Tissue blood flow in control and cold-adapted hyperthyroid rats

Chronic injections (once daily for 10-14 days) of triiodothyronine (T3) stimulated oxygen consumption by 50 and 15% in anaesthetized, control (24 degrees C), and cold-adapted (5 degrees C) rats, respectively, compared with euthyroid controls. Tissue blood flow, determined from the distribution of radioactive microspheres, was unaffected by T3 treatment in skeletal muscle, scrotum, brain, bone, skin, diaphragm, and brown adipose tissue (BAT) of rats housed at 24 degrees C, but was decreased in spleen (53% of control) and significantly increased in three white adipose tissue depots (average 267% increase) and liver (56%). Blood flow to epididymal fat and leg muscle of cold-adapted rats was increased by T3 treatment (100 and 138% increases, respectively), but other tissues were unaffected. Blood oxygen extraction and oxygen consumption in vivo by interscapular BAT was increased in hyperthyroid rats compared with euthyroid controls, but was reduced by T3 treatment in cold-adapted animals. These data show that BAT makes only a minor contribution (7%) to thyroid thermogenesis, but suggest that kidney, liver, gut, and particularly white adipose tissue may be involved.     

Effects of neonatal sympathectomy on brown fat development and susceptibility to high fat diet induced obesity in mice.

Injections of 6-hydroxydopamine in mouse neonates caused extensive and long lasting damage to the sympathetic nervous system and impaired brown fat development. Brown adipose tissue (BAT) thermogenic capacity of sympathectomized mice (up to 120 days old) was reduced because of marked reductions in the tissue mitochondrial protein content and the mitochondrial concentration of uncoupling protein, as assessed by [3H]GDP binding and immunoassay. Neonatal sympathectomy did not affect BAT DNA content. Sympathectomized mice also had reduced epinephrine-stimulated rates of oxygen consumption. BAT of sympathectomized mice failed to respond by increases in [3H]GDP binding to isolated mitochondria and uncoupling protein concentration when animals were offered a palatable high-fat dietary supplement that increased calorie intake of both normal and sympathectomized mice. The high-fat diet caused increases in body weight, carcass fat, and gonadal white fat pad weights in sympathectomized animals that were similar to those of control mice. These results show that inactivation of BAT metabolism did not accentuate the development of obesity caused by a dietary supplement rich in fat and suggest that stimulation of BAT metabolism was not very effective in counteracting the obesity-inducing effect of this diet.     

Effects of high fat diets on hibernation and adipose tissue in Turkish hamsters

Summary The effects of dietary fat saturation and fat content on hibernation and several properties of white and brown adipose tissue (WAT and BAT, respectively) were investigated in Turkish hamsters (Mesocricetus brandti). Male hamsters were housed in a long photoperiod (LD 16:8) at 23°C and fed one of three diets: (1) chow (6.5% fat per weight), (2) chow+13.5% vegetable oil (OIL, 20% fat per weight [largely unsaturated fat]) and (3) chow+13.5% vegetable shortening [SHORTENING, 20% fat per weight (largely saturated fat)]. Five weeks later body weights had stabilized and the animals were transferred to a short photoperiod (LD 8:16) at 3°C. At the peak of the hibernation season (17 weeks) the animals were sacrificed within 24 h of arousal. Chow-fed hamsters had the greatest percentage of animals hibernating and days found torpid compared with the two fat-fed groups, with no differences found between the latter two groups for these measures. There were no differences between hibernating (HIB) and nonhibernating (NON-HIB) hamsters across or within the diet groups for any of the BAT measures [uncoupling protein content, mitochondrial mass, lipoprotein lipase (LPL) activity, and in vivo lipogenesis], nor were there significant effects of the diet on these measures. CHOW-and OIL-fed HIB hamsters showed decreases in body weight. All HIB groups had decreases in each carcass component, several fat pad weights, testes weight, and food intake. No consistent differences in WAT LPL activity or in vivo lipogenesis were found between HIB and NON-HIB hamsters. Feeding saturated high fat diets inhibits hibernation in some species; however, in the present experiment, feeding of both saturated and unsaturated fat-laden diets inhibited hibernation to a similar degree.Abbreviations BAT brown adipose tissue - COA cytochrome-c oxidase - DS dorsal subcutaneus - DSWAT dorsal subcutaneous white adipose tissue - E epididymal - EWAT epididymal white adipose tissue - FFDM fat-free dry mass - HIB hibernating - I interscapular - IBAT intercapsular brown adipose tissue - IS inguinal subeutaneus - ISWAT inguinal subcutaneous white adipose tissue - LPL lipoprotein lipase - NON-HIB non-hibernating - R retroperitoneal - RWAT retroperitoneal white adipose tissue - SDS sodium dodecyl sul - UCP uncoupling protein - WAT white adipose tissue     

Lack of TRPV2 impairs thermogenesis in mouse brown adipose tissue

Brown adipose tissue (BAT), a major site for mammalian non‐shivering thermogenesis, could be a target for prevention and treatment of human obesity. Transient receptor potential vanilloid 2 (TRPV2), a Ca²⁺‐permeable non‐selective cation channel, plays vital roles in the regulation of various cellular functions. Here, we show that TRPV2 is expressed in brown adipocytes and that mRNA levels of thermogenic genes are reduced in both cultured brown adipocytes and BAT from TRPV2 knockout (TRPV2KO) mice. The induction of thermogenic genes in response to β‐adrenergic receptor stimulation is also decreased in TRPV2KO brown adipocytes and suppressed by reduced intracellular Ca²⁺ concentrations in wild‐type brown adipocytes. In addition, TRPV2KO mice have more white adipose tissue and larger brown adipocytes and show cold intolerance, and lower BAT temperature increases in response to β‐adrenergic receptor stimulation. Furthermore, TRPV2KO mice have increased body weight and fat upon high‐fat‐diet treatment. Based on these findings, we conclude that TRPV2 has a role in BAT thermogenesis and could be a target for human obesity therapy.     

Cellular changes during cold acclimatation in adipose tissues

Cold exposure is a well-known physiological stimulus that activates the sympathetic nervous system and induces brown adipose tissue (BAT) hyperplasia. The effects of cold exposure or cold acclimatation have been extensively studied in interscapular BAT (IBAT). However, it has been recently shown that brown adipocytes are present in adipose deposits considered as white fat such as periovarian (PO) fat pad. We have investigated the kinetic of brown precursor recruitment in adipose tissues using DNA measurement and specific marker expression. In IBAT, cold exposure induces proliferation of precursor cells and differentiation into preadipocytes characterized by the expression of A2COL6, a marker specific to early steps of the differentiation process. A chronic stimulation of the tissue is necessary to observe the full effect. In PO fat pad, no proliferation can be detected, whereas differentiation of brown preadipocytes and maybe phenotypic conversion of white adipocytes seems to be promoted. In conclusion, these data demonstrated that 1) the same stimulus (cold exposure) does not induce the same response in terms of preadipocyte proliferation and differentiation in periovarian and brown adipose tissues, although both contain brown adipocytes, and 2) preadipocyte recruitment in adipose tissues after cold exposure depends on the predominant type of fat cells. © 1996 Wiley-Liss, Inc.     

Sympathetic denervation of one white fat depot changes norepinephrine content and turnover in intact white and brown fat depots

It is well-established that the sympathetic nervous system (SNS) regulates adipocyte metabolism and recently it has been reported that sensory afferents from white fat overlap anatomically with sympathetic efferents to white fat. The studies described here characterize the response of intact fat pads to selective sympathectomy (local 6-hydroxydopamine (6OHDA) injections) of inguinal (ING) or epididymal (EPI) fat in male NIH Swiss mice and provide in vivo evidence for communication between individual white and brown fat depots. The contralateral ING pad, both EPI pads, perirenal (PR), and mesenteric (MES) pads were significantly enlarged 4 weeks after denervating one ING pad, but only intrascapular brown adipose tissue (IBAT) increased when both ING pads were denervated. Denervation of one or both EPI pad had no effect on fat depot weights. In an additional experiment, norepinephrine turnover (NETO) was inhibited in ING, retroperitoneal (RP), MES, and IBAT 2 days after denervation of both EPI or of both ING pads. NE content was reduced to 10-30% of control values in all fat depots. There was no relation between early changes in NETO and fat pad weight 4 weeks after denervation, even though the reduction in NE content of intact fat pads was maintained. These data demonstrate that there is communication among individual fat pads, presumably through central integration of activity of sensory afferent and sympathetic efferent fibers, that changes sympathetic drive to white adipose tissue in a unified manner. In specific situations, removal of sympathetic efferents to one pad induces a compensatory enlargement of other intact depots.     

Chronic administration of BRL 26830A for 9 weeks improves insulin sensitivity but does not prevent weight gain in gold-thioglucose obese mice.

BRL 26830A, a beta adrenoceptor agonist, has been shown to have antiobesity and antidiabetic properties in rodents. The aim of this study was to study the effects of chronic BRL 26830A treatment (20 mg/kg/day for 9 weeks) on weight gain and the development of insulin resistance in gold-thioglucose-injected mice (GTG). BRL 26830A slowed the rate of weight gain in GTG such that mice weighed significantly less between 2 w and 7 w of treatment. However, at the time of sacrifice (9 w), there was no difference in body weight between treated and untreated GTG. The obesity-induced reduction in lipogenesis in brown adipose tissue (BAT) was increased 9 fold to greater than CON levels. However, weight and fatty acid (FA) content of BAT were reduced, suggesting increased lipid turnover and thermogenesis. Lipogenesis, FA content and fat pad weight were unchanged in white adipose tissue (WAT) and decreased in liver of GTG. Glucose tolerance was improved in both CON and GTG. Hyperglycemia, hyperinsulinemia and changes in cardiac and hepatic glucose oxidation as indicated by PDHC activity were normalized. Serum triglycerides and non-esterified fatty acids were reduced. Thus, chronic BRL 26830A treatment prevented the development of insulin resistance and attenuated weight gain, but did not prevent the development of obesity in this model.     

Effects of central or peripheral leptin administration on norepinephrine turnover in defined fat depots

Leptin preserves lean tissue but decreases adipose tissue by increasing lipolysis and/or inhibiting lipogenesis. The sympathetic nervous system (SNS) is a primary regulator of lipolysis, but it is not known if leptin increases norepinephrine turnover (NETO) in white adipose tissue. In this study, we examined the effect of leptin administered either as a chronic physiological dose (40 microg/day for 4 days from ip miniosmotic pumps) or as an acute injection in the third ventricle (1.5 microg injected two times daily for 2 days) on NETO and the size of brown and white fat depots in male Sprague Dawley rats. NETO was determined from the decline in tissue norepinephrine (NE) during 4 h following administration of the NE synthesis inhibitor alpha-methyl-para-tryrosine. The centrally injected leptin-treated animals demonstrated more dramatic reductions in food intake, body weight, and fat pad size and an increase in NETO compared with the peripherally infused animals. Neither route of leptin administration caused a uniform increase in NETO across all fat pads tested, and in both treatment conditions leptin decreased the size of certain fat pads independent of an increase in NETO. Similar discrepancies in white fat NETO were found for rats pair fed to leptin-treated animals. These results demonstrate that leptin acting either centrally or peripherally selectively increases sympathetic outflow to white fat depots and that a leptin-induced change in fat pad weight does not require an increase in NETO.     

Induction of uncoupling protein-2 (UCP2) gene expression on the differentiation of rat preadipocytes to adipocytes in primary culture

We have examined uncoupling protein-2 (UCP2) gene expression in the adipose tissue of obese and normal rats and mice, and also in differentiated rat adipocytes in primary culture. Expression of the UCP2 gene was examined in rat and mouse adipose tissues using both RT-PCR and Northern blotting. Although the RT-PCR was not quantitative, the band corresponding to the UCP2 mRNA was stronger in white adipose tissue than in brown fat, regardless of the body weight of the rats. In agreement with the RT-PCR data, there was a higher level of UCP2 mRNA in the white adipocytes than in brown adipocytes, the level being greater in obese mice. Fibroblastic preadipocytes were obtained from the inguinal fat pad of suckling rats. Lipid droplets developed inside the cells upon differentiation and adipsin and UCP2 mRNAs were detected by Northern blotting. Both mRNAs were evident in the adipocytes at 4, 6, and 10 d after the induction of differentiation. There was no indication that the expression of UCP2 was markedly affected by the addition of leptin, dexamethasone or isoprenaline.     

Effects of dietary carbohydrate and phenotype on adipose cellularity in female SHR/N-cp rats.

1. Adipose mass and cellularity were studied in congenic female SHR/N-cp rats fed iosenergetic diets containing 54% carbohydrate as sucrose (SU) or cooked cornstarch (CS), 20% protein, 16% mixed dietary fat plus vitamins, minerals, and non-nutritive fiber ad libitum from 5 weeks until 8.5 months of age. Measures of adipocyte lipid content, cell number per depot, and mass of principal white (WAT) and interscapular brown (IBAT) adipoe tissue depots were determined at the end of the study. 2. Final body weights (BW) of corpulent rats were more than twice those for their lean littermates, and were greater when fed the SU than the CS diet in both phenotypes. Phenotype effects (corpulent greater than lean) were present for fat pad weight, adipocyte number, and adipocyte lipid content in the dorsal (DOR) and retroperitoneal (RP) WAT depots. Diet effects were present for depot weight, adipocyte number, and adipocyte lipid content in both WAT depots, and were of qualitatively similar magnitude in both phenotypes. 3. IBAT weights, IBAT:BW ratios, and IBAT cell number of corpulent greater than lean, and were greater than with SU than CS diet in both phenotypes. 4. These results indicate that obesity in the corpulent phenotype of the SHR/N-cp rat occurs as the result of hypertrophy and hyperplasia of white adipose tissue, and that isoenergetic substitution of simple for complex carbohydrate resulted in greater fat accretion in both phenotypes. The greater diet and phenotype-associated adiposity occurred despite greater mass and cellularity of BAT. The results also indicate that sexual dimorphism occurs regarding effects of diet and phenotype on expression of adipose tissue development in this strain.     

Seasonal adaptation of brown adipose tissue in the Djungarian hamster

Summary The composition and oxidative capacity of brown adipose tissue (BAT) were investigated in Djungarian hamsters kept under natural photoperiod, either indoors at neutralT _a (23°C) or under outdoor conditions. BAT comprises up to 5% of the body weight in summer/indoor hamster, with lipid representing 86% of the total tissue mass. Tissue mass and thermogenic capacity are inversely related during seasonal adaptation: 30% decrease of total DNA, accompanied by extensive lipid depletion, reduces the amount of BAT by almost 60% during acclimatization from summer/indoor to winter/outdoor conditions. Mitochondrial protein in BAT is increased by a factor of 2.6 concomitantly, and by a factor of 4 when related to body weight (body weight reduction 36%).Cytochrome oxidase activity in different brown fat deposits varies by up to 150% in summer/indoor hamsters; depending on the fat pad, the enzyme activity is increased 200%–700% during adaptation to winter/outdoor conditions.Natural photoperiod is decisive in determining the seasonal adaptation of DNA content in BAT and of body weight. Short photoperiod alone may lead to depletion of lipid content of BAT and thus decrease the tissue mass practically to the lowest seasonal level, even though both parameters may be also influenced byT _a. One third of the maximum adaptive increase of tissue mitochondria may be attributed to seasonal changes in photoperiod and up to two thirds toT _a. Photoperiod establishes a fixed fundament of slow-reacting functional adaptation of BAT, whereas the effect of decreasedT _a depends on the rate and duration of cold influence.Abbreviations BAT brown adipose tissue - NST nonshivering thermogenesis - T _a ambient temperature     

A Gain-of-Function Mutation in Adenylate Cyclase 3 Protects Mice from Diet-Induced Obesity

In a screen for genes that affect the metabolic response to high-fat diet (HFD), we selected one line of N-ethyl-N-nitrosourea (ENU)-mutagenized mice, Jll, with dominantly inherited resistance to diet-induced obesity (DIO). Mutant animals had dramatically reduced body weight and fat mass, and low basal insulin and glucose levels relative to unaffected controls. Both white adipose tissue (WAT) and brown adipose tissue (BAT) depots were smaller in mutant animals. Mutant animals fed a HFD gained only slightly more weight than animals fed regular chow, and were protected from hepatic lipid accumulation. The phenotype was genetically linked to a 5.7-Mb interval on chromosome 12, and sequencing of the entire interval identified a single coding mutation, predicted to cause a methionine-to-isoleucine substitution at position 279 of the Adcy3 protein (Adcy3^M279I, henceforth referred to as Adcy3^Jll). The mutant protein is hyperactive, possibly constitutively so, producing elevated levels of cyclic AMP in a cell-based assay. These mice demonstrate that increased Adcy3 activity robustly protect animals from diet-induced metabolic derangements.     

In vivo quantitative lipidic map of brown adipose tissue by chemical shift imaging at 4.7 Tesla.

In the present paper, chemical shift imaging techniques are applied to quantitative in vivo evaluation of fat and water content in interscapular brown adipose tissue (BAT). The experiments have been carried out on five female Sprague-Dawley rats after calibration and testing with suitable phantoms containing known amounts of water and oil. We found that, in the interscapular BAT, the fat is about 50% at the surface (mainly unilocular) region, but its percentage drops to 20;-30% in the deepest (mainly multilocular) portion. The perirenal deposits of white adipose tissue (WAT) contained significantly higher amount of fat with large areas ranging from 70 to 90%. Later the rats were killed and the same procedure was repeated with dead animals. Experiments performed in dead rats show a modification of the hydro-lipidic ratio more evident in the multilocular portions of the deposit. The present work demonstrates that MRI-based methods allow a non-invasive, in vivo quantitative mapping of the lipid content which can be applied to investigation of brown adipose tissue deposits in small experiment animals.     

Effect of diet on the weight of brown adipose tissue in rodents

Interscapular brown adipose tissue (BAT) weighed more in rats given access to a solution of sucrose in addition to a nutritionally complete basal diet than in rats eating only a basal diet. This incremental effect of drinking sucrose solution occurs across a variety of dietary conditions. In the first experiment, rats were fed diets containing either 9%, 18%, 27% or 36% casein. Rats given access to a sucrose solution had significantly larger brown fat pads than controls when the diets contained 9 or 18% casein, but not when diets contained either 27% or 36% casein. The second experiment examined the weight of brown adipose tissue as a function of the type of protein and the percentage of fat in the diet. Animals given a sucrose solution had significantly more BAT than animals not given sucrose. Neither the type of protein (casein or soy protein) nor the percentage of fat (14.5% or 36.4%) in the diet influenced the weight of BAT. Animals given access to either a sucrose solution or a glucose solution had significantly heavier BAT than animals given access to a fructose solution, granulated sucrose or water.     

Effect of running training on uncoupling protein mRNA expression in rat brown adipose tissue

The effect was investigated of endurance training on the expression of uncoupling protein (UCP) mRNA in brown adipose tissue (BAT) of rats. The exercised rats were trained on a rodent treadmill for 5 days per week and a total of 9 weeks. After the training programme, a marked decrease in BAT mass was found in terms of weight or weight per unit body weight; there was a corresponding decrease in DNA content and a downward trend in RNA and glycogen levels. The UCP mRNA was present at a markedly decreased level in BAT of trained animals. In consideration of the reduced levels of mRNAs for hormone-sensitive lipase and acylCoA synthetase, the brown adipose tissue investigated appeared to be in a relatively atrophied and thermogenically quiescent state.     

Ontogenetical changes in adipose tissue of the cat: Convertible adipose tissue

The ultrastructural characteristics of the inguinal, interscapular, and perirenal adipose tissue in kittens and cats were studied. There were no qualitative differences among adipocytes in the three anatomical areas. The only recorded difference was in the amount of lipids stored in the adipocytes in younger stages. Immediately after birth lipids occupied 25% of the volume in the inguinal area, 15% in interscapular fat tissue, and 10% in perirenal fat tissue. At this stage the adipose tissue morphologically resembled brown adipose tissue (BAT) of rodents. Two weeks after birth, lipids accumulated and adipocytes in the inguinal area became unilocular and appeared similar to white adipose tissue (WAT). A similar transition occurred approx 25 days after birth in interscapular fat and approx 6 weeks after birth in the perirenal area. No morphological signs of any cell degradation or destruction, nor any increased activity of preadipocytes, were seen during this conversion from BAT-like to WAT-like adipose tissue. The conversion of the adipose tissue was correlated with a decrease in vascularization and innervation, a loss of intercellular connections, and a changed mitochondrial population. Mitochondria in multilocular adipocytes resembled those in typical BAT which contain uncoupling protein (“UC-mitochondria”). After conversion to unilocular adipocytes the amount of mitochondria was halved, their cristae even more reduced, and their appearance was of a WAT-type (UCP-lacking mitochondria, which are coupled under physiological conditions; “C-mitochondria”). Since this category of adipose tissue differs from both typical brown and white adipose tissue, the name “convertible adipose tissue” (CAT) is proposed. Apparently adipose tissue from comparatively large mammals is of this convertible type.     

Brown Adipose Tissue Thermogenesis During Aging and Senescence

We have found that cold- and norepinephrine-induced brown adipose tissue (BAT) nonshiveringthermogenesis (NST) is significantly lower in old male Fischer 344 rats and is associatedwith the decreased ability of these animals to maintain homeothermy. This decline in BATthermogenesis is not as great in females. Although the mechanism(s) underlying this genderdifference in the age-related decrease in brown fat NST are not completely elucidated, theydo not appear to reflect decreased sympathetic neural activity of BAT in the older males vs.females. Rather, our investigations, strongly suggest that the blunted cold-induced heatproduction of BAT reflects less functional BAT. The fact that the older animals have less functionalBAT than do their younger counterparts may predispose them to the accumulation of excessbody fat. Our studies have also found that near the end of the natural life of these rats, theyenter a state of senescence that can be identified by spontaneous rapid body weight loss,resulting from decreased food intake. In this state, the rats are considerably more susceptibleto cold than are comparably aged presenescent (body weight stable) rats of the samechronological age. The greater hypothermia exhibited by the senescent vs. presenescent rats during coldexposure is associated with a significant reduction in the amount of functional brown fat andin the amount of heat each brown fat cell can generate. It is the intent of this review to discussthe findings of these investigations.     

Effects of iron repletion and correction of anemia on norepinephrine turnover and thyroid metabolism in iron deficiency

The reversibility of the alterations in norepinephrine (NE) content and turnover in interscapular brown adipose tissue and heart of iron-deficient rats has not been demonstrated. We therefore examined NE metabolism in age-matched male Sprague-Dawley rats depleted of iron by dietary means and after repletion with iron dextran. Heart NE content was 58, 61, and 85% of controls at 0, 3, and 7 days after repletion, whereas interscapular brown adipose tissue-NE content was 87, 103, and 104% of controls. Fractional heart NE turnover was 225% greater in iron-deficient anemics than controls but normalized within 3 days. Interscapular brown adipose tissue NE turnover was 58%, 46%, and 20% above controls in iron-deficient rats after 0, 3, or 7 days of iron repletion. Hematocrit returned to 80% of normal in 7 days. Liver triiodothyronine production also increased to 80% of control in this period. A second experiment used isovolemic exchange transfusion to examine the influence of anemia per se on these alterations in organ NE turnover. Acute correction of anemia in iron deficiency did not alter brown fat NE turnover. Heart NE turnover was significantly lower in anemic animals regardless of iron status. Defects in heart and brown fat NE metabolism are reversible within 7 days of iron treatment as are alterations in triiodothyronine production. Anemia per se has little effect on brown fat NE metabolism but does dramatically decrease heart NE content.     

Acute and chronic effects of ACTH on thermogenesis and brown adipose tissue in the rat

A single injection of ACTH stimulated metabolic rate in the rat, and this effect was enhanced in hyperphagic cafeteria-fed rats. Chronic treatment with ACTH significantly reduced body weight, energy gain and energetic efficiency in stock-fed rats. Thermogenic responses to noradrenaline and a single meal, and purine nucleotide (GDP) binding to brown adipose tissue (BAT) mitochondria were also increased. Cafeteria feeding induced hyperphagia, increases in metabolic rate, acute thermogenic responses and BAT activity, and depressed energetic efficiency. ACTH had no additional effects on energy balance, thermogenic responses or brown fat in cafeteria-fed rats. These data indicate that stimulation of thermogenesis and BAT activity by ACTH resembles that induced by hyperphagia, and this effect may be partly responsible for the changes in energy balance after adrenalectomy seen in previous studies. However, acute and chronic responses to ACTH depend upon the nutritional status of the animal.