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Wu H, Sui C, Xia F, Zhai H, Zhang H, Xu H, Weng P, Lu Y. Effects of exenatide therapy on insulin resistance in the skeletal muscles of high-fat diet and low-dose streptozotocin-induced diabetic rats. Endocr Res 2016; 41:1-7. [PMID: 26361069 DOI: 10.3109/07435800.2015.1015726] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE The glucagon-like peptide (GLP)-1 agonist exenatide shows the same multiple effects on glucose homeostasis as native GLP-1, which can reduce blood glucose levels in individuals with type-2 diabetes mellitus (T2DM). However, its underlying action mechanism on glucose metabolism in the skeletal muscle of T2DM cases is unknown. We investigated the effects and action mechanisms of exenatide on insulin resistance (IR) in the skeletal muscle of high-fat diet and low-dose streptozotocin-induced T2DM rats. METHODS Four groups of Sprague-Dawley rats were studied: non-T2DM (control, C); non-T2DM + exenatide (C + E); T2DM (D); and T2DM + exenatide (D + E). After eight weeks, isotope-tracer methodology was applied to measure the total rate of appearance (Ra) of glucose and glucose infusion rate (GIR) using a hyperinsulinemic-euglycemic clamp with 3-(3)H-glucose infusion. Glucose uptake in gastrocnemius muscles was determined by measuring 2-deoxy-D-(14)C-glucose radioactivity. Simultaneously, ultrastructural changes in the cells of gastrocnemius muscles were studied. RESULTS In the D + E group, body weight and levels of fasting plasma glucose, triglyceride, total cholesterol, low-density lipoprotein and insulin were decreased significantly (p < 0.01) compared with the D group. The Ra of glucose (94.70 ± 13.46 versus 121.07 ± 16.55 μmol/kg/min) was decreased (p < 0.01), whereas the exogenous GIR (144.68 ± 11.03 versus 114.50 ± 9.40 μmol/kg/min) and glucose uptake in muscle (0.24 ± 0.02 versus 0.17 ± 0.02 μmol/g/min) were increased markedly (p < 0.01). Ultrastructural observations revealed that exenatide attenuated the effect of swollen mitochondrial and endoplasmic reticulum within the cells of the skeletal muscle of T2DM rats. CONCLUSIONS These data suggest that exenatide can significantly improve insulin sensitivity in skeletal muscle by increasing glucose uptake in T2DM rats.
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Affiliation(s)
- Hui Wu
- a Department of Endocrinology , Zhejiang Provincial People's Hospital , Hangzhou , P.R. China and
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Chunhua Sui
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Fangzhen Xia
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Hualing Zhai
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Huixin Zhang
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Hui Xu
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Pan Weng
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
| | - Yingli Lu
- b Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine , Shanghai , P.R. China
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Wu H, Sui C, Xu H, Xia F, Zhai H, Zhang H, Weng P, Han B, Du S, Lu Y. The GLP-1 analogue exenatide improves hepatic and muscle insulin sensitivity in diabetic rats: tracer studies in the basal state and during hyperinsulinemic-euglycemic clamp. J Diabetes Res 2014; 2014:524517. [PMID: 25580440 PMCID: PMC4279913 DOI: 10.1155/2014/524517] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Revised: 10/17/2014] [Accepted: 10/18/2014] [Indexed: 12/27/2022] Open
Abstract
OBJECTIVE Glucagon-like peptide-1 (GLP-1) analogues (e.g., exenatide) increase insulin secretion in diabetes but less is known about their effects on glucose production or insulin-stimulated glucose uptake in peripheral tissues. METHODS Four groups of Sprague-Dawley rats were studied: nondiabetic (control, C); nondiabetic + exenatide (C + E); diabetic (D); diabetic + exenatide (D + E) with diabetes induced by streptozotocin and high fat diet. Infusion of 3-(3)H-glucose and U-(13)C-glycerol was used to measure basal rates of appearance (Ra) of glucose and glycerol and gluconeogenesis from glycerol (GNG). During hyperinsulinemic-euglycemic clamp, glucose uptake into gastrocnemius muscles was measured with 2-deoxy-D-(14)C-glucose. RESULTS In the diabetic rats, exenatide reduced the basal Ra of glucose (P < 0.01) and glycerol (P < 0.01) and GNG (P < 0.001). During the clamp, Ra of glucose was also reduced, whereas the rate of disappearance of glucose increased and there was increased glucose uptake into muscle (P < 0.01) during the clamp. In the nondiabetic rats, exenatide had no effect. CONCLUSION In addition to its known effects on insulin secretion, administration of the GLP-1 analogue, exenatide, is associated with increased inhibition of gluconeogenesis and improved glucose uptake into muscle in diabetic rats, implying improved hepatic and peripheral insulin sensitivity.
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Affiliation(s)
- Hui Wu
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Chunhua Sui
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Hui Xu
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Fangzhen Xia
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Hualing Zhai
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Huixin Zhang
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Pan Weng
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Bing Han
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Sichun Du
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Yingli Lu
- Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People's Hospital Affiliated Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
- *Yingli Lu:
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Badin PM, Langin D, Moro C. Dynamics of skeletal muscle lipid pools. Trends Endocrinol Metab 2013; 24:607-15. [PMID: 23988586 DOI: 10.1016/j.tem.2013.08.001] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Revised: 07/22/2013] [Accepted: 08/03/2013] [Indexed: 11/20/2022]
Abstract
Intramyocellular triacylglycerol (IMTG) is emerging as an important energy fuel source during muscle contraction and are adaptively increased in response to exercise, without adverse physiological effects. Paradoxically, elevated IMTG content in obese and type 2 diabetics has been linked to insulin resistance, highlighting the importance of IMTG pools in physiology and pathology. Two separate views suggest that IMTG dynamics are determinant for skeletal muscle fat oxidation, and that disruption of IMTG dynamics facilitates the accumulation of lipotoxic intermediates such as diacylglycerols and ceramides that interfere with insulin signaling. Thus, understanding the factors that control IMTG dynamics is crucial. Here we discuss recent literature describing the regulation of IMTG pools with a particular emphasis on lipases and lipid droplet (LD)-associated proteins.
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Affiliation(s)
- Pierre-Marie Badin
- Obesity Research Laboratory, Institut National de la Santé et de la Recherche Médicale (INSERM) Unité Mixte de Recherche (UMR) 1048, Institute of Metabolic and Cardiovascular Diseases (I2MC), Toulouse, France; University of Toulouse, UMR1048, Paul Sabatier University, Toulouse, France
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Xia F, Xu X, Zhai H, Meng Y, Zhang H, Du S, Xu H, Wu H, Lu Y. Castration-induced testosterone deficiency increases fasting glucose associated with hepatic and extra-hepatic insulin resistance in adult male rats. Reprod Biol Endocrinol 2013; 11:106. [PMID: 24238614 PMCID: PMC4225661 DOI: 10.1186/1477-7827-11-106] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/01/2013] [Accepted: 11/07/2013] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Testosterone deficiency is associated with insulin resistance. However, how testosterone deficiency affects insulin actions remains unclear. The aim of this study was to investigate the influence of castration-induced testosterone deficiency on the metabolic kinetics of glucose and to evaluate the hepatic and extra-hepatic insulin sensitivity, in advanced-age male Sprague-Dawley (SD) rats. METHODS Ten-week-old male SD rats were randomly divided into three groups: (1) a control group (n = 10) in which the rats underwent sham castration (2) a castrated group (TD group for testosterone deficiency, n = 10) in which the rats underwent bilateral orchidectomy surgery and (3) a castrated group given testosterone propionate via intraperitoneal injection (25 mg/kg/day) to supplement androgen (TD + TP group, n = 10). At ten weeks after castration in the noted groups, all rats were subjected to an oral glucose tolerance test (OGTT), a pyruvate tolerance test (PTT) and an insulin tolerance test (ITT). Twenty weeks following that treatment, all rats underwent a hyperinsulinemic-euglycemic clamp procedure in conjunction with isotope--labeled glucose and glycerol tracer infusions. The rate of appearance (Ra) of glucose, glycerol and gluconeogenesis (GNG), hepatic glucose production and the rate of glucose disappearance (Rd) were assessed. Glucose uptake was determined by measuring the 2-deoxy-D-14C-glucose in the gastrocnemius muscles. RESULTS Ten weeks after castration in the TD group, the fasting blood glucose and insulin levels were significantly increased (p < 0.01), the glucose-- induced insulin secretion was impaired and ITT revealed a temporarily increased whole body insulin sensitivity compared with the control group; 30 weeks after castration, the Ra of glucose, Ra of glycerol, as well as the HGP and GNG were also increased (p < 0.01), while the exogenous glucose infusion rate and uptake glucose in the muscle markedly decreased (p < 0.01). CONCLUSIONS Castration-induced testosterone deficiency primarily increases fasting blood glucose levels. The clamp experiments revealed a clear insulin resistance both at the hepatic and extra-hepatic levels.
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Affiliation(s)
- Fangzhen Xia
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Xiao Xu
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Hualing Zhai
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Ying Meng
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Huixin Zhang
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Shichun Du
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Hui Xu
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Hui Wu
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
| | - Yingli Lu
- Endocrinology and Metabolism Research Institute and Department of Endocrinology and Metabolism, Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai 200011, China
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Yin J, Gao Z, He Q, Zhou D, Guo Z, Ye J. Role of hypoxia in obesity-induced disorders of glucose and lipid metabolism in adipose tissue. Am J Physiol Endocrinol Metab 2009; 296:E333-42. [PMID: 19066318 PMCID: PMC2645021 DOI: 10.1152/ajpendo.90760.2008] [Citation(s) in RCA: 214] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Recent studies suggest that adipose tissue hypoxia (ATH) may contribute to endocrine dysfunction in adipose tissue of obese mice. In this study, we examined hypoxia's effects on metabolism in adipocytes. We determined the dynamic relationship of ATH and adiposity in ob/ob mice. The interstitial oxygen pressure (Po(2)) was monitored in the epididymal fat pads for ATH. During weight gain from 39.5 to 55.5 g, Po(2) declined from 34.8 to 20.1 mmHg, which are 40-60% lower than those in the lean mice. Insulin receptor-beta (IRbeta) and insulin receptor substrate-1 (IRS-1) were decreased in the adipose tissue of obese mice, and the alteration was observed in 3T3-L1 adipocytes after hypoxia (1% oxygen) treatment. Insulin-induced glucose uptake and Akt Ser(473) phosphorylation was blocked by hypoxia in the adipocytes. This effect of hypoxia exhibited cell type specificity, as it was not observed in L6 myotubes and betaTC6 cells. In response to hypoxia, free fatty acid (FFA) uptake was reduced and lipolysis was increased in 3T3-L1 adipocytes. The molecular mechanism of decreased fatty acid uptake may be related to inhibition of fatty acid transporters (FATP1 and CD36) and transcription factors (PPARgamma and C/EBPalpha) by hypoxia. The hypoxia-induced lipolysis was observed in vivo after femoral arterial clamp. Necrosis and apoptosis were induced by hypoxia in 3T3-L1 adipocytes. These data suggest that ATH may promote FFA release and inhibit glucose uptake in adipocytes by inhibition of the insulin-signaling pathway and induction of cell death.
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Affiliation(s)
- Jun Yin
- Pennington Biomedical Research Center, Louisiana State Univ. System, 6400 Perkins Rd., Baton Rouge, LA 70808, USA
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Xu J, Zhou L, Persson XM, Balagopal P, Jensen MD, Guo Z. Oxidation of Intracellular and Extracellular Fatty Acids in Skeletal Muscle: Application of kinetic modeling, stable isotopes and liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry technology. EUR J LIPID SCI TECH 2008; 110:5-15. [PMID: 23616729 DOI: 10.1002/ejlt.200600267] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Fatty acids are a major fuel for many tissues and abnormal utilization is implicated in diseases. However, tissue fatty acid oxidation has not been determined reliably in vivo. Furthermore, fatty acid oxidation has not been partitioned into intracellular and extracellular components. In this report, a one-pool model is described that enables direct quantitation of fluxes of intracellular and plasma fatty acids to mitochondria in skeletal muscle using dual stable isotopes and liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry (LC/ESI-itMS2) technology. It is validated by the determination of palmitate oxidation by skeletal muscle in lean and obese rats and the regulation by insulin. Resting postabsorptive intramyocellular and plasma palmitate oxidation by gastrocnemius muscle was determined to be 3.47±0.8 and 2.06±0.5 nmol/g min in lean and 6.96±1.8 and 1.34±0.2 nmol/g min in obese rats, respectively. In obese rats, hyperinsulinemia (1 nmol/l) suppressed intramyocellular (by 59±5% to 2.88±0.3 nmol/g min P<0.05) but not plasma (1.41±0.14 nmol/g min, P>0.05) palmitate oxidation. The fractional turnover rate of palmitoylcarnitine (0.34±0.1/min vs. 0.83±0.2/min, P<0.05) was also suppressed by insulin. In obese and lean rats, there are 83% and 51%, respectively (P=0.08), of plasma fatty acids traverse triglyceride pool before being oxidized. The results demonstrated that the methodology is feasible and sensitive to metabolic alterations and thus can be used to study fatty acid utilization at tissue level in a compartmentalized manner for the firs time.
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Affiliation(s)
- J Xu
- Endocrine Research Unit, Mayo Foundation, Rochester, MN, USA
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Guo Z. Intramyocellular lipids: maker vs. marker of insulin resistance. Med Hypotheses 2007; 70:625-9. [PMID: 17766054 PMCID: PMC2288617 DOI: 10.1016/j.mehy.2007.03.044] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2007] [Accepted: 03/23/2007] [Indexed: 11/28/2022]
Abstract
Intramyocellular triglyceride (imcTG) content in skeletal muscle is abnormally high in lipid oversupply models in obesity, type 2 diabetes (T2D) and other metabolically diseased conditions. The imcTG abnormality was also found to be significantly correlated with muscle insulin resistance (MIR). As skeletal muscle is the main site for insulin-mediated glucose utilization, the research on this topic has been active since. However, to date the pathways responsible for the imcTG excess and the mechanisms underlying the imcTG-MIR correlation have not been identified. A current view is focused on a backward mechanism that fatty acid oxidation by muscle is impaired causing imcTG to accumulate and, therefore, an enlarged imcTG pool is merely a marker of MIR. However, based on kinetic studies, it is more likely that imcTG is a source of MIR. On one hand, an enlarged and fast turning over imcTG pool interferes with insulin signaling by producing excess amounts of signaling molecules that activate PKC pathways. On the other hand, it may promote mitochondrial beta-oxidation that suppresses glucose metabolism via substrate competition. Therefore, it is hypothesized that imcTG is a source of MIR.
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Affiliation(s)
- Zengkui Guo
- Endocrine Research Unit, 5-194 Joseph, Mayo Foundation, Rochester, MN 55905, United States.
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Guo Z. Intramyocellular lipid kinetics and insulin resistance. Lipids Health Dis 2007; 6:18. [PMID: 17650308 PMCID: PMC1971250 DOI: 10.1186/1476-511x-6-18] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 07/24/2007] [Indexed: 12/31/2022] Open
Abstract
More than fifteen years ago it was discovered that intramyocellular triglyceride (imcTG) content in skeletal muscle is abnormally high in conditions of lipid oversupply (e.g. high fat feeding) and, later, obesity, type 2 diabetes (T2D) and other metabolic conditions. This imcTG excess is robustly associated with muscle insulin resistance (MIR). However, to date the pathways responsible for the imcTG excess and the mechanisms underlying the imcTG-MIR correlation remain unclear. A current hypothesis is based on a backward mechanism that impaired fatty acid oxidation by skeletal muscle causes imcTG to accumulate. As such, imcTG excess is considered a marker but not a player in MIR. However, recent results from kinetic studies indicated that imcTG pool in high fat-induced obesity (HFO) model is kinetically dynamic. On one hand, imcTG synthesis is accelerated and contributes to imcTG accumulation. On the other, the turnover of imcTG is also accelerated. A hyperdynamic imcTG pool can impose dual adverse effects on glucose metabolism in skeletal muscle. It increases the release and thus the availability of fatty acids in myocytes that may promote fatty acid oxidation and suppress glucose utilization. Meanwhile, it releases abundant fatty acid products (e.g. diacylglycerol, ceramides) that impair insulin actions via signal transduction, thereby causing MIR. Thus, intramyocellular fatty acids and their products released from imcTG appear to function as a link to MIR. Accordingly, a forward mechanism is proposed that explains the imcTG-MIR correlation.
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Affiliation(s)
- ZengKui Guo
- Endocrine Research Unit, Mayo Foundation, Rochester, Minnesota 55905, USA.
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Guo Z, Zhou L, Jensen MD. Acute hyperinsulinemia inhibits intramyocellular triglyceride synthesis in high-fat-fed obese rats. J Lipid Res 2006; 47:2640-6. [PMID: 16966492 DOI: 10.1194/jlr.m600116-jlr200] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hyperinsulinemia is common in obesity, but whether it plays a role in intramyocellular triglyceride (imcTG) buildup is unknown. In this study, hyperinsulinemic-euglycemic clamp experiments were performed in overnight-fasted lean and high-fat-fed obese rats, awake, to determine the effect of insulin on imcTG synthesis (incorporation of [(14)C]glycerol, [(14)C]glucose, and [(3)H]oleate). Insulin infusion at 25 (low insulin) and 100 (high insulin) pmol/kg/min increased plasma insulin by 5- and 16-fold, respectively, whereas plasma and intramyocellular glycerol, FFAs, triglycerides, and glucose levels were maintained at their basal levels by co-infusion of exogenous glycerol, FFAs, and triglycerides at fixed rates and glucose at varying rates. In obese rats, insulin suppressed incorporation of glycerol into the imcTG-glycerol moiety dose dependently (P < 0.01-P < 0.001) in gastrocnemius and tibialis anterior, but only the high insulin suppressed it in soleus (P < 0.05). The low insulin suppressed glucose incorporation into imcTG-glycerol in all three muscles (P = 0.01-P < 0.01). However, the low insulin did not affect (P > 0.05) and the high insulin suppressed (P < 0.05-P < 0.01) fatty acid incorporation into imcTG in all three muscles. Insulin also suppressed glycerol incorporation in lean rats (P < 0.01-P < 0.04). On the other hand, imcTG pool size was not affected by insulin (P > 0.05). These observations suggest that acute hyperinsulinemia inhibits imcTG synthesis and thus does not appear to promote imcTG accumulation via the synthetic pathway, at least in the short term.
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Affiliation(s)
- Zengkui Guo
- Endocrine Research Unit, Mayo Foundation, Rochester, MN 55905, USA.
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