ABSTRACT
This study investigated the time course of changes in heat shock protein (HSP) 72, muscle weight and cross-sectional area of muscle fibers after injection of bupivacaine (BPVC) into the soleus muscle. Adult male Wistar rats (n=36) were anesthetized by pentobarvital sodium and 0.5 ml of BPVC was injected into the left soleus muscle, whereas the contralateral right soleus muscle was served as the control. Bilateral soleus muscles were dissected at 1, 2, or 4 days or 1, 2, or 4 weeks after the injection. Muscle fibers were disrupted at days 1-2 after BPVC injection and regenerated fibers that have centrally located nuclei in cytoplasm appeared 4 days after the injection. The cross-sectional area of regenerated fibers gradually increased during 4 days-4 weeks after the injection. The soleus muscle weight decreased until 1 week after the injection, then gradually increased during 1-4 weeks of recovery. The content of HSP 72 was drastically decreased in the soleus muscle 1 day after BPVC injection (p<0.01), then gradually increased during 2 days-4 weeks of recovery, and returned to the control level at 4 weeks of recovery. A similar time course of change was observed for the cross-sectional area of the regenerating fibers and HSP 72 expression. These results suggest that the BPVC injection induces disruption of muscle fibers and degradation of HSP 72, however, regeneration of muscle fibers indicated by increases in cross-sectional area occurs with increases in HSP 72 content during 4 weeks of recovery period.
ABSTRACT
The purpose of this study was to prove the hypothesis that the effect of strength training is memorized and reinforced by retraining. Untrained university-age men participated in this training program. The retraining leg was subjected to 5 weeks of isometric training, 17 weeks of detraining and 5 weeks of retraining in knee extension. The contralateral training leg was subjected to 5 weeks of isometric training during the same period as the retraining phase of the retraining leg. Maximal isometric torque of knee extension increased after the 5-week training and remained at the trained level during the 17week detraining period. Torque gain by retraining of the retraining leg was 2.6 times greater than that of the contralateral training leg. These changes in isometric torque corres-ponded with changes in iEMG of the vastus lateralis. The cross-sectional area of the quadriceps femoris muscle did not change with training. Results support the hypothesis that the effect of strength training is memorized and reinforced by retraining. In addition, results show that these adaptations would be explained by recruitment and rate coding of motor units.
ABSTRACT
The effects of low- and high-intensity endurance training on the capillary network of rat left ventricle were studied morphometrically. Eighteen male albino rats of Wistar strain (4-wk-old) were assigned at random to a sedentary control group (Cont, n=8) and two trained groups which were both subjected to exercise on a motor-driven treadmill for 60 min a day, 5 days/wk for 9 weeks from 7 wks to 16 wks of age with different running speed; the low-intensity trained group (T-20, n=5) ran at 20 m/min and the high-intensity trained group (T-40, n=5) at 40 m/min. All morphometric parameters for the capillary and muscle fiber were determined in perfusion-fixed hearts. After the training period, the average muscle fiber cross-sectional area in the T-20 and the T-40 was not significantly different from the Cont. There were no significant differences in the capillary density and the capillary-to-fiber ratio between any groups, suggesting no significant change in capillary number. On the other hand, the number of capillary with large luminal diameter (8-10 μm) in the T-40 but not the T-20 was significantly greater than the Cont. These results indicate that the high-intensity endurance training causes enlargement of the capillary luminal area, while neither the low-nor the high-intesnity endurance training stimulate the proliferation of capillaries in the left ventriclular myocardium. In conclusion, a structure of the capillary network of rat left ventricle responds to the high-intensity endurance training by enlarging capillary luminal area rather than by increasing capillary number.
ABSTRACT
The present study was designed to determine whether conversion of fiber types (type I to II) induced by hindlimb unloading (HU) is identical along the length of fibers in the soleus (SOL) muscle. After 1 and 2 wk HU, SOL was divided into three (proximal, middle and distal) regions and the fiber type composition was determined using myosin adenosinetriphosphatase (ATPase) . There was no significant change in fiber type distribution after 1 wk of HU. The percentage of type I fibers significantly decreased in the proximal and middle regions and that of type IIc fibers increased in all regions after 2 wk of HU. The percentage of type IIc fibers greatly increased in the proximal and middle regions compared with the distal region. Serial cross-sections every 300μm were processed for myosin ATPase from the middle to the distal region, and then analyzed to show the differences in staining characteristics along the length of single fibers. After 2 wk of HU, some of the fibers (3.1±1.2%) displayed changes in the staining characteristics of myosin ATPase (pH 10.3) ; 84% of these fibers identified type IIc fibers in the middle region were observed as type I fibers in the distal region. These results suggest that muscle fibers in unloaded SOL may not transform synchronously or uniformly along their length
ABSTRACT
In this study, we investigated the possibility that GLUT4 protein concentration and mitochondrial enzyme activity is coregulated by muscle contractile activity. In the first experiment, male rats were trained by treadmill running or swimming for 3 wks and training effects in upper-and hind-limb muscle were investigated. Treadmill training program induced increases of 30% in citrate synthase activity, 51% in hexokinase activity, and 35% in GLUT4 protein concentration in hind-limb soleus muscles without causing training effects in upper-limb epitrochlearis muscles. On the other hand, swimming training program induced increases of 67% in citrate synthase activity, 139% in hexokinase activity, and 89% in GLUT4 protein concentration in epitrochlearis muscle without causing training effects in soleus muscles. These results suggest that muscle contractile activity which raises mitochondrial enzyme activity increases GLUT4 protein concentration in skeletal muscle. In a second set of experiment, we investigated relationship between muscle GLUT4 protein concentration and mitochondrial enzyme activity by use of the various type of rat muscles (soleus, plantaris, red gastrocnemius, white gastrocnemius, epitrochlearis and heart), which possese different contractile activity level. Significant correlation was observed between GLUT4 protein concentration and citrate synthase activity among different muscles (r=0.936) . They suggest that muscle GLUT4 protein concentration and mitochondrial enzyme activity level may be coregulated according to muscle contractile activity level.
ABSTRACT
This study was undertaken to determine the effect of neurotrophic substance on atrophy of denervated rat skeletal muscle. Hind-limb muscles of 14-21-week-old rats were denervated and/or artery-ligated for 1 week. Some muscles were also injected with saline buffer or a saline extract of porcine spinal cord (10 mg protein/ml) daily via the femoral artery. Atrophy was assessed by measurement of muscle wet weight and cross-sectional area of type I, type II A and type II B muscle fibers. The results obtained were as follows<BR>1. Denervation produced a significant decrease in the weights of the gastrocnemius, soleus and extensor digitorum longus (EDL) muscles. It also significantly decreased the area of each fiber type in the lateral head of the gastrocnemius (deep portion) and soleus muscles.<BR>2. Artery ligation produced a significant decrease in the weights of the gastrocnemius and EDL muscles, but did not significantly change the area of each fiber type in the lateral head of the gastrocnemius (deep portion) and soleus muscles.<BR>3. Buffer injection did not change the weight or fiber areas of hind-limb muscles to a significant extent.<BR>4. Injection of spinal cord extract significantly ameliorated the atrophy of denervated EDL muscle.<BR>In conclusion, it is suggested that a substance present in the spinal cord may ameliorate the atrophy of denervated muscle in vivo.
ABSTRACT
The purpose of this study was to investigate the optimal starting period of muscle power training during growth. Thirty-three Wistar strain male rats were used and classified into four groups, control group, 3T group started a training at 3 weeks after birth (weaning period), 8T group started a training at 8 weeks after birth (puberty period) and 13T group started a training at 13 weeks after birth (beginning of mature period) . Each training group was subjected to a power sprint training till 23 weeks after birth (mature period) .<BR>The results were summarlized as follows;<BR>1) Hypertrophy and increase of contractile properties in muscle were not seen in each training group.<BR>2) Muscle glycogen contents increased significantly in 3T group (p<0.05) and in 8T, 13T group (p<0.01) .<BR>3) Muscle fiber area increased significantly in 8T group only.<BR>4) Phosphofructokinase activity in muscle increased significantly in 8T group only.<BR>These results suggest that 8 weeks after birth, the puberty period may be the most effective starting period of power sprint training during growth in rats.