Percentage Of Type IIB Fibres Research Articles

Genomic variants associated with the number and diameter of muscle fibers in pigs as revealed by a genome-wide association study

Muscle fiber characteristics comprise a set of complex traits that influence the mea quality and lean meat production of livestock. However, the genetic and biological mechanisms regulating muscle fiber characteristics are largely unknown in pigs. Based on a genome-wide association study (GWAS) performed on 421 Large White × Min pig F2 individuals presenting well-characterized phenotypes, this work aimed to detect genome variations and candidate genes for five muscle fiber characteristics: percentage of type I fibers (FIB1P), percentage of type IIA fibers (FIB2AP), percentage of type IIB fibers (FIB2BP), diameter of muscle fibers (DIAMF) and number of muscle fibers per unit area (NUMMF). The GWAS used the Illumina Porcine SNP60K genotypic data, which were analyzed by a mixed model. Seven and 10 single nucleotide polymorphisms (SNPs) were significantly associated with DIAMF and NUMMF, respectively (P < 1.10E-06); no SNP was significantly associated with FIB1P, FIB2AP or FIB2B. For DIAMF, the significant SNPs on chromosome 4 were located in the previously reported quantitative trait loci (QTL) interval. Because the significant SNPs on chromosome 6 were not mapped in the previously reported QTL interval, a putative novel QTL was suggested for this locus. None of the previously reported QTL intervals on chromosomes 6 and 14 harbored significant SNPs for NUMMF; thus, new potential QTLs on these two chromosomes are suggested in the present work. The most significant SNPs associated with DIAMF (ALGA0025682) and NUMMF (MARC0046984) explained 12.02% and 11.59% of the phenotypic variation of these traits, respectively. In addition, both SNPs were validated as associated with DIAMF and NUMMF in Beijing Black pigs (P < 0.01). Some candidate genes or non-coding RNAs, such as solute carrier family 44 member 5 and miR-124a-1 for DIAMF, and coiled-coil serine rich protein 2 for NUMMF, were identified based on their close location to the significant SNPs. This study revealed some genome-wide association variants for muscle fiber characteristics, and it provides valuable information to discover the genetic mechanisms controlling these traits in pigs.

Early life undernutrition reduces maximum treadmill running capacity in adulthood in mice.

Undernutrition during early life causes chronic disease with specific impairments to the heart and skeletal muscle. The purpose of this study was to determine the effects of early life undernutrition on adult exercise capacity as a result of cardiac and skeletal muscle function. Pups were undernourished during gestation (GUN) or lactation (PUN) using a cross-fostering nutritive mouse model. At postnatal day 21, all mice were weaned and refed a control diet. At postnatal day 67, mice performed a maximal treadmill test. Echocardiography and Doppler blood flow analysis was performed at postnatal day 72, following which skeletal muscle cross-sectional area (CSA) and fiber type were determined. Maximal running capacity was reduced (diet: P = 0.0002) in GUN and PUN mice. Left ventricular mass (diet: P = 0.03) and posterior wall thickness during systole (diet × sex: P = 0.03) of GUN and PUN mice was reduced, causing PUN mice to have reduced (diet: P = 0.04) stroke volume. Heart rate of GUN mice showed a trend (diet: P = 0.07) towards greater resting values than other groups. PUN mice had greater CSA of soleus fibers. PUN had a reduced (diet: P = 0.03) proportion of type-IIX fibers in the extensor digitorum longus (EDL) and a greater (diet: P = 0.008) percentage of type-IIB fibers in the EDL. In conclusion, gestational and postnatal undernourishment impairs exercise capacity.

Targeted metabolomics to reveal muscle-specific energy metabolism between bovine longissimus lumborum and psoas major during early postmortem periods

Targeted metabolomics was applied to elucidate energy metabolites in bovine (Chinese Jinjiang yellow cattle, n = 4) longissimuss lumborum (LL) and psoas major (PM) muscles during the early postmortem period (1 h, 6 h, 12 h, and 24 h). The a* value increased significantly (P < .05) in both of LL and PM within 24 h postmortem. Compared with PM, LL had higher area percentage of type IIB fibers (48.41% vs 30.60%, P < .001) and lower proportion of type I fibers (24.98% vs 46.16%, P < .001). A total of 22 energy metabolites were successfully detected by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The principal component and hierarchical cluster analyses of these metabolites exhibited clear distinctions between LL and PM samples from different postmortem periods. Enzymic activities (lactate dehydrogenase, malate dehydrogenase, and succinate dehydrogenase), contents of pyruvate and numbers of metabolites involved in tricarboxylic acid (TCA) cycle evidenced different changes in LL and PM, which indicated distinguished metabolic patterns between them.

Muscle Fibre Characteristics and Physico-Chemical Parameters of m. semimembranosus from Pulawska, Polish Large White and Pietrain Pigs.

The aim of the study was to compare muscle fibre parameters and quality of m. seninembranosus in pigs. The experiment was conducted with 18 Pulawska pigs, 24 Polish Large White (PLW) pigs, and 24 Pietrain pigs slaughtered at 105 kg body weight. The results obtained indicate that the breed of pigs has a significant effect on both muscle fibre composition and vascularization. The muscles of Pulawska pigs are the most oxidative, as evidenced by the greatest number of capillaries and the highest percentage of type I and IIA fibres compared to the muscle of PLW and Pietrain pigs. In turn, the most glycolytic muscles (highest percentage of type IIB fibres, poorest vascularization as well as the greatest diameters of muscle fibres of all types under analysis) were noted in Pietrain pigs. Analysis of the physico-chemical parameters of the meat showed the lowest pH45, a* and IMF, as well as the highest L*, drip loss and shear force values in Pietrain pigs compared to Pulawska and PLW pigs. Significantly higher IMF, and a* values, as well as lower drip loss, shear force and L* values were observed in Pulawska pigs.

Microstructure of Longissimus Lumborum Muscle and Meat Quality of Native Polish Pig Breeds: Złotnicka Sp Otted and Puławska

Abstract In 50 fattening pigs representing two Polish native breeds: 24 Złotnicka Spotted, 10 Puławska and 16 F1 ♀ (Polish Large White × Polish Landrace) × F1 ♂ (Duroc × Pietrain) crosses microstructure of muscle, carcass and meat quality were studied. Puławska pigs had the thickest backfat, but the loin eye area was smaller only in comparison to crossbreds. Compared to the Puławska breed, the meat of Złotnicka Spotted pigs was darker, which was associated with a greater percentage of type I fibres and a smaller percentage of type IIB fibres. Puławska pigs distinguished themselves from the other groups under study by the greatest density of fibres per mm2. Smaller diameter of type IIA and IIB fibres and higher total number of fibres were found in Puławska breed pigs compared to Złotnicka Spotted, despite the absence of differences in the loin eye area. Smaller thickness of the fibres favourably affects meat quality, and might be considered an indicator of a delicate structure of meat.

Myofiber development during embryonic to neonatal development in duck breeds differing in muscle growth rates

AbstractLittle is known about the muscle developmental patterns during embryonic to neonatal development in ducks. We investigated the developmental patterns in the lateral gastrocnemius muscles of Gaoyou and Jinding ducks differing in their muscle growth rates during the final stages of egg incubation and the first week after hatching. Expression of the MyoD gene was quantified by quantitative real-time PCR (qRT-PCR). The average cross-sectional area and diameter of the fibers increased from embryonic day 21 (E21), peaking at E27, and then declining slightly 7 d after hatching. The density of the fibers decreased initially but increased after hatching in both breeds and sexes. The within-breed variation in muscle fiber-type composition was greater than the average variation between the breeds. Overall, the percentage of type I fibers increased and that of type IIb fibers decreased consistently. However, the percentage of type IIa fibers was almost constant as development proceeded in both duck breeds. The profiles of MyoD mRNA expression were similar in both breeds, and a significantly positive relationship was observed between the expression of MyoD and the percentage of type IIb fibers. This study firstly revealed the characteristics of duck muscle development and differences between the two breeds differing in growth rates. Moreover, type IIb fibers might convert to type I fibers in the lateral gastrocnemius, while MyoD may potentially function in controlling the muscle fiber phenotype during the secondary myogenesis of muscle development.

Expression profile of IGF-I-calcineurin-NFATc3-dependent pathway genes in skeletal muscle during early development between duck breeds differing in growth rates.

The insulin-like growth factor I (IGF-I)-calcineurin (CaN)-NFATc signaling pathways have been implicated in the regulation of myocyte hypertrophy and fiber-type specificity. In the present study, the expression of the CnAα, NFATc3, and IGF-I genes was quantified by RT-PCR for the first time in the breast muscle (BM) and leg muscle (LM) on days 13, 17, 21, 25, and 27 of embryonic development, as well as at 7days posthatching (PH), in Gaoyou and Jinding ducks, which differ in their muscle growth rates. Consistent expression patterns of CnAα, NFATc3, and IGF-I were found in the same anatomical location at different development stages in both duck breeds, showing significant differences in an age-specific fashion. However, the three genes were differentially expressed in the two different anatomical locations (BM and LM). CnAα, NFATc3, and IGF-I messenger RNA (mRNA) could be detected as early as embryonic day 13 (ED13), and the highest level appeared at this stage in both BM and LM. Significant positive relationships were observed in the expression of the studied genes in the BM and LM of both duck breeds. Also, the expression of these three genes showed a positive relationship with the percentage of type IIb fibers and a negative relationship with the percentage of type I fibers and type IIa fibers. Our data indicate differential expression and coordinated developmental regulation of the selected genes involved in the IGF-I-calcineurin-NFATc3 pathway in duck skeletal muscle during embryonic and early PH growth and development; these data also indicate that this signaling pathway might play a role in the regulation of myofiber type transition.

Histological Profile of the Longissimus Dorsi Muscle in Polish Large White and Polish Landrace Pigs and its Effect on Loin Parameters and Intramuscular Fat Content*

Abstract The objective of this study was to analyse differences in individual fibre types in the histological profile of the longissimus dorsi muscle and their effect on pork carcass lean content and level of intramuscular fat (IMF) content, which determines palatability of meat and meat products. Analysis showed that the amount of type IIB fibres had a statistically significant (P&lt;0.05) effect on the IMF content of the longissimus dorsi muscle. Animals with more than 70% of type IIB fibres in this muscle were also characterized by larger loin eye area (P&lt;0.01) and loin eye height (P&lt;0.05). Analogous relationships were noted when the analysed group of animals was divided according to the diameter of type IIA fibres. IMF was negatively correlated to the percentage of type IIB fibres (rP= -0.162). Relationships with the other two fibre types were positive (IIA - rP= 0.097; I - rP= 0.187). It was found that increased percentage of type IIB fibres resulted in a slightly greater loin weight (rP= 0.176), higher loin eye height (rP= 0.136), larger loin eye area (rP= 0.265) and higher carcass lean content (rP= 0.204). Likewise, the increase in the number of type IIA and type I fibres decreased these parameters.

Effect of Breed on Microstructure and Tenderness of Porcine Semimembranosus Muscle

Abstract The objective of the study was to analyse the effect of breed on characteristics of muscle fibres, parameters of intramuscular connective tissue, collagen content, intramuscular fat (IMF) content and tenderness of semimembranosus muscle in pigs. The study was conducted with 16 Złotnicka Spotted (ZS) and 23 Polish Landrace (PL) fattening pigs slaughtered at 210 days of age. The current study showed that compared to the PL breed, the semimembranosus muscle from the local breed of ZS pigs was characterized by a greater percentage of type I fibres, a smaller percentage of type IIB fibres and a smaller diameter of all the three muscle fibre types analysed, while the muscles of PL pigs had significantly thinner endomysium and perimysium and a more compact arrangement of collagen fibres, with a significantly lower percentage of collagen in the muscle and a lower content of total and soluble collagen compared to the muscles of ZS pigs. Furthermore, meat from ZS pigs was more tender (lower shear force value) and had a significantly higher IMF content compared to meat from PL pigs.

An examination of the association of serum IGF-I concentration, potential candidate genes, and fiber type composition with variation in residual feed intake in progeny of Red Angus sires divergent for maintenance energy EPD1

Investigating the genetic and physiological drivers of postweaning residual feed intake (RFI) and finishing phase feed efficiency (FE) may identify underlying mechanisms that are responsible for the variation in these complex FE traits. The objectives were 1) to evaluate the relationship of serum IGF-I concentration and muscle gene expression with postweaning RFI and sire maintenance energy (MEM) EPD and 2) to determine fiber type composition as it relates to postweaning RFI and finishing phase FE. Results indicate that RFI and serum IGF-I concentration were not associated (P > 0.05); however, negative correlations (P < 0.05) between sire MEM EPD and serum IGF-I concentration were observed. Gene expression differences between high- and low-RFI animals were observed in cohort 1, where IGFBP5 expression was greater (P < 0.05) in high-RFI animals. When animals were grouped according to sire MEM EPD, the low MEM EPD group of cohort 1 showed greater muscle mRNA expression (P < 0.01) of fatty acid synthase (FASN) and marginally (P < 0.10) greater expression of IGFBP5 and C/EBP alpha (C/EBPα) whereas the high MEM EPD group of cohort 2 had greater muscle mRNA expression of IGFBP2 (P < 0.05) and C/EBPα (P ≤ 0.01) and marginally (P < 0.10) greater expression of IGFBP3. Biopsy tissue samples collected at harvest revealed that the percentage of type IIa fibers was lower (P ≤ 0.05) in high-RFI steers, with a similar trend (P < 0.10) being observed in high finishing phase FE steers. The percentage of type IIb fibers was higher (P < 0.05) in high-RFI (and finishing phase FE) steers than in low-RFI (and finishing phase FE) steers. There was a marginal, negative correlation between RFI and type I (r = -0.36, P = 0.08) and IIa (r = -0.37, P = 0.07) fiber percentages and a positive correlation (r = 0.48, P = 0.01) between RFI and type IIb fiber percentage whereas finishing phase FE was negatively correlated (r = -0.43, P = 0.03) with type I fiber percentage and positively correlated (r = 0.44, P = 0.03) with type IIb fiber percentage. Therefore, our data indicate that 1) serum IGF-I (collected at weaning) is not an indicator of postweaning RFI, 2) the GH-IGF axis appears to have some involvement with RFI at the molecular level; however, muscle gene expression results were not consistent across cohorts, and 3) low-RFI animals may have the ability to more efficiently maintain and accrete muscle mass due to their fiber type composition, specifically a greater proportion of type I fibers.

Polymorphisms of the 5′ regulatory region of the porcine PPARGC1A gene and the effects on muscle fiber characteristics and meat quality

The purpose of this study was to determine the structure of the porcine PPARGC1A 5' upstream region, and to find suitable molecular markers for improved meat quality and good lean meat production. Ten DNA polymorphisms, including 7 SNPs, 2 microsatellites, and 1 insertion or deletion were newly found in the 5' upstream region of PPARGC1A. Three SNPs that had restriction enzyme site were evaluated for associations with muscle fiber characteristics and production traits. Two hundred fifty-two pigs (Yorkshire and Landrace) were used in this analysis. The c.-2894G>A genotypes was significantly associated with muscle fiber characteristics, including the number of fiber type I and IIb composition (P<0.05), mean cross-sectional area of fibers (P<0.01), and fiber number per unit area (P<0.05). The animals with the GG genotype had a higher percentage of type I fibers and a lower percentage of type IIb fibers with better meat quality [higher pH value (P<0.05) and lower drip loss (P<0.05)] and lean meat production [larger loin eye area (P<0.05)]. Moreover, the mRNA expression levels of PPARGC1A among genotypes were significantly different with the highest level of GG genotype. The c.-2885G>T and c.-1402A>T sites showed similar results that had significant effects on the mean cross-sectional area (CSA; P<0.05), fiber number per unit area (P<0.05) and loin eye area (P<0.01). Therefore, we suggest that the c.-2894G>A polymorphism in the 5' upstream region of the porcine PPARGC1A gene can be used as a meaningful molecular marker for simultaneous improvement of lean meat production and quality traits.

The influence of the PRKAG3 mutation on glycogen, enzyme activities and fibre types in different skeletal muscles of exercise trained pigs

BackgroundAMP-activated protein kinase (AMPK) plays an important role in the regulation of glucose and lipid metabolism in skeletal muscle. Many pigs of Hampshire origin have a naturally occurring dominant mutation in the AMPK γ3 subunit. Pigs carrying this PRKAG3 (R225Q) mutation have, compared to non-carriers, higher muscle glycogen levels and increased oxidative capacity in m. longissimus dorsi, containing mainly type II glycolytic fibres. These metabolic changes resemble those seen when muscles adapt to an increased physical activity level. The aim was to stimulate AMPK by exercise training and study the influence of the PRKAG3 mutation on metabolic and fibre characteristics not only in m. longissimus dorsi, but also in other muscles with different functions.MethodsEight pigs, with the PRKAG3 mutation, and eight pigs without the mutation were exercise trained on a treadmill. One week after the training period muscle samples were obtained after euthanisation from m. biceps femoris, m. longissimus dorsi, m. masseter and m. semitendinosus. Glycogen content was analysed in all these muscles. Enzyme activities were analysed on m. biceps femoris, m. longissimus dorsi, and m. semitendinosus to evaluate the capacity for phosphorylation of glucose and the oxidative and glycolytic capacity. Fibre types were identified with the myosin ATPase method and in m. biceps femoris and m. longissimus dorsi, immunohistochemical methods were also used.ResultsThe carriers of the PRKAG3 mutation had compared to the non-carriers higher muscle glycogen content, increased capacity for phosphorylation of glucose, increased oxidative and decreased glycolytic capacity in m. longissimus dorsi and increased phosphorylase activity in m. biceps femoris and m. longissimus dorsi. No differences between genotypes were seen when fibre type composition was evaluated with the myosin ATPase method. Immunohistochemical methods showed that the carriers compared to the non-carriers had a higher percentage of type II fibres stained with the antibody identifying type IIA and IIX fibres in m. longissimus dorsi and a lower percentage of type IIB fibres in both m. biceps femoris and m. longissimus dorsi. In these muscles the relative area of type IIB fibres was lower in carriers than in non-carriers.ConclusionsIn exercise-trained pigs, the PRKAG3 mutation influences muscle characteristics and promotes an oxidative phenotype to a varying degree among muscles with different functions.

Hyperbaric Oxygen Exposure Improves Blood Glucose Level and Muscle Oxidative Capacity in Rats with Type 2 Diabetes

The effects of exposure to hyperbaric oxygen on blood glucose level and muscle oxidative capacity in rats with type 2 diabetes were investigated. Five-week-old male Goto-Kakizaki rats were divided into four groups: normobaric (NN; exposed to 21% oxygen at 760 mm Hg for 8 weeks), hyperbaric to normobaric (HN; exposed to 36% oxygen at 950 mm Hg for 4 weeks, followed by 21% oxygen at 760 mm Hg for 4 weeks), normobaric to hyperbaric (NH; exposed to 21% oxygen at 760 mm Hg for 4 weeks, followed by 36% oxygen at 950 mm Hg for 4 weeks), and hyperbaric (HH; exposed to 36% oxygen at 950 mm Hg for 8 weeks). Blood glucose levels were lower in the HN, NH, and HH groups than in the NN group. Up-regulated mRNA expression levels of peroxisome proliferator-activated receptor-gamma co-activator-1alpha were observed in the soleus muscles of the HN, NH, and HH groups and in the plantaris muscles of the HN and HH groups. The soleus muscles of the NN group contained only type I fibers, whereas those of the HN, NH, and HH groups contained type I, type IIA, and type IIC fibers. An increased percentage of type I fibers and a decreased percentage of type IIB fibers were observed in the plantaris muscles of the NH, HN, and HH groups. Exposure to hyperbaric oxygen reduces high blood glucose levels and improves oxidative capacities in the skeletal muscles of rats with diabetes, and these effects are maintained under normobaric conditions even after exposure to hyperbaric oxygen.

Expression of myosin heavy chain isoforms in the postnatal mouse masseter muscle

We investigated the properties of the masseter muscle in mice from five to seven weeks of age. Myosin heavy chain (MyHC) isoforms were measured in the masseter muscle. The three types of muscle fibers (Type I, strong reaction; Type IIA, intermediate reaction; and Type IIB, weak reaction) were all present in the masseter muscle in five-weeks-old mice and seven-weeks-old mice, the three types could be clearly distinguished by their enzyme activity. The percentage of Type IIB fibers (above 50%) was the highest among all fiber types both 5- and 7-weeks-old mice. The mRNA levels for myosin slow and myosin IIb increased significantly between 5 and 7 weeks. These observations suggest that muscle fiber size, muscle fiber types and mRNA levels of the MyHC isoforms all contribute to the diminished functional adaptability of enzyme activity in the masseter muscle.

Comparing the histochemical characteristics and meat quality traits of different pig breeds

The purpose of this study was to compare the muscle histochemical characteristics and meat quality traits between Berkshire, Landrace, Yorkshire, and crossbred pigs. A total of 594 pigs were evaluated. A clear difference between histochemical properties was observed from the results for fiber type composition. In Berkshire pigs, the area percentage of type I fibers was higher (P<0.001) and that of type IIb fibers was lower (P<0.05) than those of other breeds. The muscle pH45min and pH24h were significantly higher in Berkshire pigs. Drip loss and color parameters were significantly different between the breeds (P<0.001). The Berkshire pigs, which showed the highest muscle pH and lowest drip loss and L∗ values, contained a significantly higher percentage of type I fibers than the other breeds. By comparing the fiber type compositions of the different breeds, the results imply that the longissimus dorsi muscle of Berkshire pigs is more oxidative than that of other breeds. A high pH value in Berkshire pigs is due to a high percentage of type I fibers and a low percentage of type IIb fibers. Based on these results, we conclude that muscle fiber composition can explain in parts the variation of meat quality across and within breeds.

Muscle Architecture of the Rat Hindlimb

The rat is a commonly-used experimental model, however, the architectural properties of its muscular system are poorly documented. PURPOSE: To define the architectural properties of the entire rat hindlimb and to compare the design characteristics among muscle groups. METHODS: Thirty-one muscles from each of six paired hindlimbs were dissected from adult male rats (323 g ± 15 g). Measurements of muscle mass, length, fiber length, sarcomere length, and pennation angle were measured directly and used to calculate normalized fiber length and physiological cross-sectional area (PCSA). Contralateral legs were used to quantify myosin heavy chain (MHC) isoform percentages. Muscles groups were classified according to their joint action. Average fiber length, total muscle group PCSA, and average MHC percentage were used to make among group comparisons. Mann-Whitney U-tests were used for statistical comparisons and reported values are mean ± SE. RESULTS: At the hip joint, extensors had significantly longer fiber lengths than flexors (33.0 mm ±2.2 mm vs. 17.6 mm ±2.2 mm) and larger total PCSAs (1.61 cm2 ± 0.05 cm2 vs. 1.38 cm2 ± 0.05 cm2). Flexors had a greater percentage of type IIa (10 % ± 1 % vs. 8 % ± 1 %) and IIx (25 % ± 2 % vs. 19 % ± 1 %) fibers while extensors had a greater percentage of type IIb (72 % ± 2 % vs. 63 %± 2 %) fibers. At the knee joint, flexors had longer fiber lengths than extensors (35.0 mm ±1.8 mm vs. 14.9 mm ±0.8 mm) and smaller total PCSAs (1.39 cm2 ± 0.04 cm2 vs. 1.69 cm2 ± 0.07 cm2). Knee extensors also had greater type I (9 % ± 2 % vs. 2 % ± 1 %), IIa (14 % ± 1 % vs. 8 % ± 1 %), and IIx (25 % ± 1 % vs. 18 % ± 1 %) percentages while flexors had a greater type IIb (72 % ± 2 % vs. 53 % ± 3 %) percentage. At the ankle joint, plantarflexors had a trend towards longer fiber lengths (16.3 mm ±0.8 mm vs. 13.9 mm ±0.6 mm, P = 0.064) and significantly greater total PCSA (1.45 cm2 ±0.11 cm2vs. 0.49 cm2 ±0.03 cm2). Plantarflexors also had a significantly greater type I percentage (24 % ± 67 % vs. 1 % ± 1%) while dorsiflexors had a significantly greater type IIb percentage (60 % ± 3 % vs. 42 % ± 5 %). CONCLUSIONS: Consistent with other their antigravity function, total extensor muscle group PCSA was larger compared to the total flexor muscle group PCSA at each joint. However, muscle fiber length differences were less distinct, with hip extensors, knee flexors, and ankle plantarflexors, tending to have longer fibers. MHC percentages were also less distinct, with hip extensors, knee flexors, and ankle dorsiflexors having the greater percentage of type IIb fibers. These data will form the foundation for understanding muscle group functional differences in the rat hindlimb.

Eccentric Training Causes Muscular Hypertrophy, Fiber-type Transformation and Interleuikin-6 Production in the Rat Gastrocnemius Muscle

Recent studies have shown that a single bout of muscular exercise causes a transient increase in Interleuikin-6 (IL-6) production within working muscles, though it remains unclear whether similar change of IL-6 occur after repeated bouts of eccentric exercise, i.e. eccentric training. PURPOSE:The purpose of this study was to learn the effects of moderate eccentric training on muscular size and function, and intramuscular levels of cytokines including IL-6, using originally developed isokinetic-exercise system for rats. METHODS: Male Wistar rats (N=39) were randomly assigned into eccentric training (EC) group and sham control (CON) group. After anesthetized with isoflurance, they were firmly fixed on a platform of the isokinetic dynamometer in a prone position. The exercise session consisted of twenty eccentric contractions of the triceps surae muscle, which were elicited by submaximal electric stimulation (100 Hz). Forced lengthening was applied to the muscle by an isokinetic dorsi-flexion of the ankle joint (velocity, 30 deg/s; range of motion, 45 deg). Rats in EC group were trained every second day for 10 days (5 sessions in total) or 20 days (10 sessions in total) after measurements of isometric tetanic force. Only the measurements of isometric tetanic force were made for CON group. After either 5 or 10 sessions of exercise, the muscle specimens were dissected, weighed and subjected to myosin ATPase histochemistry. Tissue concentrations of IL-6 were measured with Western-blot analysis. RESULTS: The wet weight of medial gastrocnemius muscle did not significantly increase after 5 sessions of exercise (EC 724 ± 56.3 mg, CON: 745 ± 44.7 mg), whereas that after 10 sessions significantly increased with concomitant increase in the cross-sectional area (CSA) of muscle fibers(weight, EC 814 ± 62.4 mg, CON 732 ± 46.5 mg, P<0.05; fiber CSA, EC 4000 ± 1331 umz, CON 3331 ± 1321 umz, P<0.001). The isometric tetanic forces on days 10, 16, 18, and 20 were significantly larger in EC group than in CON group (P<0.001). Myosin-ATPase staining showed a decrease in the percentage of type IIB fibers and an increase in the percentage of type IIA fibers (P<0.001).The tissue concentration of IL-6 after 5 sessions but not 10 sessions of exercise was significantly higher than in the CON group. No apparent fiber damage was observed after 10 sessions. CONCLUSIONS: The results showed that a 20-day eccentric training causes increases in muscular size and strength, and a transformation of fiber types towards slower subtypes. These changes were associated with a preceding increase in IL-6 production, suggesting roles played by muscle-derived cytokines in muscular adaptations to eccentric exercise.

Comparison of histochemical characteristics in various pork groups categorized by postmortem metabolic rate and pork quality1

The purpose of the present study was to investigate the variations in histochemical characteristics of muscle samples segregated according to metabolic rates (MR) and pork quality attributes. A total of 231 crossbred Duroc x (Yorkshire x Landrace) pigs was evaluated. Samples of the LM were taken to evaluate histochemical characteristics, postmortem MR, and meat quality. Samples were classified into fast, normal, and slow MR groups based on muscle pH at 45 min and R-value. Drip loss and lightness (L*) were used to assign samples to 1 of 4 quality classes. Pale, soft, and exudative pork belonging in the fast group had the greatest (P < 0.05) percentage of type IIb fibers, and RSE (reddish-pink, soft, and exudative) pork belonging in the fast group had a similar tendency. Additionally, RFN (reddish-pink, firm, and nonexudative) pork belonging in the normal group showed a lower (P < 0.05) percentage of type IIb fibers than PSE or RSE, regardless of MR, and DFD pork had the lowest (P < 0.05) percentage of type IIb fibers. In general, the fast-glycolyzing PSE pork with the lowest pH at both 45 min and 24 h had greater percentages of type IIb fibers than the fast-glycolyzing RFN pork. There were more fiber-type composition differences between quality classes in pork undergoing a fast rate of metabolism compared with pork undergoing a normal rate of metabolism. It can be concluded that muscle histochemical characteristics are associated with early postmortem MR, the extent of glycolysis, and, thereby, pork quality; however, these effects are limited to the pigs exhibiting a fast glycolytic rate.

Effects of running exercise on fibre‐type distribution of soleus and plantaris muscles in diabetic Otsuka Long‐Evans Tokushima fatty rats

Effect of running exercise on fibre-type distributions of the slow soleus and fast plantaris muscles was investigated in male Otsuka Long-Evans Tokushima fatty rats (OLETF) as an animal model of spontaneous type 2 diabetes mellitus. Five-week-old OLETF rats were allowed to exercise voluntarily in running wheels for 32 days and the data were compared with those of age-matched non-exercised OLETF and non-diabetic Long-Evans Tokushima Otsuka rats (LETO). In the soleus muscle, a higher percentage of type I fibres was observed in non-exercised OLETF rats compared with LETO rats, and there were no type IIA fibres in non-exercised OLETF rats. In the plantaris muscle, a higher percentage of type IIB fibres and a lower percentage of type I and type IIA fibres were observed in non-exercised OLETF rats compared with LETO rats. In contrast, there were no differences in the fibre-type distribution of soleus and plantaris muscles between exercised OLETF and LETO rats. The body weight and type I fibre percentage of the soleus muscle were related to the running distance in exercised OLETF rats. White adipose tissue weight, HbA(1c) and blood insulin and glucose concentrations were lower in exercised OLETF rats than in non-exercised OLETF rats, irrespective of the running distance. There was a difference in the gene-expression pattern of the soleus muscle among LETO rats, non-exercised OLETF and exercised OLETF rats. Running exercise can inhibit diabetes-associated type shifting of fibres, which is more apparent with postnatal growth, in skeletal muscles of diabetic OLETF rats, as a result of mRNA expression change in muscle.

Effects of carcass weight and muscle on texture, structure and myofibre characteristics of wild boar meat

Texture, histology and muscle fibre characteristic of selected muscles: m. quadriceps femoris (QF), m. biceps femoris (BF), and m. semimembranosus (SM) of wild boars of different carcass weight (20 ± 2 and 60 ± 3 kg SD) were compared. Muscle texture (hardness, cohesiveness, springiness, chewiness) was determined with the double penetration test performed with the Instron 1140 apparatus. Structural elements (muscle fibre cross-section area, perimysium and endomysium thickness) and percentage of myofibres of each type: I (slow oxidative), IIA (fast oxidative-glycolytic) and IIB (fast glycolytic) per muscle fibre bundle, were measured in muscle samples using a computer image analysis program. The young wild boar muscles showed significantly lower values for the textural parameters ( p < 0.05). The muscle fibre cross-sectional areas of the juvenile wild boar muscles were significantly lower and the perimysium and endomysium thinner ( p < 0.05) than those in the old wild boar meat, while the percentage of type IIB fibres was higher. Of all the wild boar muscles tested, the highest hardness and chewiness values were found in BF which, at the same time, showed the highest fibre cross-sectional area and the thickest perimysium and endomysium. The highest percentage of I and IIA fibre types was typical of BF and SM either in young or in old wild boars with the lowest percentage of type I and the highest percentage of type IIB fibres being found in the QF. The results suggest that a higher hardness of wild boar muscles can be connected with a thicker perimysium and endomysium, fibres of higher cross-sectional area and probably a higher content of red fibres (type I).