Differences In Thermogenesis Research Articles

Temporal and geographic distribution of gut microbial enterotypes associated with host thermogenesis characteristics in plateau pikas.

Differentiation of the gut microbiota between individuals within a species can be identified by enterotypes. However, whether different enterotypes are associated with host-related physiological status and adaptation to specific habitats is still poorly understood. In this study, we collected 308 cecal samples from plateau pikas during varying seasons and altitudes. We identified three bacterial and two fungal enterotypes. The proportion of Rikenellaceae_RC9_gut_group- and Prevotella-predominated enterotype 3 was higher than that of the other two enterotypes in all samples. Enterotype 1, distinguished by norank Muribaculaceae, was mainly detected during the warm season and at high altitudes, whereas enterotype 2, which is unclassified Lachnospiraceae, was mainly detected during the cold season. Plateau pikas with bacterial enterotypes 2 and 3 showed significantly higher alpha diversity than those with enterotype 1, while pikas with fungal enterotype 1 displayed higher diversity than those with enterotype 2. Functional pathways of lipid metabolism were enriched in bacterial enterotype 1, carbohydrate and amino acid metabolism were enriched in enterotype 2, and energy metabolism was enriched in enterotype 3. The neutral process was more important in bacterial enterotype 3 than in enterotypes 1 and 2. The body temperature and resting metabolic rate of pikas with bacterial enterotypes 1 and 3 were significantly higher than those with enterotype 2. Pikas with unclassified Sporormiaceae- and Sporormiella-dominated fungal enterotypes may engage more frequently in coprophagy. Overall, this study revealed that both gut bacterial and fungal communities in pikas can be clustered into enterotypes, and individuals with different enterotypes showed significant differences in thermogenesis. IMPORTANCE The gut microbiotas of small mammals play an important role in host energy homeostasis. However, it is still unknown whether small mammals with different enterotypes show differences in thermogenesis characteristics. Our study confirmed that plateau pikas with different bacterial enterotypes harbored distinct thermogenesis capabilities and employed various strategies against cold environments. Additionally, we also found that pikas with different fungal enterotypes may display differences in coprophagy.

Thermogenic responses to different clamped skin temperatures in cold-exposed men and women.

Despite many decades of research examining thermoregulatory responses under varying cold stresses in humans, very little is known about the variability in metabolic heat production and shivering activity. Here, we used a novel closed-loop mean skin temperature clamping technique with a liquid-conditioned suit to isolate the effects of mean skin temperature on the subjective evaluation of thermal sensation, heat production, shivering responses, and oxidative fuel selection in young, lean, and healthy men (n = 12) and women (n = 12). Our results showed a skin temperature-dependent increase in metabolic heat production (5.2 ± 1.2 kJ/min, 5.9 ± 1.5 kJ/min, and 7.0 ± 1.8 kJ/min with skin temperature maintained at 31 ± 0.1°C, 29 ± 0.2°C, and 27 ± 0.1°C, respectively; P < 0.0001) and shivering intensity in both men and women [0.6 ± 0.1% maximal voluntary contraction (MVC), 1.1 ± 0.4% MVC, and 2.5 ± 0.7% MVC, respectively; P < 0.0001], including sex-dependent differences in heat production at all three temperatures (P < 0.005). Even when controlling for lean body mass and fat mass, sex differences persisted (P = 0.048 and P = 0.004, respectively), whereas controlling for differences in body surface area eliminated these differences. Interestingly, there were no sex differences in the cold-induced change in thermogenesis. Despite clamping skin temperature, there was tremendous variability in the rate of heat production and shivering intensity. Collectively this data suggests that many of the interindividual differences in thermogenesis and shivering may be explained by differences in morphology and body composition.

Variation in physiological profiles may explain breed differences in neonatal lamb thermoregulation

Ability to adapt rapidly from the uterine environment to self-thermoregulation following birth is a vital requirement for neonatal lamb survival. This investigation reports factors that could explain differences in thermoregulation among breeds that differ in lamb survival. Breeds such as the Merino and Border Leicester have previously been shown to be divergent for birthweight, cold resistance and lamb survival. Cross-bred (Poll Dorset Border Leicester (PDBL, n = 9) and Poll Dorset Merino (PDM, n = 25)) and pure-bred (Border Leicester (BL, n = 35) and Merino (M, n = 46)) lambs were recorded for the thermogenic measures rectal temperature at birth, cold resistance (time for rectal temperature to fall to 35°C while in a cooled water bath) and cold recovery (time to restore rectal temperature after cold exposure) at 1 day of age. In pure-bred lambs, 1 kg increase in weight resulted in a 0.25°C increase in rectal temperature at birth (P &lt; 0.001) and 4.2 min increase in cold resistance (P &lt; 0.001). In contrast, cross-bred lambs did not exhibit any relationship between birthweight and rectal temperature at birth, although they displayed a 3.2 min greater cold resistance for every 1 kg increase in birthweight (P &lt; 0.001). BL-derived lambs were more cold resistant than M lambs (cross-bred: PDBL, 67.1 ± 2.5 min; PDM, 56.4 ± 1.6 min; P &lt; 0.01; and pure-bred: BL, 58.1 ± 1.5 min; M, 53.2 ± 1.3 min; P &lt; 0.01). The quadratic relationship of glucose concentration over time during cold exposure differed with lamb breed. PDBL exhibited higher peak glucose concentrations than did PDM (11.0 mmol/L and 8.9 mmol/L, respectively; P &lt; 0.01). BL took longer to reach peak glucose concentration (50 min) than did M (40 min) and this peak value was higher (BL, 9.4 mmol/L; M, 7.7 mmol/L; P &lt; 0.001). In conclusion, variations in birthweight and glucose metabolism are associated with breed differences in thermogenesis of neonatal lambs.

Differences in mitochondrial DNA inheritance and function align with body conformation in genetically lean and fat sheep.

Body weight and adiposity are determined by the balance between energy intake, energy expenditure, and nutrient deposition. We have identified differences in appetite-regulating peptides in sheep selectively bred to be either lean or fat, wherein gene expression for orexin and melanin-concentrating hormone are elevated in the lean group. Despite this, the underlying mechanisms leading to differences in body composition in the lean and fat lines remains unknown. We measured postprandial temperature in adipose tissue and muscle to ascertain whether a difference in thermogenesis is associated with the difference in body composition in genetically lean (n = 8) and fat (n = 12) ewes. Body weight was higher (P < 0.01) but percent fat mass was lower (P < 0.001) in the lean group. The percent lean mass was similar in lean and fat groups. Animals received intracerebroventricular cannulae and temperature probes implanted into the retroperitoneal fat and the hind-limb skeletal muscle (vastus lateralis). Animals were meal fed (1100-1600 h) to entrain postprandial thermogenesis. Food intake was similar between lean and fat animals. Postprandial thermogenesis was greater (P < 0.05) in the retroperitoneal adipose tissue of lean animals but not in skeletal muscle. Intracerebroventricular infusion of leptin reduced (P< 0.05) food intake by an equal extent in both groups. Postprandial expression of UCP1 mRNA was greater (P < 0.05) in retroperitoneal fat of lean animals, with similar UCP3 expression in skeletal muscle. Mitochondrial genome sequencing indicated haplotypic clustering in lean and fat animals within both the encoding and nonencoding regions. This demonstrates that differences in body composition may be underpinned by differences in thermogenesis, specifically within adipose tissue. Furthermore, thermogenic differences may be associated with specific mitochondrial DNA haplotypes, suggesting a strong genetic component inherited through the maternal lineage.

Transpulmonary hypothermia: A novel method of rapid brain cooling through augmented heat extraction from the lungs

AimDelay in instituting neuroprotective measures after cardiac arrest increases death and decreases neuronal recovery. Current hypothermia methods are slow, ineffective, unreliable, or highly invasive. We report the feasibility of rapid hypothermia induction in swine through augmented heat extraction from the lungs. MethodsTwenty-four domestic crossbred pigs (weight, 50–55kg) were ventilated with room air. Intraparenchymal brain temperature and core temperatures from pulmonary artery, lower esophagus, bladder, rectum, nasopharynx, and tympanum were recorded. In eight animals, ventilation was switched to cooled helium–oxygen mixture (heliox) and perfluorocarbon (PFC) aerosol and continued for 90min or until target brain temperature of 32°C was reached. Eight animals received body-surface cooling with water-circulating blankets; eight control animals continued to be ventilated with room air. ResultsBrain and core temperatures declined rapidly with cooled heliox–PFC ventilation. The brain reached target temperature within the study period (mean [SD], 66 [7.6]min) in only the transpulmonary cooling group. Cardiopulmonary functions and poststudy histopathological examination of the lungs were normal. ConclusionTranspulmonary cooling is novel, rapid, minimally invasive, and an effective technique to induce therapeutic hypothermia. High thermal conductivity of helium and vaporization of PFC produces rapid cooling of alveolar gases. The thinness and large surface area of alveolar membrane facilitate rapid cooling of the pulmonary circulation. Because of differences in thermogenesis, blood flow, insulation, and exposure to the external environment, the brain cools at a different rate than other organs. Transpulmonary hypothermia was significantly faster than body surface cooling in reaching target brain temperature.

Sex Differences in Thermogenesis Structure Behavior and Contact within Huddles of Infant Mice

Brown adipose tissue (BAT) is a thermogenic effector abundant in most mammalian infants. For multiparous species such as rats and mice, the interscapular BAT deposit provides both an emergency “thermal blanket” and a target for nestmates seeking warmth, thereby increasing the cohesiveness of huddling groups. Sex differences in BAT regulation and thermogenesis have been documented in a number of species, including mice (Mus musculus)–with females generally exhibiting relative upregulation of BAT. It is nonetheless unknown whether this difference affects the behavioral dynamics occurring within huddles of infant rodents. We investigated sex differences in BAT thermogenesis and its relation to contact while huddling in eight-day-old C57BL/6 mouse pups using infrared thermography, scoring of contact, and causal modeling of the relation between interscapular temperature relative to other pups in the huddle (TIS rel) and contacts while huddling. We found that females were warmer than their male siblings during cold challenge, under conditions both in which pups were isolated and in which pups could actively huddle in groups of six (3 male, 3 female). This difference garnered females significantly more contacts from other pups than males during cold-induced huddling. Granger analyses revealed a significant negative feedback relationship between contacts with males and TIS rel for females, and positive feedback between contacts with females and TIS rel for males, indicating that male pups drained heat from female siblings while huddling. Significant sex assortment nonetheless occurred, such that females made more contacts with other females than expected by chance, apparently outcompeting males for access to each other. These results provide further evidence of enhanced BAT thermogenesis in female mice. Slight differences in BAT can significantly structure the behavioral dynamics occurring in huddles, resulting in differences in the quantity and quality of contacts obtained by the individuals therein, creating sex differences in behavioral interactions beginning in early infancy.

Light-dark differences in the effects of ambient temperature on gaseous metabolism in newborn rats.

Body temperature (T(b)) of rat pups (7-9 days old) raised under a 12:12-h light-dark (L-D) regimen (L: 0700-1900, D: 1900-0700) was consistently higher in D than in L by approximately 1.1 degrees C. We tested the hypothesis that the L-D differences in T(b) were accompanied by differences in the set point of thermoregulation. Measurements were performed on rat pups at 7-9 days after birth. O(2) consumption (VO(2)) and CO(2) production (VCO(2)) were measured with an open-flow method during air breathing, as ambient temperature (T(a)) was decreased from 40 to 15 degrees C at the constant rate of 0.5 degrees C/min. At T(a) >/=33 degrees C, VO(2) was not significantly different between L and D, whereas VCO(2) was higher in L, suggesting a greater ventilation. Over the 33 to 15 degrees C range the VO(2) values in D exceeded those in L by approximately 30%. Specifically, the difference was contributed by differences in thermogenesis at T(a) = 30 to 20 degrees C. As T(a) was decreased, the critical temperature at which VO(2) began to rise was lower in L. We conclude that the higher T(b) of rat pups in D is accompanied by a higher set point for thermoregulation and a greater thermogenesis. These results are consistent with the idea that, in newborns, endogenous changes in the set point of thermoregulation contribute to the circadian oscillations of T(b).

Hypoxic depression of circadian rhythms in adult rats.

Because the circadian rhythms of oxygen consumption (VO(2)) and body temperature (T(b)) could be contributed to by differences in thermogenesis and because hypoxia depresses thermogenesis in its various forms, we tested the hypothesis that hypoxia blunts the normal daily oscillations in VO(2) and T(b). Adult rats were instrumented for measurements of T(b) and activity by telemetry; VO(2) was measured by an open-flow method. Animals were exposed to normoxia (21% O(2)), hypoxia (10.5% O(2)), and normoxia again, each 1 wk in duration, in either a 12:12-h light-dark cycle ("synchronized") or constant light ("free running"). In this latter case, the period of the cycle was approximately 25 h. In synchronized conditions, hypoxia almost eliminated the T(b) circadian oscillation, because of the blunting of the T(b) rise during the dark phase. On return to normoxia, T(b) rapidly increased toward the maximum normoxic values, and the normal cycle was then reestablished. In hypoxia, the amplitude of the activity and VO(2) oscillations averaged, respectively, 37 and 56% of normoxia. In free-running conditions, on return to normoxia the rhythm was reestablished at the expected phase of the cycle. Hence, the action of hypoxia was not on the clock itself but probably at the hypothalamic centers of thermoregulation. Hyperoxia (40% O(2)) or hypercapnia (3% CO(2)) had no significant effects on circadian oscillations, indicating that the effects of hypoxia did not reflect an undifferentiated response to changes in environmental gases. Modifications of the metabolism and T(b) rhythms during hypoxia could be at the origin of sleep disturbances in cardiorespiratory patients and at high altitude.

Influence of a “cafeteria” diet on heat production during postnatal development of the rat

1. 1. Despite different food availability for pregnant rats, the maternal diet had no effect on the weight of the pups at birth. 2. 2. There were no differences in thermogenesis during lactation in pups from dams that received cafeteria diet during pregnancy and after parturition. 3. 3. Both groups of pups grew faster than controls with, however, indistinguishable thermogenesis rates for all pups. 4. 4. After weaning, relative heat production decreased in all groups, even though cafeteria rats showed higher rates than the controls. 5. 5. The higher availability of energetic substrates resulted in increased growth in pups, but only after weaning was the heat output enhanced.

Thermogenic response to temperature, exercise and food stimuli in lean and obese women, studied by 24 h direct calorimetry.

1. Total heat loss was measured by 24 h direct calorimetry in five obese and five lean women who were maintained throughout the study on a diet supplying 3·3 MJ/d. Each subject was measured five times to assess the effect of temperature, exercise and food on energy expenditure. Within each weight group a Latin-square design was used to balance sequence effects on the thermogenic responses to temperature, exercise and food.2. Compared with the control day, on which no thermogenic stimulus was given, the increase in 24 h heat production by the lean and obese women caused by 30 min exercise on a bicycle ergometer against a load of 20 N was 10·1 and 10·3 W for obese and lean groups respectively. There was no evidence in either group of a measurable long-term increase in metabolism which would increase the energy cost of the exercise above that predicted from indirect calorimetry during the exercise.3. The increase in heat production associated with ingesting an extra 4·4 MJ (obese group) or 4·0 MJ (lean group) was 3·4 and 3·0 W respectively. This response was similar to that predicted from indirect calorimetry for a few hours after the meal.4. The obese and lean groups differed in metabolic response to calorimetry at the upper or lower limits of the thermal comfort zone, which was determined individually for each subject. The difference from control values in the obese group was an increase of 3·8 W on the ‘warm’ run, and a decrease of 2·0 W on the ‘cool’ run. Among subjects the change was an increase of 0·4 W on the ‘warm’ run, and an increase of 4·8 W on the ‘cool’ run. The differences between the groups did not achieve statistical significance. The lower and upper temperature limits were similar in the two groups: 23·2–26·4° for the obese group, and 23·3–26·2° for the lean group.5. The most striking difference between lean and obese subjects in the present study was the much higher resting metabolic rate, and total energy expenditure, of the obese group. During the control run the obese group had a mean energy expenditure of 96·1 W, compared with 61·7 W in the lean group. There was no overlap: the lowest energy expenditure for an obese subject was 81·4 W and the highest for a lean subject was 76·1 W. In comparison to this large difference in baseline the magnitude of the thermogenic responses was small.6. Under the conditions of this study there was nothing to support the view that a failure of thermogenic response is an important factor in the causation of human obesity. To support that view it would be necessary to show differences in thermogenesis in lean and obese subjects which were at least an order of magnitude greater than those which we have observed.

Effect of diet and exercise on norepinephrine-induced thermogenesis in male and female rats.

Male and female rats were fed standard laboratory chow or a highly palatable diet (cafeteria diet) for 10 wk. The cafeteria diet caused an increase in caloric intake and in body weight, and it induced thermogenesis that was associated with elevated plasma triiodothyronine (T3) levels, increased brown adipose tissue size, and enhanced metabolic response to norepinephrine. For a comparable caloric intake, body-weight gain was significantly greater in female than in male rats possibly because of difference in thermogenesis as suggested by the response to norepinephrine. Exercise training (swimming 2 h/day for 10 wk) reduced food intake and body-weight gain and failed to increase norepinephrine-induced thermogenesis in rats fed laboratory chow. In animals fed the cafeteria diet, food intake and body-weight gain were also reduced by exercise training, which at the same time diminished the diet-induced thermogenesis as evidenced by the diminution of 1) brown fat hypertrophy, 2) the elevation of plasma T3, and 3) the hyperthermic response to injected norepinephrine. It is suggested that the thyroid hormone and catecholamines through their actions on the brown adipose tissue are the important regulatory of thermogenesis. Exercise training would reduce the diet-induced thermogenesis by preventing increased T3 production. Enhanced thermogenesis may be considered an adaptive reaction as it serves to reduce fat deposition in animals fed cafeteria diet and to promote nonshivering heat production in the cold. On the other hand, exercise training reduces thermogenesis and thus prevents energy wasting.

Reduced thermogenesis in obesity

IT is often claimed that there are obese patients who find it difficult to maintain a normal body weight because they have such low energy requirements that even normal intakes of energy result in weight gain and obesity. Studies of both children1 and adults2 show that there can be a twofold difference in energy intake between individuals despite apparently similar patterns of physical activity. An individual variability in the capacity to dissipate heat by metabolic changes has therefore been suggested3 but no physiological basis for the differences in thermogenesis has yet been established. In genetically obese ob/ob mouse there are two components involved in the deposition of excess body fat: hyperphagia and increased metabolic efficiency4,5. Metabolic efficiency is the major factor responsible for obesity when the animals are kept at 20 °C so these animals provide a model study of the link between metabolic rate and obesity. Pre-obese and obese ob/ob animals have an abnormality of thermoregulatory thermogenesis with a reduced thermogenic response to cooling6. A defect in non-shivering thermogenesis can be confirmed by monitoring the thermogenic response to maximum doses of nor adrenaline: the ob/ob mouse has only half the response of its lean littermate. The abnormal thermoregulatory thermogenesis quantitatively accounts for most of the metabolic efficiency of the obese animals as pair feeding at thermoneutrality rather than at 23 °C reduces the excess fat deposited by 65%7. We report here that obese adults with a family history of obesity have a reduced metabolic response to noradrenaline infusion compared with thin adults. As the reduced non-shivering thermogenesis is also found in subjects with familial obesity who remain at normal weight by persistent dieting, the defect in non-shivering thermogenesis appears to be constitutional and not a secondary consequence of obesity.