The effects of frequency-dependent dynamic muscle stimulation on inhibition of trabecular bone loss in a disuse model

Clinical electrical muscle stimulation has been shown to alleviate muscle atrophy resulting from functional disuse, yet little is known about its effect on the skeleton. The objective of this study is to evaluate the potential of dynamic muscle stimulation on disused trabecular bone, and to investigate the importance of optimized stimulation frequency in the loading regimen. Fifty-six skeletally mature Sprague-Dawley rats were divided into seven groups for the 4-week experiment: baseline control, age-matched control, hindlimb suspended (HLS), and HLS with muscle stimulation at 1 Hz, 20 Hz, 50 Hz, and 100 Hz. Muscle stimulation was carried out for 10 min per day for 5 days per week, total of 4 weeks. The metaphyseal and epiphyseal trabecular regions of the distal femurs were analyzed with microcomputed tomography and histomorphometry methods. HLS alone for 4-week resulted in a significant amount of trabecular bone loss and structural deterioration. Muscle contraction at 1 Hz was not sufficient to inhibit trabecular bone loss and resulted in similar amount of loss to that of HLS alone. Bone quantity and structure were significantly improved by applying muscle stimulation at mid-frequency (20 Hz and 50 Hz). Dynamic stimulation at 50 Hz demonstrated the greatest preventive effect on the skeleton against functional disused alone animals (up to +147% in bone volume fraction, +38% in trabecular number and -36% in trabecular separation). Histomorphometric analysis showed that the stimulation, regardless of its frequency, did not have an effect on the bone formation indices, such as mineral apposition rate and bone formation rate. Overall, the data demonstrated the potentials of frequency-dependent dynamic muscle contraction in regulating skeletal adaptive responses under disuse conditions. Dynamic muscle stimulation, with a specific regimen, may be beneficial to future orthopedic research in developing a countermeasure for disuse osteopenia and osteoporosis.     

Transcutaneous muscle stimulation to retard disuse atrophy after open meniscectomy

Immobilization of an extremity inevitably results in disuse muscle atrophy. The effectiveness of transcutaneous muscle stimulation by a portable device in preventing atrophy has been determined. Ten patients treated by open meniscectomy and given the usual isometric training were matched with ten patients in whom electrostimulation, consisting of a strong, tetanizing, five-second sustained muscular contraction about 400 times/day, was used for two weeks. Muscular strength and leg circumference were measured before surgery and four weeks after surgery. The electrically stimulated group had a significantly smaller loss of muscle volume and muscle strength, were able to walk earlier without crutches, had a greater range of knee motion, had much less postoperative knee swelling, and used significantly less pain medication. Transcutaneous electrical stimulation may prevent muscle atrophy due to immobilization, thereby shortening rehabilitation time.     

骨骼肌废用性萎缩信号通路及蛋白质代谢的研究进展

骨骼肌废用性萎缩是临床常见问题,其机制尚未完全明确。既往研究认为废用性萎缩的发生是通过一条或多条细胞信号通路的激活来实现,但也有研究指出废用性萎缩是泛素一蛋白酶体的活化而导致蛋白大量分解的结果。目前对于废用性萎缩的研究主要集中在NF—KB、IGF-1／P13K／Akt、TGF-β／Smad及MAPK信号通路对上游信号分子MuRF1和Atroginl／MAFbx的调控作用以及多条信号通路激活或抑制及其相互作用,进而通过泛素-蛋白酶体来影响蛋白质代谢。但对于MuRF1和Atroginl／MAFbx表达的调控机制还有待研究,参与废用性萎缩基因的确认和功能验证也需要深入研究。     

Histochemical study on the changes in muscle fibers in relation to the effects of aging on recovery from muscular atrophy caused by disuse in rats

To investigate the effects of aging on the degree of muscular atrophy caused by disuse and its recovery, we evaluated the recovery from muscular atrophy induced in both young and old rats under the same conditions. The soleus was atrophied by immobilization of the foot joint in a hindlimb and unweighting of the bilateral hindlimbs for 2 weeks, and measurement of the wet weight of muscles and biochemical examination were performed 2, 4, and 6 weeks after the removal of unweighting and fixation during the recovery period of 6 weeks. There was no difference in the degree of atrophy in the fixed soleus between the young and old rats. The recovery from atrophy was delayed in the older rats compared to the young rats. In the unfixed hindlimb, the degree of atrophy was low in both the old and young rats, and the recovery was rapid. Because the recovery from disuse muscular atrophy is delayed with aging, it is necessary to avoid unweighting and immobilization, or to reduce the period spent under such conditions.     

Ultrastructural alterations of Golgi tendon organs in disuse atrophy induced by muscle immobilization in rats

In order to investigate changes in the ultrastructure of Golgi tendon organs (GTOs), the leg muscles of Wistar strain rats were immobilized over various periods. The immobilized triceps surae muscles were divided into three categories: a stretched-position group, a relaxed-position group, and Achilles tendon tenotomy group. After 1, 2, 3, 4, 6 and 8 weeks the muscle preparations dissected from the muscle belly and from the muscle-tendon junction were processed for classification of the fiber type histochemically and to find GTOs in plastic embedded-preparations. In the Achilles tenotomy group, an early fiber transformation from type I to type II fiber was observed, but in the other two groups a low rate of transition of fiber type occurred. At the end of 8 weeks, similar tendencies were observed in all groups. The ultrastructures of GTOs were not significantly different among three groups in basic and general structure when compared with the control group. However, swollen mitochondria in axons and axon terminals and damage in the lamina structure of the myelin sheath were seen in the capsule, axon terminal, and myelinated nerve fiber of GTOs. Although some differences were observed with shorter periods of immobilization, several structural changes were observed over longer periods, indicating the more profound effect of the length of the period rather than the type of immobilization.     

The effect of calcitonin on disuse atrophy of bone in the rat

In thirty female Sprague-Dawley rats the left hind leg was immobilized with plaster casts. According to treatment they were divided into the following groups: A) Control, no casts. B) No treatment. C) 50 MRC mU calcitonin (own preparation) in 5% gelatin subcutaneously per day. D) Vehicle alone subcutaneously. E) 50 MRC mU calcitonin (Ciba) in 5% gelatin subcutaneously per day. In addition, untreated rats without casts served as control (group A). After 6 weeks the femora and tibiae were X-rayed, weighed and examined histologically. The bones of the left and right legs did not differ in control group A. In groups B, C, D, and E a disuse osteoporosis had developed in the left legs (rarefication of trabecular bone volume of femur neck) which could not be seen in X-rays. Calcitonin treatment did not prevent the development of the bone atrophy. However, the pressure of the plaster casts had induced a periosteal apposition in some tibiae, and under calcitonin treatment the extent of this new formation in all femora and tibiae was markedly increased. The vehicle alone was ineffective. It can be concluded that whereas calcitonin is without effect on disuse osteoporosis, it probably favours new bone formation which is induced by other mechanisms.Supported by Deutsche Forschungsgemeinschaft, Bad Godesberg (Germany).     

Inflammation-mediated osteopenia in the rat: The effects of artificial granuloma and sham operation on cortical and trabecular bone

Recent studies have established that generalized loss of trabecular bone occurs in the growing rat following day-to-day inflammatory irritation for a period of 3 wk. We can now demonstrate that there are similar effects on bone in milder but more prolonged chronic inflammation (14 wk). Thus, there were significant decreases in trabecular bone mass as well as in cortical bone after weekly subcutaneous injections or implantations of nonspecific irritants. Osteopenia, induced by a single but extensive inflammatory lesion, remained apparent even 14 wk after induction. This indicates that inflammation-mediated osteopenia is at least incompletely reversible. A less pronounced but similar reduction of cortical and trabecular bone was observed in rats following sham operation. This might be of importance in all animal studies on bone metabolism that include surgical procedures.     

The effects of exercise training on muscle atrophy in haemodialysis patients

Background: Patients with end-stage renal disease on haemodialysis (HD) have limited work capacity. Many structural and functional alterations in skeletal muscles contribute to this disability. Methods: To evaluate the effects of exercise training on uraemic myopathy, seven HD patients (mean age 44.1±17.2 years) were studied. Open muscle biopsies were taken from their vastus lateralis muscle before and after a 6 month exercise rehabilitation programme and examined by routine light- and transmission electron-microscopy. Histochemical stainings of frozen sections were performed and morphometric analysis was also applied to estimate the proportion of each fibre type and the muscle fibre area. Spiroergometric and neurophysiological testing and peak extension forces of the lower limbs were measured before and after exercise training. Results: All patients showed impaired exercise capacity, which was associated with marked muscular atrophy (mean area 2548±463 &mgr;m²) and reduction in muscle strength and nerve conduction velocity. All types of fibres were atrophied but type II were more affected. The ultrastructural study showed severe degenerative changes in skeletal muscle fibres, mitochondria, and capillaries. Exercise training had an impressive effect on muscular atrophy; in particular the proportion of type I fibres increased by 51% and mean muscle fibre area by 29%. Favourable changes were also seen on the structure and number of capillaries and mitochondria. These results were confirmed by a 48% increase in VO2 peak and a 29% in exercise time, as well as an improvement in the peak muscle strength of the lower limbs and in nerve conduction. Conclusions: Skeletal muscle atrophy in HD patients contribute to their poor exercise tolerance. The application of an exercise training rehabilitation programme improved muscle atrophy markedly, and therefore had beneficial effects in overall work performance.     

Dynamic hydraulic flow stimulation on mitigation of trabecular bone loss in a rat functional disuse model

Bone fluid flow (BFF) has been demonstrated as a critical regulator in mechanotransductive signaling and bone adaptation. Intramedullary pressure (ImP) and matrix strain have been identified as potential generators to regulate BFF. To elevate in vivo oscillatory BFF using ImP, a dynamic hydraulic stimulation (DHS) approach was developed. The objective of this study was to evaluate the effects of DHS on mitigation of bone loss and structural alteration in a rat hindlimb suspension (HLS) functional disuse model. Sixty-one 5-month old female Sprague-Dawley rats were divided into five groups: 1) baseline control, 2) age-matched control, 3) HLS, 4) HLS+static loading, and 5) HLS+DHS. Hydraulic flow stimulation was carried out daily on a "10 min on-5 min off-10 min on" loading regime, 5 days/week, for a total of 4 weeks in the tibial region. The metaphyseal trabecular regions of the proximal tibiae were analyzed using μCT and histomorphometry. Four weeks of HLS resulted in a significant loss of trabecular bone, leading to structural deterioration. HLS with static loading alone was not sufficient to attenuate the bone loss. Bone quantity and microarchitecture were significantly improved by applying DHS loading, resulting increase of 83% in bone volume fraction, 25% in trabecular number and mitigation of 26% in trabecular separation compared to HLS control. Histomorphometry analysis on trabecular mineralization coincided with the μCT analysis, in which DHS loading yielded increases of 34% in histomorphometric BV/TV, 121% in MS/BS, 190% in BFR/BS and 146% in BFR/BV, compared to the HLS control. Overall, the data demonstrated that dynamic hydraulic flow loading has potentials to provide regulatory signals for mitigating bone loss induced by functional disuse. This approach may provide a new alternative mechanical intervention for future clinical treatment for osteoporosis.     

Effect of disuse and thermal injury on protein turnover in skeletal muscle

Both muscle inactivity and direct thermal injury increase net proteolysis and amino acid release by muscle. To assess their relative contribution to the altered protein metabolism by thermally injured muscle, rats were scalded on one hindlimb and half of these rats were fitted with casts immobilizing the lower half of the body. Three days later, soleus muscles from the burned and unburned limbs of all burned rats and from controls (uninjured, without casts) were studied in vitro. Protein synthesis was estimated by [¹⁴C]tyrosine incorporation into muscle proteins and net proteolysis was measured by tyrosine release. Protein synthesis by uncasted unburned limb muscles did not differ from that by controls but that by burned limb muscles was enhanced 134% (P < 0.001). Protein synthesis by casted unburned and burned limb muscles was augmented 56 and 309% (P < 0.003), respectively, above control. Tyrosine release by uncasted unburned muscles of burned rats did not differ from that of controls while that of burned limb muscles was elevated 163% (P < 0.007). Tyrosine release by casted unburned and burned limb muscles was increased 70 and 203% (P < 0.002), respectively, above control. It is concluded that both inactivity of and thermal injury to muscle stimulate its protein turnover. The acceleration of protein turnover by muscle underlying the burn wound far exceeds that produced by mere inactivity, suggesting that disuse is only a minor contributor to enhanced protein turnover in thermally injured muscle.     

Both hPTH(1-34) and bFGF increase trabecular bone mass in osteopenic rats but they have different effects on trabecular bone architecture.

Osteoporosis is a syndrome of excessive skeletal fragility that results from both the loss of trabecular bone mass and trabecular bone connectivity. Recently, bFGF has been found to increase trabecular bone mass in osteoporotic rats. The purpose of this study was to compare how trabecular bone architecture, bone cell activity, and strength are altered by two different bone anabolic agents, bFGF and hPTH(1-34), in an osteopenic rat model. MATERIALS AND METHODS: Six-month-old female Sprague-Dawley rats (n = 74) were ovariectomized (OVX) or sham-operated (sham) and maintained untreated for 2 months. Then OVX rats were subcutaneously injected with basic fibroblast factor (bFGF; 1 mg/kg, 5 days/week), human parathyroid hormone [hPTH(1-34); 40 microg/kg, 5 days/week], or vehicle for 60 days (days 60-120). Sham-operated and one group of OVX animals were injected with vehicle. Biochemical markers of bone turnover (urinary deoxypyridinoline cross-links; Quidel Corp., San Diego, CA, USA) and serum osteocalcin (Biomedical Technologies, Stroughton, MA, USA) were obtained at study days 0, 60, 90, and 120 and analyzed by ELISA. At death, the right proximal tibial metaphysis was removed, and microcomputed tomography was performed for trabecular bone structure and processed for histomorphometry to assess bone cell activity. The left proximal tibia was used for nanoindentation/mechanical testing of individual trabeculae. The data were analyzed with Kruskal Wallis and post hoc testing as needed. RESULTS: Ovariectomy at day 60 resulted in about a 50% loss of trabecular bone volume compared with sham-treated animals. By day 120 post-OVX, OVX + vehicle treated animals had decreased trabecular bone volume, connectivity, number, and high bone turnover compared with sham-operated animals [p < 0.05 from sham-, hPTH(1-34)-, and bFGF-treated groups]. Treatment of OVX animals with bFGF and hPTH(1-34) both increased trabecular bone mass, but hPTH(1-34) increased trabecular thickness and bFGF increased trabecular number and connectivity. Histomorphometry revealed increased mineralizing surface and bone formation rate in both bFGF and hPTH(1-34) animals. However, osteoid volume was greater in bFGF-treated animals compared with both the hPTH(1-34) and OVX + vehicle animals (p < 0.05). Nanoindentation by atomic force microscope was performed on approximately 20 individual trabeculae per animal (three animals per group) and demonstrated that elastic modulus and hardness of the trabeculae in bFGF-treated animals were similar to that of the hPTH-treated and sham + vehicle-treated animals. CONCLUSION: Both hPTH(1-34) and bFGF are anabolic agents in the osteopenic female rat. However, hPTH(1-34) increases trabecular bone volume primarily by thickening existing trabeculae, whereas bFGF adds trabecular bone mass through increasing trabecular number and trabecular connectivity. These results suggest the possibility of sequential treatment paradigms for severe osteoporosis.     

Muscle atrophy in patients receiving hemodialysis: effects on muscle strength,muscle quality,and physical function

BACKGROUND: Dialysis patients are less active and have reduced functional capacity compared to individuals with normal renal function. Muscle atrophy and weakness may contribute to these problems. This investigation was undertaken to quantify the extent of atrophy in the lower extremity muscles, to determine whether defects in muscle specific strength (force per unit mass) or central nervous system (CNS) activation are present, and to assess the relationship between muscle size and physical performance in a group of patients on hemodialysis. METHODS: Thirty-eight dialysis subjects (aged 55 +/- 15 years) and nineteen healthy sedentary controls (aged 55 +/- 13 years) were enrolled. Magnetic resonance imaging of the lower leg was used to determine the total cross-sectional area (CSA) and the area of contractile and non-contractile tissue of the ankle dorsiflexor muscles. Isometric dorsiflexor strength was measured during a maximal voluntary contraction with and without superimposed tetanic stimulation (N = 22 for dialysis subjects, N = 12 for controls). Physical activity was measured by accelerometry, and gait speed was recorded as a measure of physical performance. RESULTS: Dialysis subjects were weaker, less active, and walked more slowly than controls. Total muscle compartment CSA was not significantly different between dialysis subjects and controls, but the contractile CSA was smaller in the dialysis patients even after adjustment for age, gender, and physical activity. Central activation and specific strength were normal. Gait speed was correlated with contractile CSA. CONCLUSIONS: Significant atrophy and increased non-contractile tissue are present in the muscle of patients on hemodialysis. The relationship between contractile area and strength is intact in this population. Muscle atrophy is associated with poor physical performance. Thus, interventions to increase physical activity or otherwise address atrophy may improve performance and quality of life.     

氨哮素防治失神经骨骼肌萎缩的临床研究

目的临床研究应用氨哮素防治失神经骨骼肌肌萎缩的效果及副作用。方法随机选用双盲安慰剂对照的研究方法，对７１例因臂丛神经损伤而致肱二头肌完全失神经支配的患者，服用氨哮素（６０μｇ，每日２次）３个月。采用肌电图，肌肉ＡＴＰ酶组织化学染色，肌动蛋白、肌球蛋白免疫组织化学染色等检测手段，分别检测用药前后肱二头肌纤颤电位、肌纤维面积和收缩蛋白含量的变化。并观察患者用药前后心、肺、肝、肾及出凝血功能的变化。结果氨哮素对失神经肱二头肌纤颤电位的衰减、Ｉ型和ＩＩ型肌纤维面积的萎缩、肌动蛋白丧失的抑制率分别为３００％、６６％、６０％和５０％（Ｐ＜０．０５）。对心、肺、肝、肾及出凝血功能均无明显影响。结论氨哮素是一种能防治失神经骨骼肌萎缩的安全而有效的药物     

人参水煎剂防治去卵巢大鼠骨量丢失的骨形态计量学观察

目的 探讨人参水煎剂对去卵巢大鼠骨量丢失的骨形态学改变及其预防作用。方法4.5月龄SD雌性大鼠,按体重随机分为基础组、假手术组、去卵巢组、已烯雌酚阳性用药组、人参低剂量用药组、人参高剂量用药组,共给药10周,取胫骨上段骨组织包埋,不脱钙骨切片,用全自动图像分析仪及松质骨形态计量学软件进行测量和分析,观察人参对骨形态计量学参数的影响。结果 去卵巢10周后骨量丢失和破骨细胞活性、骨形成及骨转换率增加,差异有显著性(P<0.01)。低剂量的人参能使骨量增加26.6％,高剂量能使骨量增加35.1％,高低两剂量人参能使大鼠的骨吸收和骨转换率均下降,差异有显著性(P<0.01或0.05),不抑制藕联的骨形成。结论去卵巢大鼠骨量丢失,骨转换率增高,出现明显的骨质疏松;已烯雌酚(10μg·kg-1·d-1)能抑制骨吸收,也抑制骨形成。人参有增加骨量的趋势,增加骨形成,并对子宫无刺激作用,有弱的预防去卵巢大鼠的骨量丢失作用。     

研究缺血对失神经支配骨骼肌萎缩的影响

目的　研究缺血对失神经支配骨骼肌萎缩的影响。方法　选用 SD大鼠 2 4只 ,建立右下肢缺血加腓肠肌失神经支配的动物模型 (实验组 ) ,左侧为对照组。术后 2、4周取双侧腓肠肌 ,另取 6只正常大鼠腓肠肌作正常对照 ,观察组织学、肌电图及酶组织化学的变化。结果　术后 2、4周 ,实验组肌细胞直径比正常对照组减少 5 1.1%和 6 3.6 % (t =2 .94,P <0 .0 5 ) ,截面积减少 5 3.6 %和 6 2 .0 % (t =2 .88,P <0 .0 5 )。实验组肌细胞线粒体呈空泡状、数量减少 ;肌质网明显扩张退变。肌肉出现纤颤电位 ,和对照组比 ,其波幅无明显差异 (t=2 .11,P<0 .0 5 )。术后 2周实验组的 Na,K- ATP酶活性比正常对照组增高 74.6 % ,术后 4周则下降至对照组的 88.0 % (t=7.6 4,2 .2 4,P<0 .0 1、<0 .0 5 )。术后2周 Ca- ATP酶活性比正常对照组下降 2 8.32 % ,术后 4周下降至 35 .8% (t=2 .98、2 .2 1,P<0 .0 5 )。结论　缺血可加速失神经支配肌肉萎缩的发生与发展     

失神经骨骼肌萎缩的研究进展

周围神经损伤的治疗一直是外科研究的热点。 2 0世纪 6 0年代随着显微外科技术的应用 ,大大提高了周围神经损伤修复的水平。然而其临床疗效仍难令人满意 ,许多肢体功能仍不能恢复 ,特别是高位损伤。究其原因是周围神经损伤的实质是细胞损伤 ,是神经元的完整性受到了破坏 ,其胞体联系末梢的轴浆运输中断 ,从而使神经元的胞体和效应器发生了程度不同的变性或死亡。因此其修复涉及相应神经元胞体的保护、轴突再生和效应器的功能保存等环节。其中任何一个环节延缓或发生不可逆性损害均将影响肢体功能的康复 ,从而最终影响疗效。目前对周围神经损…     

Different effects of antiresorptive therapies on vertebral and nonvertebral fractures in postmenopausal osteoporosis.

In postmenopausal osteoporosis, controlled clinical trials with antiresorptive therapies have shown consistent effects on vertebral fracture incidence while their effects on nonvertebral fractures, especially at the hip, have been reported with some agents, but not others. These discrepancies stress the differences in the pathogenesis of vertebral and nonvertebral fractures as discussed below, and the need to further investigate the mechanisms of action of various antiresorptive agents.