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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In mitochondria, ATP synthesis is coupled to oxygen consumption by the proton electrochemical gradient established across the mitochondrial inner membrane in a process termed oxidative phosphorylation. It has long been known from stoichiometric studies that ATP synthesis is not perfectly coupled to oxygen consumption. The major inefficiency in the system is leakage of protons across the mitochondrial inner membrane driven by the proton electrochemical gradient. The kinetics of the proton leak can be determined indirectly, by measuring the oxygen consumption of mitochondria under non-phosphorylating conditions (plus oligomycin) as a function of the proton electrochemical gradient. This experimental system provides a convenient means to investigate inner membrane permeability to protons and the effect of factors that may effect that permeability. In this paper we review some results from our laboratory of indirect measurement of mitochondrial proton leak and how it has been applied to investigate the effect of aging, obesity and thyroid status on proton leak. The results show that (i) proton leak in isolated liver mitochondria is not significantly different in a comparison of young and old rats, in contrast (ii) there is an apparent increase in proton leak in in situ mitochondria in hepatocytes from old rats when compared to those from young rats, (iii) proton leak in neuronal mitochondria in situ in synaptosomes is not significantly different in young and old rats, (iv) proton leak is greater in isolated liver mitochondria from ob/ob mice compared to lean controls, (v) acute leptin (OB protein) administration restores the increased leak rate in isolated liver mitochondria from ob/ob mice to that of lean controls, (vi) administration of thyroid hormone (T3) increases proton leak in rat muscle mitochondria, and (vii) proton leak in muscle mitochondria is insensitive to the presence of GDP. It is proposed that the experimental system described here for measuring proton leak, is an ideal functional assay for determining whether the novel uncoupling proteins increase inner membrane permeability to protons.
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PMID:Indirect measurement of mitochondrial proton leak and its application. 1045 15

Patients with myelomeningocele show an increased incidence of endocrinological disorders during their childhood. These disorders can ulteriorly affect the adult height of these patients who are already extremely short. In the present study we determined the final height in 21 patients (11 females aged 20.55 +/- 3.54 years; 10 males aged 20.99 +/- 2.94 years) with myelomeningocele. The endocrinological implications were investigated by clinical and laboratory assessment at control and an accurate retrospective evaluation of individual clinical history. Auxological data indicated that in male patients mean final height was significantly less (P < 0.05) than target height, but in females the difference between final height and target height was even more marked (P < 0.001). Comparison of SDS for adult height between males (-2.04 +/- 1.89) and females (-4.36 +/- 2.24) evidenced a statistically significant difference (P < 0.05). The analysis of endocrinological data showed that 7 females had had precocious puberty not treated; no case of precocious puberty was evidenced in males. In 4 females we observed plasmatic IGF-1 and IGFBP-3 concentrations significantly reduced either for chronological age and pubertal stage; this finding emerged in only 1 male. Plasmatic thyroid hormone and adrenal steroid concentrations resulted normal in both groups. Finally, obesity, considered as BMI > 90%, resulted present since childhood in 4 females and 2 males. Our data show that females with myelomeningocele have a statistically greater decrease of their adult stature respect to males. This difference is probably due to a more significant incidence in females of endocrinological diseases. Thus, we believe that a better statural prognosis may be joined in these patients (particularly in girls), through a careful endocrinological follow-up, performed from their births, in order to ensure a prompt identification and treatment of the cases of precocious puberty, impaired GH secretion or obesity.
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PMID:[Precocious puberty, Gh deficiency and obesity can affect final height in patients with myelomeningocele: comparison of males and females]. 1057 Jul 85

Uncoupling protein-3 (UCP3) is a mitochondrial protein that can diminish the mitochondrial membrane potential. Levels of muscle Ucp3 mRNA are increased by thyroid hormone and fasting. Ucp3 has been proposed to influence metabolic efficiency and is a candidate obesity gene. We have produced a Ucp3 knockout mouse to test these hypotheses. The Ucp3 (-/-) mice had no detectable immunoreactive UCP3 by Western blotting. In mitochondria from the knockout mice, proton leak was greatly reduced in muscle, minimally reduced in brown fat, and not reduced at all in liver. These data suggest that UCP3 accounts for much of the proton leak in skeletal muscle. Despite the lack of UCP3, no consistent phenotypic abnormality was observed. The knockout mice were not obese and had normal serum insulin, triglyceride, and leptin levels, with a tendency toward reduced free fatty acids and glucose. Knockout mice showed a normal circadian rhythm in body temperature and motor activity and had normal body temperature responses to fasting, stress, thyroid hormone, and cold exposure. The base-line metabolic rate and respiratory exchange ratio were the same in knockout and control mice, as were the effects of fasting, a beta3-adrenergic agonist (CL316243), and thyroid hormone on these parameters. The phenotype of Ucp1/Ucp3 double knockout mice was indistinguishable from Ucp1 single knockout mice. These data suggest that Ucp3 is not a major determinant of metabolic rate but, rather, has other functions.
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PMID:Lack of obesity and normal response to fasting and thyroid hormone in mice lacking uncoupling protein-3. 1074 95

Thyroid hormones influence the function of many organs and mediate their diverse actions through two types of thyroid hormone receptors, TRalpha and TRbeta. Little is known about effects of ligands that preferentially interact with the two different TR subtypes. In the current study the comparison of the effects of the novel synthetic TRbeta-selective compound GC-1 with T3 at equimolar doses in hypothyroid mice revealed that GC-1 had better triglyceride-lowering and similar cholesterol-lowering effects than T3. T3, but not GC-1, increased heart rate and elevated messenger RNA levels coding for the I(f) channel (HCN2), a cardiac pacemaker that was decreased in hypothyroid mice. T3 had a larger positive inotropic effect than GC-1. T3, but not GC-1, normalized heart and body weights and messenger RNAs of myosin heavy chain alpha and beta and the sarcoplasmic reticulum adenosine triphosphatase (Serca2). Additional dose-response studies in hypercholesteremic rats confirmed the preferential effect of GC-1 on TRbeta-mediated parameters by showing a much higher potency to influence cholesterol and TSH than heart rate. The preferred accumulation of GC-1 in the liver vs. the heart probably also contributes to its marked lipid-lowering effect vs. the absent effect on heart rate. These data indicate that GC-1 could represent a prototype for new drugs for the treatment of high lipid levels or obesity.
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PMID:The thyroid hormone receptor-beta-selective agonist GC-1 differentially affects plasma lipids and cardiac activity. 1096 73

Thyroid hormones have important thermogenic function. Nevertheless, thyroid dysfunctions are often associated with minor changes in body weight and fat mass. On the other hand, both overfeeding and fasting have important effects on iodothyronine metabolism and regulation of deiodinase activity. Although under debate, there are clinical and theoretical reasons to administer low-dose thyroid hormones (T3) in selected obese patients. This short review deals with both pathophysiological and clinical aspects of thyroid hormone used in the therapy of obesity.
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PMID:Thyroid hormones and treatment of obesity. 1099 25

Leptin is a mainly adipocyte-secreted protein that was discovered 5 years ago. Most of the research following this discovery focused on the role of leptin in body weight regulation, aiming to illuminate the pathophysiology of human obesity. However, more and more data are emerging that leptin is not only important in the regulation of food intake and energy balance, but that it also has a function as a metabolic and neuroendocrine hormone. It is now clear that it is especially involved in glucose metabolism, as well as in normal sexual maturation and reproduction. Besides this, interactions with the hypothalamic-pituitary-adrenal, thyroid and GH axes and even with haematopoiesis and the immune system have also been described. It has been shown that leptin secretion by the adipocyte is partly regulated by other hormones, such as insulin, cortisol, and sex steroids, mainly testosterone. Also, other hormones like thyroid hormone and GH are possibly involved in leptin synthesis. Leptin itself exerts effects on different endocrine axes, mainly on the hypothalamic-pituitary-gonadal axis and on insulin metabolism, but also on the hypothalamic-pituitary-adrenal, thyroid and GH axes. Leptin may thus be considered a new endocrine mediator, besides its obvious role in body weight regulation.
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PMID:Human leptin: from an adipocyte hormone to an endocrine mediator. 1102 69

Physicians have struggled with the pharmacological treatment of obesity. In the past, thyroid hormone was often used inappropriately. Dangerous drugs such as dinitrophenol and amphetamines were prescribed, with serious side effects. In the 1980s, a 3 1/2-year study using antiobesity medications with different mechanisms of action supported the theory that patients treated with combination therapy experienced greater weight loss than the placebo-treated patients and that those who remained on therapy were more likely to keep the weight off. Thus, physicians began prescribing "fen-phen" to their patients in the mid-1990s. In 1997, manufacturers voluntarily withdraw the fenfluramines from the market after study results linked their use with valvular heart disease. Since then, two new drugs with different mechanisms of action have been approved for use by the FDA. Sibutramine (Meridia) is a serotonin-norepinephrine reuptake inhibitor acting on the appetite center in the hypothalamus, and orlistat (Xenical) is a pancreatic lipase inhibitor. Research on antiobesity drugs continues. More than 30 potentially new drugs are in various stages of research. It could be years, however, before any of them are proven useful and safe. Antiobesity pharmacology is meant to be used as a tool to treat the disease. Lifestyle changes in the form of diet and exercise patterns are still the crux of therapy.
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PMID:Pharmacological treatment of obesity. Past, present, and future. 1112 76

The aim of this retrospective study was to investigate the frequency of thyroid dysfunction as assessed by TSH, T3 and T4 in a large cohort of 290 obese and 280 healthy children. In addition, thyroid autoantibodies were measured in random subgroups of 123 obese and 80 control children, iodine excretion in 50 and thyroid volume in 23 of the obese children. Elevated TSH levels (>4 U/l) were found in 22 obese children (7.5%), but only in one control (0.3%). The medians of TSH and T3 concentrations were normal, but significantly higher in the obese group than in the controls, while T4 levels did not differ. The prevalence of positive thyroid autoantibodies was increased in the obese children, for the most part in those with elevated TSH. There was no evidence for iodine deficiency as a cause of the average increase of TSH. We conclude that in childhood obesity TSH and T3 levels are significantly increased; in most cases, however, these increases are not accounted for by thyroid autoimmunity or iodine deficiency. As a consequence, TSH elevations with normal thyroid hormone levels in obese children don't need any thyroxine treatment, if thyroid disorders were definitely excluded beforehand.
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PMID:Thyroid function and obesity in children and adolescents. 1118 30

There is accumulating evidence to support the hypothesis that a low-energy-output phenotype is at high risk of weight gain and obesity, irrespective of whether this is owing to a low resting metabolic rate and/or physical inactivity. The low-energy-output phenotype is associated with impaired appetite control, which is improved if energy output is increased. This is the background for pharmacologic stimulation of energy expenditure as a tool to improve the results of obesity management. Targets are the leptin receptors, the sympathetic nervous system and its peripheral beta-adrenoceptors, selective thyroid hormone derivatives, and stimulation of the mitochondrial uncoupling proteins. Currently available compounds such as recombinant leptin, ephedrine/caffeine, and sibutramine possess thermogenic properties owing to their activation of the sympathoadrenal system. Compounds acting selectively on the human beta3-adrenoceptor are still promising tools to achieve a sustained stimulation of lipolysis and energy expenditure, and several are in the pipeline.
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PMID:Thermogenic drugs as a strategy for treatment of obesity. 1118 22

Thyroid hormone T3/T4 is a major regulator of energy metabolism in vertebrates, and defects in thyroid status are frequently associated with changes in body weight. It is demonstrated here that thyroid hormone regulates in vivo and in vitro the tub gene, which when mutated in tubby mice causes obesity, insulin resistance and sensory deficits. Hypothyroidism in rats altered tub mRNA and protein in discrete brain areas. These changes could be attributed to thyroid hormone deficiency since T3/T4 treatment restored normal tub expression. T3 also upregulated tub mRNA within 4-6 h in neuronal cells in culture, suggesting that T3 is a positive regulator of tub gene expression. Thus, these results establish a novel pathway of T3 action and provide an important molecular link between thyroid status and the tubby-associated syndrome.
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PMID:Thyroid hormone regulates the obesity gene tub. 1141 82


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