Heat Production In Brown Adipose Tissue Research Articles

Atractylenolide III from Atractylodes macrocephala Koidz promotes the activation of brown and white adipose tissue through SIRT1/PGC-1α signaling pathway

BackgroundHypothermia is a complex pathophysiological response that can be life-threatening in low-temperature environment because of impaired thermoregulation. However, there is currently no clinically effective drugs that can prevent or treat this disease. Brown adipose tissue (BAT) activation or browning of white adipose tissue (WAT) is a promising therapeutic strategy to prevent or treat hypothermia. Atractylodes macrocephala Koidz extract (AE) and its active compound Atractylenolide III (AIII) has been reported to regulate glycolipid metabolism, which might be relevant to BAT activation. However, the thermogenic effect and mechanism of AE and AIII on adipose tissues have not been explored yet. Therefore, this study firstly investigated the role of AE and AIII on hypothermia by promoting heat production of BAT and WAT. PurposeTo explore the anti-cold effect of AE and AIII in cold exposure model and explore their biological function and mechanism underlying thermogenesis. MethodsThe effect of thermogenesis and anti-hypothermia of AE and AIII on C57BL/6J mice were evaluated with several experiment in cold environment, such as toxicity test, cold exposure test, metabolism estimation, histology and immunohistochemistry, and protein expression. Additionally, BAT, inguinal WAT (iWAT) and brown adipocytes were utilized to explore the mechanism of AE and AIII on thermogenesis in vivo and in vitro. Finally, SIRT1 agonist and inhibitor in brown adipocytes to verify that AIII activated BAT through SIRT1/PGC-1α pathway. ResultsBoth AE and AⅢ could significantly maintain the core body temperature and body surface temperature of mice during cold exposure. Besides, AE and AⅢ could significantly improve the capacity of total antioxidant and glucose, lipid metabolism of mice. In addition, AE and AIII reduced mitochondrial membrane potential and ATP content both in BAT and brown adipocytes, and decreased the size of lipid droplets. Moreover, AE and AⅢ promoted the expression of proteins related to heat production in BAT and iWAT. And AIII might activate BAT via SIRT1/PGC-1α pathway. ConclusionAE and AⅢ were potential candidate drugs that treated hypothermia by improving the heat production capacity of the mice. Mechanistically, they may activate SIRT1/PGC-1α pathway, thus enhancing the function of BAT, and promoting the browning of iWAT, to act as anti-hypothermia candidate medicine.

SK-Channel Activation Alters Peripheral Metabolic Pathways in Mice, but Not Lipopolysaccharide-Induced Fever or Inflammation.

PurposePreviously, we have shown that CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), a pharmacological small-conductance calcium-activated potassium (SK)–channel positive modulator, antagonizes lipopolysaccharide (LPS)-induced cytokine expression in microglial cells. Here, we aimed to test its therapeutic potential for brain-controlled sickness symptoms, brain inflammatory response during LPS-induced systemic inflammation, and peripheral metabolic pathways in mice.MethodsMice were pretreated with CyPPA (15 mg/kg IP) 24 hours before and simultaneously with LPS stimulation (2.5 mg/kg IP), and the sickness response was recorded by a telemetric system for 24 hours. A second cohort of mice were euthanized 2 hours after CyPPA or solvent treatment to assess underlying CyPPA-induced mechanisms. Brain, blood, and liver samples were analyzed for inflammatory mediators or nucleotide concentrations using immunohistochemistry, real-time PCR and Western blot, or HPLC. Moreover, we investigated CyPPA-induced changes of UCP1 expression in brown adipose tissue (BAT)–explant cultures.ResultsCyPPA treatment did not affect LPS-induced fever, anorexia, adipsia, or expression profiles of inflammatory mediators in the hypothalamus or plasma or microglial reactivity to LPS (CD11b staining and CD68 mRNA expression). However, CyPPA alone induced a rise in core body temperature linked to heat production via altered metabolic pathways like reduced levels of adenosine, increased protein content, and increased UCP1 expression in BAT-explant cultures, but no alteration in ATP/ADP concentrations in the liver. CyPPA treatment was accompanied by altered pathways, including NFκB signaling, in the hypothalamus and cortex, while circulating cytokines remained unaltered.ConclusionOverall, while CyPPA has promise as a treatment strategy, in particular according to results from in vitro experiments, we did not reveal anti-inflammatory effects during severe LPS-induced systemic inflammation. Interestingly, we found that CyPPA alters metabolic pathways inducing short hyperthermia, most likely due to increased energy turnover in the liver and heat production in BAT.

Effect of sex and sex steroids on brown adipose tissue heat production in humans

Retrospective studies suggest that women have more active brown adipose tissue (BAT) than men, but little is known of the effect of fluctuating sex steroids across the menstrual cycle on thermogenesis in women. To characterise the effects of sex and sex steroids on BAT activity we recruited healthy weight men (n = 14) and women at two stages of the menstrual cycle (luteal, n = 9; follicular, n = 11). Infrared thermography measured supraclavicular temperature to index BAT thermogenesis in response to both cold (immersion of one hand in water at 15°C) and meal (Ensure, 10 kcal/kg body weight) stimuli. Adaptive BAT temperature responses were greater (P < 0.05) in women than men, irrespective of stage of menstrual cycle. Whereas during cold exposure, the increase in BAT temperature was abrogated (P < 0.05) in women during follicular phase compared to men and women during luteal phase. Plasma concentrations of progesterone, 17β-estradiol, testosterone and cortisol were measured. Regression analyses demonstrated that baseline BAT temperature was positively correlated (P < 0.05) with progesterone levels, but was inversely associated (P < 0.05) with cortisol concentration. Both cold- and meal-induced changes in BAT temperature mildly correlated (P = 0.07; P < 0.05) with 17β-estradiol levels, but not with testosterone concentrations. Baseline supraclavicular temperature is elevated in women during the luteal phase of the menstrual cycle, which correlated with elevated progesterone concentrations. Women exhibited greater thermogenic responses than men, irrespective of the state of the menstrual cycle, which was associated with plasma levels of 17β-estradiol. We conclude that sex steroids may regulate BAT thermogenesis in healthy adults.

Switching on the furnace: Regulation of heat production in brown adipose tissue

Endothermy requires a source of endogenous heat production. In birds, this is derived primarily from shivering, but in mammals it is mostly non-shivering thermogenesis (NST). Brown adipose tissue (BAT) is a specialized tissue found in Eutherian mammals that is the source of most NST. Heat production in BAT depends primarily on the activity of uncoupling protein 1 (UCP1), which decouples transport of protons across the inner mitochondrial membrane from synthesis of ATP. UCP1 and hence heat production of BAT is regulated by many factors. In this paper we discuss the main factors activating UCP1 and increasing heat production. Probably the most well-known activator is the catecholamine norepinephrine (NE) which is released from sympathetic nerve endings and binds to adrenergic receptors that are abundantly expressed on BAT. NE stimulates release of free-fatty acids. It was previously thought that such FFAs were essential for activation of UCP1. However recent work has suggested intracellular lipolysis is not essential and FFAs can be derived from extracellular sources. Thyroid hormones also exert impacts on metabolic rate via effects on brown adipocytes which express type 2 deiodinase. Knocking out DIO2 makes mice cold intolerant. Parathyroid hormone appears to also be a potent regulator of BAT activity and may be an important mediator of elevated expenditure during cancer cachexia, although this is disputed by observations that cachexia wasting is not blunted in UCP1 KO mice. Cardiac natriuretic peptides have also been implicated in regulating BAT thermogenesis and the interconversion of beige adipocytes from their white to brown form. Activation of BAT thermogenesis may be an important component of the post-ingestion rise in heat production. Recent work suggests the gut derived hormone secretin may play a key role in this effect, directly linking BAT activation to the alimentary tract. Not only gut hormones but also metabolites derived from gut microbiota such as butyrate may be an important activator of BAT during cold exposure. Additional regulatory factors include bone morphogenic proteins, fibroblast growth factor 21, Vascular endothelial growth factors and transient receptor potential vanilloid receptors which are important components of thermal sensing and hence how brown adipose tissue responds to the cold. In the future the main challenge is to understand how these regulatory factors combine with each other and with inhibitory factors to control heat production from BAT, and what their relative importance is in differing circumstances. Knocking out UCP1 has revealed other sources of heat production in BAT including creatine-dependent cycles and a futile cycle of Ca2+ shuttling into and out of the endoplasmic reticulum via the SERCA and ryanodine receptors.

GPR120 controls neonatal brown adipose tissue thermogenic induction.

Adaptive induction of thermogenesis in brown adipose tissue (BAT) is essential for the survival of mammals after birth. We show here that G protein-coupled receptor protein 120 (GPR120) expression is dramatically induced after birth in mouse BAT. GPR120 expression in neonatal BAT is the highest among GPR120-expressing tissues in the mouse at any developmental stage tested. The induction of GPR120 in neonatal BAT is caused by postnatal thermal stress rather than by the initiation of suckling. GPR120-null neonates were found to be relatively intolerant to cold: close to one-third did not survive at 21°C, but all such pups survived at 25°C. Heat production in BAT was significantly impaired in GPR120-null pups. Deficiency in GPR120 did not modify brown adipocyte morphology or the anatomical architecture of BAT, as assessed by electron microscopy, but instead impaired the expression of uncoupling protein-1 and the fatty acid oxidation capacity of neonatal BAT. Moreover, GPR120 deficiency impaired fibroblast growth factor 21 (FGF21) gene expression in BAT and reduced plasma FGF21 levels. These results indicate that GPR120 is essential for neonatal adaptive thermogenesis.

ZW290 Increases Cold Tolerance by Inducing Thermogenesis via the Upregulation of Uncoupling Protein 1 in Brown Adipose Tissue In Vitro and In Vivo.

To provide molecular evidence on the thermogenic mechanism of primary brown adipocytes, western blot analysis was used to detect brown adipose tissue (BAT)-specific gene expressions. BAT protects the mammals from hypothermia injury with a large amount of mitochondria and high expression of uncoupling Protein 1 (UCP1), which is the vital protein to determine the heat production in BAT. In our previous study, the compound ZW290 (the structure shown in Fig. 1) was obtained by molecular docking with a UCP1 inducer. In the present study, ZW290 not only significantly upregulated the expression of UCP1 protein (p < 0.01) and its related signaling pathway in the primary brown adipocytes, but also remarkably decreased the mitochondrial membrane potential and the concentration of adenosine triphosphate (ATP) (p < 0.01). Kunming (KM) mice were kept under acute cold exposure (-20°C) to evaluate the preventive and protective effects of ZW290 on cold injury, and revealed its regulating mechanism in vitro. The rectal and body temperatures of ZW290-treated mice were significantly higher than those of the control (or model) group both at room temperature and at -20°C (p < 0.001). Hematoxylin-eosin (HE) staining and immunohistochemistry indicated that ZW290 notably decreased the size of lipid droplets in BAT and increased the content of mitochondria and the expression of UCP1 in BAT and white adipose tissue (WAT). Furthermore, the survival rate showed that ZW290 could prolong the overall survival of mice. Therefore, we obtained the conclusion that ZW290 might transform energy into heat by inhibiting ATP synthesis and increasing the expression of UCP1. Additionally, ZW290 may enhance cold tolerance by increasing heat production through increasing the content of mitochondria and the expression of UCP1 in BAT and WAT.

Skeletal muscle non‐shivering thermogenesis in hibernating Arctic Ground Squirrels

All mammals depend on heat producing mechanisms to maintain homeostasis. Skeletal muscle shivering and brown adipose tissue (BAT) uncoupling through the expression of uncoupling protein 1 (UCP‐1) are the identified major sources of heat production, though recently, skeletal muscle has also been highlighted as a thermogenic source. Skeletal muscle nonshivering heat production occurs via sarcolipin (SLN) uncoupling of sarcoendoplasmic reticulum (SR) calcium ATPase (SERCA)‐mediated ATP hydrolysis. SLN may play a significant role in hibernating animals due to the wide temperature range that requires regulation. A thermoregulatory mechanism needs to be in place to suppress heat production during hibernation and also initiate rapid thermogenesis during arousal. We hypothesized that skeletal muscle uncoupling driven by SLN activity is a significant source of thermogenesis and inhibiting this pathway can alter the metabolic rate during hibernation in Arctic ground squirrels (AGS). Specifically, this work aimed to elucidate the role of skeletal muscle SLN uncoupling and its connection with BAT heat production in thermoregulation and metabolic control during temperature fluctuations. AGS were treated with inhibitors of BAT‐uncoupling or skeletal muscle‐uncoupling during hibernation to assess skeletal muscle and BAT ability to aid in heat production. Rate of temperature increase and changes in VO2 were compared to internal controls during inter‐bout arousals to quantify the effect of suppressing BAT or skeletal muscle uncoupling throughout hibernation. Results show that suppressing skeletal muscle uncoupling by SLN causes a significant reduction in metabolic rate during AGS rewarming. Interestingly, inhibition of BAT thermogenesis did not reduce metabolic rate. Inhibition of thermogenic sources highlighted the importance of SLN uncoupling and metabolism in thermogenesis and systemic thermoregulation. Thermogenesis control is directly linked to metabolic rate and energy loss regulation, and thus influencing thermoregulation processes has the potential for translation to innovative treatments for obesity and other diseases and conditions relevant to metabolism.Support or Funding InformationResearch reported in this publication was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under grant number P20GM103395. The content is solely the responsibility of the authors and does not necessarily reflect the official views of the NIH.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Recruiting Brown Adipose Tissue in Human Obesity.

Obesity remains a major biomedical challenge with its associated diseases, particularly insulin resistance and type 2 diabetes, imposing a substantial and increasing burden on health care systems. In the U.S., one-third of adults are classed as obese (BMI ≥30), while in the U.K., which has one of the highest incidence rates in Europe, 25% are obese. Conceptually, the treatment of obesity is simple: energy expenditure must exceed energy intake. In the late 1970s it was proposed, primarily on the basis of studies on rats and mice, that reduced expenditure on adaptive heat production (thermogenesis) associated with a specialized fat tissue—brown adipose tissue (BAT)—is central to the development of obesity. Correspondingly, for a period, stimulation of heat production in BAT was seen as a potential therapeutic route for reversing obesity, and there was a search for agents that would stimulate the activity of the tissue. In the four centuries following its identification, different roles have been attributed to BAT, but in the early 1960s the tissue was firmly identified as a thermogenic organ generating heat through nonshivering mechanisms. Heat is produced by dissipation of the proton gradient across the mitochondrial inner membrane resulting in the uncoupling of oxidative phosphorylation (1). This process, which is critically dependent on the mitochondrial uncoupling protein 1 (UCP-1), is stimulated by noradrenaline from the sympathetic innervation acting through β3-adrenoceptors (1). The …

Using the Human ″Heater″ to Burn Fat

Mammals have several mechanisms to maintain homeostasis with respect to body temperature. One such mechanism is brown adipose tissue (BAT), which when activated by cold, functions as a “heater” by converting chemical energy into heat. This reaction is fueled by lipids from both BAT and white adipose tissue, and has the potential to cause significant weight loss. BAT is found in the upper back, neck, between the collarbone and shoulder, and along the spine. Estrogen related receptor gamma (ERRg) is a protein that binds to DNA and regulates genes important for heat production in BAT. The structure of ERRg consists of multiple domains, including a DNA binding domain (DBD) and a regulatory ligand binding domain (LBD). The activity of ERRg is regulated by proteins binding to the LBD; these proteins can either activate gene expression or repress it. It was recently discovered that a cold‐induced protein, Gadd45g, activates ERRg. However, it is unknown how these two proteins interact. Using 3D printing technology, the Francis Parker SMART (Students Modeling A Research Topic) Team modeled the LBD of ERRg and its protein activator Gadd45g. Supported by a grant from the HHMI Pre‐ College Program.

Carnitine is necessary to maintain the phenotype and function of brown adipose tissue

The juvenile visceral steatosis (JVS) mouse is a mutant strain with an inherited systemic carnitine deficiency. Mice of this strain show clinical signs attributable to impaired heat production and disturbed energy production. Brown adipose tissue (BAT) is the primary site of non-shivering thermogenesis in the presence of uncoupling protein-1 (UCP-1) in rodents and humans, especially in infants. To investigate the possible cause of impaired heat production in BAT, we studied the morphological features, carnitine concentration, and UCP-1 production of BAT in JVS mice. The effect of carnitine administration on these parameters was also examined. JVS mice aged 5 or 10 days (60 each) and age-matched control mice were used in this study, along with 10-day-old JVS mice treated subcutaneously with L-carnitine once a day between postpartum days 5 and 10. JVS mice showed lower body temperatures and lower concentrations of carnitine in BAT. Morphologically, BAT cells in JVS mice contained large lipid vacuoles and small mitochondria, similar to those present in white adipose tissue cells. In addition, UCP-1 mRNA and protein expression levels were significantly reduced in JVS as compared with control mice. Carnitine treatment resulted in significant increases in body temperature and carnitine concentrations in BAT, together with the recovery of normal morphological features. UCP-1 mRNA and protein expression levels were also significantly increased. These findings strongly suggest that carnitine is essential for maintaining the function and morphology of BAT.

Effect of denervation on the generation of glycerol‐3‐phosphate (G3P) in brown adipose tissue (BAT) from rats adapted to a cafeteria diet

Hydrolysis of stored triacylglycerol (TAG) to produce fatty acids is an obligatory step in the process of activation of heat production in BAT in both nonshivering and diet‐induced thermogenesis. There are three pathways for generation of the G3P needed for TAG synthesis and storage: glycolysis, glyceroneogenesis and glycerokinase (GyK) activity. Here we investigated the effect of BAT denervation on G3P synthesis in rats adapted to a cafeteria diet. Experiments were performed 7 days after surgical hemidenervation of BAT from rats previously fed for 3 weeks a cafeteria diet. BAT denervation blocked the increase in GyK activity (6.8±0.9 vs 14.5±1.7 nmol.mg protein−1. min−1), but did not effect the increase in glucose uptake (3.74±0.68 vs 3.84±0.47 ng.mg tissue−1. min−1) and the decrease in glyceroneogenesis, evaluated by PEPCK activity (5.8±0.7 vs 5.1±0.8 nmol.mg protein−1. min−1) and by the rate of incorporation of 14C‐pyruvate into TAG‐glycerol (2.2±0.1 vs 2.1±0.2 nmol.g BAT−1. 2h−1), induced by cafeteria diet. The data suggest that in BAT from cafeteria diet‐fed rats the generation of G3P from glucose (via glucose) and glyceroneogenesis, in contrast to GyK, are not under control of the sympathetic nervous system. Financial Support FAPESP, CNPq.

Ghrelin affects gastrectomy-induced decrease in UCP1 and β 3-AR mRNA expression in mice

In this study we investigated the effects of gastrectomy (Gx) and of the gastric hormone, ghrelin, on the expression of proteins in brown adipose tissue (BAT) that are thought to be involved in thermogenesis. Heat production in BAT is known to depend upon activation and increased expression of β 3-adrenergic receptors (β 3-AR) and the consequent up-regulation of uncoupling protein 1 (UCP1). Mice were subjected to Gx or sham operation. One week later they started to receive daily subcutaneous injections of either saline or ghrelin (12 nmol) for two or eight weeks. Neither Gx nor ghrelin affected daily food intake. Gx did not lower body weight gain (except during the first post-operative week) but Gx mice responded to eight weeks of ghrelin treatment with a greater body weight increase (37%, p < 0.05) than saline-injected Gx mice; sham-operated mice did not respond to ghrelin. Gx resulted in a greatly reduced expression of both UCP1 and β 3-AR mRNA in BAT (50% reduction or more, p < 0.01) compared to sham-operated mice. Eight weeks of ghrelin treatment raised the UCP1 as well as the β 3-AR mRNA expression in the Gx mice, whereas two weeks of ghrelin treatment decreased UCP1 and β 3-AR mRNA expression compared to Gx mice receiving saline. In fact, mRNA expression in Gx mice after treatment with ghrelin for eight weeks was similar to that in saline-treated sham-operated mice. Ghrelin did not affect UCP1 and β 3-AR mRNA in sham-operated mice neither two nor eight weeks after the operation. The results suggest 1) that signals from the stomach stimulate BAT UCP1 (and possibly thermogenesis) and 2) that ghrelin may contribute to the control of UCP1 expression.

PGC-1β: A Regulator of Mitochondrial Function with Subtle Roles in Energy Metabolism

The evolutionary success of mammals is owed in part to their ability to adjust their metabolism to the demands of their environment. For instance, mice faced with dropping external temperatures crank up the output of a specialized type of fat—called brown adipose tissue (BAT) —that generates heat. Faced with a lack of food, they turn on the production of glucose, a highly energetic sugar, by the liver. Both of these adaptive responses depend on a nuclear protein called PGC-1α. PGC-1α simultaneously increases the expression of genes acting at multiple steps along the heat- or glucose-production pathways, thereby quickly boosting the pathways’ efficacy. A related protein, PGC-1β, shares many of PGC-1α’s functional characteristics: for instance, both proteins can, when overexpressed in mice, increase the activity of mitochondria, the intracellular organelles that turn sugars and fats into heat or the cellular fuel ATP. To determine what role PGC-1β normally plays in energy metabolism, Christopher Lelliott, Gema Medina-Gomez, Antonio Vidal-Puig, and their colleagues created mice lacking the PGC-1β gene. Their recent study of the resulting phenotype shows that PGC-1β has different functions than PGC-1α and plays a subtler role than PGC-1α in energy metabolism. As expected from PGC-1β’s ability to stimulate mitochondrial function, the loss of PGC-1β decreased the transcription of genes encoding many of the mitochondrial proteins that generate ATP and heat. Yet the mutant mice appeared essentially healthy under normal conditions. Still, a slight impairment of mitochondrial function might lead to some metabolic imbalance, for instance obesity, since mitochondria burn energy that would otherwise be stored as fat. But the mutant mice were in fact smaller and leaner than their wild-type counterparts. This phenotype did not reflect differences in appetite or digestion, since the mutants ate and eliminated similar amounts of food as wild types. Instead, the mutants had higher metabolic rates than wild types at ambient temperature: they burnt more calories than wild types did to sustain basal physiological functions such as respiration, heartbeat, and body temperature, which would suggest that their mitochondrial functions were increased, rather than decreased. The explanation for these counterintuitive findings is that loss of PGC-1β led to increased expression of PGC-1α in fat tissues. The researchers propose that the increase in PGC-1α, which can stimulate heat production in BAT, compensates for the loss of PGC-1β at ambient temperature. To remove the compensatory effect of PGC-1α, the researchers measured the metabolic rate of mutants housed at 30 °C, a temperature close to body temperature, at which PGC-1α expression is largely abolished. At this temperature, mice lacking PGC-1β had a reduced metabolic rate, suggesting that PGC-1β can contribute to maintaining normal metabolic rates. The mutant mice were able to withstand and adapt to cold, presumably because cold temperatures could still trigger PGC-1α expression. However, when mutant mice that were acclimatized to 4 °C were further stimulated by norepinephrine, a neurotransmitter that normally induces BAT to respond to cold, their BAT heat output was blunted compared to that of wild-type BAT. Therefore, PGC-1β must normally play a role in thermal regulation, though its role is obscured by PGC-1α’s induction at low temperatures. In other tissues such as liver, muscle, and heart, loss of PGC-1β did not trigger PGC-1α expression, which made the role of PGC-1β easier to discern. In the liver, PGC-1β proved necessary for the proper disposal of cholesterol and other lipid forms when mice were fed a diet rich in saturated fat. In muscles and heart, PGC-1β was found necessary to maintain a normal number of mitochondria. But even with a reduced mitochondrial count, the hearts of mice lacking PGC-1β functioned normally. Their only anomaly was a failure to increase their pulse rate properly when challenged with the heart stimulant dobutamine. By comparison, mice lacking PGC-1α develop severe heart failure. These observations show that although PGC-1β and PGC-1α share sequence and functional similarities and are expressed in the same tissues, they cannot completely substitute for one another. The researchers propose that PGC-1β maintains basal metabolic functions, whereas PGC-1α allows the body to step up it response to high energetic demands.

Brown fat thermogenesis and cardiac rate regulation during cold challenge in infant rats.

Infants rats depend on heat production by brown adipose tissue (BAT) during cold challenge. Although it has been suggested that BAT thermogenesis protects the heart in the cold, the relationship of BAT activation to cardiac rate has not been examined directly. In the first experiment, the cardiac rate of 2- and 7- to 8-day-old rat pups was monitored during moderate and extreme cold challenge. Pups at both ages maintained cardiac rate during moderate cold challenge while BAT thermogenesis was increasing. In contrast, cooling to air temperatures at which BAT thermogenesis could increase no further resulted in pronounced bradycardia. In the second experiment, ganglionic blockade was used to eliminate BAT heat production and autonomic control of the heart in 7- to 8-day olds. Blockade suppressed BAT thermogenesis in the cold and led to pronounced decreases in interscapular temperature and cardiac rate. These data suggest that cardiac rate in infant rats is modulated both by the autonomic nervous system and BAT thermogenesis.

1905 Capsaicin attenuates the noradrenaline-induced temperature increase in brown adipose tissue in the rat

E series prostaglandins (PGE) are known to elicit potent hyperthermia when injected into the anterior hypothalamic preoptic area (POAH) in rats, but the effector mechanisms mediating the rise in temperature are not well defined. In the present study, microinjection of PGE2 into the POAH dose-dependently increased non-shivering thermogenesis in brown adipose tissue (BAT) in urethananesthetized rats, bringing about a marked and sustained rise in interscapular BAT (IBAT) and core temperatures. The effect of intra-POAH PGE2 injection on IBAT and core temperatures could be blocked by systemic pretreatment with the sympathetic ganglionic blocker chlorisondamine chloride or the β-adrenergic receptor blocker propranolol, thus implicating the involvement of the sympathetic system. Furthermore, the increase in IBAT and core temperatures induced by intra-POAH PGE2 could be blocked by prior injection of the local anesthetic procaine or the GABA receptor agonist muscimol into the ipsilateral ventromedial hypothalamic nucleus (VMH). Taken together, the results suggest that PGE2 increases body temperature by acting in the POAH to stimulate heat production in BAT via a sympathetic efferent mechanism located in the VMH.

Activation of brown adipose tissue thermogenesis by chemical stimulation of the hypothalamic supraoptic nucleus

Glutamate microinjection (1 M, 250 nl) into the hypothalamic supraoptic nucleus (SON) stimulated heat production in brown adipose tissue (BAT) and caused a rapid and sustained increase in interscapular BAT and core temperatures in urethane-anaesthetized rats. This effect was blocked by intraperitoneal pretreatment with a sympathetic ganglionic blocker, chlorisondamine chloride (2.5 mg/kg), or a ß-adrenergic receptor blocker, propranolol (2.5 mg/kg), but not by prior hypophysectomy or intracerebroventricular pretreatment with specific receptor blockers to vasopressin (d(CH 2)5[Tyr(Me) 2]AVP, 5 μg) or oxytocin (d(CH 25[Tyr(Me) 2,Thr 4,Tyr-NH 2 9]OVT, 5 μg). The results demonstrate that stimulation of SON cells with glutamate elicits a non-vasopressinergic/non-oxytocinergic neural signal that can bring about a sympathetically-mediated increase in BAT thermogenesis. Heat production in BAT is an important mechanism of thermal protection during cold stimulation, and there is evidence that osmotic stimulation can influence thermoregulation. SON neurons play a major role in osmoregulation via release of the peptide hormones vasopressin and oxytocin. The present results suggest the possibility that apart from releasing peptide hormones for osmoregulation, SON neurons might be involved in mediating the effect of osmotic stimulation on thermoregulatory responses involved in thermal adaptation.

Activation of brown adipose tissue thermogenesis by chemical stimulation of the posterior hypothalamus

The posterior hypothalamus (PH) is involved in the generation of behavioral thermoregulatory responses, but the importance of the PH in the control of autonomic thermoregulatory responses such as heat production in brown adipose tissue (BAT) is not well defined. In the present study, selective stimulation of PH neurons by local application of the excitatory amino acid glutamate (250 nl of 1 M solution, unilaterally) caused a sharp, transient increase in interscapular BAT (IBAT) and core temperature in urethane-anesthetized rats. This effect was blocked by pretreatment with the sympathetic ganglionic blocker, chlorisondamine chloride (2 mg/kg) or the β-adrenergic receptor blocker, propranolol (2 mg/kg), implicating the involvement of the sympathetic system. The effect of intra-PH injection of glutamate on IBAT and core temperatures could be mimicked by injection of the γ-aminobutyric acid (GABA) receptor antagonist, bicucullin methiodide (BMI, 50 ng), into the same PH site. This effect of BMI could be blocked by co-injection of the GABA A receptor agonist, muscimol (25 ng). Further, BMI co-injection potentiated the effect of intra-PH injection of glutamate on IBAT and core temperatures. Conversely, muscimol co-injection prevented the stimulatory effect of intra-PH injection of glutamate. Taken together, the results indicate that direct chemical stimulation of neurons in the PH can activate an autonomic mechanism controlling heat production in BAT. Further, they suggest the neural mechanism in the PH mediating this effect is tonically inhibited by GABA, as blockade of GABAergic function in the PH produces an effect similar to that observed after direct stimulation of PH neurons with glutamate. Earlier studies have shown that the GABA functions in the PH to tonically inhibit a sympathoexcitatory neural mechanism recruited in response to stress, and that stress is capable of stimulating thermogenesis via the sympathetic outflow. On the basis of these observations and the results reported here, we speculate that the effect of stress on thermogenesis may involve disinhibition of a GABA-regulated sympathoexcitatory neural mechanism located in the PH.

Injection of prostaglandin E 2 into the anterior hypothalamic preoptic area activates brown adipose tissue thermogenesis in the rat

E series prostaglandins (PGE) are known to elicit potent hyperthermia when injected into the anterior hypothalamic preoptic area (POAH) in rats, but the effector mechanisms mediating the rise in temperature are not well defined. In the present study, microinjection of PGE 2 into the POAH dose-dependently increased non-shivering thermogenesis in brown adipose tissue (BAT) in urethananesthetized rats, bringing about a marked and sustained rise in interscapular BAT (IBAT) and core temperatures. The effect of intra-POAH PGE 2 injection on IBAT and core temperatures could be blocked by systemic pretreatment with the sympathetic ganglionic blocker chlorisondamine chloride or the β-adrenergic receptor blocker propranolol, thus implicating the involvement of the sympathetic system. Furthermore, the increase in IBAT and core temperatures induced by intra-POAH PGE 2 could be blocked by prior injection of the local anesthetic procaine or the GABA receptor agonist muscimol into the ipsilateral ventromedial hypothalamic nucleus (VMH). Taken together, the results suggest that PGE 2 increases body temperature by acting in the POAH to stimulate heat production in BAT via a sympathetic efferent mechanism located in the VMH.

The effects of essential fatty acid deficiency on brown adipose tissue activity in rats maintained at thermal neutrality

1. 1. The consequences of essential fatty acid (EFA) deficiency on the resting metabolism, food efficiency and brown adipose tissue (BAT) thermogenic activity were examined in rats maintained at thermal neutrality (28°C). 2. 2. Weanling male Long-Evans rats were fed a hypolipidic semi-purified diet (control diet: 2% sunflower oil; EFA-deficient diet: 2% hydrogenated coconut oil) for 9 weeks. 3. 3. They were kept at 28°C for the last 5 weeks. Compared to controls, in EFA-deficient rats the growth shortfall reached 21% at killing. 4. 4. As food intake was the same in EFA-deficient and control rats, food efficiency was thus decreased by 40%. 5. 5. Resting metabolism expressed per surface unit was 15% increased. 6. 6. Non-renal water loss was increased by 88%. 7. 7. BAT weight was 28% decreased but total and mitochondrial proteins were not modified. 8. 8. Heat production capacity, tested by GDP binding per BAT was 69% increased in BAT of deficient rats. 9. 9. The stimulation of BAT was established by two other tests: GDP inhibition of mitochondrial O 2 consumption and swelling of mitochondria. 10. 10. It is suggested that the observed enhancement of resting metabolism in EFA-deficient rats is, in part, due to an activation of heat production in BAT.

Ventromedial hypothalamic stimulation accelerates norepinephrine turnover in brown adipose tissue of rats

To establish a functional link between the ventromedial hypothalamus (VMH) and brown adipose tissue (BAT), effects of electrical stimulation of the VMH and the lateral hypothalamus (LH) on norepinephrine (NE) turnover in the interscapular BAT were examined in rats. Stimulation of the VMH elicited about 3-fold increase in the rate of NE turnover in BAT, whereas stimulation of the LH had no appreciable effects. The effect of VMH stimulation was abolished after sympathetic ganglion blockade or by surgical sympathetic denervation of BAT. It was concluded that there is a sympathetic nerve-mediated connection between the VMH and BAT, and that stimulation of the VMH induces metabolic activation and heat production in BAT through an increase in sympathetic nerve activity.