Lasting consistency of cold adaptability in rats reared in cold for many generations

Wistar rats were successively reared in cold at 5 degrees C from 1969 to 1984. The historical changes observed in these rats were reported. The cold-adapted rats reared in cold for 8 to 11 successive generations (C8-11G) were examined on their cold tolerance and non-shivering thermogenesis. C8-11G rats showed greater nonshivering thermogenesis than that of the warm-adapted control group (W), and rats exposed to cold for periods of 2 to 8 weeks (C). The nonshivering thermogenesis of C8-11G rats was diminished to a similar level to that of W and C rats by administration of a ganglion blocker, of reserpine, or of beta-adrenoceptor blocker. The de-adapted rats reared in warm at 25 degrees C for 3 generations after being reared for many generations in cold (DA-3G) showed much more nonshivering thermogenesis as compared to W rats. Cold tolerance of DA-3G rats was at a level of intermediate between that of W and C rats. Brown adipose tissue (BAT) weight of DA-3G rats was similar to that of C rats, while chemical composition of BAT in DA-3G rats differed from that of C and W rats.     

Cross adaption between stress and cold in rats

Three-hour immobilization stress was imposed on male adult rats of Wistar strain by restraining them on a board 6 days a week for 1–8 weeks. The stressed rats showed less body weight gain during the experiment compared to the controls. These stressed animals manifested an improved cold tolerance as shown by no significant fall in colonic temperature in the cold at –5° C for 300 min during the experimental period, while the colonic temperature of the controls fell progressively. Nonshivering thermogenesis as assessed by noradrenaline-induced increase in oxygen consumption was significantly potentiated in the stressed rats. The weight and protein content of the intercapsular brown adipose tissue (BAT) increased and BAT mitochondria were more packed in the stressed rats. Plasma insulin, insulin/glucagon molar ratio and thyroxine levels were lowered in the stressed rats, while the plasma triiodothyronine level remained unchanged. Removal of interscapular BAT led to a loss of improved cold tolerance and a significant reduction of nonshivering thermogenesis in the stressed rats.These results indicate that repetitive stress may induce cross adaptation between stress and cold through an enhanced capacity of nonshivering thermogenesis mediated, at least in part, via stimulation of BAT function.     

Brown adipose tissue and thermogenesis in hypophysectomized rats in relation to temperature acclimation

The aim of this work was to test the role of pituitary dependent hormones in cold-induced non-shivering thermogenesis. In the 28°C-acclimated rat, hypophysectomy inhibited body growth and led to an atrophy of thyroid and adrenals. In brown adipose tissue (BAT) some alterations were induced which are usually observed after cold acclimation of the animal: increase in relative weight, decreases in the relative amount of lipids, increases in the amounts of protein and DNA and modification of the proportions of several phospholipid fatty acids; moreover, basal lipolysis, in vitro, was enhanced to the same extent as that following cold acclimation of the normal rat. The in vivo stimulation by norepinephrine (NE) of O₂ consumption (test for nonshivering thermogenesis) and of fatty acid release into blood were suppressed.Progressive cold acclimation of the hypophysectomized rats at 15°C led to a hypertrophy of BAT to the same extent as in the sham-operated animals. The in vivo sensitivity to NE was partially restored. The results suggest that hypophysectomy does not suppress the ability to acclimate to moderate cold by means of BAT dependent non-shivering thermogenesis. However, the low ability to produce heat seems to indicate that pituitary or pituitary-dependent hormones are necessary to optimize the cold stimulation of brown fat thermogenesis.     

Effect of immobilization stress on in vitro and in vivo thermogenesis of brown adipose tissue.

Repetitive intermittent stress such as immobilization has been shown to induce an improved cold tolerance through an enhanced capacity of nonshivering thermogenesis (NST), causing positive cross adaptation between nonthermal stress and cold. In the present study, effect of 3-h-daily immobilization stress for 4-5 weeks was investigated on in vitro and in vivo thermogenesis of interscapular brown adipose tissue (BAT). In vitro thermogenesis was measured in the minced tissue blocks incubated in Krebs-Ringer phosphate buffer with glucose and albumin at 37 degrees C, using a Clark-type oxygen electrode. The stressed rats showed less body weight gain during the experiment. The BAT weight, its protein and DNA contents were significantly greater in the stressed rats. Basal, noradrenaline- and glucagon-stimulated oxygen consumptions were significantly greater in the stressed rats. In vivo thermogenesis was assessed by the changes of temperatures in colon (Tcol), BAT (TBAT), and tail skin (Tsk) induced by noradrenaline or glucagon infusion in the anesthetized rats. Noradrenaline and glucagon increased the TBAT and the extent of increase was greater in the stressed rats. These results indicate that cross adaptation between nonthermal stress and cold may be mediated through an enhanced thermogenic activity of BAT.     

Cold-induced changes in glucagon of brown adipose tissue

In order to evaluate the role of glucagon in brown adipose tissue (BAT) function under cold or stress, the changes in immunoreactive glucagon of BAT and plasma as well as uptake and metabolism of radioactive glucagon (125I-G) in this tissue were studied in rats. Glucagon per g fresh tissue was higher in the dorso-cervical BAT than in the interscapular BAT. In warm controls (WC), acute cold exposure (-5 degrees C, 15 min) (CE) or stress (immobilization, 30 min) (AS) elevated glucagon of both sites of BAT as well as plasma. In cold-acclimated animals (CA), the resting levels of BAT glucagon, but not plasma glucagon, were higher than WC. CE caused elevation of plasma glucagon, but not BAT glucagon in CA. AS did not affect glucagon levels in both plasma and BAT in CA. Cold acclimation did not influence 125I-G uptake by BAT, but resulted in a rather lower 125I-G level in plasma and liver. The present results suggest that BAT is a target tissue for glucagon to cause nonshivering thermogenesis in response to cold or stress and that turnover of glucagon is enhanced by cold acclimation.     

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-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 intage 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.     

内源性精氨酸加压素在昼光期大鼠紧张性体温调节中的作用

目的: 探讨内源性精氨酸加压素(AVP)在昼光期大鼠紧张性体温调节中的作用及其机制。方法: 使用成年雄性SD大鼠,在22 ℃环境温度下,明暗时间各12 h,同步无线遥测体核温度(Tc)和棕色脂肪(BAT)温度。上午10:00给大鼠腹腔注射AVP(10 μg/kg)或精氨酸加压素V_1a(AVP V_1a)受体阻断剂(30 μg/kg)。用酶联免疫吸附测定法,分别检测昼光期和暗光期大鼠血浆中AVP浓度。给AVP 60 min 后测定血清中甘油三酯、游离脂肪酸和甘油浓度变化。给予AVP后间隔10 min 记录大鼠的理毛活动。结果: (1)在昼光期中AVP V_1a受体阻断剂能够升高Tc和BAT温度。(2)在昼光中Tc和BAT温度处于低温期时,血浆中AVP水平则明显提高。(3)腹腔注射AVP引起Tc快速降低时,伴有BAT温度明显降低和大鼠的理毛行为明显增加。(4)AVP可以降低血清游离脂肪酸与甘油浓度,提高血清甘油三酯的浓度。结论: (1)内源性AVP通过AVP V_1a受体参与昼光期大鼠紧张性体温调节过程,因为在昼光期中不仅血浆AVP浓度明显高于暗光期,而且AVP V_1a受体阻断剂也能明显升高Tc和BAT温度。(2)AVP能降低BAT温度、血中游离脂肪酸和甘油浓度,提高理毛活动,证明AVP引起低温的机制可能与抑制脂肪分解、降低BAT产热和提高散热反应有关。     

Thermogenesis in brown adipose tissue with age: Post-receptor activation by forskolin

₃-Adrenergic-stimulated thermogenesis in brown adipose tissue (BAT) is diminished with age. ₃-Adrenergic receptors are positively coupled to adenylyl cyclase in BAT. To determine whether thermogenesis, in response to direct activation of adenylyl cyclase, is also impaired with age, we examined whole body oxygen consumption, mitochondrial guanosine diphosphate (GDP) binding and BAT mitochondrial uncoupling protein (UPC) mRNA levels in 4- and 24-month-old F-344 rats following forskolin administration. We also examined the forskolin-induced change in body temperature in 4-month-old rats. In some instances, the results were compared with administration of the specific ₃-adrenergic agonist, CGP-12177. Forskolin (3.5 mg/kg) increased oxygen consumption but decreased body temperature. In subsequent experiments the BAT was unilaterally denervated. In these rats, the forskolin-(1.8 mg/kg) stimulated increase in oxygen consumption was similar in young and old rats. Forskolin increased GDP binding and UCP mRNA levels in both the denervated and innervated BAT pads. The increases were equal or greater in the BAT from senescent rats. These findings, coupled with our previous report of an impaired CGP-12177-stimulated increase in GDP binding in senescent rats, suggests ₃-adrenergic-stimulated, but not post-receptor-stimulated, thermogenesis is diminished with age.     

Rat behavioral thermoregulation integrates with nonshivering thermogenesis during postnatal development

Rat pups are capable of behavioral thermoregulation, both in the nest and on a thermocline, as early as the 1st week of postnatal life, and these pups can also produce heat metabolically without shivering. The rat pup's primary source of nonshivering thermogenesis is the sympathetically mediated metabolism of brown adipose tissue (BAT). BAT is well formed in newborns and functions shortly after birth. While infant behavioral thermoregulation and BAT thermogenesis have been extensively studied, little is known about the extent to which thermoregulatory behavior can be influenced by BAT thermogenesis. In the present study, 2-, 7-, and 14-day-old pups were observed on a thermal gradient following pharmacological stimulation or inhibition of BAT thermogenesis, and their thermal preferences were quantified. The authors found that 7- and 14-day-old pups treated with norepinephrine (NE), which increases BAT thermogenesis, preferred cooler portions of the gradient than saline-treated controls, whereas 2-day-olds failed to show a similar NE-induced behavioral adjustment. These findings indicate that the ability to adjust thermoregulatory behavior to compensate for enhanced metabolic thermogenesis develops during the 1st week of postnatal life.     

Functional and anatomical characterization of brown adipose tissue in heart failure with blood oxygen level dependent magnetic resonance

Recent studies have suggested that brown adipose tissue (BAT) plays an important role in obesity, insulin resistance and heart failure. The characterization of BAT in vivo, however, has been challenging. No technique to comprehensively image BAT anatomy and function has been described. Moreover, the impact on BAT of the neuroendocrine activation seen in heart failure has only recently begun to be evaluated in vivo. The aim of this study was to use MRI to characterize the impact of heart failure on the morphology and function of BAT. Mice subjected to permanent ligation of the left coronary artery were imaged with MRI 6 weeks later. T₂ weighted MRI of BAT volume and blood oxygen level dependent MRI of BAT function were performed. T₂* maps of BAT were obtained at multiple time points before and after administration of the β₃ adrenergic agonist CL 316 243 (CL). Blood flow to BAT was studied after CL injection using the flow alternating inversion recovery (FAIR) approach. Excised BAT tissue was analyzed for lipid droplet content and for uncoupling protein 1 (UCP1) mRNA expression. BAT volume was significantly lower in heart failure (51 ± 1 mm³ versus 65 ± 3 mm³; p < 0.05), and characterized by a reduction in lipid globules and a fourfold increase in UCP1 mRNA (p < 0.05). CL injection increased BAT T₂* in healthy animals but not in mice with heart failure (24 ± 4% versus 6 ± 2%; p < 0.01), consistent with an increase in flow in control BAT. This was confirmed by a significant difference in the FAIR response in BAT in control and heart failure mice. Heart failure results in the chronic activation of BAT, decreased BAT lipid stores and decreased BAT volume, and it is associated with a marked decrease in ability to respond to acute physiological stimuli. This may have important implications for substrate utilization and overall metabolic homeostasis in heart failure. Copyright © 2016 John Wiley & Sons, Ltd.     

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 thoroughout the experimental period, it could be that progesterone does not affect BAT, either at thermoneutrality or in the cold.     

Lasting effect of infantile cold experience on cold tolerance in adult rats.

The effect of short and repetitive exposure to cold (5 degrees C, 4 hr/day for 2 weeks) from the birth up to the 14th day of newborn rats onthe thermal regulation in adulthood and on the tolerance to cold was investigated. After being exposed to cold, they were transferred to a room at 25 degrees C (N-CA). The control rats were raised at 25 degrees C (N-WA). An acute cold exposure test was performed by placing the animals in a room at 5 degrees C under urethane anesthesia. Electrical activity of neck muscles as an index of shivering was recorded. The colonic temperature fell at a significantly slower rate in N-CA rats with less shivering than in N-WA ones. Nonshivering thermogenesis tested by norepinephrine was significantly greater in N-CA rats than in N-WA ones. These results suggest that N-CA rats developed improved cold tolerance accompanied by greater nonshivering thermogenesis. Such a phenomenon in N-CA lasted for 18 weeks after the termination of cold exposure. Adult rats subjected to the same scheme of cold exposure (A-CA) (5 degrees C, 4 hr/day, 2 weeks) showed essentially the same results as seen in N-CA, but its improved cold tolerance and elevated nonshivering thermogenesis disappeared 4 weeks after the termination of cold exposure. Extirpation of interscapular brown adipose tissue immediately before the cold test did not appreciably affect the cold tolerance in N-CA and A-CA rats. The colonic temperature at the onset of shivering was significantly lower in N-CA as well as A-CA rats than in each of the corresponding control rats, indicating a shift of the shivering threshold to lower temperature values in the animals exposed intermittently to cold. These results indicate that an infantile experience with cold results in a greater and longer sustained ability to tolerate cold in adulthood, characterized by enhanced nonshivering thermogenesis.     

Reduced norepinephrine turnover in brown adipose tissue of ob/ob mice

Obese (ob/ob) mice have a lower thermogenic capacity than lean mice. The possible role of brown adipose tissue (BAT) in this defect was investigated. Lean and obese mice were exposed to 33 (thermoneutral), 25, or 14 degrees C for up to 3 wk. BAT cytochrome oxidase activity and numbers of Na+-K+-ATPase enzyme units, enzymes involved in thermogenesis, were similar at 33 or 25 degrees C. Chronic exposure to 14 degrees C increased these enzymes 34 and 62%, respectively, in lean mice and nearly 150% in obese mice. Sympathetic nervous system activity, which stimulates thermogenesis in BAT, was evaluated by measuring norepinephrine (NE) turnover. At 25 degrees C, NE turnover rate in BAT of obese mice was only 40% as rapid as in BAT of lean mice. Chronic exposure to 33 degrees C depressed NE turnover in BAT of lean mice, but not in obese mice, whereas exposure to 14 degrees C accelerated NE turnover in both lean and obese mice. Lower sympathetic nervous system activity in BAT of obese mice at 25 degrees C is likely a major factor in their reduced nonshivering thermogenesis and resultant high efficiency of energy storage.     

Propranolol and pyrogen effects of shivering and nonshivering thermogenesis in rats.

Injection of bacterial endotoxin (Piromen) into unanesthetized rats elicited increases in shivering and nonshivering thermogenesis as well as in colonic temperature. In animals exposed to 24-25 degrees C, treatment with propranolol (a beta-adrenergic antagonist) markedly diminished the pyrogen-induced increases in oxygen consumption (heat production) and colonic temperature with little change occurring in shivering activity. In contrast, in rats exposed to mild cold (17-18 degrees C), propranolol did not significantly alter the magnitude of the pyrogen-evoked thermogenesis. Rather in these animals, shivering tended to increase when nonshivering thermogenesis was blocked. These data are interpreted as reflecting differential effects of pyrogen on the pathways controlling the two modes of heat production in the rat.     

Baroreflexive suppression of heat production and fall in body temperature following peripheral administration of vasopressin in rats

Intravenous injection of vasopressin (lysin-8-vasopressin, LVP) in unanesthetized rats at an ambient temperature of 18 degrees C caused a decrease in heat production (M) followed by a fall in colonic temperature (Tco1). These changes were preceded by an elevation of aortic blood pressure (BP) and bradycardia, and were related to the dosage of LVP administered. Temperature of the interscapular brown adipose tissue (BAT) significantly fell after LVP injections. Therefore, it can be said that the decrease in metabolism by the peripheral LVP is at least partly due to suppression of BAT thermogenesis. After bilateral sino-aortic deafferentation, however, the changes in these variables were greatly but not completely reduced except for the elevation of BP. LVP of 0.25 micrograms, more than sufficient to cause a significant elevation of BP when administered peripherally, had no effect on M and Tco1 when injected into the anterior hypothalamus. From these results, we conclude that the hypothermic effect of vasopressin administered peripherally is largely attributed to the baroreflexive suppression of nonshivering thermogenesis, and is not due to the action on the temperature regulatory centers. The slight but insignificant suppression of metabolism in the sinoaortic denervated rats following injection of LVP may be caused by a decreased blood flow to the thermogenic tissues.     

Effects of cold and immobilization stress on noradrenaline turnover in brown adipose tissue of rat

Noradrenaline (NA) turnover of the interscapular brown adipose tissue (BAT) was determined in order to evaluate a role of sympathetic NA of this tissue in an enhanced nonshivering thermogenesis which had been previously evidenced in the repetitively stressed rats by immobilization (daily 3-h immobilization for 4 weeks) and the cold-acclimated ones (5 degrees C, 4 weeks). The disappearance rate of NA from the BAT following blockade of NA synthesis with alpha-methyl-p-tyrosine was adopted for estimation of NA turnover of the tissue. Cold acclimation increased both fractional turnover rate (%/h) (k) and turnover rate (ng/(g BAT.h)). Repetitive immobilization stress also elevated turnover rate, but not k. In the warm non-stressed controls acute cold exposure to -5 degrees C and acute immobilization stress elevated the turnover rate. The effect of cold exposure was significantly greater than that of immobilization stress for both indices of NA turnover. In the cold-acclimated rats acute cold exposure increased k as well as turnover rate, but not acute immobilization stress. In the repetitively immobilized rats both acute cold exposure and acute immobilization stress elevated k and turnover rate. These results indicate that immobilization enhances sympathetic activity of thermogenic tissue, BAT. The results also suggest that the extent of sympathetic participation is not necessarily the same between the cold-acclimated and the stressed rats.     

Influence of ambient temperature on calorigenic action of thyroid hormones in young mice

In 5- and 7-day-old HAICR mice the calorigenic action of thyroxine (T₄) and triiodothyronine (T₃) was investigated at different ambient temperatures. After treating animals with 5 g T₄ or 1 g T₃ per g body weight and day, their oxygen consumption was compared with that of litter mate controls at 23°, 27°, 31° and 35°C. The hormone action was highly dependent on ambient temperature, 1 g T₃ being most effective. A thyroid hormone effect could never be observed at 31°C, the animals' nest temperature. By application of propranolol, which almost selectively blocks nonshivering thermogenesis (NST), we could show that T₃ increases minimal oxygen consumption (MOC) as well as the capacity for NST. In addition, it could be shown that also oxygen consumption of liver tissue of 5-day-old mice is elevated by preceding treatment with thyroid hormones. The ambient temperature effects are discussed in relation to the thermoregulatory situation of the mice during the early postnatal period.     

In vivo morphometry and functional morphology of brown adipose tissue by magnetic resonance imaging.

Brown adipose tissue (BAT) is the main effector of nonshivering thermogenesis and diet-induced thermogenesis in mammals. Assessment of the magnitude and perturbations of BAT deposits in the intact, living body would be of much relevance for quantitative studies of BAT functions, but such studies have been impossible to date. In this paper it is shown that magnetic resonance imaging (MRI) morphometry can provide the means for accurate, repeated determinations of the volume of BAT deposits in a living animal; moreover, tissue modifications due to acclimation at different ambient temperatures are revealed in vivo by MRI, which correlates with histology and ultrastructure. Furthermore, MRI differentiates areas of BAT responsive to acute adrenergic stimulation, thereby giving information on the thermogenetically active tissue in the intact animal. Therefore, MRI represents a reliable tool for correlative morphological and functional studies of BAT in the living animal.     

In vivo morphometry and functional morphology of brown adipose tissue by magnetic resonance imaging

Brown adipose tissue (BAT) is the main effector of nonshivering thermogenesis and diet-induced thermogenesis in mammals. Assessment of the magnitude and perturbations of BAT deposits in the intact, living body would be of much relevance for quantitative studies of BAT functions, but such studies have been impossible to date. In this paper it is shown that magnetic resonance imaging (MRI) morphometry can provide the means for accurate, repeated determinations of the volume of BAT deposits in a living animal; moreover, tissue modifications due to acclimation at different ambient temperatures are revealed in vivo by MRI, which correlates with histology and ultrastructure. Furthermore, MRI differentiates areas of BAT responsive to acute adrenergic stimulation, thereby giving information on the thermogenetically active tissue in the intact animal. Therefore, MRI represents a reliable tool for correlative morphological and functional studies of BAT in the living animal.     

Oxygen consumption of oestradiol-treated rats

Rectal temperature and oxygen consumption (üüO₂) were monitored in female rats acclimated either to cold or to thermoneutrality and with and without chronic administration of oestradiol. The hormone is known to inactivate brown adipose tissue (BAT) and to reduce its response to noradrenaline (NA). The role of sympathetic control was studied by administering NA or the adrenergic blocker propranolol. Oestradiol treatment did not affect rectal temperature in the states of acclimation to thermoneutrality and to cold, nor did it change the hypothermic response of cold-exposed rats to temporary food deprivation. In the cold-acclimated rats, both controls and oestradiol-treated animals exhibited similar degrees of metabolic reduction after propranolol administration in the cold and similar degrees of metabolic activation by NA at thermoneutrality. Rats acclimated to thermoneutrality showed a larger metabolic response to NA when treated with oestradiol. The results suggest that oestradiol, while inactivating the BAT response to NA, activates the NA responsiveness of other metabolically active tissues in cold-induced thermogenesis. The observation of a greater oxidative capacity in the kidney and the rectus abdominis muscle of oestradiol-treated, cold-acclimated rats would be in line with this proposal.