Gold Thioglucose Research Articles

Food Restriction Normalizes Chylomicron Remnant Metabolism in Murine Models of Obesity as Assessed by a Novel Stable Isotope Breath Test

Evidence is increasing that defective metabolism of postprandial remnants of triglyceride-rich lipoproteins contributes to atherogenesis. In obesity, postprandial lipemia is increased by mechanisms that are not currently established. In the present study, a recently developed (13)CO(2) breath test was used to assess the metabolism of chylomicron remnants (CR) in obese mice. Six murine obese models ob/ob, fat/fat, New Zealand Obese (NZO), db/db, gold thioglucose (GTG)-treated and agouti (A(y)) were studied. All obese mice were hyperphagic and their breath test metabolism was markedly impaired (P < 0.01) compared with control, nonobese mice. The breath test was also impaired (P < 0.01) in all obese mice except A(y) mice after 24-h food deprivation. However, after restriction to the food intake of paired control mice for 6 wk, the breath test in all obese mice improved to values of control, nonobese mice. The obese NZO, fat/fat and ob/ob mice had significant (P < 0.02) weight loss when food restricted, whereas A(y), GTG, and db/db mice did not. In all obese mice, plasma cholesterol levels decreased (P < 0.02) after the 6-wk period of food restriction. Plasma triglyceride levels significantly decreased (P < 0.02) in NZO, GTG and db/db mice, but not in other obese mice. Plasma glucose levels were significantly decreased (P < 0.02) after the 6-wk period in the obese mice except for the A(y) and NZO mice; levels were greater in food-restricted db/db mice. Although some of the obese models such as db/db were diabetic, our data suggest that the defective breath test was independent of diabetes because all obese and diabetic models responded similarly to food restriction. Impaired hepatic catabolism of CR was excluded as a cause of the abnormal breath tests. In summary, the impairment (P < 0.05) in remnant metabolism as assessed by the breath test in obese mice was corrected by food restriction, associated with improvements in plasma glucose, triglyceride and cholesterol levels.

Leptin deficiency, not obesity, protects mice from Con A-induced hepatitis.

Leptin-deficient ob/ob mice are protected from Con A-induced hepatitis. However, it is unclear whether leptin deficiency or obesity itself is responsible for this protection. To address this question, wild-type (WT) obese mice with high serum leptin levels were generated by injection of gold thioglucose (WT GTG). Both Con A-injected WT and WT GTG mice developed hepatitis, whereas no hepatic damage was observed in ob/ob mice. Moreover, TNF-alpha and IFN-gamma levels as well as expression of the activation marker CD69 were elevated in liver mononuclear cells of WT and WT GTG mice, but not in ob/ob mice following administration of Con A. The liver of WT and WT GTG mice had the same percentage of NK T cells, a lymphocyte population involved in Con A-induced hepatitis. This population decreased equally in both WT and WT GTG mice after Con A injection. In contrast, the liver of ob/ob mice contained 50% less NK T cells compared to WT and WT GTG mice. Furthermore, no decrease in NK T cells was observed in Con A-injected ob/ob mice. We conclude that leptin-deficiency, not obesity, is responsible for protection from Con A-induced hepatitis.

Decreased Resistin Expression in Mice with Different Sensitivities to a High-Fat Diet

The regulation of resistin, a new adipose-derived circulating factor, is the subject of controversy. In particular, the question of its modulation in obesity led to opposite results reported by two different groups. In the current study, we assayed adipocyte resistin mRNA using fluorescent real-time RT-PCR. We studied the expression of resistin in mice which are differently sensitive to diet-induced obesity: the FVB/n strain, which poorly responds to high-fat diet and transgenic mice that express human α2A-AR in adipose tissue in the absence of β3-adrenergic receptor (AR) under the FVB genetic background which are highly sensitive to high-fat diet and develop hyperplastic obesity. We observed that FVB mice, which have no significant increased body weight after an 8-week high-fat diet period, exhibited no alteration of resistin expression. In contrast, the transgenic mice developing high-fat diet-induced obesity exhibited markedly downregulated adipocyte resistin mRNA. We also showed that obesity induced by gold thioglucose injection in FVB/n mice reduces the expression of resistin in isolated adipocytes. This argues for decreased expression of resistin as a hallmark of obesity. Moreover, our data show that feeding a high-fat diet is not a primary determinant of resistin regulation.

The Matricellular Protein SPARC/Osteonectin as a Newly Identified Factor Up-regulated in Obesity

Alterations in the expression level of genes may contribute to the development and pathophysiology of obesity. To find genes differentially expressed in adipose tissue during obesity, we performed suppression subtractive hybridization on epididymal fat mRNA from goldthioglucose (GTG) obese mice and from their lean littermates. We identified the secreted protein acidic and rich in cysteine (SPARC), a protein that mediates cell-matrix interactions and plays a role in modulation of cell adhesion, differentiation, and angiogenesis. SPARC mRNA expression in adipose tissue was markedly increased (between 3- and 6-fold) in three different models of obesity, i.e. GTG mice, ob/ob mice, and AKR mice, after 6 weeks of a high fat diet. Immunoblotting of adipocyte extracts revealed a similar increase in protein level. Using a SPARC-specific ELISA, we demonstrated that SPARC is secreted by isolated adipocytes. We found that insulin administration to mice increased SPARC mRNA in the adipose tissue. Food deprivation had no effect on SPARC expression, but after high fat refeeding SPARC mRNA levels were significantly increased. Our results reveal both hormonal and nutritional regulation of SPARC expression in the adipocyte, and importantly, its alteration in obesity. Finally, we show that purified SPARC increased mRNA levels of plasminogen activator inhibitor 1 (PAI-1) in cultured rat adipose tissue suggesting that elevated adipocyte expression of SPARC might contribute to the abnormal expression of PAI-1 observed in obesity. We propose that SPARC is a newly identified autocrine/paracrine factor that could affect key functions in adipose tissue physiology and pathology.

Characterization of hepatic low- Km outer-ring deiodination in red drum (Sciaenops ocellatus)

The more biologically active thyroid hormone 3,5,3′-triiodothyronine (T 3), is primarily derived from peripheral deiodination of thyroxine (T 4). We characterized hepatic deiodination for a commercially important, warmwater teleost fish, the red drum (Sciaenops ocellatus). Low K m outer-ring deiodination (ORD) activity was determined by production of free iodide ( 125I) upon incubation of hepatic microsomes with radiolabeled T 4. HPLC analysis demonstrated that 125I, and T 3 were produced in equal amounts, thereby validating 125I as a measure of T 3 production. A small amount of 3,3′,5′-triiodothyronine (reverse T 3) was also produced by inner-ring deiodination. Production of 125I was linear over a range of 0–100 μg protein/ml and for incubations of 30 min–4 h. Maximal ORD activity was measured at pH 6.6, 50 mM dithiothreitol (DTT) and an incubation temperature of 20°C. Double reciprocal plots demonstrated that the average apparent K m was 5.1 nM and the average V max was 3.7 pmol T 4 converted/h per mg protein. ORD was not inhibited by propylthiouracil but was 50% inhibited by 90 μM of iodoacetic acid and 7 μM of gold thioglucose. The substrate analog preference was T 4=tetraiodoacetic acid=reverse T 3>triiodoacetic acid≫T 3. In relation to other tissues, ORD for liver>gill>intestine>kidney. Similar hepatic deiodination activity was present in adult wild, aquacultured and laboratory-reared red drum, but in adult wild red drum the optimum temperature was higher. Red drum hepatic low- K m deiodination activity appears to most closely resemble rainbow trout hepatic and mammalian Type II deiodination. Evidence of inner-ring T 4 deiodination suggests a more active hepatic iodothyronine catabolic pathway than in other teleost species.

Expression of UCPs in Obese and Insulin Resistant Mice Induced by Gold Thioglucose

Expression of UCPs in Obese and Insulin Resistant Mice Induced by Gold Thioglucose

Amelioration of insulin resistance but not hyperinsulinemia in obese mice overexpressing GLUT4 selectively in skeletal muscle

The effects of gold-thioglucose (GTG) treatment were examined in mice overexpressing GLUT4 selectively in skeletal muscle (MLC-GLUT4 mice) and in age-matched controls. Groups of MLC-GLUT4 and control mice were injected with GTG or saline at 5 weeks of age. At 12 weeks following the injections, GTG-treated control mice exhibited a 35% increase in body weight versus saline-treated controls. Similarly, a 30% increase in body weight was observed in GTG-treated MLC-GLUT4 mice compared with saline-treated MLC-GLUT4 mice 12 weeks after the injections. In saline-treated lean MLC-GLUT4 and control mice, intraperitoneal injection of insulin decreased blood glucose in 1 hour by 63% and 38%, respectively. Insulin also decreased blood glucose by 40% in GTG-treated obese MLC-GLUT4 mice after 1 hour. However, insulin did not reduce blood glucose levels in GTG-treated obese control mice. The ability of insulin to clear blood glucose in GTG-treated obese MLC-GLUT4 mice is associated with increased skeletal muscle GLUT4 content and white adipose tissue (WAT) GLUT4 content as compared with GTG-treated obese controls. However, fasting blood glucose levels in GTG-treated obese MLC-GLUT4 and control mice were elevated by approximately 30% compared with saline-treated groups. Lastly, although GTG-treated obese MLC-GLUT4 mice exhibited improved glucose clearance in response to insulin, they nevertheless remained as hyperinsulinemic as GTG-treated obese control mice. These results suggest that genetic overexpression of GLUT4 in skeletal muscle may ameliorate the development of insulin resistance associated with obesity but cannot restore normal glucose and insulin levels.

A comparison of extrahepatic lipogenesis from a small glucose meal in obob and gold thioglucose obese mice fed low- or high-fat diets with or without the addition of δ 22-5β-taurocholenic acid

Extrahepatic fatty acid synthesis from a 250 mg meal of [U- 14C]-glucose was measured in epidymal fat pads and the remaining carcass of hyperglycemic obese (obob), gold thioglucose obese, and nonobese controls under conditions of maximum and minimum lipogenesis. Also assessed was the effect of Δ 22-5β-taurocholenic acid, previously shown to inhibit hepatic fatty acid synthesis. Both types of obese and nonobese mice were fed for 6 weeks glucose-based diets containing either 1% corn oil or 40% lard with or without the addition of 0.05% taurocholenic acid. In mice fed 1% corn oil, incorporation of labeled glucose into carcass fatty acids was 25% greater in nonobese than obese mice of either type of obesity. On this diet incorporation of labeled glucose into epididymal fatty acids was reduced 83% in hyperglycemic obese mice compared with nonobese littermates. The corresponding reduction in lipogenesis in gold thioglucose obese mice was only 23% compared with nonobese controls. Feeding 40% lard reduced incorporation of labeled glucose into epididymal and carcass fatty acid 67 to 95% compared with mice fed 1% corn oil in both types of obese and nonobese mice whether or not taurocholenic acid had been fed. Both types of obesity or feeding 40% lard reduced lipogenesis in fat pads to a greater extent than glucose uptake by the pads with the reductions additive. Feeding taurocholenic acid reduced pad weight 30% across strain and obesity status, increased uptake of labeled glucose into epididymal fat pads and increased the percentage of the labeled glucose in the pad recovered as fatty acid in both types of obese and nonobese mice when the diet was 1% corn oil. Similarities and differences between the two obesity models are discussed.

Hepatic Outer-Ring Deiodinase in a Mexican Endemic Lizard (Sceloporus grammicus)

The kinetic characterization of the outer-ring deiodination pathway using rT3 (rT3-ORD) in male, female, and pregnant female livers of an endemic lizard, Sceloporus grammicus, is reported. The ORD pathway does not have the characteristics of deiodinase type II; it is exclusively carried out by deiodinase type I (DI). DI enzymatic activity in lizard liver contains one of the highest activities reported in vertebrates. This activity is sexually dimorphic, with males presenting the highest activity during the reproductive season. The properties of this enzyme correspond to those described in mammals, such as specificity for rT3, susceptibility to inhibition by 6-n-propyl-2-thiouracil and gold–thioglucose, cofactor requirement, and kinetic pattern. Unlike other vertebrates, the lizard DI exhibits conspicuous stability in the thermal range of 15 to 42°C and in the pH range of 5.0 to 9.0. Male true kinetic constants exhibit a direct correlation with temperature. This is in agreement with short-term adaptation to microenvironmental changes and the feasible expression of enzymatic forms/variants which, together, endow this lizard species with a greater adaptation to natural daily ambient thermal fluctuations.

Effect of δ 22-5β-taurocholenic acid on hepatic cholesterol and fatty acid in gold thioglucose obese mice fed low- or high-fat diets

We previously demonstrated that hyperglycemic-obese (obob) mice fed a 1% corn oil diet accumulated 10 times as much hepatic cholesterol as did their non-obese (+/?) littermates fed this diet because of difficulty in removal of cholesterol from the liver rather than from increased synthesis. Furthermore, feeding the bile acid analog Δ 22-5β-taurocholenic acid completely prevented the accumulation of hepatic cholesterol in obob mice fed the 1% corn oil diet. The hypothesis to be tested in the current study is that these aspects of cholesterol metabolism in the obob mouse do not occur in the hyperinsulinemic and insulin-resistant gold thioglucose obese mouse. Gold thioglucose obese (gtgo) and non-obese (ngtgo) mice were fed diets containing either 1% corn oil or 40% lard each with or without added taurocholenic acid for 6 weeks and then given a 250 mg meal of [U- 14C]-glucose with incorporation of label into hepatic cholesterol and fatty acid measured 2 hours later. Consistent with earlier results in the obob model, incorporation of labeled glucose was significantly increased in obese compared with non-obese mice fed 1% corn oil and significantly reduced either by feeding 40% lard or by adding taurocholenic acid to the diet. In addition, taurocholenic acid greatly increased incorporation of labeled glucose into hepatic cholesterol in obese or non-obese mice fed either diet. In contrast to obob mice, the percentage of fat in the liver of gtgo mice was increased only 50% compared with ngtgo mice. The comparable increase in obob mice was 480%. Hepatic cholesterol did not increase significantly in the liver of gtgo mice fed 1% corn oil when compared with the ngtgo controls. The comparable increase in obob mice fed 1% corn oil was 350%. Also in marked contrast to obob mice, feeding taurocholenic acid increased hepatic cholesterol compared with non-obese controls fed either diet. The results are discussed in the light of the presence of circulating leptin in gtgo but not in obob mice.

Cloning and characterization of type III iodothyronine deiodinase from the fish Oreochromis niloticus.

Type III iodothyronine deiodinase (D3) catalyzes the inner ring deiodination (IRD) of T4 and T3 to the inactive metabolites rT3 and 3,3'-diiodothyronine (3,3'-T2), respectively. Here we describe the cloning and characterization of complementary DNA (cDNA) coding for D3 in fish (Oreochromis niloticus, tilapia). This cDNA contains 1478 nucleotides and codes for a protein of 267 amino acids, including a putative selenocysteine (Sec) residue, encoded by a TGA triplet, at position 131. The deduced amino acid sequence shows 57-67% identity with frog, chicken, and mammalian D3, 33-39% identity with frog, fish (Fundulus heteroclitus) and mammalian D2, and 30-35% identity with fish (tilapia), chicken, and mammalian D1. The 3' UTR contains a putative Sec insertion sequence (SECIS) element. Recombinant tilapia D3 (tD3) expressed in COS-1 cells and native tD3 in tilapia brain microsomes show identical catalytic activities, with a strong preference for IRD of T3 (Km approximately 20 nM). IRD of [3,5-125I]T3 by native and recombinant tD3 are equally sensitive to inhibition by substrate analogs (T3 > T4 >> rT3) and inhibitors (gold thioglucose >> iodoacetate > propylthiouracil). Northern analysis using a tD3 riboprobe shows high expression of a 1.6-kb messenger RNA in gill and brain, although D3 activity is much higher in brain than in gill. The characterization of tD3 cDNA provides new information about the structure-activity relationship of iodothyronine deiodinases and an important tool to study the regulation of thyroid hormone bioactivity in fish.

Hyperphagia and weight gain after gold-thioglucose: relation to hypothalamic neuropeptide Y and proopiomelanocortin.

Genetic obesity is associated with increased neuropeptide Y (NPY) messenger RNA (mRNA) and decreased POMC mRNA in the hypothalamus of ob/ob and db/db mice, or impaired sensitivity to alphaMSH (derived from POMC) in the yellow agouti mouse. Acquired obesity can be produced by chemically lesioning the hypothalamus with either monosodium glutamate (MSG) in neonates or gold thioglucose (GTG) in adult mice. The present study examined whether elevated NPY mRNA and/or decreased POMC mRNA in the hypothalamus are associated with obesity due to hypothalamic lesions. GTG injection into adult mice produced a profound obese phenotype, including hyperphagia, increased body weight, and increased leptin mRNA and peptide, in association with reduced hypothalamic NPY mRNA and POMC mRNA. MSG treatment produced virtual elimination of NPY mRNA in the arcuate nucleus and a reduction of hypothalamic POMC mRNA, and led to elevated leptin. MSG pretreatment did not attenuate GTG-induced hyperphagia and obese phenotype. These results do not support a role for NPY-synthesizing neurons in the arcuate nucleus in mediating hypothalamic acquired obesity, but are consistent with the hypothesis that decreased activity of hypothalamic neurons synthesizing POMC play a role in mediating hypothalamic obesity.

Role of neuropeptide Y in diet-, chemical- and genetic-induced obesity of mice.

The goal of this study was to ascertain whether neuropeptide Y (NPY) is required in mice for the development of obesity induced by a high-fat diet (HFD), chemical lesions of the hypothalamus caused by monosodium glutamate (MSG) or gold thioglucose (GTG), impaired brown adipose tissue (BAT) due to a diphtheria toxin transgene driven by the uncoupling protein 1 promoter (UCP-DTA) or the lethal yellow agouti mutation (Ay). The obesity syndrome of the leptin-deficient (ob/ob) mouse can be partially reversed by the genetic removal of NPY. In the murine models of obesity examined in this study, the animals become obese despite increased serum leptin levels, indicating that they are resistant to the weight-limiting actions of leptin. The role of NPY in these obesity models with elevated leptin levels is unknown. Mice lacking NPY due to genetic disruption of the gene and wildtype littermates were made obese by allowing them access to a highly palatable HFD, by treatment with MSG, or GTG, or by inheriting the dominant UCP-DTA or Ay alleles. Food consumption, body weight and dissectable fat pad weights were measured and compared to values obtained from non-obese littermates. In each model of obesity tested, NPY-deficient mice achieved the same food intake, body weight and fat content as wildtype littermates. NPY is not necessary for the progressive development of obesity exhibited by multiple murine models with leptin resistance.

Inhibition of Erythrocyte Selenium-Glutathione Peroxidase by Auranofin Analogues and Metabolites

The effect of gold ligation on the inhibition of bovine erythrocyte selenium-glutathione peroxidase (GSH-Px) was examined. The anti-arthritic drug auranofin [2,3,4,6-tetra- O-acetyl-1-thio-β- d-glucopyranosato- S)(triethylphosphine) gold(I)] (Et 3PAuSATg) and its analogue, Et 3PAuCl, exhibited experimentally equivalent K i values (11.6 ± 0.8 and 10.8 ± 0.5 μM, respectively), despite the greatly disparate affinities of their ligands for gold(I): 2,3,4,6-tetra- O-acetyl-1-thiolato-β- d-glucopyranose (ATgS −) ≫ Cl −. This similarity reflects ligand exchange reactions that generate the glutathione complex Et 3PAuSG from the excess glutathione (GSH, 1 mM) used in the assay. The K i values for bis(glutathionato)gold(I) (Au(SG) 2 −) and gold(I) thioglucose (AuSTg) were also found to be equal (2.8 ± 0.4 and 2.4 ± 0.5 μM, respectively). This confirms the previous postulate of Chaudiere and Tappel ( J Inorg Biochem20: 313–325, 1984) that Au(SG) 2 − is generated from AuSTg in the presence of excess glutathione. Since auranofin metabolites accumulate in red blood cells, the inhibition of intracellular GSH-Px was examined by using intact erythrocytes. There was greater inhibition of the reaction when the cells were resuspended in isotonic buffer than in whole blood, because serum albumin in the latter competes for the auranofin and decreases the uptake by erythrocytes. After correction for the extent of gold uptake, the K i values were determined to be the same as those observed for Au(SG) 2 − in the extracellular assay, indicating loss of both the Et 3P and ATgS − ligands from auranofin. Thus, the inhibition of GSH-Px by gold complexes is dependent on their ligation, and the ultimate gold(I) compound that interacts with erythrocyte GSH-Px in intact red cells, Au(SG) 2 −, is radically different from the original auranofin molecule.

Anatomic localization of alternatively spliced leptin receptors (Ob-R) in mouse brain and other tissues.

Leptin's effects are mediated by interactions with a receptor that is alternatively spliced, resulting in at least five different murine forms: Ob-Ra, Ob-Rb, Ob-Rc, Ob-Rd, and Ob-Re. A mutation in one splice form, Ob-Rb, results in obesity in mice. Northern blots, RNase protection assays, and PCR indicate that Ob-Rb is expressed at a relatively high level in hypothalamus and low level in several other tissues. Ob-Ra is expressed ubiquitously, whereas Ob-Rc, -Rd, and -Re RNAs are only detectable using PCR. In hypothalamus, Ob-Rb is present in the arcuate, ventromedial, dorsomedial, and lateral hypothalamic nuclei but is not detectable in other brain regions. These nuclei are known to regulate food intake and body weight. The level of Ob-Rb in hypothalamus is reduced in mice rendered obese by gold thioglucose (GTG), which causes hypothalamic lesions. The obesity in GTG-treated mice is likely to be caused by ablation of Ob-Rb-expressing neurons, which results in leptin resistance.

Exploring the expression of the melanin-concentrating hormone messenger RNA in the rat lateral hypothalamus after goldthioglucose injection

Melanin-concentrating hormone (MCH) is expressed in a large neuronal population of the rat lateral hypothalamus. This area is known to be implicated in the regulation of thirst and hunger and to contain glucose-sensitive cells. In the present study, we investigated the effects of goldthioglucose (GTG), a toxic form of glucose, on the expression of the MCH gene in the rat lateral hypothalamus by immunocytochemistry, in situ hybridization and competitive RT-PCR. We observed that the MCH immunoreactivity and the level of MCH mRNA were not changed after intraperitoneal GTG injection (0.35 mg/g body weight). These results together with previous data suggest that the glucose-sensitive cells of the lateral hypothalamus are different from the MCH neurons and remain to be identified.

Characterization of a propylthiouracil-insensitive type I iodothyronine deiodinase.

Mammalian type I iodothyronine deiodinase (D1) activates and inactivates thyroid hormone by outer ring deiodination (ORD) and inner ring deiodination (IRD), respectively, and is potently inhibited by propylthiouracil (PTU). Here we describe the cloning and characterization of a complementary DNA encoding a PTU-insensitive D1 from teleost fish (Oreochromis niloticus, tilapia). This complementary DNA codes for a protein of 248 amino acids, including a putative selenocysteine (Sec) residue, encoded by a TGA triplet, at position 126. The 3' untranslated region contains two putative Sec insertion sequence (SECIS) elements. Recombinant enzyme expressed in COS-1 cells catalyzes both ORD of T4 and rT3 and IRD of T3 and T3 sulfate with the same substrate specificity as native tilapia D1 (tD1), i.e. rT3 >> T4 > T3 sulfate > T3. Native and recombinant tD1 show equally low sensitivities to inhibition by PTU, iodoacetate, and gold thioglucose compared with the potent inhibitions observed with mammalian D1s. Because the residue 2 positions downstream from Sec is Pro in tD1 and in all (PTU-insensitive) type II and type III iodothyronine deiodinases but Ser in all PTU-sensitive D1s, we prepared the Pro128Ser mutant of tD1. The mutant enzyme showed strongly decreased ORD and somewhat increased IRD activity, but was still insensitive to PTU. These results provide new information about the structure-activity relationship of D1 concerning two characteristic properties, i.e. catalysis of both ORD and IRD, and inhibition by PTU.

Injection with gold thioglucose impairs sensitivity to glucose: evidence that glucose-responsive neurons are important for long-term regulation of body weight

It has been proposed, but never demonstrated, that glucose-responsive neurons are essential for the long-term regulation of body weight, and that mice injected with gold-thio-glucose (GTG) become obese due to destruction of glucose-responsive neurons. To assess these hypotheses, mice were injected with either saline (control) or a dose of GTG that produces obesity, and the effects on feeding of peripheral injection of saline, glucose, 2-deoxyglucose (2-DG), or cholecystokinin (CCK) were measured. In control mice, 2-DG increased, whereas glucose and CCK decreased, food intake significantly. In contrast, in GTG-treated mice, 2-DG and glucose did not have a significant effect on food intake. The GTG-treated mice remained sensitive to the inhibitory effect of CCK on food intake. These data indicate that i.p. injection of GTG, which produces obesity, also destroys glucose-responsive neurons, consistent with the hypothesis that glucose-responsive neurons contribute to the long-term regulation of body weight.

Injection with gold thioglucose impairs sensitivity to glucose: evidence that glucose-responsive neurons are important for long-term regulation of body weight

It has been proposed, but never demonstrated, that glucose-responsive neurons are essential for the long-term regulation of body weight, and that mice injected with gold-thio-glucose (GTG) become obese due to destruction of glucose-responsive neurons. To assess these hypotheses, mice were injected with either saline (control) or a dose of GTG that produces obesity, and the effects on feeding of peripheral injection of saline, glucose, 2-deoxyglucose (2-DG), or cholecystokinin (CCK) were measured. In control mice, 2-DG increased, whereas glucose and CCK decreased, food intake significantly. In contrast, in GTG-treated mice, 2-DG and glucose did not have a significant effect on food intake. The GTG-treated mice remained sensitive to the inhibitory effect of CCK on food intake. These data indicate that i.p. injection of GTG, which produces obesity, also destroys glucose-responsive neurons, consistent with the hypothesis that glucose-responsive neurons contribute to the long-term regulation of body weight.

Hepatic gluconeogenesis and the activity of PDH in individual tissues of GTG-obese mice following adrenalectomy.

Adrenalectomy (ADX) lowers circulating glucose levels in animal models of non-insulin dependent diabetes (NIDDM) and obesity. To investigate the role of hepatic glucose production (HGP) and tissue glucose oxidation in the improvement in glucose tolerance, hepatocyte gluconeogenesis and the activity of pyruvate dehydrogenase (PDH) were examined in different tissues of gold thioglucose (GTG) obese mice 2 weeks after ADX or sham ADX. GTG-obese mice which had undergone ADX weighed significantly less than their adrenal intact counterparts (GTG ADX: 37.5 +/- 0.7 g; GTG: 44.1 +/- 0.4; p < 0.05), and demonstrated lower serum glucose (GTG ADX: 22.5 +/- 1.6 mmol/L; GTG: 29.4 +/- 1.9 mmol/L; p < 0.05) and serum insulin levels (GTG ADX: 76 +/- 10 microU/mL; GTG: 470 +/- 63 microU/mL; p < 0.05). Lactate conversion to glucose by hepatocytes isolated from ADX GTG mice was significantly reduced compared with that of hepatocytes from GTG mice (GTG ADX: 125 +/- 10 nmol glucose/10(6) cells; GTG: 403 +/- 65 nmol glucose/10(6) cells; p < 0.05). ADX also significantly reduced both the glycogen (GTG ADX: 165 +/- 27 mumol/liver; GTG: 614 +/- 60 mumol/liver; p < 0.05) and fatty acid content (GTG ADX: 101 +/- 9 mg fatty acid/g liver; GTG: 404 +/- 40 mg fatty acid/g liver; p < 0.05) of the liver of GTG-obese mice. ADX of GTG-obese mice reduced PDH activity by varying degrees in all tissues, except quadriceps muscle. These observations are consistent with an ADX induced decrease in hepatic lipid stores removing fatty acid-induced increases in gluconeogenesis and increased peripheral availability of fatty acids inhibiting PDH activity via the glucose/fatty acid cycle. It is also evident that the improvement in glucose tolerance which accompanies ADX of GTG-obese mice is not due to increased PDH activity resulting in enhanced peripheral glucose oxidation. Instead, it is more likely that reduced blood glucose levels after ADX of GTG-obese mice are the result of decreased gluconeogenesis in the liver.