Interscapular brown adipose tissue blood flow in the rat

The xenon clearance method was adapted to continuous measurement of interscapular brown adipose tissue (ISBAT) blood flow in anaesthetized rats.The ISBAT-blood partition coefficient for xenon was determined to 3.6 ml·g^–1. The blood flow values obtained by Xe clearance were compared with flow values obtained concomitantly by the microsphere technique in 17 cold acclimated rats, at ISBAT blood flows between 0.1 and 6 ml·g^–1·min^–1. Variations in blood flows were obtained by infusion of noradrenaline at different rates.The blood flow values obtained from the xenon clearance method showed a close correlation to the blood flow values determined with microspheres.Y=0.98.X+0.15 (r=0.96,P<0.001).The Xe clearance method has the advantages compared to the microsphere technique that it permits continuous monitoring of the blood flow and does not require the sacrifice of the animal.     

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.     

大鼠白色和棕色脂肪来源的间充质干细胞成脂分化特性的比较

目的探讨白色脂肪组织(WAT)和棕色脂肪组织(BAT)来源的间充质干细胞成脂分化特性的差异。方法雄性SD大鼠15只,3只用于细胞分离培养,12只用于细胞移植。体外分离培养WAT和BAT两种来源的脂肪干细胞,用油红O染色检测两种干细胞的成脂分化率,用免疫荧光技术检测成脂诱导、分化后的细胞是棕色脂肪细胞还是白色脂肪细胞。4’6-二脒基-2-苯基吲哚(DAPI)标记两种来源的干细胞后移植至腹股沟区,分别在第1、2、3周取材,免疫荧光技术检测植入细胞的分化趋向。结果 WAT来源的干细胞增殖速度明显快于BAT来源的干细胞,前者成脂分化率为0.205±0.069,后者为0.165±0.053,两种干细胞的成脂诱导率差异无统计学意义(P0.05)。两种干细胞分别植入体内后,在第1、2、3周发现,两种干细胞均表达棕色脂肪特异性蛋白解耦联蛋白1(UCP1)。结论 WAT和BAT来源的干细胞在体外及体内诱导成脂后均分化为棕色脂肪细胞。     

Lack of diet-induced thermogenesis in brown adipose tissue of obese medial hypothalamic-lesioned rats

Radiofrequency heat lesions were made in the medial hypothalamus of 12-week old male and female Holtzman rats. Two to three days later rats were offered a palatable cafeteria diet in addition to chow or were fed chow alone for the next 3-4 weeks. Male lesioned rats were only slightly hyperphagic on the chow diet and gained little extra weight. When fed the cafeteria diet, energy intake of male lesioned rats almost doubled in comparison with chow-fed lesioned rats and a very rapid extra weight gain occurred. Despite the marked hyperphagia, thermogenesis in brown adipose tissue was suppressed in the cafeteria-fed lesioned rats, as indicated by low mitochondrial guanosine diphosphate (GDP) binding. In female rats, lesions induced much greater hyperphagia and body weight gain than in male rats, particularly when they ate the cafeteria diet. Again, thermogenesis in brown adipose tissue was suppressed in the cafeteria-fed female lesioned rats. The proportion of energy derived from carbohydrate was not altered by the cafeteria diet in either male or female rats, whether lesioned or not, but there was an increase in the proportion of energy derived from fat at the expense of protein. No sex differences in food selection were observed. The accumulation of body fat was always greater in female lesioned rats than in male lesioned rats for similar food intakes. It is concluded that medial hypothalamic lesions prevent the normal occurrence of diet-induced thermogenesis in brown adipose tissue despite extreme overeating by the rats of a palatable cafeteria diet.     

Temperature- and capsaicin-sensitive nerve fibers in brown adipose tissue attenuate thermogenesis in the rat

 We examined the function of putative sensory fibers that are contained in intercostal nerves and innervate interscapular brown adipose tissue (IBAT) in urethane-anesthetized rats. Warming the IBAT to 40–44°C with two small heaters placed bilaterally on the skin above it attenuated the subsequent noradrenaline-induced thermogenesis (NIT) of the IBAT. In this range of warming, higher IBAT temperatures resulted in more attenuation. Denervation of IBAT blocked the effect of thermal stimulation on the NIT. Thus, activation of nerve fibers in IBAT that are sensitive to warmth or to the nociceptive effects of heat probably attenuated the NIT. Since the putative sensory fibers in the IBAT contain calcitonin gene-related peptide (CGRP) and substance P, which are thought to act in peripheral tissues, we tested the effects of injection of these neuropeptides into the IBAT. Administration of 5.2 nmol CGRP but not substance P or vehicle saline mimicked the effect of thermal stimulation of IBAT. As the neuropeptide-containing primary sensory neurons are characterized by their sensitivity to capsaicin, we also tested its effects (1 mg/kg, s.c.) and found that it also attenuated the NIT. Denervation of the IBAT or pretreatment with capsazepine, a capsaicin receptor antagonist, blocked the effect of capsaicin. We propose that temperature- and capsaicin-sensitive nerve fibers release CGRP to attenuate the NIT of brown adipocytes. Received: 14 May 1998 / Received after revision: 6 August 1998 / Accepted: 11 August 1998     

Comparison of DNA synthesis in white and brown adipose tissue in rats with ventromedial hypothalamic lesions

Ventromedial hypothalamic (VMH) lesions cause excessive fat accumulation in white adipose tissue (WAT), and brown adipose tissue (BAT); however, little information is available on whether or not cell proliferation occurs in WAT and BAT after VMH lesioning. In this study, we determined the DNA content and thymidine incorporation in unilateral parametrial WAT and interscapular BAT 0, 1, 3, and 7 days after VMH lesioning, and examined the mechanism of increased DNA content in WAT. In rats with VMH lesions, the weight of WAT and BAT had increased significantly at 7 days, and the DNA content and thymidine incorporation of WAT had increased significantly at 3 days and continued to increase for up to 7 days, while those of BAT did not increase for as long as 7 days after VMH lesioning. Restricted food intake according to the pair-feeding method partially inhibited the increased DNA content in WAT. The increased DNA content in WAT was mostly restored but not completely by the administration of anti-insulin antibody, and by administration of propranolol, a -adrenergic blocker. The results demonstrated that VMH lesions induced DNA synthesis in WAT early after VMH lesioning, but did not induce DNA synthesis in BAT, and suggested that either hyperinsulinemia or a -adrenergic receptor mechanism or both may be responsible for the increased DNA content in WAT.     

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.     

Nicotine suppresses energy storage through activation of sympathetic outflow to brown adipose tissue via corticotropin-releasing factor type 1 receptor

Nicotine is known to stimulate energy expenditure, although the precise mechanism is unclear. To clarify the involvement of corticotropin-releasing factor (CRF) in the mechanism by which nicotine increases energy expenditure, the effect of intraperitoneal injection of nicotine (0.1 or 0.5 mg/kg) on the release of noradrenaline (NA), a stimulator of thermogenesis, in brown adipose tissue (BAT) important for energy expenditure was examined in rats. We also examined the effects of CRF receptor subtype antagonists on the nicotine-induced change in BAT NA release. Nicotine significantly increased BAT NA release at a dose of 0.5 mg/kg, and the increase was completely blocked by antalarmin, a CRF type 1 receptor antagonist, but not by antisauvagine-30, a CRF type 2 receptor antagonist. These results suggest that nicotine increases energy expenditure by activating BAT function, and that CRF type 1 receptors are involved in the mechanism by which nicotine affects energy balance.     

Functional disconnection of brown adipose tissue in hypothalamic obesity in rats

The metabolic responses to electrical nerve stimulation, norepinephrine or octanoate additions were studied using continuous monitoring of NAD(P)H/NADP redox state by reflexion spectrophotometry of interscapular brown adipose tissues from control and ventromedial hypothalamic (VMH) lesioned rats. The responses to these stimuli were all greatly decreased already 3 days after VMH lesions, indicating a reduced cell capacity to oxidize free fatty acids. Measurements of interscapular brown adipose tissue composition 4–5 weeks after VMH lesions showed a decrease of both DNA concentration and total content, indicating some tissue involution.It is concluded that the involvement of the ventromedial bypothalamus in the activation of brown adipose tissue provided a possible anatomical clue concerning pathways connecting thermal and weight regulations.     

Long-term alcohol consumption and brown adipose tissue in man

Summary The purpose of the present work was to study whether long-term alcohol consumption in man affects the develeopment of brown adipose tissue. The adipose tissue around the thoracic aorta and common carotid arteries was collected at medicolegal autopsies on adults with a positive record of heavy alcohol consumption. Adults without any evident history of alcohol consumption served as controls. Histochemical reactions of the oxidative mitochondrial enzymes, cytochrome oxidase and succinate dehydrogenase were studied in samples of this adipose tissue and the activities of the enzymes were measured biochemically.There was histological evidence of some multilocular adipose tissue around the thoracic aorta and common carotid arteries of the alcohol consumers, whereas the adipose tissue from the non-drinkers was mostly unilocular resembling white adipose tissue. Histochemical evidence of brown adipose tissue was found in all alcohol consumers, but also in some of the controls. Biochemical cytochrome oxidase (CYO) and succinate dehydrogenase measurements in isolated mitochondria showed activity in 70% of the cases of drinkers and in one of the eight controls. Activity of CYO was measurable in the mitochondria from two other controls. The protein content of the samples from the alcoholics was twice that of the controls. The results suggest that chronic alcohol intake may induce a change in the white adipose tissue around the thoracic aorta and common carotid arteries of human adults into brown fat.     

Effect of ventromedial hypothalamic stimulation on blood flow of brown adipose tissue in rats

The changes in regional blood flows to the rat's interscapular brown adipose tissue and several other tissues during electrical stimulation of the ventromedial hypothalamus (VMH) were studied using radioactively labelled microspheres. Measurement of blood flow was carried out, along with monitoring heart rate, under anesthesia and at thermoneutrality. During VMH stimulation the heart rate was clearly augmented and cardiac output increased about 45%. Regional blood flows were significantly increased in response to VMH stimulation in interscapular brown adipose tissue, adrenal glands, diaphragm and gastrocnemius muscles. The response of interscapular brown adipose tissue was the most prominent (approx. fiftyfold increase). Blood flows tended to decrease in spleen, lungs and kidneys during VMH stimulation, but did not change in liver or in other visceral organs. These observations suggest that the VMH is concerned with the regulation of regional blood flow to brown adipose tissue and contributes to thermogenesis in this tissue.     

Cold-induced thermogenesis in hypothyroid rats

Hypothyroidism was induced in adult rats by oral administration of methimazole. Euthyroid and hypothyroid rats were maintained at 23 °C or exposed at 6 °C for 3 weeks. Both euthyroid and hypothyroid rats maintained at 23 °C had similar interscapular brown adipose tissue (BAT) composition and thermogenic activity. Cold-exposed hypothyroid rats showed the same interscapular BAT mass and gross tissue composition as cold-exposed euthyroid animals, but the interscapular BAT of cold-exposed hypothyroid rats did not show the characteristic increase in GDP binding, and the increase in mitochondrial mass was lower than in euthyroid rats. From these results we conclude that thyroid hormones do not influence BAT significantly when thermogenic requirements are moderate, but they participate in the trophic response of the tissue when thermogenic requirements are intense. This thyroid hormone participation in the BAT trophic response occurs at the mitochondrial level, both in quantitative (mitochondrial mass) and qualitative (GDP-binding) aspects.     

Prenatal and lactation nicotine exposure affects morphology and function of brown adipose tissue in male rat offspring

The aim of this study was to investigate the effects of prenatal and lactation nicotine exposure on the morphology and function of brown adipose tissue (BAT) in male rat offspring. We conducted a morphological assay and gene expression study of interscapular BAT (iBAT) in male rat offspring. The male offspring from nicotine-exposed dams exhibited higher body weight and iBAT weight. Hematoxylin and eosin staining and transmission electron microscopy showed that iBAT from nicotine-exposed male offspring presented a “whitening” phenotype characterized by lipid droplet accumulation and impaired mitochondria with a randomly oriented and fractured cristae. The expression of the iBAT structure and function-related genes all decreased in nicotine-exposed male offspring. These data indicate that prenatal and lactation nicotine exposure affects morphology and function of iBAT in male rat offspring.     

Non-selective cationic channel in primary cultured cells of brown adipose tissue

Single channel current events were recorded from membranes of cultured brown adipose tissue cells with the patch-clamp technique. In excised inside-out patches the predominant type of events showed a slope conductance of about 30 pS (25 °C). The current was carried by both, Na⁺ ions and K⁺ ions. Discrimination between them was poor. The frequency of events increased with increasing temperature. Their amplitude was temperature dependent as well (Q₁₀1.4). A single exponential was not sufficient for fitting the histograms of on-time or off-time. We conclude that these events belong to a type of non-selective cation channel described previously for other tissues.     

Orexin receptor type 2 agonism inhibits thermogenesis in brown adipose tissue by attenuating afferent innervation

Orexin signaling has been associated with energy expenditure and brown adipose tissue (BAT) function. However, conflicting data exist in the field about how orexin signaling regulates BAT thermogenesis. In this study, we show that a specific orexin receptor type 2 (OX2R) agonist [Ala11, D-Leu15]-OxB (OB-Ala) inhibited intrascapular brown adipose tissue (iBAT) thermogenesis by reducing sympathetic output to iBAT. This effect is mediated by OX2Rs located on afferent nerve endings innervating iBAT instead of brown adipocyte itself. Microinjection of OB-Ala into iBAT inhibited iBAT thermogenesis in mice upon cold exposure and neuronal activity in the paraventricular nucleus. Findings suggest that OB-Ala could inhibit iBAT thermogenesis by attenuating sensory input thereby inhibiting the sympathetic-sensory iBAT feedback loop. Our study uncovers a novel primary action site of orexin in the regulation of energy balance.     

Small effect of brown adipose tissue and major effect of photoperiod on body weight in hamsters (Mesocricetus auratus)

It has been suggested that brown adipose tissue plays a special role in the control of body weight. This hypothesis was investigated by measuring the body weight of female hamsters over a two month period following removal of interscapular brown adipose tissue. Two groups of animals were used, one maintained on a short day (10:14 light: dark ratio) and the other on a long day (16:8 light: dark ratio) photoperiod. Under both photoperiod conditions hamsters with interscapular brown adipose tissue removed gained somewhat more weight than their corresponding sham operated controls. Photoperiod, however, had a much larger effect on body weight. Hamsters maintained on short days increased their body weight by about 60 percent during the two months of the experiment whereas the hamsters maintained on long days increased their body weight by only about 17 percent. It was concluded that brown adipose tissue plays a small non special role in the control of body weight in the female hamster, but that the light-dark ratio is quantitatively much more important under these experimental conditions.     

Inverse relationship between brown fat thermogenesis and meal size: The thermostatic control of food intake revisited

This study examines a new hypothesis whereby heat production from brown fat in response to eating may serve as a feedback signal for satiety. To test this hypothesis, in vitro respiration rate of brown adipose tissue (BAT) was determined in relation to the voluntary caloric intake of the preceding test meal. This relationship was examined as a function of meal composition and of obesity. It was found that in rats fed a high fat diet, as well as in two types of obese rats (VMH and Zucker), respiration rate per 100 mg tissue was significantly reduced, and energy intake of the preceding test meal increased compared to rats receiving a low fat diet or to respective lean rats. These data lend support to a brown fat mediated thermostatic hypothesis for the control of food intake.     

Role of sympathetic nervous system in immobilization- and cold-induced brown adipose tissue thermogenesis in rats

The role of the sympathetic nervous system in 10-min cold (5 degrees C)- or 2-min immobilization-induced thermogenesis in brown adipose tissue (BAT) was studied in warm (25 degrees C)-acclimated rats. Both cold- and immobilization-stresses increased heat production (M), interscapular brown adipose tissue temperature ( Tbat ), and colonic temperature ( Tcol ). Resulting from both stresses, the increase in Tbat was greater than that in Tcol , the differences (delta Tbat ) becoming approximately 0.48 and 0.46 degrees C by the cold exposure and the immobilization, respectively. After sympathectomy, Tbat and delta Tbat did not change on immobilization but increased significantly on the cold exposure. Delta Tbat was 0.31 degrees C in the sympathectomized rats at the end of the cold exposure period. Immobilization-induced BAT thermogenesis may be mainly controlled by the sympathetic nervous system. On the other hand cold-induced BAT thermogenesis seems to be controlled by certain hormonal factors as well as the sympathetic nervous system.     

Leanness of Lou/C rats does not require higher thermogenic capacity of brown adipose tissue

Lou/C rats, an inbred strain of Wistar origin, remain lean throughout life and therefore represent a remarkable model of obesity resistance. To date, the exact mechanisms responsible for the leanness of Lou/C rats remain unknown. The aim of the present study was to investigate whether the leanness of Lou/C rats relies on increased thermogenic capacities in brown adipose tissue (BAT).Results showed that although daily energy expenditure was higher in Lou/C than in Wistar rats, BAT thermogenic capacity was not enhanced in Lou/C rats kept at thermoneutrality as demonstrated by reduced thermogenic response to norepinephrine in vivo, similar oxidative activity of BAT isolated mitochondria in vitro, similar levels of UCP1 mRNA and lower abundance of UCP1 protein in interscapular BAT depots. Relative abundance of β₃-adrenergic receptor mRNA was lower in Lou/C BAT while that of GLUT4, FABP or CPT1 was not altered. Activity-related energy expenditure was however considerably increased at thermoneutrality as Lou/C rats demonstrated an impressively high spontaneous running activity in voluntary running wheels. Prolonged cold-exposure (4 °C) depressed the spontaneous running activity of Lou/C rats while BAT thermogenic capacity was increased as reflected by rises in BAT mass, oxidative activity and UCP1 expression.It is concluded that the leanness of Lou/C rats cannot be ascribed to higher thermogenic capacity of brown fat but rather to, at least in part, increased locomotor activity. BAT is not deficient in this rat strain as it can be stimulated by cold exposure when locomotor activity is reduced suggesting some substitution between these thermogenic processes.