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Query: UMLS:C0155339 (Brown)
 12,436 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The energizing balance of the body is the result of intake and output of energy. Intake corresponds to eating and output corresponds to basal metabolism, physical exercise and heat production. Recent studies conducted on man suggest that obesity could be associated with a lack of heat production. Thus, a decreased thermogenic consumption associated with eating could contribute to the development of obesity. This hypothesis seems valid as far as obese rodents are concerned. In this case, it is a known fact that a specific organ, the brown fatty tissue, main effector of the thermogenesis induced by cold and eating. The molecular mechanisms of heat production by the brown fatty tissue, have been recently explained. Brown adipocytes are present in man, but their specific contribution to the energizing balance or imbalance is not yet established. This will be subject of further studies.
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PMID:[Thermogenesis and obesity: molecular aspects]. 322 99

Older rats exposed to low environmental temperatures show attenuated thermogenesis. However, the mechanisms responsible for this attenuation are not clear. This investigation evaluated the possibility that reduced nonshivering thermogenic capacity is associated with this attenuation. O2 consumption was measured in male Fischer 344 rats ages 7 and 24 mo at thermoneutrality (26 degrees C), during exposure to cold (6 degrees C) for 2 h, and during norepinephrine (NE) infusion (an in vivo measure of nonshivering thermogenesis). In addition, the binding of GDP to isolated mitochondria of brown fat, an in vitro estimate of nonshivering thermogenesis, was also measured. Resting mass-independent O2 consumption (ml.min-1.g body mass -0.67) was not different between the two age groups. However, mass-independent O2 consumption was significantly greater in the younger vs. older rats during 2 h of cold exposure (younger, 2.86 +/- 0.19 l/kg body mass 0.67; older, 2.39 +/- 0.10 l/kg body mass 0.67) and during 20 min of maximum NE infusion (younger, 410.4 +/- 15.1 ml/kg body mass)] was greater in younger than ml/kg body mass 0.67). Brown fat mass [absolute (g) as well as relative (g tissue/kg body mass)] was greater in younger than in older rats. Furthermore, younger rats had significantly greater binding of GDP to isolated mitochondria of brown fat than did the older rats. This effect was true whether the data were expressed as nanomoles bound per milligram mitochondrial protein (32% lower in older rats), bound nanomoles recovered (57% lower), or bound picogram per kilogram body mass 0.67 (59% lower).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Cold- and norepinephrine-induced thermogenesis in younger and older Fischer 344 rats. 334 40

Transcriptionally active macronuclei and transcriptionally inert micronuclei of the ciliated protozoan Tetrahymena thermophila contain similar DNA sequences but have very different histones associated with the linker regions of chromatin. In situ hybridization showed that a gene coding for micronuclear linker histone is expressed only in association with micronuclear DNA replication, whereas the gene for macronuclear H1 histone is expressed during macronuclear (but not during micronuclear) S phase. These results indicate that cell-cycle regulation plays an important role in directing proteins to the appropriate nucleus in Tetrahymena and that the replication-expression model [Gottesfeld, J. & Bloomer, L. S. (1982) Cell 28, 781-791; Wormington, W. M., Schlissel, M. & Brown, D. D. (1983) Cold Spring Harbor Symp. Quant. Biol. 47, 879-884] for establishing appropriate transcriptionally active or repressed chromatin complexes during DNA replication is generally applicable.
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PMID:Cell-cycle regulation as a mechanism for targeting proteins to specific DNA sequences in Tetrahymena thermophila. 335 76

Brown adipose tissue plays a thermoregulatory role influencing energy balance in experimental animals and possibly also in humans. In the present study we have reevaluated whether brown adipose tissue may contribute to the development of cancer cachexia in non-growing mice bearing an isogeneic tumor. Interscapular brown adipose tissue mass decreased by 20% in freely-fed sarcoma-bearing mice housed at room temperature. Increased mitochondrial density and increased oxidation rate of acetate at low acetate concentrations were found in brown fat from sarcoma-bearing mice, while the oxidation capacity was unchanged compared with that of freely-fed controls. Metabolic and morphologic changes in brown fat from sarcoma-bearing mice were similar to those found in weight-paired controls, which had experienced the same loss of body weight as the tumor-bearing mice. Selective and non-selective B-receptor blockade and surgical removal of interscapular brown fat before tumor implantation did not influence the nutritional state of freely-fed tumor-bearing mice. Injections of noradrenaline caused a proportionately lower increase in oxygen uptake in tumor-bearing animals than in freely-fed controls. Exposure to cold (+5 degrees C) doubled food intake and led to hypertrophy of brown fat in both sarcoma-bearing mice and control animals. Tumor growth was lower although not statistically different in animals housed at +5 degrees C compared with animals housed at +25 degrees C. It is concluded that brown adipose tissue from sarcoma-bearing mice could not account quantitatively for the host wasting in tumor-bearing mice housed at room temperature.
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PMID:Metabolic and morphologic changes in brown adipose tissue from non-growing mice with an isogeneic sarcoma. Evaluation with respect to development of cachexia. 369 34

Brown adipocytes from cold-adapted guinea-pigs (C-cells) are more sensitive to uncoupling by exogenous palmitate than are cells from warm-adapted animals (W-cells) with much less uncoupling protein. Half-maximal respiratory stimulation of C-cells requires 80 nM free palmitate. Noradrenaline-stimulated lipolysis is not rate-limiting for the respiration of either C-cells or W-cells. Half-maximal stimulation of fatty acid oxidation by mitochondria from warm-adapted guinea-pigs (W-mitochondria) and cold-adapted guinea-pigs (C-mitochondria) both require 12 nM free palmitate. Palmitate uncouples C-mitochondria much more readily than M-mitochondria, paralleling its action on the adipocytes. The uncoupling is partially saturable, about 100 nM free palmitate being required for half-maximal response of C-mitochondria. W- and C-mitochondria show identical binding characteristics for palmitate. The respiratory increase of mitochondria is calculated as a function of bound palmitate. After correcting for the residual uncoupling protein present in W-mitochondria, palmitate is estimated to be almost ineffective as an uncoupler of brown fat mitochondria in the absence of the protein. It is concluded that fatty acids display characteristics required of a necessary and sufficient physiological activator of the uncoupling protein.
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PMID:Quantification of fatty acid activation of the uncoupling protein in brown adipocytes and mitochondria from the guinea-pig. 370 41

Five models predicting shivering thermogenesis on the basis of steady state skin and core temperature were evaluated: Hayward et al., Stolwijk and Hardy,; Nadel et al.,; Timbal et al., and Brown and Brengelmann, using the empirical data derived from a cold water immersion study by Morrison et al. A residual analysis indicated that all models generated substantial errors of prediction. The best overall predictors were expressions suggested by Hayward et al., while the predictive equation of Nadel et al. ranked second. Derivation of personal coefficients significantly improved the prediction of all models and a subsequent modification of the standard models, adding temperature derivative terms, further reduced the magnitude of the error. An analysis of the residuals indicated that peripheral and core temperatures should be weighted according to the characteristics of thermosensitive neural structures in these regions.
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PMID:Evaluation of predictive formulae for determining metabolic rate during cold water immersion. 374 Dec 91

Brown adipose tissue (BAT) thermogenesis is important in the adaptation of body energy expenditure to cold exposure, fasting, and overfeeding and in the pathogenesis of obesity. Thyroid hormones are required for the normal functioning of BAT. The mechanism of their effect on BAT, however, has not yet been elucidated. Since most thyroid hormone effects are mediated via the binding of T3 to nuclear receptors (NT3R) the present studies were performed to investigate whether BAT contained NT3R and whether these NT3R were affected by cold exposure, fasting, overfeeding, or hypo- or hyperthyroidism. Rat BAT was found to contain NT3R with a maximum binding capacity (MBC) of 0.28 ng T3/mg DNA and a dissociation constant (Kd) of 3.2 X 10(-10) M. These parameters were unaffected by any of the experimental conditions studied. A major alteration of BAT NT3R MBC or Kd is thus not a causal factor in the changes in BAT thermogenesis induced by the above experimental conditions. In contrast, 3-wk overfeeding increased (+48%) and fasting decreased (-29%) the MBC of hepatic NT3R. Overfeeding increased serum T3 (+110%), while fasting decreased it (-37%).
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PMID:Brown fat nuclear triiodothyronine receptors in rats. 377 60

Brown adipose tissue, a major effector of nonshivering thermogenesis (NST) in mammals, is activated by the sympathetic neurotransmitter norepinephrine. Prolonged increases in norepinephrine levels, whether elicited by cold exposure or exogenous application of catecholamines, lead to increased NST and increased thermogenic capacity of brown fat. Exercise training is also accompanied by enhanced sympathetic activity. The possibility exists that this enhancement may alter brown fat function. The present study was designed to assess the effect of a running exercise regimen on whole animal NST and the in vivo response of brown fat. Rats were trained by running on a treadmill (an average of 17 m/min, 0 degrees incline, for 90 min/d) for a period of at least 6 weeks. Whole animal NST capacity was assessed by monitoring oxygen consumption in response to infusion of norepinephrine. As a measure of the contribution of brown fat to whole body NST, the mass and norepinephrine-stimulated blood flow (microsphere technique) to the tissue were measured. None of these variables differed between the exercised (n = 10) and sedentary (n = 10) groups. That is, there were no significant differences between the two groups with respect to resting oxygen consumption, norepinephrine-induced oxygen consumption, brown fat mass, and brown fat blood flow--whether expressed per gram of tissue or as total tissue blood flow (ie, tissue mass X blood flow per gram). Further study is needed to explain the differential responses of brown fat to the increased sympathetic activity occurring during exercise v that occurring during cold exposure.
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PMID:Thermogenic capacity and brown fat in rats exercise-trained by running. 379 99

In small-bowel transplantation, the transfer of large numbers of donor lymphocytes with the intestinal allograft may provoke a lethal graft-versus-host reaction. The effectiveness of allograft irradiation in vitro as a method of preventing graft-versus-host disease (GVHD) was studied in a rat model of small-bowel transplantation, with the Lewis----Lewis X Brown Norway F1 hybrid strain combination. Cold harvested small-bowel allografts were irradiated immediately prior to heterotopic or orthotopic transplantation. Animals that had received heterotopic allografts irradiated with 0, 250, or 500 rad all died of GVHD after 14.4 +/- 3.0, 15.0 +/- 1.3, and 14.2 +/- 1.9 days, respectively. None of the animals that had received allografts treated with 1000 rad developed clinical or pathologic evidence of GVHD, however, and all survived for more than 6 months (P less than 0.001). Allograft function was studied in animals that underwent orthotopic transplantation. Recipients of nonirradiated orthotopic allografts all died of GVHD after 14.0 +/- 0.7 days, whereas recipients of allografts irradiated with 1000 rad all survived for more than 5 months (P less than 0.001). After 120 days, weight gain (51.8 +/- 11.7%), serum albumin (3.9 +/- 0.7 g/dl), serum triglycerides (67.0 +/- 24.3 mg/dl), CBC, and differential in these animals were not statistically different from those in either age-matched isograft recipients or normal animals, and when the rats were sacrificed, irradiated allografts showed no changes suggestive of radiation injury. These results indicate that irradiation of small-bowel allografts in vitro prevents development of GVHD, and that this can be achieved at a dose which does not cause injury to or malfunction of the allograft.
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PMID:In vitro allograft irradiation prevents graft-versus-host disease in small-bowel transplantation. 387 77

The winter athlete has several potential tactics for sustaining body temperature in the face of severe cold. An increase in the intensity of physical activity may be counter-productive because of increased respiratory heat loss, increased air or water movement over the body surface, and a pumping of air or water beneath the clothing. Shivering can generate heat at a rate of 10 to 15 kJ/min, but it impairs skilled performance, while the resultant glycogen usage hastens the onset of fatigue and mental confusion. Non-shivering thermogenesis could arise in either brown adipose tissue or white fat. Brown adipose tissue generates heat by the action of free fatty acids in uncoupling mitochondrial electron transport, and by noradrenaline-induced membrane depolarisation and sodium pumping. The existence of brown adipose tissue in human adults is controversial, and although there are theoretical mechanisms of heat production in white fat, their contribution to the maintenance of body temperature is small. Acclimatisation to cold develops over the course of about 10 days, and in humans the primary change is an insulative, hypothermic type of response; this reflects the intermittent nature of most occupational and athletic exposures to cold. Nevertheless, with more sustained exposure to cold air or water, humans can apparently develop the humoral type of acclimatisation described in small mammals, with an increased output of noradrenaline and/or thyroxine. The associated mobilisation of free fatty acids suggests the possibility of using winter sport as a pleasant method of treating obesity. In men, a combination of moderate exercise and facial cooling induces a substantial fat loss over a 1- to 2-week period, with an associated ketonuria, proteinuria, and increase of body mass. Possible factors contributing to this fat loss include: (a) a small energy deficit; (b) the energy cost of synthesising new lean tissue; (c) energy loss through the storage and excretion of ketone bodies; (d) catecholamine-induced 'futile' metabolic cycles with increased resting metabolism; and (e) a specific reaction to cold dehydration. Current limitations for the clinical application of such treatment include uncertainty regarding optimal environmental conditions, concern over possible pathological reactions to cold, and suggestions of a less satisfactory fat mobilisation in female patients. Possible interactions between physical fitness and metabolic reactions to cold remain controversial.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Adaptation to exercise in the cold. 388 60


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