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ABSTRACT: Most of the central circadian clock genes in the mouse exist as paralog pairs (Per1 and Per2, Cry1 and Cry2, Clock and Npas2) in which each gene of the pair must be knocked out to confer arrhythmicity. The only exception to this pattern is Bmal1 (also known as Mop3), the single knockout of which confers arrhythmicity, despite the presence of its paralog, Bmal2 (also known as Mop9). The knockout of Bmal1 also has significant effects on longevity, metabolism, etc. These results have led to the conclusion that Bmal1 is a singularly essential clock gene and that Bmal2 has a minimal role in the clock system. In contrast, we find that expression of Bmal2 from a constitutively expressed promoter can rescue the clock and metabolic phenotypes of Bmal1-knockout mice, including rhythmic locomotor activity, rhythmic metabolism, low body weight, and enhanced fat deposition. Combined with the data of Bunger and colleagues, who reported that knockout of Bmal1 downregulates Bmal2, we conclude that Bmal1 and Bmal2 form a circadian paralog pair that is functionally redundant and that, in the mouse, Bmal2 is regulated by Bmal1 such that knockout of Bmal1 alone results in a functionally double Bmal1 and Bmal2 knockout. Therefore, the role(s) of Bmal2 may be more important than has been appreciated heretofore.
Current biology: CB 02/2010; 20(4):316-21. · 10.99 Impact Factor
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Diabetes 10/2009; 58(9):1947-50. · 8.29 Impact Factor
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ABSTRACT: The hepatic energy state, defined by adenine nucleotide levels, couples metabolic pathways with energy requirements. This coupling is fundamental in the adaptive response to many conditions and is impaired in metabolic disease. We have found that the hepatic energy state is substantially reduced following exercise, fasting, and exposure to other metabolic stressors in C57BL/6 mice. Glucagon receptor signaling was hypothesized to mediate this reduction because increased plasma levels of glucagon are characteristic of metabolic stress and because this hormone stimulates energy consumption linked to increased gluconeogenic flux through cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) and associated pathways. We developed what we believe to be a novel hyperglucagonemic-euglycemic clamp to isolate an increment in glucagon levels while maintaining fasting glucose and insulin. Metabolic stress and a physiological rise in glucagon lowered the hepatic energy state and amplified AMP-activated protein kinase signaling in control mice, but these changes were abolished in glucagon receptor- null mice and mice with liver-specific PEPCK-C deletion. 129X1/Sv mice, which do not mount a glucagon response to hypoglycemia, displayed an increased hepatic energy state compared with C57BL/6 mice in which glucagon was elevated. Taken together, these data demonstrate in vivo that the hepatic energy state is sensitive to glucagon receptor activation and requires PEPCK-C, thus providing new insights into liver metabolism.
The Journal of clinical investigation 09/2009; 119(8):2412-22. · 15.39 Impact Factor
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ABSTRACT: This article addresses two topics. We provide an overview of the National Institutes of Health Mouse Metabolic Phenotyping Center (MMPC) Program. We then discuss some observations we have made during the first eight years of the Vanderbilt MMPC regarding common phenotyping practices. We include specific recommendations to improve phenotyping practices for tests of glucose tolerance and insulin action. We recommend that methods for experiments in vivo be described in manuscripts. We make specific recommendations for data presentation, interpretation, and experimental design for each test. To facilitate and maximize the exchange of scientific information, we suggest that guidelines be developed for methods used to assess glucose tolerance and insulin action in vivo.
AJP Endocrinology and Metabolism 08/2009; 297(4):E849-55. · 4.75 Impact Factor
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ABSTRACT: AMP-activated protein kinase (AMPK) has been postulated as a super-metabolic regulator, thought to exert numerous effects on skeletal muscle function, metabolism, and enzymatic signaling. Despite these assertions, little is known regarding the direct role(s) of AMPK in vivo, and results obtained in vitro or in situ are conflicting. Using a chronically catheterized mouse model (carotid artery and jugular vein), we show that AMPK regulates skeletal muscle metabolism in vivo at several levels, with the result that a deficit in AMPK activity markedly impairs exercise tolerance. Compared with wild-type littermates at the same relative exercise capacity, vascular glucose delivery and skeletal muscle glucose uptake were impaired; skeletal muscle ATP degradation was accelerated, and arterial lactate concentrations were increased in mice expressing a kinase-dead AMPKalpha2 subunit (alpha2-KD) in skeletal muscle. Nitric-oxide synthase (NOS) activity was significantly impaired at rest and in response to exercise in alpha2-KD mice; expression of neuronal NOS (NOSmicro) was also reduced. Moreover, complex I and IV activities of the electron transport chain were impaired 32 +/- 8 and 50 +/- 7%, respectively, in skeletal muscle of alpha2-KD mice (p < 0.05 versus wild type), indicative of impaired mitochondrial function. Thus, AMPK regulates neuronal NOSmicro expression, NOS activity, and mitochondrial function in skeletal muscle. In addition, these results clarify the role of AMPK in the control of muscle glucose uptake during exercise. Collectively, these findings demonstrate that AMPK is central to substrate metabolism in vivo, which has important implications for exercise tolerance in health and certain disease states characterized by impaired AMPK activation in skeletal muscle.
Journal of Biological Chemistry 07/2009; 284(36):23925-34. · 4.77 Impact Factor
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ABSTRACT: Fibroblast growth factor 21 (FGF21) is a novel metabolic regulator shown to improve glycemic control. However, the molecular and functional mechanisms underlying FGF21-mediated improvements in glycemic control are not completely understood. We examined FGF21 effects on insulin sensitivity and glucose fluxes upon chronic (daily injection for 8 d) and acute (6 h infusion) administration in ob/+ and ob/ob mice. Results show that chronic FGF21 ameliorated fasting hyperglycemia in ob/ob mice via increased glucose disposal and improved hepatic insulin sensitivity. Acute FGF21 suppressed hepatic glucose production, increased liver glycogen, lowered glucagon, and improved glucose clearance in ob/+ mice. These effects were blunted in ob/ob mice. Neither chronic nor acute FGF21 altered skeletal muscle or adipose tissue glucose uptake in either genotype. In conclusion, FGF21 has potent glycemic effects caused by hepatic changes in glucose flux and improved insulin sensitivity. Thus, these studies define mechanisms underlying anti-hyperglycemic actions of FGF21 and support its therapeutic potential.
Endocrinology 06/2009; 150(9):4084-93. · 4.46 Impact Factor
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Ethan J Anderson,
Mary E Lustig,
Kristen E Boyle,
Tracey L Woodlief,
Daniel A Kane,
Chien-Te Lin,
Jesse W Price,
Li Kang,
Peter S Rabinovitch,
Hazel H Szeto,
Joseph A Houmard,
Ronald N Cortright, David H Wasserman,
P Darrell Neufer
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ABSTRACT: High dietary fat intake leads to insulin resistance in skeletal muscle, and this represents a major risk factor for type 2 diabetes and cardiovascular disease. Mitochondrial dysfunction and oxidative stress have been implicated in the disease process, but the underlying mechanisms are still unknown. Here we show that in skeletal muscle of both rodents and humans, a diet high in fat increases the H(2)O(2)-emitting potential of mitochondria, shifts the cellular redox environment to a more oxidized state, and decreases the redox-buffering capacity in the absence of any change in mitochondrial respiratory function. Furthermore, we show that attenuating mitochondrial H(2)O(2) emission, either by treating rats with a mitochondrial-targeted antioxidant or by genetically engineering the overexpression of catalase in mitochondria of muscle in mice, completely preserves insulin sensitivity despite a high-fat diet. These findings place the etiology of insulin resistance in the context of mitochondrial bioenergetics by demonstrating that mitochondrial H(2)O(2) emission serves as both a gauge of energy balance and a regulator of cellular redox environment, linking intracellular metabolic balance to the control of insulin sensitivity.
The Journal of clinical investigation 03/2009; 119(3):573-81. · 15.39 Impact Factor
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ABSTRACT: Glucagon-like peptide-1 (GLP-1) diminishes postmeal glucose excursions by enhancing insulin secretion via activation of the beta-cell GLP-1 receptor (Glp1r). GLP-1 may also control glucose levels through mechanisms that are independent of this incretin effect. The hyperinsulinemic-euglycemic clamp (insulin clamp) and exercise were used to examine the incretin-independent glucoregulatory properties of the Glp1r because both perturbations stimulate glucose flux independent of insulin secretion. Chow-fed mice with a functional disruption of the Glp1r (Glp1r(-/-)) were compared with wild-type littermates (Glp1r(+/+)). Studies were performed on 5-h-fasted mice implanted with arterial and venous catheters for sampling and infusions, respectively. During insulin clamps, [3-(3)H]glucose and 2[(14)C]deoxyglucose were used to determine whole-body glucose turnover and glucose metabolic index (R(g)), an indicator of glucose uptake. R(g) in sedentary and treadmill exercised mice was determined using 2[(3)H]deoxyglucose. Glp1r(-/-) mice exhibited increased glucose disappearance, muscle R(g), and muscle glycogen levels during insulin clamps. This was not associated with enhanced muscle insulin signaling. Glp1r(-/-) mice exhibited impaired suppression of endogenous glucose production and hepatic glycogen accumulation during insulin clamps. This was associated with impaired liver insulin signaling. Glp1r(-/-) mice became significantly hyperglycemic during exercise. Muscle R(g) was normal in exercised Glp1r(-/-) mice, suggesting that hyperglycemia resulted from an added drive to stimulate glucose production. Muscle AMP-activated protein kinase phosphorylation was higher in exercised Glp1r(-/-) mice. This was associated with increased relative exercise intensity and decreased exercise endurance. In conclusion, these results show that the endogenous Glp1r regulates hepatic and muscle glucose flux independent of its ability to enhance insulin secretion.
Endocrinology 12/2008; 150(3):1155-64. · 4.46 Impact Factor
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ABSTRACT: Insulin resistance is characterized by elevated rates of cardiac fatty acid utilization resulting in reduced efficiency and cardiomyopathy. One potential therapeutic approach is to limit the uptake and oxidation of fatty acids. The aims of this study were to determine whether a quantitative reduction in heart-type fatty acid binding protein (FABP3) normalizes cardiac substrate utilization without altering cardiac function. Transgenic (FABP3(+/-)) and wild-type (WT) littermates were studied following low fat (LF) or high fat (HF) diets, with HF resulting in obese, insulin-resistant mice. Cardiovascular function (systolic blood pressure, % fractional shortening) and heart dimension were measured at weaning and every month afterward for 3 mo. During this period cardiovascular function was the same independent of genotype and diet. Catheters were surgically implanted in the carotid artery and jugular vein for sampling and infusions in mice at 4 mo of age. Following 5 d recovery, mice underwent either a saline infusion or a hyperinsulinemic-euglycemic clamp (4 mU kg(-1) min(-1)). Indices of long chain fatty acid and glucose utilization (R(f), R(g); mumol g wet weight(-1) min(-1)) were obtained using 2-deoxy[(3)H]glucose and [(125)I]-15-rho-iodophenyl)-3-R,S-methylpentadecanoic acid. FABP3(+/-) had enhanced cardiac R(g) compared with WT during saline infusion in both LF and HF. FABP3(+/-) abrogated the HF-induced decrement in insulin-stimulated cardiac R(g). On a HF diet, FABP(+/-) but not WT had an increased reliance on fatty acids (R(f)) during insulin stimulation. In conclusion, cardiac insulin resistance and glucose uptake is largely corrected by a reduction in FABP3 in vivo without contemporaneous deleterious effects on cardiac function.
Biochimica et Biophysica Acta 08/2008; 1782(10):586-92. · 4.66 Impact Factor
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ABSTRACT: To characterize differences in whole-body glucose metabolism between commonly used inbred mouse strains.
Hyperinsulinemic-euglycemic (approximately 8.5 mmol/l) and -hypoglycemic (approximately 3.0 mmol/l) clamps were done in catheterized, 5-h-fasted mice to assess insulin action and hypoglycemic counter-regulatory responsiveness. Hyperglycemic clamps (approximately 15 mmol/l) were done to assess insulin secretion and compared with results in perifused islets.
Insulin action and hypoglycemic counter-regulatory and insulin secretory phenotypes varied considerably in four inbred mouse strains. In vivo insulin secretion was greatest in 129X1/Sv mice, but the counter-regulatory response to hypoglycemia was blunted. FVB/N mice in vivo showed no increase in glucose-stimulated insulin secretion, relative hepatic insulin resistance, and the highest counter-regulatory response to hypoglycemia. In DBA/2 mice, insulin action was lowest among the strains, and islets isolated had the greatest glucose-stimulated insulin secretion in vitro. In C57BL/6 mice, in vivo physiological responses to hyperinsulinemia at euglycemia and hypoglycemia were intermediate relative to other strains. Insulin secretion by C57BL/6 mice was similar to that in other strains in contrast to the blunted glucose-stimulated insulin secretion from isolated islets.
Strain-dependent differences exist in four inbred mouse strains frequently used for genetic manipulation and study of glucose metabolism. These results are important for selecting inbred mice to study glucose metabolism and for interpreting and designing experiments.
Diabetes 08/2008; 57(7):1790-9. · 8.29 Impact Factor
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Byoung Geun Han,
Chuan-Ming Hao,
Elena E Tchekneva,
Ying-Ying Wang,
Chieh Allen Lee,
Benyamin Ebrahim,
Raymond C Harris,
Timothy S Kern, David H Wasserman,
Matthew D Breyer,
Zhonghua Qi
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ABSTRACT: The present studies examined the relationship between fasting blood glucose and Hb A(1c) in C57BL/6J, DBA/2J, and KK/HlJ mice with and without diabetes mellitus. Daily averaged blood glucose levels based on continuous glucose monitoring and effects of 6-h vs. overnight fasting on blood glucose were determined. Daily averaged blood glucose levels were highly correlated with Hb A(1c), as determined with a hand-held automated device using an immunodetection method. R(2) values were 0.90, 0.95, and 0.99 in KK/HIJ, C57BL/6J, and DBA/2J, respectively. Six-hour fasting blood glucose correlated more closely with the level of daily averaged blood glucose and with Hb A(1c) than did blood glucose following an overnight fast. To validate the immunoassay-determined Hb A(1c), we also measured total glycosylated hemoglobin using boronate HPLC. Hb A(1c) values correlated well with total glycosylated hemoglobin in all three strains but were relatively lower than total glycosylated hemoglobin in diabetic DBA/2J mice. These results show that 6-h fasting glucose provides a superior index of glycemic control and correlates more closely with Hb A(1c) than overnight-fasted blood glucose in these strains of mice.
AJP Endocrinology and Metabolism 08/2008; 295(4):E981-6. · 4.75 Impact Factor
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ABSTRACT: The incretins glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide have been postulated to play a role in regulating insulin action, although the mechanisms behind this relationship remain obscure. We used the hyperinsulinemic-euglycemic clamp to determine sites where insulin action may be modulated in double incretin receptor knockout (DIRKO) mice, which lack endogenous incretin action.
DIRKO and wild-type mice were fed regular chow or high-fat diet for 4 months. Clamps were performed on 5-h-fasted, conscious, unrestrained mice using an arterial catheter for sampling.
Compared with wild-type mice, chow and high fat-fed DIRKO mice exhibited decreased fat and muscle mass associated with increased energy expenditure and ambulatory activity. Clamp rates of glucose infusion (GIR), endogenous glucose production (endoR(a)), and disappearance (R(d)) were not different in chow-fed wild-type and DIRKO mice, although insulin levels were lower in DIRKO mice. Liver Akt expression was decreased but Akt activation was increased in chow-fed DIRKO compared with wild-type mice. High-fat feeding resulted in fasting hyperinsulinemia and hyperglycemia in wild-type but not in DIRKO mice. GIR, suppression of endoR(a), and stimulation of R(d) were inhibited in high fat-fed wild-type mice but not in DIRKO mice. High-fat feeding resulted in impaired tissue glucose uptake (R(g)) in skeletal muscle of wild-type mice but not of DIRKO mice. Liver and muscle Akt activation was enhanced in high fat-fed DIRKO compared with wild-type mice.
In summary, DIRKO mice exhibit enhanced insulin action compared with wild-type mice when fed a regular chow diet and are protected from high-fat diet-induced obesity and insulin resistance.
Diabetes 03/2008; 57(2):288-97. · 8.29 Impact Factor
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ABSTRACT: Muscle glucose uptake (MGU) is regulated by glucose delivery to, transport into, and phosphorylation within muscle. The aim of this study was to determine the role of limitations in glucose phosphorylation in the control of MGU during either physiological insulin stimulation (4 mU x kg(-1) x min(-1)) or exercise with chow or high-fat feeding.
C57BL/6J mice with (HK(+/-)) and without (WT) a 50% hexokinase (HK) II deletion were fed chow or high-fat diets and studied at 4 months of age during a 120-min insulin clamp or 30 min of treadmill exercise (n = 8-10 mice/group). 2-deoxy[(3)H]glucose was used to measure R(g), an index of MGU.
Body weight and fasting arterial glucose were increased by high-fat feeding and partial HK II knockout (HK(+/-)). Both high-fat feeding and partial HK II knockout independently created fasting hyperinsulinemia, a response that was increased synergistically with combined high-fat feeding and HK II knockout. Whole-body insulin action was suppressed by approximately 25% with either high-fat feeding or partial HK II knockout alone but by >50% when the two were combined. Insulin-stimulated R(g) was modestly impaired by high-fat feeding and partial HK II knockout independently ( approximately 15-20%) but markedly reduced by the two together ( approximately 40-50%). Exercise-stimulated R(g) was reduced by approximately 50% with high-fat feeding and partial HK II knockout alone and was not attenuated further by combining the two.
In summary, impairments in whole-body metabolism and MGU due to high-fat feeding and partial HK II knockout combined during insulin stimulation are additive. In contrast, combining high-fat feeding and partial HK II knockout during exercise causes no greater impairment in MGU than the two manipulations independently. This suggests that MGU is impaired during exercise by high-fat feeding due to, in large part, a limitation in glucose phosphorylation. Together, these studies show that the high-fat-fed mouse is characterized by defects at multiple steps of the MGU system that are precipitated by different physiological conditions.
Diabetes 11/2007; 56(10):2476-84. · 8.29 Impact Factor
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ABSTRACT: The absence of GLUT4 severely impairs basal glucose uptake in vivo, but does not alter glucose homeostasis or circulating insulin. Glucose uptake in isolated contracting skeletal muscle (MGU) is also impaired by the absence of GLUT4, and onset of muscle fatigue is hastened. Whether the body can compensate and preserve glucose homeostasis during exercise, as it does in the basal state, is unknown. One aim was to test the effectiveness of glucoregulatory compensation for the absence of GLUT4 in vivo. The absence of GLUT4 was also used to further define the role of hexokinase (HK) II, which catalyses glucose phosphorylation after it is transported in the cell. HK II increases MGU during exercise, as well as exercise endurance. In the absence of GLUT4, HK II expression will not affect MGU. A second aim was to test whether, in the absence of GLUT4, HK II retains its ability to increase exercise endurance. Wild-type (WT), GLUT4 null (GLUT4(-/-)), and GLUT4 null overexpressing HK II (GLUT4(-/-)HK(Tg)) mice were studied using a catheterized mouse model that allows blood sampling and isotope infusions during treadmill exercise. The impaired capacity of working muscle to take up glucose in GLUT4(-/-) is partially offset by an exaggerated increase in the glucagon: insulin ratio, increased liver glucose production, hyperglycaemia, and a greater capillary density in order to increase the delivery of glucose to the exercising muscle of GLUT4(-/-). Hearts of GLUT4(-/-) also exhibited a compensatory increase in HK II expression and a paradoxical increase in glucose uptake. Exercise tolerance was reduced in GLUT4(-/-) compared to WT. As expected, MGU in GLUT4(-/-)HK(Tg) was the same as in GLUT4(-/-). However, HK II overexpression retained its ability to increase exercise endurance. In conclusion, unlike the basal state where glucose homeostasis is preserved, hyperglycaemia results during exercise in GLUT4(-/-) due to a robust stimulation of liver glucose release in the face of severe impairments in MGU. Finally, studies in GLUT4(-/-)HK(Tg) show that HK II improves exercise tolerance, independent of its effects on MGU.
The Journal of Physiology 08/2007; 582(Pt 2):801-12. · 4.72 Impact Factor
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ABSTRACT: Stimulation of nitric oxide-cGMP signaling results in vascular relaxation and increased muscle glucose uptake. We show that chronically inhibiting cGMP hydrolysis with the phosphodiesterase-5 inhibitor sildenafil improves energy balance and enhances in vivo insulin action in a mouse model of diet-induced insulin resistance. High-fat-fed mice treated with sildenafil plus L-arginine or sildenafil alone for 12 weeks had reduced weight and fat mass due to increased energy expenditure. However, uncoupling protein-1 levels were not increased in sildenafil-treated mice. Chronic treatment with sildenafil plus L-arginine or sildenafil alone increased arterial cGMP levels but did not adversely affect blood pressure or cardiac morphology. Sildenafil treatment, with or without l-arginine, resulted in lower fasting insulin and glucose levels and enhanced rates of glucose infusion, disappearance, and muscle glucose uptake during a hyperinsulinemic (4 mU x kg(-1) x min(-1))-euglycemic clamp in conscious mice. These effects occurred without an increase in activation of muscle insulin signaling. An acute treatment of high fat-fed mice with sildenafil plus l-arginine did not improve insulin action. These results show that phosphodiesterase-5 is a potential target for therapies aimed at preventing diet-induced energy imbalance and insulin resistance.
Diabetes 05/2007; 56(4):1025-33. · 8.29 Impact Factor
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Journal of Applied Physiology 01/2007; 101(6):1803-5. · 3.75 Impact Factor
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Journal of Applied Physiology 09/2006; · 3.75 Impact Factor
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ABSTRACT: Islets in most species respond to increased glucose with biphasic insulin secretion, marked by a sharp first-phase peak and a slowly rising second phase. Mouse islets in vitro, however, lack a robust second phase. To date, this observation has not been extended in vivo. We thus compared insulin secretion from conscious mice with isolated mouse islets in vitro. The arterial plasma insulin response to a hyperglycemic clamp was measured in conscious mice 1 wk after surgical implantation of carotid artery and jugular vein catheters. Mice were transfused using clamps with blood from a donor mouse to maintain blood volume, allowing frequent arterial sampling. When plasma glucose in vivo was raised from approximately 5 to approximately 13 mM, insulin rose to a first-phase peak of 403+/-73% above basal secretion (n=5), followed by a rising second phase of mean 289+/- 41%. In contrast, perifused mouse islets ( approximately 75 islets/trial) responded with a similar first phase of 508+/- 94% (n=4) but a smaller and virtually flat second phase of 169+/- 9% (n=4, P<0.05). Furthermore, the slope of the second-phase response differed significantly from zero in mice (2.63+/-0.39%/min, P<0.01), in contrast to perifused islets (0.18+/- 0.14%/min, P>0.30). Mice also displayed pulsatile patterns in insulin concentration (period: 4.2+/- 0.4 min, n=8). Conscious mice thus responded to increased glucose with biphasic and pulsatile insulin secretion, as in other species. The robust second phase observed in vivo suggests that the processes needed to generate second-phase insulin secretion may be abrogated by islet isolation.
AJP Endocrinology and Metabolism 04/2006; 290(3):E523-9. · 4.75 Impact Factor
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ABSTRACT: Despite increased use of the hyperinsulinemic-euglycemic clamp to study insulin action in mice, the effects of experimental parameters on the results obtained have not been addressed. In our studies, we determined the influences of sampling sites, fasting duration, and insulin delivery on results obtained from clamps in conscious mice. Carotid artery and jugular vein catheters were implanted in C57BL/6J mice (n = 6-10/group) fed a normal diet for sampling and infusions. After a 5-day recovery period, mice underwent a 120-min clamp (2.5-mU . kg(-1) . min(-1) insulin infusion; approximately 120-130 mg/dl glucose) while receiving [3-(3)H]glucose to determine glucose appearance (endoR(a)) and disappearance (R(d)). Sampling large volumes (approximately 100 mul) from the cut tail resulted in elevated catecholamines and basal glucose compared with artery sampling. Catecholamines were not elevated when taking small samples ( approximately 5 mul) from the cut tail. Overnight (18-h) fasting resulted in greater loss of total body, lean, and fat masses and hepatic glycogen but resulted in enhanced insulin sensitivity compared with 5-h fasting. Compared with a 16-mU/kg insulin prime, a 300-mU/kg prime resulted in hepatic insulin resistance and slower acquisition of steady-state glucose infusion rates (GIR) after a 5-h fast. The steady-state GIR was expedited after the 300-mU/kg prime in 18-h-fasted mice. The GIR and R(d) rose with increasing insulin infusions (0.8, 2.5, 4, and 20 mU . kg(-1) . min(-1)), but endoR(a) was fully suppressed with doses higher than 0.8 mU . kg(-1) . min(-1). Thus, common variations in experimental factors yield different results and should be considered in designing and interpreting clamps.
Diabetes 03/2006; 55(2):390-7. · 8.29 Impact Factor
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ABSTRACT: A portal venous 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside infusion that results in hepatic 5-aminoimidazole-4-carboxamide-1-beta-D-ribosyl-5-monophosphate (ZMP) concentrations of approximately 4 micromol/g liver increases hepatic glycogenolysis and glucose output. ZMP is an AMP analog that mimics the regulatory actions of this nucleotide. The aim of this study was to measure hepatic AMP concentrations in response to increasing energy requirements to test the hypothesis that AMP achieves concentrations during exercise, consistent with a role in stimulation of hepatic glucose metabolism. Male C57BL/6J mice (27.4+/- 0.4 g) were subjected to 35 min of rest [sedentary (SED), n=8], underwent short-term (ST, 35 min) moderate (20 m/min, 5% grade) exercise (n=8), or underwent treadmill exercise under similar conditions but until exhaustion (EXH, n=8). Hepatic AMP concentrations were 0.82+/- 0.05, 1.17+/- 0.11, and 2.52+/- 0.16 micromol/g liver in SED, ST, and EXH mice, respectively (P< 0.05). Hepatic energy charge was 0.66+/- 0.01, 0.58+/- 0.02, and 0.33+/- 0.22 in SED, ST, and EXH mice, respectively (P< 0.05). Hepatic glycogen was 11.6+/- 1.0, 8.8+/- 2.2, and 0.0+/- 0.1 mg/g liver in SED, ST, and EXH mice, respectively (P< 0.05). Hepatic AMPK (Thr(172)) phosphorylation was 1.00+/- 0.14, 1.96+/- 0.16, and 7.44+/- 0.63 arbitrary units in SED, ST, and EXH mice, respectively (P< 0.05). Thus exercise increases hepatic AMP concentrations. These data suggest that the liver is highly sensitive to metabolic demands, as evidenced by dramatic changes in cellular energy indicators (AMP) and sensors thereof (AMP-activated protein kinase). In conclusion, AMP is sensitively regulated, consistent with it having an important role in hepatic metabolism.
AJP Endocrinology and Metabolism 03/2006; 290(3):E405-8. · 4.75 Impact Factor
