Duration of improved muscle glucose uptake after acute exercise in obese Zucker rats

Skeletal muscle is insulin resistant in the obese Zucker rat. Endurance training reduces muscle insulin resistance, but the effects of a single acute exercise session on muscle insulin resistance in the obese Zucker rat are unknown. Therefore, insulin responsiveness of muscle glucose uptake was measured in 15-week-old obese rats either 1, 48, or 72 hours after two hours of intermittent exercise (30:30 min; work:rest). Hindlimbs of sedentary lean (LS) and obese (OS) rats and exercised obese (OE) rats were perfused after a 10-hour fast under both basal (0 mU x ml(-1)) and maximal (20 mU x ml(-1)) insulin concentrations to measure net glucose uptake. Insulin responsiveness of net glucose uptake was significantly reduced in OS compared to LS (8.5 +/- 1.6 vs 15.3 +/- 2.0 micromol x g(-1) x h(-1), respectively). Compared to OS, insulin responsiveness of net glucose uptake was significantly increased by 56% and 80% at 1 hour and 48 hours after acute exercise. However, 72 hours after acute exercise, the increased insulin responsiveness of net glucose uptake was no longer evident. These results indicate that improved responsiveness of muscle glucose uptake persists for at least 48 hours after two hours of acute intermittent exercise in 15-week-old obese Zucker rats.     

Limb and skeletal muscle blood flow measurements at rest and during exercise in human subjects

The aim of the present review is to present techniques used for measuring blood flow in human subjects and advice as to when they may be applicable. Since blood flow is required to estimate substrate fluxes, energy turnover and metabolic rate of skeletal muscle, accurate measurements of blood flow are of extreme importance. Several techniques have therefore been developed to enable estimates to be made of the arterial inflow to, venous outflow from, or local blood flow within the muscle. Regional measurements have been performed using electromagnetic flow meters, plethysmography, indicator methods (e.g. thermodilution and indo-cyanine green dye infusion), ultrasound Doppler, and magnetic resonance velocity imaging. Local estimates have been made using 133Xe clearance, microdialysis, near i.r. spectroscopy, positron emission tomography and laser Doppler. In principle, the aim of the study, the type of interventions and the limitations of each technique determine which method may be most appropriate. Ultrasound Doppler and continuous indo-cyanine green dye infusion gives the most accurate limb blood flow measurements at rest. Moreover, the ultrasound Doppler is unique, as it does not demand a steady-state, and because its high temporal resolution allows detection of normal physiological variations as well as continuous measurements during transitional states such as at onset of and in recovery from exercise. During steady-state exercise thermodilution can be used in addition to indo-cyanine green dye infusion and ultrasound Doppler, where the latter is restricted to exercise modes with a fixed vessel position. Magnetic resonance velocity imaging may in addition be used to determine blood flow within deep single vessels. Positron emission tomography seems to be the most promising tool for local skeletal muscle blood-flow measurements in relation to metabolic activity, although the mode and intensity of exercise will be restricted by the apparatus design.     

Exercise signalling to glucose transport in skeletal muscle

Contraction-induced glucose uptake in skeletal muscle is mediated by an insulin-independent mechanism that leads to translocation of the GLUT4 glucose transporter to the muscle surface membrane from an intracellular storage site. Although the signalling events that increase glucose transport in response to muscle contraction are not fully elucidated, the aim of the present review is to briefly present the current understanding of the molecular signalling mechanisms involved. Glucose uptake may be regulated by Ca(2+)-sensitive contraction-related mechanisms, possibly involving Ca(2+)/calmodulin-dependent protein kinase II and some isoforms of protein kinase C. In addition, glucose transport may be regulated by mechanisms that reflect the metabolic status of the muscle, probably involving the 5'AMP-activated protein kinase. Furthermore, the p38 mitogen-activated protein kinase may be involved in activating the GLUT4 translocated to the surface membrane. Nevertheless, the picture is incomplete, and fibre type differences also seem to be involved.     

Indices of skeletal muscle growth in lean and obese Zucker rats

Skeletal muscle growth was studied in gastrocnemius muscle of lean and obese ad libitum or pair-fed Zucker rats. Skeletal muscle cellularity was determined by DNA, RNA and protein analysis. The length and weight of the tibia and femur were determined. All rats were killed at 15 weeks of age. Lean rats had heavier gastrocnemius, total DNA and total protein than either the ad libitum (ALO) or pair-fed (PFO) obese rats. Lean rats had longer and heavier tibias. Femur length was greater in lean animals while femur weight did not differ between lean and ALO groups. Both had heavier femur than the PFO rats. Comparison of the obese rats revealed that the ALO rats had greater gastrocnemius weight, total DNA and total protein than the PFO group. Total RNA was not different between the lean and ALO group. Comparison of tibias and femurs showed the ALO rats to have longer and heavier bones than the PFO rats. In summary, there are marked differences in the bones of the hindlimb and the cellularity of the gastrocnemius muscle between lean and obese Zucker rats. The differences were accentuated by pair feeding the obese rat.     

Isoleucine, a blood glucose-lowering amino acid, increases glucose uptake in rat skeletal muscle in the absence of increases in AMP-activated protein kinase activity

Leucine and isoleucine were shown to stimulate insulin-independent glucose uptake in skeletal muscle cells in vitro. In this study, we examined the effects of leucine and isoleucine on blood glucose in food-deprived rats and on glucose metabolism in skeletal muscle in vivo. Furthermore, we investigated the possible involvement of the energy sensor, 5'-AMP-activated protein kinase (AMPK), in the modulation of glucose uptake in skeletal muscle, which is independent of insulin, and also in leucine- or isoleucine-stimulated glucose uptake. Oral administration of isoleucine, but not leucine, significantly decreased the plasma glucose concentration. An i.v. bolus of 2-[1,2-3H]-deoxyglucose (2-[3H]DG) was administered to calculate glucose uptake. Glucose uptake in the skeletal muscle did not differ after leucine administration, but glucose uptake in the muscles of rats administered isoleucine was 73% greater than in controls, suggesting that isoleucine increases skeletal muscle glucose uptake in vivo. On the contrary, in the skeletal muscles, administration of leucine but not isoleucine significantly increased [U-14C]-glucose incorporation into glycogen compared with controls. AMPK alpha1 activity in skeletal muscle was not affected by leucine or isoleucine administration. However, isoleucine, but not leucine, significantly decreased AMPK alpha2 activity. The decrease in AMPK alpha2 activity was thought to be due to decreases in AMP content and the AMP:ATP ratio, which were related to the isoleucine administration. This is the first report of isoleucine stimulating glucose uptake in rat skeletal muscle in vivo, and these results indicate that there might be a relation between the reduction in blood glucose and the increase in skeletal muscle glucose uptake that occur with isoleucine administration in rats. The alterations in glucose metabolism caused by isoleucine may result in an improvement of the availability of ATP in the absence of increases in AMP-activated protein kinase activity in skeletal muscle.     

Inhibited amino acid uptake in skeletal muscle during starvation

Amino acid uptake in skeletal muscle is reduced during different catabolic conditions such as sepsis, endotoxic shock, and uremia. The present study was designed to determine the effect of another catabolic condition, starvation, on amino acid transport in skeletal muscle. Male Sprague-Dawley rats (40-60 g) were starved for 24, 48, or 72 hr and soleus (SOL) muscles were removed intact and incubated for 2 hr in a medium consisting of Krebs-Henseleit bicarbonate buffer (pH 7.4) with glucose (5 mM), [14C]-inulin, and [3H]-alpha-aminoisobutyric acid (AIB). Amino acid uptake was determined from intracellular to extracellular ratio of AIB following incubation. AIB uptake was significantly reduced after 24 hr of starvation and remained low with further fasting. After 72 hr the AIB distribution ratio was approximately 50% of initial value. Amino acid uptake returned to normal within 24 hr after refeeding of animals that had been starved for 72 hr. Plasma (0.25 ml) from starved rats, added to the incubation medium (2.75 ml) of muscles from nonfasted rats, significantly inhibited AIB uptake. The present results suggest that amino acid uptake in skeletal muscle is progressively reduced during starvation, an effect that may be mediated by a circulating factor(s) present in blood.     

Epigallocatechin gallate stimulates glucose uptake through the phosphatidylinositol 3-kinase-mediated pathway in L6 rat skeletal muscle cells

The effect of epigallocatechin gallate (EGCG) on glucose uptake was studied in L6 rat skeletal muscle cells. Glucose uptake assay revealed that EGCG increased glucose uptake >70% compared to control. EGCG-stimulated glucose uptake was blocked by LY294002, an inhibitor of phosphatidylinositol (PI) 3-kinase, which is a major regulatory molecule in glucose uptake pathways. However, AMP-activated protein kinase (AMPK), which is another crucial mediator in independent glucose uptake pathways, did not inhibit EGCG-stimulated glucose uptake by SB203585, a specific inhibitor of the AMPK downstream mediator, p38 mitogen-activated protein kinase (MAPK). We also found that EGCG increased the phosphorylation level of protein kinase B and PI 3-kinase activity, when assessed by PI 3-kinase assay, whereas no increase in the phosphorylation level of AMPK and p38 MAPK was observed. Taken together, these results suggest that EGCG might stimulate glucose uptake, not AMPK-mediated but PI 3-kinase-mediated, in skeletal muscle cells, thereby contributing to glucose homeostasis.     

Impaired superficial femoral artery vasodilation and leg blood flow in young obese women following an oral glucose tolerance test

This study was designed to test the hypothesis that glucose ingestion following an overnight fast increases leg vascular conductance (LVCd) and superficial femoral artery (SFA) vasodilation in lean but not obese young women. Obese (23.5 ± 4.0 years, 84.7 ± 14.7 kg, 37.2% ± 6.4% fat; mean ± SD, n = 8) and lean (23.8 ± 2.4 years, 60.6 ± 4.0 kg, 22.3% ± 2.8% fat; n = 8) women arrived in the laboratory at 0830 h after a 12-h overnight fast for body composition (densitometry) assessment. Then, capillary blood glucose (BGlu), plasma insulin, heart rate, cardiac output, mean arterial pressure, leg blood flow (Doppler ultrasound), and LVCd were measured (after 15 min in the supine position), and at 30-min intervals for 2 h following glucose ingestion (75 g glucose load, 12.5% solution). Fasting BGlu concentration was not different between groups (obese = 5.1 ± 0.47 vs. lean = 4.9 ± 0.37 mmol·L(-1), p = 0.71) but 60, 90, and 120 min post ingestion BGlu was elevated (p ≤ 0.03) in the obese women. Insulin differences were not significant. Fasting LVCd was not different between groups (lean = 0.72 ± 0.49 vs. obese = 0.70 ± 0.19 mL·min(-1)·mm Hg(-1); p = 0.48); however, LVCd, as well as Δ in SFA diameter were significantly elevated (p ≤ 0.04) in the lean compared with the obese group at 60, 90, and 120 min postglucose ingestion (LVCd, peak lean = 1.4 ± 0.5 vs. peak obese = 0.8 ± 0.1 mL·min(-1)·mm Hg(-1); Δ in SFA, peak lean = 0.51 ± 0.30 vs. peak obese = 0.09 ± 0.45 mm). The reduced LVCd following glucose ingestion could contribute to impaired glucose tolerance. Further, the lack of SFA dilation may be evidence of impaired vascular insulin responsiveness in these obese young women.     

铬、鱼油对肥胖模型大鼠血脂、血糖的影响

肥胖在全球范围内流行 ,而且严重危害身体健康。铬、鱼油参与并调节糖、脂肪代谢 ,因此 ,我们选择了铬、鱼油作为影响因素 ,观察其对饮食诱导肥胖大鼠的影响。方法 :将肥胖模型大鼠按体重随机分为 4组 ,每组 8只。分别为肥胖组 ;鱼油组 ;鱼油 +铬组和铬组 ,另设基础对照组。喂养 6周后处死动物。取睾周及肾周脂肪称重记录。测定全血血糖和血清血脂。结果 :三个实验组的血糖值、胆固醇、甘油三酯低于肥胖组 ,高密度脂蛋白胆固醇高于肥胖组。结论 :铬、鱼油能降低高血脂、高血糖 ,调节糖、脂代谢 ,这提示我们铬、鱼油能降低肥胖引起的健康危害     

4-Hydroxyisoleucine stimulates glucose uptake by increasing surface GLUT4 level in skeletal muscle cells via phosphatidylinositol-3-kinase-dependent pathway

Purpose

To determine the effect of 4-Hydroxyisoleucine (4-HIL), an unusual amino acid isolated from the seeds of Trigonella foenum-graecum, on glucose uptake and the translocation of glucose transporter 4 (GLUT4) to plasma membrane in skeletal muscle cells and to investigate the underlying mechanisms of action.

Methods

Rat skeletal muscle cells (L6-GLUT4myc) were treated with 4-HIL, and the effect on glucose uptake was determined by measuring the incorporation of radio-labeled 2-deoxy-[³H]-d-glucose (2-DG) into the cell. Translocation of GLUT4myc to plasma membrane was measured by an antibody-coupled colorimetric assay.

Results

The prolonged exposure (16?h) of L6-GLUT4myc myotubes to 4-HIL caused a substantial increase in the 2-DG uptake and GLUT4 translocation to the cell surface, without changing the total amount of GLUT4 and GLUT1. Cycloheximide treatment reversed the effect of 4-HIL on GLUT4 translocation to the basal level suggesting the requirement of new protein synthesis. The 4-HIL-induced increase in GLUT4 translocation was completely abolished by wortmannin, and 4-HIL significantly increased the basal phosphorylation of AKT (Ser-473), but did not change the mRNA expression of AKT, IRS-1, GLUT4, and GSK3β.

Conclusion

Results suggest that 4-HIL stimulates glucose uptake in L6-GLUT4myc myotubes by enhancing translocation of GLUT4 to the cell surface in a PI-3-kinase/AKT-dependent mechanism.     

Bolus arginine supplementation affects neither muscle blood flow nor muscle protein synthesis in young men at rest or after resistance exercise

The aim of this study was to investigate the ergogenic potential of arginine on NO synthesis, muscle blood flow, and skeletal muscle protein synthesis (MPS). Eight healthy young men (22.1 ± 2.6 y, 1.79 ± 0.06 m, 76.6 ± 6.2 kg; mean ± SD) participated in 2 trials where they performed a bout of unilateral leg resistance exercise and ingested a drink containing either 10 g essential amino acids with 10 g l-arginine (ARG) or an isonitrogenous control (CON). Femoral artery blood flow of both the nonexercised and exercised leg was measured continuously using pulsed-wave Doppler ultrasound, while rates of mixed and myofibrillar MPS were determined using a primed continuous infusion of L-[ring-(13)C(6)] or L-[ring-(2)H(5)]phenylalanine. The plasma arginine concentration increased 300% during the ARG trial but not during the CON trial (P < 0.001). Plasma nitrate, nitrite, and endothelin-1, all markers of NO synthesis, did not change during either the ARG or CON trial. Plasma growth hormone increased to a greater degree after exercise in the ARG trial than CON trial (P < 0.05). Femoral artery blood flow increased 270% above basal in the exercised leg (P < 0.001) but not in the nonexercised leg, with no differences between the ARG and CON trials. Mixed and myofibrillar MPS were both greater in the exercised leg compared with the nonexercised leg (P < 0.001), but did not differ between the ARG and CON treatments. We conclude that an oral bolus (10 g) of arginine does not increase NO synthesis or muscle blood flow. Furthermore, arginine does not enhance mixed or myofibrillar MPS either at rest or after resistance exercise beyond that achieved by feeding alone.     

单纯性肥胖儿童脂肪肝、血糖及相关因素的研究

目的 探讨单纯性肥胖儿童脂肪肝、血糖及相关因素。方法 采用B超、快速微量血糖仪及其他有关仪器,对62名8－11岁儿童（其中肥胖组32名、正常组30名）进行了肝脏、血糖及有关形态与机能等指标的测定。结果 肥胖组脂肪肝患病率为93．8％,对照组为10％,差异有非常显性;肥胖组血糖为5．42mmol/L,对照组为4．54mmol/L,差异有显性;心功能良好率肥胖组为62．5％,对照组为93．3％,差异有显性。经相关分析,脂肪肝患病率与皮褶厚度、腰臀围比和体质指数呈显正相关,相关系数分别为0．8786、0．6256和0．8454。逐步回归分析表明,皮褶厚度和腰臀围比是脂肪肝主要危险因素。血糖与皮褶厚度和体质指数呈显正相关,相关系数分别为0．3403和0．3155。 逐步回归分析表明,皮褶厚度是高血糖的主要危险因素。结论 单纯性肥胖对儿童的肝脏、糖代谢和心功能均造成危害,是成人期心血管病、糖尿病及脂代谢障碍潜在的危险因素。     

Hormonal and lifestyle determinants of appendicular skeletal muscle mass in men: the MINOS study

BACKGROUND: Aging-related sarcopenia is characterized by a loss of muscle mass and strength and increased fatigability. However, studies of its determinants in elderly men are scarce. OBJECTIVE: We investigated risk factors for sarcopenia in a large cohort of men. DESIGN: We analyzed 845 men aged 45-85 y who belonged to the MINOS cohort. Lifestyle factors (physical activity, tobacco smoking, alcohol intake, caffeine intake) were evaluated by using a standardized questionnaire. Appendicular skeletal muscle mass (ASM) was estimated by using dual-energy X-ray absorptiometry. The relative appendicular skeletal muscle mass index (RASM) was calculated as ASM/body height(2.3). Apparent free testosterone concentration (AFTC) and free testosterone index (FTI) were calculated on the basis of concentrations of total testosterone and sex hormone-binding globulin. RESULTS: RASM decreased with age (r = -0.29, P < 0.0001). Current smokers had lower RASM than did subjects who never smoked (-3.2%; P < 0.003). RASM increased with the intensity of physical activity at work (P for trend < 0.001). Men who participated in regular exercise during leisure time had 2.2% higher RASM than did those who did not (P < 0.03). Men whose values for AFTC, FTI, or 25-hydroxycholecalciferol [25(OH)D] were >2 SDs below the mean for young men had significantly lower RASM than did men with higher values. Men with sarcopenia, defined as the lowest quartile of RASM in the studied cohort (<6.32 kg/m(2.3)), were significantly older than men with normal RASM, weighed significantly less, smoked more, and spent significantly less time on leisure-time activities. Sarcopenic men also had lower values for testosterone, AFTC, FTI, and 25(OH)D. CONCLUSION: In elderly men, low physical activity, tobacco smoking, thinness, low testosterone (AFTC and FTI), and decreased 25(OH)D concentrations are risk factors for sarcopenia.