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1.
Non‐invasive measurement of perfusion in skeletal muscle by in vivo magnetic resonance remains a challenge due to its low level and the correspondingly low signal‐to‐noise ratio. To enable accurate, quantitative, and time‐resolved perfusion measurements in the leg muscle, a technique with a high sensitivity is required. By combining a flow‐sensitive alternating inversion recovery (FAIR)‐sequence with a single‐voxel readout, we have developed a new technique to measure the perfusion in the rat gastrocnemius muscle at rest, yielding an average value of 19.4 ± 4.8 mL/100 g/min (n = 22). In additional experiments, perfusion changes were elicited by acute ischemia and reperfusion or by exercise induced by electrical, noninvasive muscle stimulation with varying duration and intensity. The perfusion time courses during these manipulations were measured with a temporal resolution of 2.2 min, showing increases in perfusion of a factor of up to 2.5. In a direct comparison, the results agreed closely with values found with microsphere measurements in the same animals. The quantitative and noninvasive method can significantly facilitate the investigation of atherosclerotic diseases and the examination of drug efficacy. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.  相似文献   

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The creatine kinase reaction has been studied by 31P NMR in exercising human calf muscle. Quantitative analysis of high energy phosphates and saturation transfer study of the creatine kinase flux in the direction of ATP synthesis (Vfor) were performed at rest and during exercise. As expected, exercise induced a [PCr] decrease (from 28.5 ± 0.9 to 21.9 ± 1.5 mM, P < 0.01) matched by a P1, increase (from 4.5 ± 0.2 to 8.9 ± 1.8 mM,P = 0.06). pHi and [ATP] remained unchanged. Vfor did not change from rest (12.4 ± 0.9 mM s?1) to moderate exercise and decreased at the highest exercise level (8.4 ± 1.4 mM s?1, P = 0.006). This observation differs from the prediction of the creatine kinase rate equation, showing an increase in the flux with exercise intensity. Computations suggest that this discrepancy arises from metabolite compartmentalization and/or from the reaction kinetics of a dead end complex stabilized by planar anions.  相似文献   

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PURPOSE: To develop a noninvasive protocol for measuring local perfusion and metabolic demand in muscle tissue with sufficient sensitivity and time resolution to monitor kinetics at the onset of low-level exercise and during recovery. MATERIALS AND METHODS: Capillary-level perfusion, the critical factor that determines oxygen and substrate delivery to active muscle, was measured by an arterial spin labeling (ASL) technique optimized for skeletal muscle. Phosphocreatine (PCr) kinetics, which signal the flux of oxidative phosphorylation, were measured by (31)P MR spectroscopy. Perfusion and PCr measurements were made in parallel studies before, during, and after three different intensities of low-level, stimulated exercise in rat hind limb. RESULTS: The data reveal close coupling between the perfusion response and PCr changes. The onset and recovery time constants for PCr changes were independent of contractile force over the range of forces studied. Perfusion time constants during both onset of exercise and recovery tended to increase with contractile force. CONCLUSION: These results demonstrate that the protocol implemented can be useful for probing the mechanisms that control skeletal muscle blood flow, the physiological limits to muscle performance, and the causes for the attenuated exercise-induced hyperemia observed in disease states.  相似文献   

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PURPOSE: To detect skeletal muscle ischemia with transverse relaxometry after ischemic exercise. MATERIALS AND METHODS: Ten subjects with intermittent claudication were studied. T2 was measured in the gastrocnemius and soleus muscles (m. gastrocnemius and m. soleus) at rest and repeatedly after exercise during 45 minutes of recovery. Prior to MRI a symptom-limited treadmill exercise was performed, and the ankle-arm blood pressure index (AAI) was measured at rest and after exercise. RESULTS: In the 14 legs with ischemic pain, a diverging response was found in the calf: T2 increased in m. gastrocnemius by 5.6% +/- 4.9%, but decreased in m. soleus by -1.2% +/- 4.4% (P < 0.001). Moreover, 13 regions in legs with ischemic pain and reduced AAI (from 0.7 +/- 0.2 at rest to 0.31 +/- 0.15 after exercise) had shortened T2 (-3.6% +/- 1.8%) immediately after exercise. This finding was most frequent in m. soleus and two regions of m. gastrocnemius. Recovery was delayed in the latter two regions. CONCLUSION: T2 may identify ischemic muscles after hypoxic exercise. Shortened T2 suggests a reduced water content (e.g., distribution volume of water) and may affect the upslope kinetics of an extravascular perfusion tracer. The different responses to ischemia by the soleus and gastrocnemius muscle may be due in part to their different fiber type compositions.  相似文献   

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Purpose:

To assess the effects of strenuous exercise on magnetic resonance diffusion parameters and muscle–tendon complex function in skeletal muscle.

Materials and Methods:

Six men performed ankle plantar flexion exercises with eccentric contraction. The fractional anisotropy (FA), λ1, λ2, λ3, mean diffusivity (MD), and T2 values in the triceps surae muscles were measured by magnetic resonance diffusion tensor and spin‐echo imaging. Passive torque of plantar flexors, maximal voluntary isometric plantar flexion torques (MVIP), and Achilles tendon stiffness during MVIP were measured by combined ultrasonography and dynamometry. Plasma creatine kinase and muscle soreness were also assessed. These parameters were measured before and 1–8 days postexercise.

Results:

The medial gastrocnemius exhibited significantly decreased FA 2–5 days after, increased λ2 3 days after, and increased λ3 2 and 3 days after exercise. This muscle also showed significantly increased MD and T2 values 3 days postexercise. MVIP significantly decreased 2 and 3 days postexercise, while passive torque significantly increased 2 days postexercise. Creatine kinase and muscle soreness increased 3–5 days and 1–5 days postexercise, respectively.

Conclusion:

Exercise‐induced muscle damage manifested as significant changes in muscle diffusion parameters with muscle–tendon complex dysfunction and delayed‐onset muscle soreness. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.  相似文献   

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A novel method based on interleaved localized 31P- and 1H MRS is presented, by which lactate accumulation and the accompanying changes in high energy phosphates in human skeletal muscle can be monitored simultaneously during exercise and recovery. Lactate is quantified using a localized double quantum filter suppressing the abundant lipid signals while taking into account orientation dependent signal modulations. Lactate concentration after ischemic exercise directly quantified by DQF 1H spectroscopy was 24 +/- 3 mmol/L cell water, while 22 +/- 3 mmol/L was expected on the basis of 31P MRS acquired simultaneously. Lactate concentration in a sample of porcine meat was estimated to be 40 +/- 7 mmol/L by means of DQF quantitation, versus 39 +/- 5 mmol/L by biochemical methods. Excellent agreement is shown between lactate concentrations measured noninvasively by 1H MRS, measured biochemically ex vivo, and inferred indirectly in vivo from changes in pH, P(i), and PCr as obtained from 31P MRS data.  相似文献   

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The extracellular matrix (ECM) of skeletal muscle is critical for force transmission and for the passive elastic response of skeletal muscle. Structural, biochemical, cellular, and functional changes in skeletal muscle ECM contribute to the deterioration in muscle mechanical properties with aging. Structural changes include an increase in the collagen concentration, a change in the elastic fiber system, and an increase in fat infiltration of skeletal muscle. Biochemical changes include a decreased turnover of collagen with potential accumulation of enzymatically mediated collagen cross-links and a buildup of advanced glycation end-product cross-links. Altered mechanotransduction, poorer activation of satellite cells, poorer chemotactic and delayed inflammatory responses, and a change in modulators of the ECM are important cellular changes. It is possible that the structural and biochemical changes in skeletal muscle ECM contribute to the increased stiffness and impairment in force generated by the contracting muscle fibers seen with aging. The cellular interactions provide and potentially coordinate an adaptation to mechanical loading and ensure successful regeneration after muscle injury. Some of the changes in skeletal muscle ECM with aging may be preventable with resistance or weight training, but it is clear that more human studies are needed on the topic.  相似文献   

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The mechanism of water and sodium apparent diffusion coefficient (ADC) changes in rat skeletal muscle during global ischemia was examined by in vivo 1H and 23Na magnetic resonance spectroscopy (MRS). The ADCs of Na+ and water are expected to have similar characteristics because sodium is present as an aqua-cation in tissue. The shift reagent, TmDOTP5(-), was used to separate intra- and extracellular sodium (Na+i and Na+e, respectively) signals. Water, total tissue sodium (Na+t), Na+i, and Na+e ADCs were measured before and 1, 2, 3, and 4 hr after ischemia. Contrary to the general perception, Na+i and Na+e ADCs were identical before ischemia. Thus, ischemia-induced changes in Na+e ADC cannot be explained by a simple change in the size of relative intracellular or extracellular space. Na+t and Na+e ADCs decreased after 2-4 hr of ischemia, while water and Na+i ADC remained unchanged. The correlation between Na+t and Na+e ADCs was observed because of high Na+e concentration. Similarly, the correlation between water and Na+i ADCs was observed because cells occupy 80% of the tissue space in the skeletal muscle. Ischemia also caused an increase in the Na+i and an equal decrease in Na+e signal intensity due to cessation of Na+/K+-ATPase function.  相似文献   

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目的 研究大鼠骨髓间充质干细胞(BMSCs)的定向分化及其在体内的形态发育情况。方法 Wistar大鼠24只,向其左胫前肌处注射0.2ml无水乙醇,致其无菌坏死,右胫前肌注射等渗盐水0.2ml作为对照,制成动物模型后备用;取大鼠第3代BMSCs,5-氮杂胞苷、成肌调节因子(MyoD)、转化生长因子-β1(TGF-β1)、胰岛素样生长因子-1(IGF-1)联合进行诱导分化。诱导后第9天,收集BMSCs,用BrdU标记并诱导后注射到大鼠双下肢胫前肌处,分别在3,6,9和12d取材进行形态观察和免疫组织化学检查。结果 注射诱导后3d,实验组的成活率明显高于注射单纯注射BMSCs的对照组,BrdU标记细胞向骨骼肌分化,结蛋白、骨骼肌特异肌球蛋白均为弱阳性表达,6,9d可见BrdU标记细胞向骨骼肌分化,结蛋白、骨骼肌特异肌球蛋白阳性表达,第9天更为明显,注射后12d后可见新生骨骼肌细胞形成肌小管,细胞核结蛋白、骨骼肌特异肌球蛋白强阳性表达。结论 大鼠损伤肌肉的微环境中,BMSCs可向骨骼肌定向分化,并伴有结蛋白和骨骼肌肌球蛋白阳性表达;定向诱导后BMSCs在体内成活率高,增殖速率快,向骨骼肌分化纯度更高。  相似文献   

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Mechanisms generating BOLD contrast are complex and depend on parameters that are prone to large variations, in particular in skeletal muscle. Here, we simultaneously measured perfusion by ASL, and BOLD response in the calf muscle of 6 healthy volunteers during post-ischemic reactive hyperemia. We tested whether the relation between the two was altered for varying degrees of leg vascular replenishment induced by prior positioning of the leg at different heights relative to the heart. We found that the BOLD response depended on perfusion, but also on the degree of repletion of leg blood vessels. We conclude that simultaneous determination of perfusion by ASL is important to identify the mechanisms underlying BOLD contrast in the skeletal muscle.  相似文献   

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Human skeletal muscle perfusion, oxygenation, and high-energy phosphate distribution were measured simultaneously by interleaved (1)H and (31)P NMR spectroscopy and (1)H NMR imaging in vivo. From these parameters, arterial oxygen supply (DO(2)), muscle reoxygenation rate, mitochondrial ATP production, and O(2) consumption (VO(2)) were deduced at the recovery phase of a short ischemic exercise bout. In addition, by using a reformulation of the mass conservation law, muscle maximum O(2) extraction was calculated from these parameters.  相似文献   

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目的研究脓毒症时骨骼肌中糖皮质激素受体(GR)表达与低氧诱导因子(HIF-1α)的关系,进一步阐明脓毒症时骨骼肌蛋白高分解代谢的机制。方法 54只Balb/c小鼠随机分为对照组、脓毒症组和治疗组。脓毒症组通过采用腹腔注射脂多糖(10mg/kg)诱导脓毒症(n=24);治疗组(n=24)在伤前2h分别使用糖皮质激素受体拮抗剂(RU38486(10mg/kg)灌胃,余处理同脓毒症组。同时设立对照组(n=6),于伤后24、6、1、2h取材。利用蛋白免疫印迹(western blot)测定肌组织重链肌球蛋白(MHC),半定量逆转录聚合酶链反应(RT-PCR)法检测GR和HIF-1αmRNA的表达变化。结果在内毒素注射6h后,脓毒症小鼠骨骼肌MHC的含量较对照组显著减少,伤前使用糖皮质激素受体拮抗剂RU38486灌胃,于6h后骨骼肌MHC含量增多,后期均高于脓毒症组。脓毒症小鼠GR与HIF-1αmRNA表达在整个实验过程中显著增加;使用RU38486灌胃后,于伤后6h GR mRNA的表达明显降低(P<0.05),并维持在较低水平,在整个治疗过程中HIF-1α明显降低。相关性分析表明,脓毒症中GR与HIF-1α的表达呈正相关。结论体内GR表达增高是脓毒症大鼠骨骼肌蛋白降解显著增加的原因之一,其作用可能是在基因水平与HIF-1α协同作用,进而导致骨骼肌蛋白分解增强。  相似文献   

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To study the upper limit of glycogen storage in human muscle, two healthy male subjects were infused with glucose and insulin for 8 h reaching plasma concentrations of about 21 mM glucose and approximately 2000 microU/ml insulin. Prior to the infusion subjects performed for 1 h one-legged knee-extensor exercise at 75% of their maximum one-legged work capacity in order to lower muscle glycogen stores in one leg. During the 8-h hyperglycemic clamp procedure, glycogen concentrations increased and levelled off at 2- and 5-fold above the pre-infusion levels in the resting and the working leg, respectively. However, the absolute glycogen levels reached in both legs were quite similar, close to 4 g per 100 g wet muscle (about 1000 mumol/g d.w.), independent of prior exercise. Previous studies have shown that glycogen levels, after a bout of glycogen-depleting exercise and subsequent ingestion of a carbohydrate-rich diet for 3 days, can be increased to values around 3-4 g per 100 g wet muscle. It appears that the maximal attainable glycogen concentration in human muscle seems to be close 4 g per 100 g wet muscle. This glycogen level can thus be reached either by a prolonged infusion of supra-physiological concentrations of glucose and insulin or by glycogen-depleting exercise followed by ingestion of a carbohydrate-rich diet.  相似文献   

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A trimethylamine (TMA) moiety is present in carnitine and acetylcarnitine, and both molecules play critical roles in muscle metabolism. At 7 T, the chemical shift dispersion was sufficient to routinely resolve the TMA signals from carnitine at 3.20 and from acetylcarnitine at 3.17 ppm in the 1H‐MRS (Magnetic Resonance Spectroscopy) of human soleus muscle with a temporal resolution of about 2 min. In healthy, sedentary adults, the concentration of acetylcarnitine increased nearly 10‐fold, to 4.1 ± 1.0 mmol/kg, in soleus muscle after 5 min of calf‐raise exercise and recovered to a baseline concentration of 0.5 ± 0.3 mmol/kg. While the half‐time for decay of acetylcarnitine was the same whether measured from the TMA signal (18.8 ± 5.6 min) or measured from the methyl signal (19.4 ± 6.1 min), the detection of acetylcarnitine by its TMA signal in soleus has the advantage of higher sensitivity and without overlapping from lipid signals. Although the activity of carnitine acetyltransferase is sufficient to allow equilibrium between carnitine and coenzyme‐A pools, the exchange in TMA signal between carnitine and acetylcarnitine is slow in soleus following exercise on 7T 1H‐NMR time scale. The TMA signal provides a simple and direct measure of the relative amounts of carnitine and acetylcarnitine. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.  相似文献   

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