrial GDB-binding capacity. Comparison of nonshivering thermogenesis and the maximal thermogenic capacity of brown fat, estimated from the maximal respiration of the isolated mitochondria and the total amount of mitochondria in the tissue, suggests that brown fat may contribute about 20% to the whole-body nonshivering thermogenesis in warm-adapted controls and 45% in cold-adapted hamsters. The estimated increase in thermogenic capacity of the tissue in response to 21 days of cold-adaptation corresponds to the increase in nonshivering thermogenesis, suggesting a central thermoregulatory role of brown fat during cold-adaptation.

Acclimatization↗
PubMed1987

Genetic association between nest building and brown adipose tissue thermogenesis in female house mice.

Mice selectively bred for either high or low levels of thermoregulatory nest building were cold-acclimated (5 degrees C) for 3 weeks without nesting material; then body weight and food intake were measured. The mice selected for low nest building (Lows) of both sexes showed lower feed efficiencies than the high nest-building mice (Highs), although their body weights were not significantly different (Table 1). This adds to a large body of evidence which suggests that nest building and feed efficiency were influenced by a common mechanism (Lacy et al. 1978; Sulzbach and Lynch 1984; Lynch et al. 1981; Lynch and Roberts 1984). Brown adipose tissue mitochondrial GDP binding and cytochrome c oxidase activity were measured in the above mice. In females, the Lows had 100% higher levels of total GDP binding than the Highs, while no difference between the lines was seen in males. Thus in the High females, lower energy expenditure through brown fat thermogenesis may account for their greater feed efficiency. In males, the genetic differences in feed efficiency must be due to differences in either thermogenesis in tissues other than brown fat, or mechanisms which reduce heat loss.

Adipose Tissue, Brown↗
PubMed1986

Reduced cold-induced thermogenesis in familial human obesity.

It is well known that cold and diet-induced thermogenesis, which is mediated in small rodents by the hypothalamic-noradrenergic fibers-brown adipose tissue axis, is impaired in genetically obese mice. To test whether these adaptive mechanisms are also impaired in obese humans, 12 young males who were otherwise healthy (6 lean and 6 obese) were examined. The obese subjects had an early-onset type of obesity with a strong family history of it as well. Deep body temperature was measured by using a deep body thermometer furnished with three thermocouples. They were respectively placed on the sternum, on the interscapular area immediately under the neck (HIS), and on the 4th intercostal space (LIS) in order to study core temperature as well as heat production where brown adipose tissue could also be present in adults. Both lean and obese subjects were kept in a thermoneutral environment (28 degrees C) until they reached a steady-state body temperature and then rapidly transferred into a cold room (6-8 degrees C) where they remained up to 60 min. Body temperature decreased in both groups, but the decrease was more marked in the obese individuals on the sternum (P less than 0.01), on HIS (P less than 0.05) and on LIS (P less than 0.05) when compared to lean individuals. In conclusion, cold-induced thermogenesis is impaired in familial early-onset human obesity and in genetically obese mice.

Adult↗
PubMed1990

Cold-induced and diet-induced thermogenesis in progesterone-treated rats.

Both cold-acclimated rats and rats at thermoneutrality received 1.5 mg/day of progesterone over a period of 15 days by means of two subcutaneously implanted Silastic capsules. Progesterone treatment increased total food intake and body mass gain in both groups of treated animals when compared with their controls at the same ambient temperature. However, the interscapular brown adipose tissue (BAT) of the treated rats showed the same thermogenic activity (assessed by GDP-binding), mass and gross composition as that of their respective controls. If it is assumed that enhanced food intake is the physiological drive for diet-induced thermogenesis, it could be concluded that progesterone inhibits diet-induced thermogenesis at thermoneutrality, but has no effect in cold-induced thermogenesis. However, if the physiological drive for diet-induced thermogenesis is not enhanced food intake, but an imbalance in the diet, then given that the same diet was offered to all animals throughout the experimental period, it could be that progesterone does not affect BAT, either at thermoneutrality or in the cold.

Acclimatization↗