Bovine longissimus muscle glycogen concentration in response to isometric contraction and exogenous epinephrine

Isometric contraction was elicited in cattle by electrical stimulation (electrical immobilization) and was used as a means of investigating the interaction between muscle contraction and epinephrine-induced muscle glycogen degradation. At 0.5 and 24 hours after a 15-minute period of continuous muscle contraction, glycogen content of longissimus muscle specimens collected via needle biopsy was not different from precontraction concentrations. Epinephrine (13.2 mg/kg of body weight) given subcutaneously resulted in a 30% to 35% reduction of muscle glycogen. Reduction of muscle glycogen was slightly greater when epinephrine was used in conjunction with isometric contraction, compared with epinephrine treatment alone. Muscle glycogen increased, and free glucose, lactate, and glucose-6-phosphate decreased, with increases in body weight. In younger, lighter cattle (370 kg), epinephrine decreased muscle glycogen and lactate concentrations and generally decreased muscle glucose concentrations. Muscle-free glucose and lactate concentrations were increased in older, heavier cattle (446 kg) by contraction and epinephrine injection when the animals were immobilized for 30 minutes, with intermittent periods of muscle relaxation. In these cattle, muscle glycogen concentration slightly decreased with isometric contraction. Data indicate that reports of increased glycogenolysis observed in cattle subjected to stress by mixing strange animals or exercise is due to dynamic muscle contraction and not due to isometric muscle contraction.     

Effect of postmortem storage on mu-calpain and m-calpain in ovine skeletal muscle.

Casein zymography was used to determine the effect of postmortem storage on the proteolytic activity of mu-calpain and m-calpain in lamb longissimus. Casein zymography assays were conducted on crude muscle extracts (only one centrifugation). Six market weight crossbred lambs were slaughtered and a portion of the longissimus lumborum was removed at death (within 15 min of exsanguination) and after 3, 6, 9, 12, 24, 72, and 360 h postmortem. Muscle samples were snap-frozen in liquid nitrogen and stored at -70 degrees C. Soluble muscle proteins were extracted from muscle samples and analyzed by in-gel casein assay to measure calpain proteolytic activity. There was a gradual decline in mu-calpain activity (P < 0.05) such that after 24 and 72 h postmortem, mu-calpain had lost 42 and 95% of its activity, respectively. After 360 h postmortem, no mu-calpain activity could be detected (under the conditions used in this study). Autolysis of mu-calpain could be detected as early as 3 h postmortem. It was demonstrated that the detectable level of mu-calpain activity is a function of the amount of muscle protein electrophoresed. Hence, the activity data reported are in relative terms, rather than absolute values. Furthermore, it was demonstrated that the activity data also are a function of the assay methods used. Different methods have different lower detection limits. Of the three assays examined, 14C-labeled casein was the most sensitive, then the in-gel casein assay, and the least-sensitive method was the standard casein assay. Unlike mu-calpain, postmortem storage had no effect on m-calpain (P > 0.05). When the calcium concentration of a muscle extract was increased to the level that induces m-calpain autolysis, m-calpain was autolyzed and its autolysis was readily detected by the in-gel casein assay. Collectively, these results demonstrate that calcium concentration in postmortem muscle is only high enough to activate mu-calpain. These results support the widely believed conclusion that mu-calpain-mediated proteolysis of key myofibrillar and cytoskeletal proteins is responsible for postmortem tenderization. Hence, understanding the regulation of mu-calpain in postmortem muscle should be the focus of future studies.     

Copper-induced skeletal myopathy in rabbits.

Doses of 1.66 mg Cu/kg/day, as cupric acetate in aqueous solution, were injected intramuscularly into the lateral thigh muscles of rabbits. The rate of loss of Cu from the injection site was estimated from in vivo measurements of 64Cu injected on the 15th day. Biological half-life values were 1.0 h for the first component (accounting for 65.2% of the 64 Cu) and 14.6 h for the second component (34.8% of the 64Cu). For the control group, values were 0.8 h and 62.2%, 14.6 h and 37.8%. Grossly visible lesions of dermatitis were noted on the paws, i.e. at sites removed from the site of injection, in some rabbits injected with Cu acetate two days post injectionem (p.i.). Histologically detectable lesions of acute inflammation were seen as early as 24 hours p.i. at the injection site of rabbits which had been exposed to the Cu once. Multiple injections and longer time periods resulted in lesions of acute and chronic inflammation. Cu was detected by the use of rubeanic acid stain. Signs of muscle degeneration and regeneration were seen as early as three days p.i. in rabbits which had received two injections of Cu. Rabbits which had been killed six days p.i. after a single injection showed chronic inflammatory changes and newly formed myofibres. Rabbits which had been killed 37 days p.i. after 17 injections showed lesions of acute and chronic inflammation of muscle and surrounding connective tissue, as well as signs of muscle regeneration. The gangrene visible grossly was attributed to the ischaemia caused by conglomerations of Cu.     

Effect of dietary protein on calpastatin in canine skeletal muscle

The cysteine proteinases, mu- and m-calpain, along with their inhibitor, calpastatin, have been hypothesized to play a role in skeletal muscle protein degradation. Because nutrition has previously been shown to influence the expression of calpastatin, the working hypothesis of this study was that the quantity and source of dietary protein could influence regulation of the calpain system in muscle. The objectives to support this hypothesis were to determine the effects of dietary protein (amount and source) on the expression of calpastatin in canine skeletal muscle. This study comprised eight diets with seven dogs per diet. A biopsy was taken from the biceps femoris of all 56 dogs before and after 10 wk on their respective diets. This experimental design allowed examination of change within individual dogs. Diets 1 to 4 contained 12% total protein derived from chicken and/or corn gluten meal in ratios of 100:0, 67:33, 33:67, and 0:100%, respectively. Diets 5 to 8 contained 28% total protein with protein sources and ratios identical to Diets 1 to 4. Differences in calpastatin were examined qualitatively using SDS-PAGE and immunoblotting, and semiquantitatively with densitometric analyses. The majority of the calpastatin blots showed three distinct calpastatin bands, the uppermost appearing at approximately 110 kDa. Diet 5 (28% CP, 100% chicken) resulted in an increase in the expression of the 110-kDa calpastatin band compared with the other two lower molecular weight bands in the same samples. Muscle from dogs fed Diet 5 showed greater increase in (P < 0.05) calpastatin intensity of the topmost band than those fed Diet 8 (0:100; chicken:corn gluten meal). Diet 5 (100:0; chicken:corn gluten meal) showed greater total calpastatin intensity than Diet 8 (0:100; chicken:corn gluten meal). These data suggest that dogs fed a diet containing a higher total percentage of chicken protein may have a greater potential to regulate calpain-mediated degradation of muscle protein than dogs fed diets containing corn gluten meal.     

Effect of skeletal muscle decorin on collagen fibrillogenesis in vitro

The effect of skeletal muscle decorin on collagen fibrillogenesis was investigated, in order to provide background for understanding the functions of decorin in skeletal muscle. The self‐assembly of type I and III collagen with the addition of decorin or the core protein of decorin from bovine neonatal skeletal muscle was monitored using a spectrophotmeter. Time course changes in the absorbance of collagen solutions showed typical sigmoidal curves composed of three phases. The time of the initial phase was not different between the collagen solution with decorin and that without decorin. The increase rate of the absorbance in the second phase decreased with concentration of decorin added in collagen solutions. Similar effects on fibrillogenesis of type I and III collagens were observed when the core protein of decorin was added in collagen solutions. These results suggest that regulation of collagen fibrillogenesis by decorin depends on its core protein. The networks of reconstructed collagen fibrils with decorin were looser than those without decorin. Bovine skeletal muscle decorin could participate in the regulation of collagen fibrillogenesis and in the arrangement of collagen fibrils in the intramuscular connective tissue.     

Abnormal regulation of muscle contraction in horses with recurrent exertional rhabdomyolysis.

OBJECTIVE: To determine whether abnormal regulation of muscle contraction similar to that associated with malignant hyperthermia (MH) was evident in intact external intercostal muscle cells from Thoroughbreds with recurrent exertional rhabdomyolysis (RER). ANIMALS: 5 adult Thoroughbred horses with RER and 7 clinically normal adult Thoroughbred or mixed-breed horses. PROCEDURES: Twitch time course variables and contracture responses to various concentrations of potassium, caffeine, and halothane were measured in small bundles of intact external intercostal muscle cells from clinically normal horses and horses with RER. RESULTS: Threshold for significant contracture induced by potassium depolarization was lower for RER-affected muscles, compared with normal muscles, although the relationship between potassium concentration and membrane potential were not different. Thresholds for contracture induced by caffeine and halothane were also lower for RER-affected muscles, compared with normal muscles. Lower thresholds for caffeine- and halothane-induced contractures, as well as depolarization-elicited contractures, in RER-affected muscles suggest a defect in myoplasmic calcium regulation. CONCLUSIONS AND CLINICAL RELEVANCE: Regulation of muscle contraction is abnormal in Thoroughbreds with RER. The specific defect may be attributable to abnormal intracellular calcium regulation. Knowledge of the specific defect involved in RER may lead to improved prevention and treatment of RER-affected horses.     

Comparison of calpain and calpastatin activities in skeletal muscle of broiler and layer chickens

1. The objective of this study was to estimate the difference between broiler and layer chicks in the activities of calpain and calpastatin (inhibitor of calpain) in breast muscle. Differences between broilers and layers in body weight, daily gain at 3 weeks of age and fractional growth rate (FGR) during 2 and 3 weeks of age were statistically significant (P < 0.01).

2. Calpain and calpastatin activities were measured at three weeks of age with alkali‐denatured casein as a substrate. The m‐calpain (calpain activated by millimolar calcium concentration) activities in units/g muscle and units/ mg extractable muscle protein were 0.779 and 0.353 for broilers, and 1.042 and 0.440 for layers, respectively. The calpastatin activities in units/g muscle and units/mg extractable muscle protein were 0.332 and 0.153 for broilers, and 0.262 and 0.112 for layers, respectively.

3. Broilers with high FGR showed low m‐calpain and high calpastatin activities. In contrast, layers with low FGR showed high m‐calpain and low calpastatin activities.

4. These results suggest that m‐calpain and calpastatin activities in skeletal muscle vary between breeds which have different rates of muscle production.     

Effect of short-chain fatty acids on contraction of smooth muscle in the canine colon

OBJECTIVE: To determine effects of short-chain fatty acids (SCFA) on canine colonic smooth muscle. SAMPLE POPULATION: Colonic tissue obtained from 14 healthy dogs. PROCEDURE: Short-chain fatty acid (SCFA; acetate, propionate, and butyrate; 1 to 100 mmol/L)-induced contractions were compared with responses obtained with acetylmethylcholine (AMCh; 10(-4) mol/L). Roles of enteric neurons, cholinergic receptors, calcium stores in the sarcoplasmic reticulum, and extracellular calcium in the SCFA-induced responses were investigated by incubating muscle strips with tetrodotoxin (1 micromol/L), atropine (1 micromol/L), ryanodine (10 micromol/L), nifedipine (1 micromol/L), ethylene glycol-bis (beta-aminoethylether)-N,N,N',N'-tetra-acetate (EGTA; 0.1 mmol/L), or an extracellular calcium-depleted (zero extracellular calcium) solution prior to the addition of propionate or butyrate. RESULTS: Incubation with SCFA elicited isometric stress responses (0.25 to 2.15 x 10(4) N/m2) in colonic longitudinal smooth muscle. Maximal responses to butyrate and propionate (50 mmol/L) were 37 and 23%, respectively, of the maximal AMCh response. Acetate was least effective in stimulating contractile responses. Tetrodotoxin and atropine did not affect SCFA-induced contractions. Nifedipine and zero extracellular calcium solution abolished responses to butyrate and propionate, whereas EGTA attenuated (> 60%) but did not abolish those responses. Ryanodine did not affect SCFA-induced contractile responses. The SCFA did not affect colonic circular smooth muscle. CONCLUSIONS AND CLINICAL RESPONSE: The SCFA stimulate longitudinal but not circular colonic smooth muscle contractions via a direct effect on smooth muscle. The mechanism of the SCFA effect appears to involve the influx of extracellular calcium. These findings may account for some of the effects of fiber on canine colonic motility [corrected].     

Fiber types and size in equine skeletal muscle.

Frozen sections of equine musculus semitendinosus were examined for myosin adenosine triphosphatase (ATPase) and reduced nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), using standard histochemical procedures, and the proportions of the various fiber types and average fiber sectional size were determined. With ATPase staining, approximately 70% of the fibers were classified as alpha fibers (ATPase positive), and 30%, as beta fibers (ATPase negative). In addition, 2 populations of alpha fibers could be readily distinguished on the basis of the intensity of the ATPase reaction, and these were designated alpha positive and alpha intermediate. The relationship of this difference in ATPase reaction to contraction speed of the fibers is not known. With NADH-TR staining, fibers were classified as either red fibers (positive) having aerobic metabolism or white fibers (negative) having primarily anaerobic metabolism. All beta fibers were red by NADH-TR; thus, they conformed to the criteria for beta R fibers. All alpha positive fibers were white by NADH-TR, as were most of the alpha intermediate fibers, and would be classified alpha W. Some of the alpha intermediate fibers gave an intermediate reaction with NADH-TR and could be classified as alpha R fibers which have not transformed to alpha W fibers. The alpha positive fibers were 7 to 10 mum larger in diameter than either beta or alpha intermediate fibers.     

Effect of clenbuterol on growth,carcase and skeletal muscle characteristics in broiler chickens

1. Male and female broiler chickens (144 in total) were given diets supplemented with clenbuterol (CB) at 0 (control) and at 1 mg/kg between 28 and 49 d of age to study the effect of CB on growth, carcase and skeletal muscle.

2. CB improved growth in males by increasing daily weight gain and final live weight and by lowering food conversion ratio. In females it changed the carcase composition by reducing abdominal fat pad and by increasing the proportion of protein. Consequently, carcase protein gain was increased in both sexes (11% and 16%, respectively).

3. Skeletal muscle weights were enhanced by between 6% and 22%. Muscle fibre diameters were increased in extensor hallucis longus (EHL) but not in gastrocnemius (GAS) muscle. This increase was more pronounced in females. EHL total muscle fibre number remained unchanged. The proportion of fast‐twitch glycolytic fibres was increased at the expense of fast‐twitch oxidative fibres in males only. Nuclear/cytoplasm and DNA/protein ratios tended to be decreased by CB.

4. From the elevated EHL muscle RNA/DNA, unchanged protein/RNA and translation activity it is suggested that CB stimulated protein synthesis at the pretranslational level. Reduced protein degradation is deduced from decreased neutral calcium‐dependent proteolytic activity.

5. It is concluded that broiler chickens respond to long‐term CB treatment as has been shown in various mammals. However, the sex‐specific response in growth, carcase composition and skeletal muscle cellularity is more clearly apparent in broiler chickens.     

抗蠕虫药对人工感染豆状囊尾蚴家兔肌肉主要营养成分的影响

为分析不同驱虫药对感染豆状囊尾蚴肌肉营养成分含量的影响,本试验采用3种抗蠕虫药（甲苯咪唑、吡喹酮、丙硫苯咪唑）对人工感染豆状囊尾蚴家兔进行驱虫试验,并对感染豆状囊尾蚴后和驱虫后家兔肌肉营养成分（水分、灰分、脂肪和蛋白质）含量变化进行分析。结果表明,3种抗蠕虫药对家兔感染豆状囊尾蚴均有不同程度的驱虫效果,家兔肌肉营养成分含量有不同程度的升高。其中,甲苯咪唑和丙硫苯咪唑对家兔肌肉中的水分、脂肪和蛋白质含量影响较大,吡喹酮驱虫后家兔肌肉中灰分含量增加较明显。     

丁酸钠对兔离体回肠运动的影响

试验研究了不同剂量（0.025%、0.05%、0.1%、0.15%、0.2%）的丁酸钠对兔离体回肠运动性能（张力和频率）的影响,并探讨其对肠道平滑肌收缩的影响机制。结果表明,丁酸钠对兔离体回肠的收缩张力及收缩频率均有显著地促进作用（P〈0.05）,并且剂量越大促进作用越明显。试验结果还表明丁酸钠对兔离体回肠的收缩活动的促进作用与丁酸钠对肠道pH的影响无关。     

Effect of selection for backfat thickness in swine on fetal skeletal muscle metabolism

At 110 d of gestation, fetuses were removed from sows selected for high (obese) or for low (lean) backfat thickness. The body weights of lean (1,031 +/- 64 g) and obese (864 +/- 55 g) fetuses were not significantly different. Analysis of muscle composition and of in vitro metabolic characteristics was conducted on the biceps femoris muscle. The percentage of dry weight, protein and glycogen was greater in the muscle of obese fetuses than in the muscle of lean fetuses (P less than .01, P less than .05, and P less than .05, respectively). Percentage of muscle triglyceride was similar (P greater than .05) between the two phenotypes. The rate of glucose oxidation to CO2 tended to be greater (P less than .07) and the rate of lactate production was lower (P less than .05) in the muscle from obese fetuses than in the muscle from lean fetuses. The rates of leucine oxidation to CO2 and of palmitate oxidation to CO2 did not differ between phenotypes. The rate of alpha-ketoisocaproate release from the muscle of obese fetuses was greater (P less than .05) than from that of the lean fetuses. The rate of release of alanine and of glutamine plus glutamate did not differ between phenotypes. The rate of esterification of palmitate did not differ between phenotypes. It was concluded that abnormalities in glucose metabolism and in the partitioning of leucine between oxidation and release as the keto acid existed at 110 d of gestation in the muscle of obese fetuses. Any relation between these differences and ultimate differences in carcass composition were not evident.     

Effect of pH, temperature, and inhibitors on autolysis and catalytic activity of bovine skeletal muscle mu-calpain.

To improve our understanding of the regulation of calpain activity in situ during postmortem storage, the effects of pH, temperature, and inhibitors on the autolysis and subsequent proteolytic activity of mu-calpain were studied. Calpains (mu- and m-calpain) and calpastatin were purified from bovine skeletal muscle. All autolysis experiments were conducted in the absence of substrate at different pH (7.0, 6.2, and 5.8) and temperatures (25 and 5 degrees C). Autolysis of mu-calpain generated polypeptides with estimated masses of 61, 55, 40, 27, 23, and 18 kDa. The rate of autolysis was significantly increased with decreasing pH. The rate of degradation of the 80-kDa subunit was significantly decreased with decreasing temperature. However, degradation of the 30-kDa subunit was not affected by decreasing temperature. By conducting autolysis experiments at 5 degrees C and immunoblotting of autolytic fragments with anti-80 kDa, it was demonstrated that with the exception of 18 kDa, which originates from 30 kDa, all other fragments probably originate from degradation of the 80-kDa subunit. Calpastatin, leupeptin, and E-64 did not inhibit the initial step of autolysis, but they did inhibit further breakdown of these fragments. However, zinc, which also inhibits the proteolytic activity of calpain, only reduced the rate of autolysis, but did not inhibit it. The possible significance of these results in terms of the regulation of calpain in postmortem muscle is discussed.     

Effect of exercise on development of capillary supply and oxidative capacity in skeletal muscle of horses

OBJECTIVE: To determine whether postnatal development of oxidative capacity and capillary supply of skeletal muscle is affected by various movement regimens in horses. ANIMALS: 35 foals. PROCEDURES: Dutch Warmblood foals were allocated into 3 groups (box stall rest, box stall rest with training, and free pasture exercise). Training comprised an increasing number of gallop sprints from 1 week after birth to 22 weeks of age. From 22 to 48 weeks, the 3 groups were combined and allowed to exercise freely. Capillary supply (diffusion index [ie, area supplied by 1 capillary]), citrate synthase (CS) activity, and succinate dehydrogenase (SDH) activity were measured in biopsy specimens of deep gluteus medius muscle. RESULTS: During the first 22 weeks, diffusion index increased in all 3 groups (the training and pasture groups had a smaller increase, compared with the box stall rest group), total SDH activity increased in the training and pasture groups and decreased in the box stall rest group, and CS activity decreased in all groups. The effect of the various movement regimens on the diffusion index remained after the groups were combined. CONCLUSIONS AND CLINICAL RELEVANCE: Withholding of exercise had a negative effect on the capillary supply (ie, diffusion index increased) that remained after box stall rest was discontinued and on oxidative capacity. Box stall rest with training prevented the negative effects and eventually had the same positive effect as pasture exercise.     

Effect of heat exposure on uncoupling protein-3 mRNA abundance in porcine skeletal muscle

Exposure to cold increases abundance of mRNA for uncoupling protein-3 (UCP3) in skeletal muscle, whereas the influence of exposure to heat is unknown. Thus, we conducted a study to investigate the influence of heat exposure on UCP3 mRNA abundance in porcine skeletal muscle. Three pigs aged 110 to 120 d, with an average BW of 75 kg, from each of eight litters were used. Each littermate was assigned to one of three treatment groups; one group was reared at 32 degrees C and fed ad libitum (32AL) for 4 wk, whereas the other two groups were maintained at 23 degrees C for the same period, and either pair-fed the intake of their 32AL littermates (23PF), or fed ad libitum (23AL). The RNase protection assay revealed that UCP3 mRNA abundance in longissimus dorsi and rhomboideus muscles was higher (P < 0.05) in the 32AL group than the 23PF group. The 23AL group also had significantly higher UCP3 mRNA abundance than the 23PF group in these muscles. Plasma total 3,5,3'-triiodothyronine concentration of the 32AL group was lower (P < 0.05) than that of the 23PF group, whereas mRNA abundance of thyroid hormone receptor (TR) isoforms, TRalpha1 and TRalpha2, in these muscles was not affected, suggesting that the 32AL group was in a relatively hypo-thyroid state. Because thyroid hormone up-regulates UCP3 expression, these results indicate that factors other than thyroid hormone may play a role in regulating UCP3 mRNA abundance in skeletal muscle of heat-exposed pigs.     

Pulmonary dysfunction and skeletal muscle changes in horses with RAO

BACKGROUND: Chronic pulmonary diseases (recurrent airway obstruction [RAO]) have been reported to alter skeletal muscle cells in humans. The purpose of this study was to evaluate a potential relationship between pulmonary and muscle variables in horses with a clinical diagnosis of RAO. Muscle biopsies from healthy horses and from horses with RAO were investigated and the relationship between the severity of lung disease and the degree of muscular changes was determined. HYPOTHESIS: We hypothesized that chronic pulmonary disease can lead to changes of the skeletal muscle in horses. ANIMALS: Fifteen healthy horses (control) and 50 horses with RAO were examined. METHODS: In a prospective clinical trial, a complete lung examination was performed in all horses. In all horses, muscle enzyme activity at rest and after exercise and muscle biopsies from the M. gluteus medius were examined. RESULTS: None of the horses had clinical or histologic signs of primary or neurogenic myopathies. According to the clinical, endoscopic, and radiographic findings and with a scoring system, the horses with RAO were grouped according to the severity of pulmonary findings (15 horses mild, 24 horses moderate, 11 horses severe RAO). Pathologic changes of the skeletal muscle (fiber atrophy or fiber hypertrophy, myofibrillar degeneration, hyperplasia of mitochondria, and ragged-red-like fibers) were identified in most horses with RAO but in only a few individual control horses. In addition, a marked depletion of muscle glycogen storage was evident in the RAO horses but not in the control group. Other pathologic changes of skeletal muscle such as centralized nuclei and regenerating fibers were rare, but were more frequent in horses with lung diseases than in the control group. The degree of muscle cell changes was also graded with a scoring system and correlated with the severity of pulmonary disease (r= 0.55). CONCLUSION: Chronic pulmonary disease in horses is associated with structural changes in skeletal muscle. CLINICAL IMPORTANCE: Because chronic pulmonary disease may affect muscles, early and effective therapy may prevent these changes. This finding could be of clinical importance but requires further studies.     

Effect of the repartitioning agent cimaterol on growth, carcass and skeletal muscle characteristics in lambs

Ten crossbred (Suffolk X Rambouillet) whether lambs were randomly assigned to receive 0 or 10 ppm cimaterol (CIM) in a completely mixed high-concentrate diet for 8 wk. Total weight gain and feed efficiency were improved 29% (P less than .05) and 14%, respectively, in the CIM-fed group. CIM also improved (P less than .01) dressing percent by 4.9 percentage points and improved yield grade by one grade. CIM increased longissimus muscle (LD) area 38% (P less than .01) and the yield of four lean cuts 28% (P less than .01). No difference was found in the proportion of type I (slow-contracting, oxidative) and type II (fast-contracting, mixed glycolytic/oxidative) fibers in LD and semitendinosus (ST) muscles between control and CIM groups, indicating no change in fiber type. The cross-sectional area of type II fibers in LD and ST muscles of the CIM group was 2,081 and 1,951 micron 2 as compared with 1,391 and 1,296 micron2 of the control group, respectively. The increase was approximately 50% (P less than .01). No difference was found in cross-sectional area of type I fibers, indicating that the increase of muscle mass was due to hypertrophy of type II fibers only. DNA concentration (micrograms/g wet muscle or microgram/g protein) of CIM muscle was much lower (P less than .01) than that of control muscle, suggesting that the protein accretion in muscle was accomplished without additional incorporation of nuclei from satellite cells.