Rapid increase in the number of androgen receptors following electrical stimulation of the rat muscle

Summary The changes in the number of androgen receptors in rat gastrocnemius muscle following muscle contraction caused by electrical stimulation were investigated. The gastrocnemius muscle of one leg, which was selected at random for each rat, was stimulated with needle type electrodes, e.g. for 2 s at 10 V and 100 Hz, with 5-s intervals. The contralateral leg was left unstimulated as a control. One set consisted of ten such stimuli, followed by 5-min rest. Three sets every 2 days caused a statistically significant increase in muscle mass, the increase being about 2.5% after the 3rd day of stimulation, 4.4% after the 5th day, 5.9% after the 13th day and 8.3% after the 27th day compared with each control muscle (P< 0.001 in each case). The protein content also increased but the water content did not change. Stimulation over 4 weeks induced an increase in the area of the cross-section of the muscle fibres to about 30076 more than that of the control muscles, though the total muscle fibre numbers were slightly, but significantly, reduced. Electromechanical properties supported the development of the muscle by stimulation, because the maximal isometric tetanic force and peak twitch force markedly increased in the stimulated muscle. The androgen receptors in the muscle cytosol fraction were determined by means of a binding assay involving [³H]methyltrieno-lone, which is an analogue of testosterone, the number having rapidly increased in the stimulated leg, when compared with that in the control leg, by about 25% after the 3rd day. The increase then slowed down, reaching a plateau after the 5th-day of stimulation. The receptor dissociation constants for [³H]methyltrienolone remained unchanged, i.e. approximately 0.3 to 0.4 nmol throughout the experimental period. These findings suggested that a rapid increase in the number of androgen receptors occurred as an early event for a practical increase in muscle mass and thus it may have contributed in part to the triggering of muscle hypertrophy by enhancing the muscle sensitivity to androgen.     

Expression of HIF-1alpha, VEGF and VEGF receptors in the carotid body of chronically hypoxic rat

We examined the protein expression and localization of HIF-1alpha, VEGF, VEGF receptors in the carotid body (CB) of rats breathing 10% inspired oxygen for up to 4 weeks. The immunoreactivity (IR) of HIF-1alpha was distributed numerously in the nuclei of glomus (type-I) and other cells since hypoxia for 1 day, but was faint and scattered in the normoxic CBs. Cytoplasmic staining of the VEGF was intense in glomus cells of the hypoxic but not the normoxic group. The IR levels of HIF-1alpha and VEGF reached plateau at 4 weeks, and the IRs of VEGFR-1 and VEGFR-2 were strongly positive in the hypoxic group. Yet, the expression of VEGFR-1-IR was mild, whereas the VEGFR-2-IR was intense in normoxic CBs, suggesting an upregulation of VEGFR-1 but not VEGFR-2 in hypoxia. Hence, HIF-1 may activate the expression of VEGF and VEGFR-1 in the CB and the expression of VEGF in the chemoreceptors may play a paracrine role in the vascular remodeling during chronic hypoxia.     

低氧复合运动对大鼠骨骼肌线粒体含量的影响

 目的：探讨低氧复合运动对线粒体含量的影响及线粒体生物合成和自噬在其中的作用。方法：雄性SD大鼠随机分为常氧对照（NC）组、常氧运动（NT）组、低氧对照（HC）组和低氧复合运动（HT）组。低氧干预为常压低氧帐篷,11.3%氧浓度持续暴露4周。运动干预为跑台训练（5°,15 m/min）,60 min/d,每周5 d,共4周。JC-1荧光探针检测线粒体膜电位;萤光素酶法检测线粒体ATP合成能力;Western blotting检测骨骼肌过氧化物酶体增殖物激活受体γ辅激活因子1（PGC-1α）、线粒体转录因子A（Tfam）、Bcl-2/腺病毒E1B 19kD相互作用蛋白3（Bnip3）、苄氯素1（beclin-1）、细胞色素C氧化酶亚基IV（COXIV）和电压依赖性阴离子通道1（VDAC-1）蛋白表达量。结果：HC组与NC组比较,线粒体膜电位、ATP合成能力及COXIV、VDAC-1、PGC-1α和Tfam蛋白表达显著降低（P<005或P<001）,Bnip3和beclin-1蛋白表达显著升高（P<005）。HT组与HC组比较,线粒体膜电位、ATP合成能力及COXIV、VDAC-1、PGC-1α、Tfam、Bnip3和beclin-1蛋白表达均显著升高（P<005或P<001）。结论：慢性低氧暴露提高了线粒体自噬但抑制了线粒体生物合成,导致线粒体含量减少。低氧复合运动促进低氧状态下骨骼肌线粒体自噬,并促进线粒体生物合成,从而提高线粒体含量及功能。     

低氧诱导因子-1在调控骨骼肌缺氧时能量代谢发生适应性变化的机制研究进展

低氧诱导因子-1(HIF-1)是一种调控组织细胞氧稳态的关键性核转录因子,广泛存在于哺乳动物和人体内,其表达和活性受到细胞氧浓度的严密调控。它能在生理性和病理性缺氧缺血的情况下,通过调控细胞能量代谢、血管发生、红细胞生成、细胞生存、细胞增殖和凋亡等生物学效应,使细胞适应低氧环境得以生存或者走向凋亡。本文中我们主要概述了HIF-1的结构功能,及其在缺氧时调控骨骼肌能量代谢方面发生适应性变化的机制及研究进展。     

Heterogeneity of response to exercise of rat muscle pyruvate dehydrogenase complex

Muscle glucose uptake is greatly stimulated by moderate exercise, but full oxidation of the glucose to CO₂ depends on the activity of the pyruvate dehydrogenase (PDH) complex. Our aim was to determine how PDH complex in different muscle groups responds to varying periods of moderate exercise. Rats were run on a motor-driven treadmill for 5–30 min and muscle PDH complex activity was determined in heart, diaphragm and red quadriceps muscles after isolation of mitochondria in the presence of inhibitors of PDH complex interconversion. In heart and diaphragm muscle, exercise caused an increase in PDH complex activity after 5 min, but this was followed by a significant decrease in activity as exercise progressed. In red quadriceps muscle, PDH complex activity was reduced after 5 min of exercise and was decreased further as exercise continued. We conclude that increased duration of exercise can lead to reduced PDH complex activity in rat muscles. We propose that this is a consequence of elevated fatty acid oxidation, the products of which stimulate PDH kinase. This implies that increased glycolysis to lactate and increased fatty acid oxidation can simultaneously provide energy for contracting muscle.     

Enhancement of muscle regeneration in the rat gastrocnemius muscle by low energy laser irradiation

Summary The effect of low-energy laser (He-Ne) irradiation on the rate of skeletal muscle regeneration after partial excision of the rat gastrocnemius muscle was studied using quantitative histological morphometric methods. The injured zones of the experimental rats were subjected to direct He-Ne laser (632.8 nm wavelength) irradiation (6.0 mW for 2.3 min) immediately following injury and once daily thereafter for 5 days. Muscles that were injured as above and subjected to red or room light irradiation served as a control group. The volume fraction (percent of total volume of injured zone) of the mononucleated cells in the injured zone decreased gradually with time after injury, but more rapidly in the laser irradiated muscles than in the control. At 3 days post-injury the myotubes in the laser-irradiated muscles populated a significantly higher percentage (13.9 ± 1.1%) of the injured area than in the control muscles (7.8 ± 1.0%). The volume fraction of the young myofibers in the laser irradiated muscles exceeded 30.6 ± 2.2% and 49.6 ± 5.6% at 8 and 11 days post-injury, respectively, while in control muscles these structures comprised only 9.6 ± 1.0% and 27.2 ± 3.8% of the injured zone at 8 and 11 days after injury, respectively. It is concluded that He-Ne laser irradiation during the regeneration process promotes muscle maturation in the injured zone following partial excision of the rat gastro-cnemius muscle.     

陈旧性坐骨神经缺损对大鼠腓肠肌组织蛋白含量及泛素表达的影响

目的：了解陈旧性坐骨神经缺损后肌肉萎缩过程中蛋白质降解的机制。方法：用SD大鼠建立坐骨神经缺损模型,切断大鼠右侧坐骨神经,形成10 mm缺损。测定术后1、2、3、4、6、9及12个月腓肠肌肌总蛋白的含量;免疫组化法观察组织中泛素的表达变化;Western印迹法测定组织中泛素蛋白的表达水平。结果：坐骨神经缺损后腓肠肌肌总蛋白含量随缺损时间延长呈进行性下降;正常腓肠肌组织中泛素呈低表达,随缺损时间延长泛素表达水平增强,持续到9个月,随后呈下调趋势。结论：陈旧性坐骨神经缺损后腓肠肌蛋白的降解、肌总蛋白量下降及肌萎缩可能和泛素-蛋白酶体途径有关。     

Effects of hypoxia on capillary density and fiber composition in rat skeletal muscle

Summary Capillary density, fiber composition and myoglobin concentration were determined in skeletal muscle of Sprague-Dawley female rats. P_IO₂ for control (C) rats was 123 mm Hg; for hypoxic (H) rats the O₂ concentration in air was lowered to 12.6% (P_IO₂=73 mm Hg) over 4 days and then kept at this level for 39 days. Body weight (BW) in C rats went from 182 to 258 g in 6 weeks. H rats showed an initial 13 g drop in BW but later gained weight at the same rate. A difference of 20 g was maintained between C and H rats. Five groups of about 10 rats each (3 C and 2 H) were studied by histochemistry using frozen samples from the tibialis anterior, gastrocnemius (medial head) and soleus muscles. 20 m slices, cut transversely, were treated for alkaline phosphatase and ATPase after preincubation at pH's of 3.8 to 9.4 in order to visualize capillaries and typify fibers. In both C and H rats, capillary density decreased at the same rate with increasing BW, as a consequence of the increase in the size of the fibers resulting from growth. At the same BW capillary densities for a given muscle were not statistically different. No consistent differences in fiber composition were found in the soleus after exposure to hypoxia. In the gastrocnemius and the tibialis anterior, however, the percentage population of white fibers tended to be higher in the H rats than in the C rats, while the population of red fibers decreased. Myoglobin concentration was higher in the soleus, a muscle with a preponderant intermediate fiber population, than in the other two muscles. Hypoxia did not systematically affect myoglobin concentration.Supported by GRS 523 and HL 18145, N.I.H.Supported by a fellowship from the Rockefeller Fndn.     

Correlation between VEGF and HIF-1alpha expression in human oral squamous cell carcinoma

Understanding the development and progression of oral cancer is critical in the quest for successful therapeutic intervention. The hypoxic microenvironment present in human oral tumor in vivo may actively influence tumor growth and neovascularization. This study correlates expression of both VEGF and HIF-1alpha in normal keratinocytes and oral cancer cell lines and determine whether hypoxia played a role in VEGF and HIF-1alpha regulation. Three human oral cancer cell lines and three normal keratinocytes were exposed to both normoxia and hypoxia culture conditions. Northern and Western blot analysis were used to assess VEGF and HIF-1alpha expression in the different culture conditions. ELISA assays were performed to measure VEGF production in the different cell lines tested. Hypoxia upregulated VEGF and HIF-1alpha expression on both normal and oral cancer cell lines, with a statistically significant difference between normal and oral cancer cell lines. Pattern of hypoxia-induced VEGF mRNA level tightly followed the HIF-1alpha mRNA expression in the cell lines tested. These results suggest that hypoxia regulates both VEGF and HIF-1alpha expression in head and neck carcinoma cell lines, thus establishing a biochemical pathway between tumor hypoxia and neoangiogenesis in these aggressive neoplasms.     

一氧化氮合酶在坐骨神经夹伤后腓肠肌中的表达变化

目的:探讨外周神经损伤后同侧腓肠肌中3种一氧化氮合酶(nitric oxide synthase,NOS)的表达变化及定位。方法:采用H-E染色及Masson三色染色法分析大鼠坐骨神经夹伤后同侧腓肠肌的病理变化,NADPH-黄递酶组织化学研究其总NOS的改变,并利用Western印迹法、免疫荧光双标法,对3种NOS表达变化及定位进行分析。结果:神经夹伤后相应腓肠肌发生了明显的病理变化且总NOS发生改变,3种NOS变化不尽相同,其表达高峰均约在4周左右。nNOS与神经丝标记物NF-200有共定位,iNOS、eNOS则分别在巨噬细胞、血管内皮细胞中有表达。结论:3种NOS在坐骨神经夹伤后相应腓肠肌中表达变化不同,可能对肌肉损伤及再生修复发挥不同作用。     

Hypertrophic response of human skeletal muscle to strength training in hypoxia and normoxia

The purpose of this study was to test the hypothesis that work-induced skeletal muscle hypertrophy may be reduced by training in chronic hypobaric hypoxia compared to normoxia. Five healthy males [mean age 34.4 (SEM 2.2) years] performed strength training of the elbow flexors for 1 month, at altitude (A) (5050 m) and with the same absolute loads at sea level (SL), 8 months later. The EF cross-sectional area (CSA), determined at mid-arm by nuclear magnetic resonance imaging, increased by 11.3 (SEM 3.7)% (P < 0.05) at A and 17.7 (SEM 4.5) % (P < 0.05) at SL. Isometric maximal voluntary contraction (MVC) increased by 9.5 (SEM 2.6)% (P<0.05) at A and 13.6 (SEM 2.4)% (P<0.05) at SL. The CSA and MVC changes in A were significantly smaller than at SL (P<0.05). Muscle specific tension did not change in either condition. No changes in muscle plus bone or MVC of the untrained, controlateral arm were observed. Thus, although there was no indication of muscle wasting at A, the hypertrophic response of skeletal muscle when trained in chronic hypoxia seemed to be significantly lower than that produced in normoxia. This effect could have arisen either from a direct depression of protein synthesis and/or hormonal changes provoked by hypoxia.     

Torque and surface mechanomyogram parallel reduction during fatiguing stimulation in human muscles

The purpose of the study was to verify, by means of torque and mechanomyogram (MMG) compared analysis, the validity of MMG as a tool to investigate the contractile changes due to localized muscular fatigue induced by stimulation protocols usually employed for sport training and rehabilitation programs. Ten healthy sedentary subjects participated in the study. Torque produced by the dominant biceps brachii (BB) and vastus lateralis (VL) during transcutaneous stimulated contractions has been recorded by a load cell strapped to the subjects’ wrist and distal one-third of the tibia, respectively. MMG was detected over the muscle bellies during a monopolar supramaximal stimulation of the main motor point. After potentiation, the fatiguing stimulation was administered. It consisted of 50 cycles, with 2 s of 50 Hz and 25 s of 2 Hz. Averaged normalized values of peak torque (pT) and MMG peak-to-peak (MMG-pp) of the subjects group decreased from their initial 100% values to 55% (pT) and 60% (MMG-pp) for BB and to 43% (pT) and 47% (MMG-pp) for VL. The pT% and MMG-pp% changes throughout the stimulation protocol presented high correlation (BB: R=0.95, P<0.001; VL: R=0.94, P<0.001). This correlation suggests that MMG could be used to follow muscle mechanical fatigue development when torque output is not or hardly detectable such as during electrical stimulation programs employed for sport training or rehabilitation protocols.     

Post-exercise leg and forearm flexor muscle cooling in humans attenuates endurance and resistance training effects on muscle performance and on circulatory adaptation

The influence of regular post-exercise cold application to exercised muscles trained by ergometer cycling (leg muscles) or handgrip exercise using a weight-loaded handgrip ergometer (forearm flexor muscles) was studied in human volunteers. Muscle loads were applied during exercise programs three to four times a week for 4–6 weeks. Besides measuring parameters characterizing muscle performance, femoral and brachial artery diameters were determined ultrasonographically. Training effects were identified by comparing pre- and post-training parameters in matched groups separately for the trained limbs cooled after exercise by cold-water immersion and the corresponding trained limbs kept at room temperature. Significant training effects were three times more frequent in the control than in the cold group, including increases in artery diameters in the control but not in the cold group. It is concluded that training-induced molecular and humoral adjustments, including muscle hyperthermia, are physiological, transient and essential for training effects (myofiber regeneration, muscle hypertrophy and improved blood supply). Cooling generally attenuates these temperature-dependent processes and, in particular, hyperthermia-induced HSP formation. This seems disadvantageous for training, in contrast to the beneficial combination of rest, ice, compression and elevation in the treatment of macroscopic musculo-tendinous damage. Part of the results were presented at the Congress on Physiology and Pharmacology of Temperature Regulation held in Rhodes (Greece) in October 14, 2004 [Ohnishi N, Yamane M, Uchiyama N, Shirasawa S, Kosaka M, Shiono H, Okada T (2004) Adaptive changes in muscular performance and circulation by resistance training with regular cold adaptation. J Therm Biol 29: 839–843].     

Plasma accumulation of hypoxanthine,uric acid and creatine kinase following exhausting runs of differing durations in man

Summary During exhausting exercise adenylate kinase in the muscle cells is activated and a degradation of adenosine 5-diphosphate occurs. Consequently, degradation products of adenosine 5-monophosphate including hypoxanthine and uric acid, accumulate in plasma. The aim of this study was to compare the concentration changes of hypoxanthine and uric acid in plasma following running of varying duration and intensity. In addition, plasma creatine kinase activity was measured to assess the possible relationship between metabolic stress and protein release. Four groups of competitive male runners ran 100 m (n = 7), 800 m (n = 11), 5000 m (n = 7) and 42 000 m (n = 7), respectively, at an exhausting pace. Subsequent to the 100 m event (mean running time 11 s) plasma concentrations of hypoxanthine and uric acid increased by 364% and 36% respectively (P<0.05), indicating a very high rate of adenine nucleotide degradation during the event. Following the 800-m event (mean running time 125 s), hypoxanthine and uric acid concentrations had increased by 1598% and 66%, respectively (P<0.05). Both the events of longer duration, 5000 m and 42 000 m, also caused a significant increase in plasma concentration of hypoxanthine (742% and 237% respectively,P< 0.05) and plasma uric acid (54% and 34% respectively,P<0.05). Plasma activities of creatine kinase were significantly increased at 24 h only following the 5000 m and 42 000 m events (64% and 1186% respectively,P<0.05). Changes in plasma creatine kinase activity showed no correlation with changes in plasma concentration of either hypoxanthine or uric acid for the 5000 m and 42000 m events (r=0.00–0.45,P>0.05). These findings suggest that metabolic stress induced by exhausting exercise cannot be considered an important factor for the release of intracellular proteins. It was, furthermore, concluded that the rate of elimination of adenine nucleotides from cells was markedly elevated with the increasing intensity of exercise and only moderately affected by the duration of running.     

Effects of low-frequency electrical stimulation on fast and slow muscles of the rat

Leg muscles of adult rats were stimulated chronically at a low-frequency, and the histochemical reactions of various enzymes (succinic dehydrogenase, mitochondrial -glycerophosphate dehydrogenase, phosphorylase, alkali-ATPase and acid-ATPase), capillary density, resistance to fatigue, and contractile properties were studied. Following stimulation, the histochemical properties of muscle fibres in the fast extensor digitorum longus (EDL) and tibialis anterior (TA) muscles became similar to those of the majority of fibres in the slow soleus muscle. In the soleus muscle, the histochemical properties of the few fast type fibres became similar to the majority of slow fibres so that its fibre composition was homogeneously slow. The stimulated fast muscles also had higher capillary density and were more resistant to fatigue than normal. Despite the prolonged stimulation, the twitch duration of the fast muscles was little changed. This result differs from the findings obtained previously for the rabbit and cat, which show that slowing of contraction can be achieved by low-frequency activity of similar duration. Thus it may be that there is a species difference regarding the readiness with which the transformation of fast to slow muscles can be brought about.