Myosin heavy chain composition in the rat diaphragm: effect of age and exercise training.

Increases in aerobic capacity in both young and senescent rats consequent to endurance exercise training are now known to occur not only in locomotor skeletal muscle but also in diaphragm. In the current study the effects of aging and exercise training on the myosin heavy chain (MHC) composition were determined in both the costal and crural diaphragm regions of female Fischer 344 rats. Exercise training [treadmill running at 75% maximal oxygen consumption (1 h/day, 5 day/wk, x 10 wk)] resulted in similar increases in plantaris muscle citrate synthase activity in both young (5 mo) and old (23 mo) trained animals (P < 0.05). Computerized densitometric image analysis of fast and slow MHC bands revealed the ratio of fast to slow MHC to be significantly higher (P < 0.005) in the crural compared with costal diaphragm region in both age groups. In addition, a significant age-related increase (P < 0.05) in percentage of slow MHC was observed in both diaphragm regions. However, exercise training failed to change the relative proportion of slow MHC in either the costal or crural region.     

沙棘汁对大鼠骨骼肌自由基代谢和血液血红蛋白、肌酸激酶、睾酮的影响

目的:探讨沙棘汁对大鼠骨骼肌自由基代谢和血液部分生化指标的影响。方法:30只SD大鼠随机分为安静组、训练组、沙棘训练组,6周训练和补充沙棘汁后,测定大鼠骨骼肌和血液的有关指标。结果:沙棘训练组与训练组相比,运动至力竭的时间明显延长;骨骼肌抗氧化酶活性明显升高,丙二醛(MDA)含量极为显著降低;血睾酮(T)和血红蛋白(Hb)均明显升高;肌酸激酶(CK)显著降低。结论:沙棘汁能增强大鼠骨骼肌抗氧化能力,提高血睾酮和血红蛋白水平,延缓疲劳出现,提高其有氧耐力运动的能力。     

Strategies of adaptation of small arteries in diaphragm and gastrocnemius muscle to aerobic exercise training

Aerobic exercise training is associated with adaptive changes in skeletal muscles and their vascular bed; such changes in individual muscles may vary depending on their characteristics and recruitment. This study was aimed at comparing the effects of eight-week treadmill training on the locomotor and respiratory muscles in rats. The training course increased the aerobic performance in rats, which was evidenced by an increase in maximum O₂ consumption and a decrease in the blood lactate concentration in ramp test. The succinate dehydrogenase activity was increased in the red portion of the gastrocnemius muscle, but not in the diaphragm of trained rats. Arterial segments were isolated from feed arteries and studied by wire myography. The relaxation in response to acetylcholine in gastrocnemius arteries in trained animals was higher as compared with controls (due to higher NO production), while contractile responses to noradrenaline (in the presence of propranolol) were not changed. On the contrary, the endothelial function of diaphragm arteries was not affected by training, but contractile responses to activation of α-adrenoceptors were markedly increased. Thus, aerobic training may increase the blood supply rate to both locomotor and respiratory muscles, but the underlying regulatory mechanisms are different. The results obtained allow us to reveal the physiological mechanisms that determine the physical performance of the body under conditions of compromised functioning of the respiratory system.     

Testosterone stimulates myoglobin expression in different muscles of the mouse

The regulation of energy metabolism is one of the major functions of steroid hormones. This study was performed to explore whether testosterone can regulate the aerobic capacity of skeletal muscles via myoglobin expression. To study this, changes in testosterone level were quantified, and the level of myoglobin protein was analyzed using Western blot in mice subjected to 6 weeks of training (T) or testosterone administration (A). Both treatments significantly increased the plasma testosterone level when compared to the untrained (U) or control (C) group. Training induced a significant increase in the myoglobin content in gastrocnemius and plantaris muscles (287 and 83%, respectively). Testosterone administration increased myoglobin concentration in plantaris (183%) but not in gastrocnemius. In extensor digitorum longus muscle the protein content decreased slightly after exercise, but increased 78% after testosterone administration. In soleus and rectus femoris muscles the myoglobin content was unchanged after both treatments. The data show that testosterone and training have differential effects on the concentration of myoglobin in some, but not all muscles. This may have an influence on the aerobic capacity in mouse skeletal muscles. The data demonstrated that both testosterone administration and training induced an increase in plasma testosterone level. However, the effects of the treatments on the myoglobin concentration differ.     

Skeletal muscle enlargement with weight-lifting exercise by rats

A rat model of weight lifting that produces skeletal muscle enlargement utilizing regimens of resistance training similar to those employed in human training programs is described. The model consists of electrically stimulating the lower leg muscles to contract against a weighted pulley bar. Animals were subjected to training protocols employing low-frequency repetitions with high training loads within a training session. Initial maximum loads of between 200 and 800 g were progressively increased during the 16 wk of training. Work done at the end of the training period increased to an average value 66% higher than that performed at the start of training. The gastrocnemius wet weight and protein content increased (P less than 0.001) by 18 and 17%, respectively, in the stimulated loaded leg in all but one training protocol, a program in which rats were exercised more frequently. RNA content, but not concentration, was increased in the trained gastrocnemius muscle from each protocol, resulting in muscle enlargement. These data indicate that the basic model presented here provides a suitable vehicle for future studies into the biochemical events that may cause skeletal muscle enlargement during resistance training but, based on limited data, suggests that an increased frequency of training days may hinder muscle enlargement in this model.     

Effect of acute nutritional deprivation on diaphragm structure and function

The influence of 90 h of acute nutritional deprivation (ND) on the cross-sectional areas of muscle fibers and the contractile and fatigue properties of the adult rat diaphragm were determined. Isometric contractile properties and fatigue resistance of the diaphragm were measured by means of an in vitro nerve-muscle strip preparation. Contractions were evoked by using phrenic nerve stimulation (left hemidiaphragm) or direct muscle stimulation (right hemidiaphragm) in the presence of curare. Acute ND resulted in a 20% reduction in body weight. No significant decrements in diaphragm or soleus weights were noted in the ND animals compared with controls (CTL), whereas the weight of the medial gastrocnemius was reduced by 20% in the ND animals. Peak twitch and tetanic tensions (normalized for the weight of the diaphragm strip) were not reduced in ND compared with CTL animals after either nerve or muscle stimulation. The fatigue index of the diaphragm was significantly reduced in ND animals only after nerve stimulation. After the fatigue test, there was rapid recovery of the additional fatigue noted with nerve stimulation. The proportions of type I and II muscle fibers of the diaphragm were similar in the CTL and ND animals. No differences in diaphragm cross-sectional areas were noted for either type I or II muscle fibers in the CTL and ND animals. It is concluded that acute ND has no effect on diaphragm contractility or morphometry and only an inconsequential influence on diaphragm fatigue.     

Effect of acute nutritional deprivation on diaphragm structure and function in adolescent rats.

The influence of 90 h of acute nutritional deprivation (ND; water ad libitum only) on in vitro contractile and fatigue properties, muscle fiber type proportions, and cross-sectional areas (CSA) of the adolescent rat diaphragm was determined. Diaphragm muscle properties in the ND rats were compared with those in control rats (CTL; food and water ad libitum). Acute ND resulted in a 32% reduction in body mass, whereas the body mass of CTL rats increased by 29%. Acute ND resulted in a significant reduction in the mass of the diaphragm (costal, 36%; crural, 43%), soleus (36%), and medial gastrocnemius (45%) muscles. Isometric twitch characteristics of the diaphragm muscle (contraction and half-relaxation times) were prolonged in the ND animals. Peak twitch and maximum tetanic forces were unaffected by ND. Fatigue resistance of the diaphragm muscle was improved in ND animals. Diaphragm muscle fiber type proportions were similar in ND and CTL groups. The CSA of type I and II diaphragm muscle fibers were reduced by 22 and 40%, respectively, in ND animals compared with CTL. We conclude that, whereas an identical protocol of acute ND had no significant effects on diaphragm muscle structure and function in adult rats, adolescent animals exhibit significantly less nutritional reserve. These differences may be due to curtailment of the rapid anabolic rate in growing animals.     

Effect of endurance training on muscle fiber type composition and capillary supply in rat diaphragm

Muscle fiber type composition and capillary supply in rat diaphragm were investigated after 14 weeks of endurance training: body weight and muscle fiber area were significantly decreased, the muscle fiber type composition, capillary to fiber ratio and number of capillaries around each fiber type were unchanged, and the capillary density and number of capillaries around each fiber relative to fiber type areas were significantly increased. These small fiber areas and increased capillary supplies in the trained rats would facilitate oxygen transport to all parts of the muscle fiber during exercise. It is concluded that the changes observed in the trained rat diaphragm appear to enhance the capacity for oxidative metabolism.     

Effects of Estrogen on Glucose Uptake by Rat Muscle

The isolated rat diaphragm was used to study the effects of 17β-estradiol on basal and insulin-mediated glucose uptake. Rats were injected with estradiol for 2 wk in daily doses of 10 μg/100 g of body weight and were compared to untreated control animals. Estrogen treatment resulted in a 16% decrease in basal glucose uptake by diaphragm muscle as compared to controls. In contrast, in the presence of insulin, glucose uptake by muscle increased 103% above basal in estradiol-treated animals as compared to a 38% rise in the control group. The absolute rate of glucose uptake induced by insulin in the estradiol treated animals (5.8 mg/g/hr) was 22% higher than in controls. These findings were not accompanied by changes in weight gain, plasma glucose and plasma immunoreactive insulin concentrations in the treated animals. In vitro incubation of diaphragm muscle with estradiol did not have an effect on basal or insulin-mediated glucose uptake.     

Nandrolone decanoate does not enhance training effects but increases IGF-I mRNA in rat diaphragm.

To examine whether concomitant anabolic steroid treatment combined with training might enhance previously observed training effects (A. Bisschop, G. Gayan-Ramirez, H. Rollier, R. Gosselink, R. Dom, V. de Bock, and M. Decramer. Am. J. Respir. Crit. Care Med. 155: 1583-1589, 1997) and whether insulin-like growth factor I (IGF-I) was involved in these changes, male and female rats were submitted to inspiratory muscle training (IMT) for 8 wk (30 min/day, 5 times/wk) and were compared with untrained controls. During the last 5 wk of training, trained rats were divided to receive weekly either low-dose (LD; 1.5 mg/kg) or high-dose (HD; 7.5 mg/kg) nandrolone decanoate or saline for the IMT and control rats. In both sexes, diaphragm muscle mass and contractile properties were unchanged with treatment. In males, HD resulted in decreased diaphragm type I cross-sectional area (-15%; P < 0.05, HD vs. IMT), whereas no changes were observed in females. Finally, an increase in IGF-I mRNA levels was present in HD male (+73%; P < 0.05, HD vs. IMT) and female treated rats [LD (+58%) and HD (+96%) vs. IMT; P < 0.001]. We conclude that administration of nandrolone decanoate did not enhance the previously observed training effects in rat diaphragm, although it increased the IGF-I mRNA expression levels.     

Adaptation of skeletal muscle fibers to endurance training, confinement or selection for body weight and physical endurance of laboratory mice

By the help of histological methods the changes in skeletal muscle of laboratory mice, which had different levels of exercise during postweaning period (training, confinement) or had been selected for body weight and endurance fitness (Du-6+LB), were investigated. The animal groups with the better endurance fitness (Du-6+LB, trained) had a higher total number of muscle fibres. An increased aerobic capacity of metabolism for the trained and selected animals, a decreased one for the confined animals resulted, indicated by the composition of muscle fibre types of M. rectus femoris. The appearance of stress-induced pathological changes of muscle fibres was observed, with the highest extent in the confined group with decreased endurance fitness. Similar correlations between structure of muscle and fitness in domestic animals are to be expected.     

Fiber type changes in rat skeletal muscle after intense interval training

Female Sprague-Dawley rats were subjected to a ten week training program to determine the influence of intense interval running on the fiber type composition of selected hindlimb muscles; soleus (S), plantaris (P), deep vastus lateralis (DVL), and superficial vastus lateralis (SVL). The muscles of one hindlimb were used for histochemical ATPase analysis to determine the distribution of fiber types and those of the contralateral hindlimb were assayed biochemically for citrate synthase activity (an aerobic marker). Training induced a significant increase in citrate synthase activity in each muscle section. The largest absolute increase occurred in the DVL and the largest relative increase occurred in the SVL. The distribution of fiber types within the S (85% slow-twitch) and SVL (100% fast-twitch) remained unchanged with training. However, significant increases in the percentage of type I (slow-twitch) fibers in both the P (2-fold) and DVL (3-fold) were observed with concomitant decreases in the type II (fast-twitch) population. In addition, training induced significant changes in the fast-twitch subtype populations of the DVL (IIB----IIA). These data suggest exercise-induced fiber type transformations occurring both within the fast-twitch population and between fast-twitch and slow-twitch fibers in certain hindlimb muscles of the rat following a high intensity interval training program.     

Relative contribution of neurotransmission failure to diaphragm fatigue

Two procedures were used to estimate the relative contribution of neurotransmission failure (NF) to fatigue of the rat diaphragm at different rates of phrenic nerve stimulation. In one, direct muscle stimulation was intermittently superimposed on neural stimulation of the diaphragm, and the relative contribution of NF was estimated by the difference in generated tension. In a second procedure, diaphragm fatigue was induced by using either direct muscle stimulation (with complete blockade of the neuromuscular junction by d-tubocurare) or phrenic nerve stimulation. The relative contribution of NF to diaphragm fatigue was then estimated by comparing the force loss during these two modes of stimulation. With both procedures, it was observed that 1) the relative contribution of NF to diaphragm fatigue was less than 45% at each frequency of phrenic nerve stimulation; 2) the relative contribution of NF to diaphragm fatigue increased at higher rates of phrenic stimulation, reaching a maximum at 75 pulses/s; and 3) the relative contribution of NF to diaphragm fatigue reached a plateau after 2 min of repetitive stimulation.     

Glycogen utilization in rat respiratory muscles during intense running

Glycogen concentration in the adult rat diaphragm and intercostal muscles has been examined following heavy treadmill exercise to determine the recruitment strategy and the significance of glycogen as a substrate to satisfy the elevated energy requirements accompanying hyperpnea. Short-term continuous running at 60 m/min and a 12 degree grade resulted in a reduction (p less than 0.05) in the concentration of glycogen (39%) in the costal region of the rat diaphragm. Similarly, glycogen concentration was significantly reduced (p less than 0.05) with this exercise protocol in all respiratory muscles studied, with the exception of the sternal region of the diaphragm. With the less intense running protocols, glycogen degradation continued to be pronounced (p less than 0.05) in the majority of the respiratory muscles sampled. The significance of muscle glycogen as a substrate for energy metabolism in the respiratory muscles was not affected by the procedure used to prepare the animal for tissue sampling (Somnitol, diethyl ether, decapitation). Examination of selected locomotor muscles revealed extensive glycogen loss in muscles composed of essentially slow oxidative fibres (soleus), fast oxidative glycolytic fibres (vastus lateralis red), and fast glycolytic fibres (vastus lateralis white). It is concluded that during heavy exercise in the rat, recruitment of motor units occurs in all regions of the diaphragm and in the intercostal muscles. At least for the costal region of the diaphragm and as evidenced by the modest (two- to four-fold) but significant (p less than 0.05) increases in lactate concentration, the increased ATP requirements in these muscles are met to a large degree by increases in aerobic metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

The therapeutic effect of aerobic exercise with resistance training in elderly men with type 2 diabetes mellitus

Objective: This study was conducted to examine the effects of aerobic exercise alone and aerobic exercise with resistance training on the quality of life in men over the age of 55 years with type 2 diabetes mellitus. Methods: A total of 54 participants were divided into the following three groups so that there were no significant differences in blood chemistry or physical ability indexes among the three groups: control, aerobic exercise, and aerobic exercise with resistance training. The latter two groups exercised for 24 weeks, while the control group performed no exercise. Blood chemistry levels and measures of physical ability in each group members were examined one day before and one day after the exercise regimens. Results: Compared with those before the study, blood glucose, glycated hemoglobin, triglycerides, cholesterol, and low-density lipoprotein levels as well as vital capacity, reaction time, sit-and-reach ability, and balancing while standing on one leg with closed eyes were significantly improved in the aerobic exercise only group(P 0.05). All these measures as well as high-density lipoprotein levels and grip, back, and leg strength were significantly improved in the combined aerobic and resistance training group(P 0.05). By contrast, no significant differences before and after the experiment were found in any measure for the control group(P 0.05). Conclusion: Although both aerobic exercise and aerobic exercise combined with resistance training for 24 weeks effectively improved the quality of life in patients with type 2 diabetes, the effect of the combined training was better than that of aerobic exercise alone. These results suggest that resistance training may be safely added to the rehabilitation training regimen of patients with type 2 diabetes mellitus.     

Effects of training on axial muscle of two cyprinid species: Chondrostoma nasus (L.) and Leuciscus cephalus (L.)

The effect of an endurance training program lasting 17 weeks was studied in two cyprinid species, Chondrostoma nasus (L.) and Leuciscus cephalus (L.). Red, intermediate and white axial muscle were investigated. Morphometrical analysis revealed that training induced, in both species, increased red and intermediate muscle mass, fibre diameter and capillarization. Differences between species in the response to training were observed for volume densities of mitochondria and lipid. In contrast to C. nasus, L. cephalus show higher values for these compartments in red and intermediate fibres. The results are considered adaptational changes which increase the aerobic capacity of red and intermediate muscle fibres to meet higher sustained swimming activities.     

Polymorphism of myosin among skeletal muscle fiber types

An immunocytochemical approach was used to localize myosin with respect to individual fibers in rat skeletal muscle. Transverse cryostat sections of rat diaphragm, a fast-twitch muscle, were exposed to fluorescein-labeled immunoglobulin against purified chicken pectoralis myosin. Fluorescence microscopy revealed a differential response among fiber types, identified on the basis of mitochondrial content. All white and intermediate fiber but only about half of the red fiber reacted with his antimyosin. In addition, an alkali-stable ATPase had the same pattern of distribution among fibers, which is consistent with the existence of two categories of red fibers. The positive response of certain red fibers indicates either that their myosin has antigenic determinants in common with "white" myosin, or that the immunogen contained a "red" myosin. Myosin, extracted from a small region of the pectorlis which consists entirely of white fibers, was used to prepare an immunoadsorbent column to isolate antibodies specific for white myosin. This purified anti-white myosin reacted with the same fibers of the rat diaphragm that had reacted with the white, intermediate, and some red fibers are sufficiently homologous to share antigenic determinants. In a slow-twitch muscle, the soleus, only a minority of the fiber reacted with antipectoralis myosin. The majority failed to respond; hence, they are not equivalent to intermediate fibers of the diaphragm; despite their intermediate mitochondrial content. Immunocytochemical analysis of two different musles of the rat has demonstrated that more than one isoenzyme of myosin can exist in a single muscle, and that individual fiber types can be recognized by immunological differences in their myosin. We conclude that, in the rat diaphragm, there are at least two immunochemically distinct types of myosin and four types of muscle fibers: white, intermediate, and two red. We suggest that these fibers correspond to the four types of motor units described by Burke et al. (Burke, R. E., D. N. Levine, P. Tsairis, and F. E. Zajac, III 1973. J. Physiol. (Lond) 234:723-748.)in the cat gastrocnemius.`     

Fiber capillarization relative to mitochondrial volume in diaphragm of shrew.

The objective was to examine fiber capillarization in relation to fiber mitochondrial volume in the highly aerobic diaphragm of the shrew, the smallest mammal. The diaphragms of four common shrews [Sorex araneus; body mass, 8.2 +/- 1.3 (SE) g] and four lesser shrews (Sorex minutus, 2.6 +/- 0.1 g) were perfusion fixed in situ, processed for electron microscopy, and analyzed by morphometry. Capillary length per fiber volume was extremely high, at values of 8,008 +/- 1,054 and 12,332 +/- 625 mm(-2) in S. araneus and S. minutus, respectively (P = 0.012), with no difference in capillary geometry between the two species. Fiber mitochondrial volume density was 28.5 +/- 2.3% (S. araneus) and 36.5 +/- 1.4% (S. minutus; P = 0.025), yielding capillary length per milliliter mitochondria values (S. araneus, 27.8 +/- 1.5 km; S. minutus, 33.9 +/- 2.2 km; P = 0.06) as high as in the flight muscle of the hummingbird and small bats. The size of the capillary-fiber interface (i.e., capillary surface per fiber surface ratio) per fiber mitochondrial volume in shrew diaphragm was also as high as in bird and bat flight muscles, and it was about two times greater than in rat hindlimb muscle. Thus, whereas fiber capillary and mitochondrial volume densities decreased with increased body mass in S. araneus compared with S. minutus Soricinae shrews, fiber capillarization per milliliter mitochondria in both species was much higher than previously reported for shrew diaphragm, and it matched that of the intensely aerobic flight muscles of birds and mammals.     

Exercise training reverses impaired skeletal muscle metabolism induced by artificial selection for low aerobic capacity

We have used a novel model of genetically imparted endurance exercise capacity and metabolic health to study the genetic and environmental contributions to skeletal muscle glucose and lipid metabolism. We hypothesized that metabolic abnormalities associated with low intrinsic running capacity would be ameliorated by exercise training. Selective breeding for 22 generations resulted in rat models with a fivefold difference in intrinsic aerobic capacity. Low (LCR)- and high (HCR)-capacity runners remained sedentary (SED) or underwent 6 wk of exercise training (EXT). Insulin-stimulated glucose transport, insulin signal transduction, and rates of palmitate oxidation were lower in LCR SED vs. HCR SED (P < 0.05). Decreases in glucose and lipid metabolism were associated with decreased β?-adrenergic receptor (β?-AR), and reduced expression of Nur77 target proteins that are critical regulators of muscle glucose and lipid metabolism [uncoupling protein-3 (UCP3), fatty acid transporter (FAT)/CD36; P < 0.01 and P < 0.05, respectively]. EXT reversed the impairments to glucose and lipid metabolism observed in the skeletal muscle of LCR, while increasing the expression of β?-AR, Nur77, GLUT4, UCP3, and FAT/CD36 (P < 0.05) in this tissue. However, no metabolic improvements were observed following exercise training in HCR. Our results demonstrate that metabolic impairments resulting from genetic factors (low intrinsic aerobic capacity) can be overcome by an environmental intervention (exercise training). Furthermore, we identify Nur77 as a potential mechanism for improved skeletal muscle metabolism in response to EXT.