Effect of insulin and contraction on glycogen synthase phosphorylation and kinetic properties in epitrochlearis muscles from lean and obese Zucker rats

2012 ◽  
Vol 302 (10) ◽  
pp. C1539-C1547 ◽  
Author(s):  
Fang Chin Lin ◽  
Astrid Bolling ◽  
Jorid T. Stuenæs ◽  
Kristoffer T. Cumming ◽  
Ada Ingvaldsen ◽  
...  
Keyword(s):  
Protein Expression ◽  
Glycogen Synthase ◽  
Zucker Rats ◽  
Kinetic Properties ◽  
Physiological Concentration ◽  
Obese Rats ◽  
Obese Zucker Rats

In the present study, the effects of insulin and contraction on glycogen synthase (GS) kinetic properties and phosphorylation were investigated in epitrochlearis muscles from lean and obese Zucker rats. Total GS activity and protein expression were ∼15% lower in epitrochlearis from obese rats compared with lean rats. Insulin-stimulated GS fractional activity and affinity for UDP-glucose were lower (higher Km) in muscles from obese rats. GS Ser641 and Ser645,649,653,657 phosphorylation was higher in insulin-stimulated muscles from obese rats, which agreed with lower GS activation. Contraction-mediated GS dephosphorylation of Ser641, Ser641+645, Ser645,649,653,657, and Ser7+10 was normal in muscles from obese Zucker rats, and GS fractional activity increased to similar levels in epitrochlearis muscles from lean and obese rats. GS affinity for UDP glucose was ∼0.8, ∼0.4, and ∼0.1 mM with assay buffers containing 0, 0.17, and 12 mM glucose 6-phosphate, respectively. Contraction increased affinity for UDP-glucose (reduced Km) at a physiological concentration of glucose 6-phosphate (0.17 mM) to ∼0.2 mM in muscles from both lean and obese rats. Interestingly, in the absence of glucose 6-phosphate in the assay buffer, contraction (and insulin) did not influence GS affinity for UDP-glucose, indicating that affinity is regulated by sensitivity for glucose 6-phosphate. In conclusion, contraction-mediated activation and dephosphorylation of GS were normal in muscles from obese Zucker rats, whereas insulin-mediated GS activation and dephosphorylation were impaired.

LKB1-AMPK signaling in muscle from obese insulin-resistant Zucker rats and effects of training

2006 ◽  
Vol 290 (5) ◽  
pp. E925-E932 ◽  
Author(s):  
Apiradee Sriwijitkamol ◽  
John L. Ivy ◽  
Christine Christ-Roberts ◽  
Ralph A. DeFronzo ◽  
Lawrence J. Mandarino ◽  
...  
Keyword(s):  
Protein Expression ◽  
Protein Content ◽  
Citrate Synthase ◽  
Zucker Rats ◽  
Ampk Signaling ◽  
Insulin Resistant ◽  
Ampk Pathway ◽  
Ampk Phosphorylation ◽  
Obese Rats ◽  
Obese Zucker Rats

AMPK is a key regulator of fat and carbohydrate metabolism. It has been postulated that defects in AMPK signaling could be responsible for some of the metabolic abnormalities of type 2 diabetes. In this study, we examined whether insulin-resistant obese Zucker rats have abnormalities in the AMPK pathway. We compared AMPK and ACC phosphorylation and the protein content of the upstream AMPK kinase LKB1 and the AMPK-regulated transcriptional coactivator PPARγ coactivator-1 (PGC-1) in gastrocnemius of sedentary obese Zucker rats and sedentary lean Zucker rats. We also examined whether 7 wk of exercise training on a treadmill reversed abnormalities in the AMPK pathway in obese Zucker rats. In the obese rats, AMPK phosphorylation was reduced by 45% compared with lean rats. Protein expression of the AMPK kinase LKB1 was also reduced in the muscle from obese rats by 43%. In obese rats, phosphorylation of ACC and protein expression of PGC-1α, two AMPK-regulated proteins, tended to be reduced by 50 ( P = 0.07) and 35% ( P = 0.1), respectively. There were no differences in AMPKα1, -α2, -β1, -β2, and -γ3 protein content between lean and obese rats. Training caused a 1.5-fold increase in AMPKα1 protein content in the obese rats, although there was no effect of training on AMPK phosphorylation and the other AMPK isoforms. Furthermore, training also significantly increased LKB1 and PGC-1α protein content 2.8- and 2.5-fold, respectively, in the obese rats. LKB1 protein strongly correlated with hexokinase II activity ( r = 0.75, P = 0.001), citrate synthase activity ( r = 0.54, P = 0.02), and PGC-1α protein content ( r = 0.81, P < 0.001). In summary, obese insulin-resistant rodents have abnormalities in the LKB1-AMPK-PGC-1 pathway in muscle, and these abnormalities can be restored by training.

scholarly journals Chronic suppression of insulin by diazoxide alters the activities of key enzymes regulating hepatic gluconeogenesis in Zucker rats

2002 ◽  
pp. 871-879 ◽  
Author(s):  
R Alemzadeh ◽  
S Holshouser ◽  
P Massey ◽  
J Koontz
Keyword(s):  
Phosphoenolpyruvate Carboxykinase ◽  
Glucose Transporter ◽  
Glycogen Synthase ◽  
Zucker Rats ◽  
Hepatic Glycogen ◽  
Hepatic Gluconeogenesis ◽  
Key Enzymes ◽  
Glucose Transporter 2 ◽  
Obese Rats ◽  
Obese Zucker Rats

OBJECTIVES: Chronic attenuation of hyperinsulinemia by diazoxide (DZ), an inhibitor of glucose-mediated insulin secretion, improved insulin sensitivity and glucose tolerance and caused down-regulation of lipid metabolizing enzymes in adipose tissue and decreased the rate of weight gain in mildly hyperglycemic obese Zucker rats. Since the liver plays a central role in glucose homeostasis, we studied the effect of chronic insulin suppression on key insulin-sensitive enzymes regulating hepatic gluconeogenesis. METHODS: DZ (150 mg/kg per day) or vehicle (control) was administered to 7-week-old female obese and lean Zucker rats for a period of 4 weeks. RESULTS: DZ-treated animals showed lower fasting plasma insulin levels (P<0.001) than their controls. Plasma glucose levels were lower in DZ obese rats than in controls (P<0.001), without a significant change in DZ lean animals. DZ had no effect on glucose transporter 2 protein expression in either strain. DZ treatment resulted in lower hepatic glucokinase (P<0.001) and glucose-6-phosphatase (P<0.0001) and phosphoenolpyruvate carboxykinase (PEPCK) activities only in obese rats compared with controls (P<0.001). However, DZ-treated lean rats demonstrated higher PEPCK activity than controls (P<0.002). DZ-treated animals demonstrated enhanced hepatic glucose-6-phosphate content (P<0.01), glycogen synthase activity (P<0.0001) and glycogen content (P<0.02) compared with their controls despite increased hepatic glycogen phosphorylase a activity in these animals (P<0.02). CONCLUSIONS: Chronic suppression of hyperinsulinemia in obese Zucker rats by DZ decreased the activities of key enzymes regulating hepatic gluconeogenesis, implying that attenuation of the hyperinsulinemic state by DZ may be therapeutically beneficial.

Glucose transport: locus of muscle insulin resistance in obese Zucker rats

1988 ◽  
Vol 255 (3) ◽  
pp. E374-E382 ◽  
Author(s):  
W. M. Sherman ◽  
A. L. Katz ◽  
C. L. Cutler ◽  
R. T. Withers ◽  
J. L. Ivy
Keyword(s):  
Insulin Resistance ◽  
Glucose Uptake ◽  
Glucose Transport ◽  
Glycogen Synthase ◽  
Fiber Type ◽  
Zucker Rats ◽  
Muscle Insulin Resistance ◽  
Obese Rats ◽  
Obese Zucker Rats ◽  
Fast Twitch

The purposes of this study were to determine whether the muscle insulin resistance of the obese rat is due to a defect in the glucose transport process and whether the insulin resistance is fiber-type specific. The hindlimbs of fasted, 14-wk-old obese (fa/fa) and lean (fa/?) Zucker rats were perfused with perfusate containing 8 mM glucose and no insulin or 8 mM glucose and either a physiological (0.15 mU/ml), a submaximal (1.50 mU/ml), or a maximal (15.0 mU/ml) insulin concentration. Glucose uptake was determined after which the initial rate of glucose transport was determined using 3-O-methyl-D-glucose (3-OMG). Glucose uptake of the obese rats was depressed by 40, 33, 42, and 47% in the absence of insulin and in the presence of the physiological, submaximal, and maximal insulin concentrations, respectively, when compared with lean littermates. Glucose transport in the absence and in the presence of the three insulin concentrations was significantly lower in the soleus (slow-twitch, oxidative fibers), red quadriceps (fast-twitch, oxidative, glycolytic fibers), and gastrocnemius (mixed fibers) of the obese rats when compared with lean rats. Glucose transport in the white quadriceps (fast-twitch, glycolytic fibers) was significantly lower in the obese rats in the absence of insulin and in the presence of the submaximal and maximal insulin concentrations. The glycogen concentration and the activity of hexokinase were the same and the glycogen synthase activity was higher in the muscles for the obese rats when compared to lean rats.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals High Na intake increases renal angiotensin II levels and reduces expression of the ACE2-AT2R-MasR axis in obese Zucker rats

2012 ◽  
Vol 303 (3) ◽  
pp. F412-F419 ◽  
Author(s):  
Preethi Samuel ◽  
Quaisar Ali ◽  
Rifat Sabuhi ◽  
Yonnie Wu ◽  
Tahir Hussain
Keyword(s):  
Sodium Intake ◽  
Zucker Rats ◽  
Kidney Cortex ◽  
Complex Nature ◽  
Ang Ii ◽  
Pronounced Increase ◽  
High Sodium ◽  
High Sodium Intake ◽  
Obese Rats ◽  
Obese Zucker Rats

High sodium intake is known to regulate the renal renin-angiotensin system (RAS) and is a risk factor for the pathogenesis of obesity-related hypertension. The complex nature of the RAS reveals that its various components may have opposing effects on natriuresis and blood pressure regulation. We hypothesized that high sodium intake differentially regulates and shifts a balance between opposing components of the renal RAS, namely, angiotensin-converting enzyme (ACE)-ANG II-type 1 ANG II receptor (AT1R) vs. AT2-ACE2-angiotensinogen (Ang) (1–7)-Mas receptor (MasR), in obesity. In the present study, we evaluated protein and/or mRNA expression of angiotensinogen, renin, AT1A/BR, ACE, AT2R, ACE2, and MasR in the kidney cortex following 2 wk of a 8% high-sodium (HS) diet in lean and obese Zucker rats. The expression data showed that the relative expression pattern of ACE and AT1BR increased, renin decreased, and ACE2, AT2R, and MasR remained unaltered in HS-fed lean rats. On the other hand, HS intake in obese rats caused an increase in the cortical expression of ACE, a decrease in ACE2, AT2R, and MasR, and no changes in renin and AT1R. The cortical levels of ANG II increased by threefold in obese rats on HS compared with obese rats on normal salt (NS), which was not different than in lean rats. The HS intake elevated mean arterial pressure in obese rats (27 mmHg) more than in lean rats (16 mmHg). This study suggests that HS intake causes a pronounced increase in ANG II levels and a reduction in the expression of the ACE2-AT2R-MasR axis in the kidney cortex of obese rats. We conclude that such changes may lead to the potentially unopposed function of AT1R, with its various cellular and physiological roles, including the contribution to the pathogenesis of obesity-related hypertension.

scholarly journals Plasma calcitonin gene-related peptide is increased prior to obesity, and sensory nerve desensitization by capsaicin improves oral glucose tolerance in obese Zucker rats

2005 ◽  
Vol 153 (6) ◽  
pp. 963-969 ◽  
Author(s):  
Dorte X Gram ◽  
Anker J Hansen ◽  
Michael Wilken ◽  
Torben Elm ◽  
Ove Svendsen ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Glucose Tolerance ◽  
Sensory Nerve ◽  
Zucker Rats ◽  
Oral Glucose ◽  
Oral Glucose Tolerance ◽  
Nerve Activity ◽  
Calcitonin Gene ◽  
Obese Rats ◽  
Obese Zucker Rats

Objective: It has earlier been demonstrated that capsaicin-induced desensitization improves insulin sensitivity in normal rats. However, whether increased capsaicin-sensitive nerve activity precedes the onset of insulin resistance in diet-induced obesity – and therefore might be involved in the pathophysiology – is not known. Further, it is of relevance to investigate whether capsaicin desensitization improves glycaemic control even in obese individuals and we therefore chose the obese Zucker rats to test this. Design and methods: Plasma levels of calcitonin gene-related peptide (CGRP; a marker of sensory nerve activity) was assessed in 8-week-old Zucker rats. To investigate whether capsaicin desensitization (100 mg/kg at 9 weeks of age) would also ameliorate glycaemia in this non-diabetic model, we assessed oral glucose tolerance at 7 weeks after capsaicin. Results: It was found that plasma CGRP levels were elevated in obese Zucker rats prior to the onset of obesity (16.1±3.4 pmol/l in pre-obese Zucker rats vs 6.9±1.1 pmol/l in lean littermates; P = 0.015) despite similar body weights. Furthermore, capsaicin desensitization reduced both fasting blood glucose (4.3±0.2 mmol/l vs 5.1±0.2 mmol/l in controls; P = 0.050) as well as the mean blood glucose level during an oral glucose tolerance test (OGTT) (6.8±0.3 mmol/l vs 8.6±0.5 mmol/l in control obese rats; P = 0.024) whereas the plasma insulin levels during the OGTT were unchanged. However this did not lead to an improvement in insulin resistance or to a reduction of tissue triglyceride accumulation in muscle or liver. Conclusion: We concluded that capsaicin-induced sensory nerve desensitization improves glucose tolerance in Zucker rats. Since, in this study, plasma CGRP levels, a marker of sensory nerve activity, were increased in the pre-obese rats, our data support the hypothesis that increased activity of sensory nerves precedes the development of obesity and insulin resistance in Zucker rats.

scholarly journals Adipose-tissue-specific increase in glyceraldehyde-3-phosphate dehydrogenase activity and mRNA amounts in suckling pre-obese Zucker rats. Effect of weaning

1988 ◽  
Vol 254 (2) ◽  
pp. 483-487 ◽  
Author(s):  
I Dugail ◽  
A Quignard-Boulange ◽  
R Bazin ◽  
X Le Liepvre ◽  
M Lavau
Keyword(s):  
Gene Expression ◽  
Adipose Tissue ◽  
Zucker Rats ◽  
Tissue Specific ◽  
Gapdh Gene ◽  
Gapdh Activity ◽  
Weanling Rats ◽  
Obese Rats ◽  
Specific Increase ◽  
Obese Zucker Rats

The regulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression was studied during the onset of obesity in the genetically obese (fa/fa) rat by determination of GAPDH activity and hybridizable mRNA amounts in adipose tissue and liver from suckling and weanling rats. GADPH activity remained low throughout the suckling period, and a burst of activity occurred after weaning in both lean and obese pups. As early as 7 days of age, adipose tissue from pre-obese rats displayed a significant increase in enzyme activity, whereas no difference could be detected in the liver. In both suckling (16 days of age) and weanling (30 days of age) obese rats a proportionate increase in GAPDH activity and mRNA amounts was observed in adipose tissue, but not in liver. It is concluded that the obese genotype influences GAPDH gene expression at a pretranslational level and in a tissue-specific manner. This phenomenon could partly contribute to the hyperactive fat accretion in the obese rat, since glycolysis is the major metabolic pathway for lipogenic substrates in adipose tissue.

Abstract P184: Co-localization and Natriuretic Interdependence of Angiotensin AT2R and MasR in Obese Rat Kidney

Hypertension ◽  
2016 ◽  
Vol 68 (suppl_1) ◽  
Author(s):  
Sanket N Patel ◽  
Quaisar Ali ◽  
Ulrike Muscha Steckelings ◽  
Tahir Hussain
Keyword(s):  
Rat Kidney ◽  
Sulfhydryl Groups ◽  
Zucker Rats ◽  
Diabetic Rat ◽  
Physical Interaction ◽  
Potential Mechanism ◽  
Obese Rats ◽  
Obese Zucker Rats ◽  
Made In

The actions of angiotensin II type 2 receptor (AT 2 R) and receptor mas (MasR) are complex but show similar pro-natriuretic function; particularly AT 2 R expression and natriuretic function are enhanced in obese/diabetic rat kidney. In light of previous reports, we tested hypothesis that AT 2 R and MasR are interdependent to produce natriuresis in obese rats due to potential physical interaction. Infusion of AT 2 R agonist C21 (5 μg/kg/min) in obese Zucker rats (OZR) caused diuresis/natriuresis which were attenuated by simultaneous infusion of the AT 2 R antagonist PD123319 (50 μg/kg/min) or the MasR antagonist A-779 (50 μg/kg/min). Similarly, infusion of MasR agonist Ang-(1-7) (110 fmol/kg/min) in OZR caused diuresis/netriuresis, which were attenuated by simultaneous infusion of A-779 or PD123319. Dual labeling of AT 2 R and MasR in OZR kidney slices revealed four-fold co-localization of AT 2 R and MasR (9.83 vs. 2.50 dual labeled cells/1600 μm 2 ) compared with lean rats in which AT 2 R is not natriuretic. Moreover, the AT 2 R co-immunoprecipitates with MasR in cortical homogenate of OZR. Immunoblotting of AT 2 R and MasR with zero length oxidative (sulfhydryl groups) cross-linker cupric-phenanthroline in OZR cortical homogenate revealed a shift of AT 2 R (~62 kDa) and MasR (~54 kDa) bands upward with overlapping migration for their complexes (~160 kDa and 245 kDa) which were sensitive to the reducing β-mercaptoethanol. Similar observations were made in HK-2 cells, where glucose (25 mM) treatment enhanced the crosslinking. Collectively, the study reveals AT2R and MasR are co-localized and functionally interdependent in producing natriuretic response. Hyperglycemic oxidative stress affecting sulfhydryl groups present a potential mechanism of such physical interaction between these receptors. (Support: R01DK061578)

Effect of hypophysectomy on energy balance and brown fat activity in obese Zucker rats

1988 ◽  
Vol 254 (2) ◽  
pp. E162-E166
Author(s):  
S. Holt ◽  
N. J. Rothwell ◽  
M. J. Stock ◽  
D. A. York
Keyword(s):  
Energy Balance ◽  
Binding Capacity ◽  
Zucker Rats ◽  
Bat Activity ◽  
Reduced Body ◽  
Brown Adipose ◽  
Obese Rats ◽  
Obese Zucker Rats ◽  
Energy Gains ◽  
Pituitary Adrenal Axis

Hypophysectomy (HYPX) in genetically obese (fa/fa) Zucker rats significantly reduced body weight and energy gains and stimulated energy expenditure (by 34%), the thermic response to food (by 144%), and brown adipose tissue (BAT) mitochondrial GDP-binding capacity (by 190%) compared with pair-fed, sham-operated obese rats. These changes in energy balance in obese HYPX rats were reversed by corticosterone replacement (1 mg/day), but the increased BAT activity was only partly restored to normal. HYPX had only small effects on energy balance in lean Zucker rats compared with pair-fed, sham-operated lean controls but increased the acute thermic response to food and BAT mitochondrial GDP-binding capacity; these effects were inhibited by replacement of HYPX rats with corticosterone. The results suggest that alterations in the hypothalamic-pituitary-adrenal axis play a fundamental role in the development and maintenance of genetic obesity.

Relationship of adipocyte size to hyperphagia in developing male obese Zucker rats

1992 ◽  
Vol 262 (1) ◽  
pp. R33-R38 ◽  
Author(s):  
J. R. Vasselli ◽  
J. A. Fiene ◽  
C. A. Maggio
Keyword(s):  
Adipose Tissue ◽  
Body Weight Gain ◽  
Zucker Rats ◽  
Lipoprotein Lipase Activity ◽  
Adipocyte Size ◽  
High Fat ◽  
Obese Rats ◽  
Obese Zucker Rats ◽  
Relationship Of ◽  
Cumulative Intake

In growing male obese Zucker rats, hyperphagia reaches a maximum or “breakpoint” and declines at an earlier age with high fat than with chow-type diets. A serial adipose tissue biopsy technique was used to correlate changes of retroperitoneal adipocyte size and feeding behavior in 5- to 7-wk-old male lean and obese rats fed laboratory chow or a 35% fat diet until 30 wk of age. Although chow-fed groups had significantly greater cumulative intake, fat-fed groups had significantly greater body weight gain, retroperitoneal depot weight, and adipocyte number. Mean adipocyte size increased continuously in chow-fed groups but decreased over weeks 20-30 in fat-fed groups, reflecting increased adipocyte number. In fat-fed obese rats, hyperphagia reached a breakpoint at 11 wk and disappeared by 13 wk. In chow-fed obese rats, hyperphagia reached a breakpoint at 15-16 wk and disappeared by 19 wk. Biopsy samples revealed that adipocyte size of fat-fed obese rats was already close to maximal at 10 wk (1.12 micrograms lipid), while that of chow-fed obese rats only approached maximal at 20 wk (0.81 microgram lipid). At these time points, lipoprotein lipase activity paralleled adipocyte size. These data indicate that the duration of the growing obese rat's hyperphagia coincides with adipocyte filling and suggest the existence of feeding stimulatory and inhibitory signals from adipose tissue.

scholarly journals Mechanism controlling sleep organization of the obese Zucker rats

1998 ◽  
Vol 84 (1) ◽  
pp. 253-256 ◽  
Author(s):  
David Megirian ◽  
Jacek Dmochowski ◽  
Gaspar A. Farkas
Keyword(s):  
Eye Movement ◽  
Rem Sleep ◽  
Nrem Sleep ◽  
Zucker Rats ◽  
Rapid Eye Movement ◽  
Zucker Rat ◽  
Obese Zucker Rat ◽  
Obese Rats ◽  
Obese Zucker Rats ◽  
The Mean

Megirian, David, Jacek Dmochowski, and Gaspar A. Farkas. Mechanism controlling sleep organization of the obese Zucker rat. J. Appl. Physiol. 84(1): 253–256, 1998.—We tested the hypothesis that the obese ( fa/fa) Zucker rat has a sleep organization that differs from that of lean Zucker rats. We used the polygraphic technique to identify and to quantify the distribution of the three main states of the rat: wakefulness (W), non-rapid-eye-movement (NREM), and rapid-eye-movement (REM) sleep states. Assessment of states was made with light present (1000–1600), at the rats thermoneutral temperature of 29°C. Obese rats, compared with lean ones, did not show significant differences in the total time spent in the three main states. Whereas the mean durations of W and REM states did not differ statistically, that of NREM did ( P = 0.046). However, in the obese rats, the frequencies of switching from NREM sleep to W, which increased, and from NREM to REM sleep, which decreased, were statistically significantly different ( P = 0.019). Frequency of switching from either REM or W state was not significantly different. We conclude that sleep organization differs between lean and obese Zucker rats and that it is due to a disparity in switching from NREM sleep to either W or REM sleep and the mean duration of NREM sleep.

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