Fast-twitch Oxidative Glycolytic Research Articles

Effects of Exercise on Fiber Properties in the Denervated Rodent Diaphragm

In a unilaterally denervated diaphragm, atrophy of fast-twitch glycolytic (FG) fibers, but not of fast-twitch oxidative glycolytic (FOG) or slow-twitch oxidative (SO) fibers, occurs. The inhibition of atrophy in FOG and SO fibers may be due to the effects of stretch stimuli caused by respiratory contraction of the contralateral diaphragm. We examined the effects of exercise (treadmill running) on the histochemical and biochemical properties of muscle fibers of the costal diaphragm in three groups. Eighteen rats were distributed in (i) a denervation + treadmill running (Dn ex) group, (ii) a denervation (Dn) group, and (iii) a control (Ct) group. After 4 weeks of running, we measured the expression of myosin heavy chain (MHC) isoforms and cross-sectional area of the diaphragm muscle. The expression of MHC 1 and MHC 2a increased 4 weeks after denervation. In contrast, the expression of MHC 2d decreased significantly. After 4 weeks of running, the cross-sectional area of FG fibers increased significantly (85.5%; P < 0.05) compared with that in the Dn group. We suggest that exercise enhances the morphological properties and myosin heavy chain isoforms of the denervated diaphragm. This exercise-mediated adaptation may be associated with the improvement of FG fibers in the denervated diaphragm.

A new perspective: An italian autochthonous pig and its muscle and fat tissue characteristics

The research was aimed at identifying the key characteristics of muscle and fat tissues when comparing two pig breeds: Black Sicilian pig and Landrace pig. In Psoas minor (Pm) and Psoas major (PM) muscles the morphometric characteristics of fibre types and their percentage were determined. The area of adipocytes from internal and external layer of adipose tissue was also determined. The results showed that slow twitch oxidative (SO) fibres were larger than fast twitch glycolytic (FG) and fast twitch oxidative glycolytic (FOG); Pm muscle was characterized by larger FG and SO fibres than PM; males had larger fibres than females in both muscles and breeds. Landrace pig has smaller adipocytes cells than Black Sicilian while Black Sicilian pig showed more essential fatty acids than Landrace. The results in favour of Black Sicilian pig show how conservation of animal biodiversity becomes important because of the high independent homeostatic capability exhibited by autochthonous genetic types for the management and control of the land.

Distribution of myofiber types in the crural musculature of sheep

In domestic animals, the legs function in both postural maintenance and propulsion. The crural muscles participate in actions of the tarsal and toe joints. Mammalian skeletal muscles consist of myofibers, which are histochemically classified into three myofiber types, slow-twitch/oxidative (SO) or type I, fast-twitch/oxidative/glycolytic (FOG) or type IIA, and fast-twitch/glycolytic (FG) or type IIB myofibers. The histochemical characteristics of myofiber types reflect an aspect of function that myofibers possess. In the present study, we investigated the composition and average diameter of myofiber types of each muscle in crus of sheep and determined their roles in the movement of tarsal and toe joints. The tibialis cranialis muscle was a flat unipennate muscle and not capable to generate a large tension; however, it could function primarily in posture maintenance and play a cooperative role in adjusting standing posture. The flexor hallucis longus and flexor digitorum superficialis muscles were the major muscles that contributed to posture maintenance in leg musculature. These muscles were capable to generate a large tension and participate primarily in standing posture maintenance. The composition and diameter of myofiber types in ovine crural musculature reflected the role of each muscle in posture maintenance and locomotion.

Carcass and muscle characteristics of beef cull cows between 4 and 9 years of age

AbstractThe effects of age and breed on carcass and muscle characteristics of cull cows slaughtered at the same fattening state between 4 and 9 years of age were analysed in four French breeds: Aubrac (AU), Charolais (CH), Limousin (LI), and Salers (SA). Muscle characteristics were determined in three muscles: longissimus thoracis (LT), semitendinosus (ST) and triceps brachii (TB). They included: (1) the % frequency, cross-sectional area and % area of the different fibre types classified according to their contraction rate and metabolic properties (slow twitch oxidative (SO), fast twitch oxidative glycolytic (FOG) and fast twitch glycolytic (FG)), (2) the isocitrate dehydrogenase (ICDH) and lactate dehydrogenase (LDH) activities, representative of oxidative and glycolytic metabolism respectively, and (3) the total and insoluble collagen contents. Whatever the age of the animals at slaughter, the same carcass composition, fibre characteristics (% frequency, area, % area) and metabolic enzyme activities were obtained whatever the muscles considered. In contrast, important differences between breeds were observed in carcass composition (muscle, fat, bone) and enzyme activities. CH cows presented the highest final live weight and LI carcasses were characterized by higher muscle weight, lower fat and bone weights and more glycolytic muscles. Among the muscle characteristics, collagen was the most influenced by age and breed in a breed and muscle dependent manner respectively. AU and LI cows exhibited lower total and insoluble collagen contents than CH and SA cows, particularly at 6 to 7 years of age and for the LT and ST muscles. Thus collagen could explain an important part of the variability in meat quality from cull cows. In conclusion, results of this study provide consistent data on muscle characteristics of cull cows, few studies were available until then.

The Expression of MMP-2 Following Immobilization and High-Intensity Running in Plantaris Muscle Fiber in Rats

The effect of 2-week, high-intensity running and a 2-week immobilization on muscle fiber type composition of the plantaris muscle from 18 female, 6-month-old Wistar rats (running, n = 6; immobilization, n = 6; sedentary control, n = 6) was bio- and histochemically investigated. The high-intensity treadmill running began with 20 min (32 m/min, 0% gradient, 75% VO2 max), up to 50 min/day. Right hind limbs were immobilized by an external fixation procedure for 13 days. Muscle mass of the plantaris muscle in the immobilized groups was reduced by 16% in comparison with the sedentary control group. High-intensity running and immobilization increased both mRNA and protein levels of matrix metalloproteinase type 2 (MMP-2) in plantaris. Running and immobilization decreased the percentages of transverse sectional area of fast-twitch glycolytic (FG) type IIb fibers, running increased relative cross-sectional area of fast-twitch oxidative glycolytic (FOG) type IIa muscle fibers, whereas immobilization increased relative cross-sectional area of slow-twitch oxidative (SO) muscle fibers (type I). Our results suggest that both high-intensity running and immobilization are enough to induce overwhelming changes in plantaris.

Muscle fiber-type variation in lizards (Squamata) and phylogenetic reconstruction of hypothesized ancestral states

Previously, we found that phrynosomatid lizards, a diverse group common in the southwestern USA, vary markedly in fiber-type composition of the iliofibularis (a hindlimb muscle important in locomotion). Phrynosomatidae comprises three subclades: the closely related sand and horned lizards, and their relatives the Sceloporus group. The variation in muscle fiber-type composition for 11 phrynosomatid species is attributable mainly to differences between the sand- and horned-lizard subclades. Here, we expand the phrynosomatid database with three additional species and compare these results with data collected for 10 outgroup (distantly related) species. Our goal was to determine if the patterns found in Phrynosomatidae hold across a broader phylogenetic range of the extant lizards and to elucidate the evolution of muscle fiber-type composition and related traits. To allow for meaningful comparisons, data were collected from species that are primarily terrestrial and relatively small in size (3.5-65 g body mass). Results indicate that the fiber-type variation observed within the Phrynosomatidae almost spans the range of variation observed in our sample of 24 species from eight families. However, one species of Acanthodactylus (Lacertidae) had a consistent region of large tonic fibers (that did not stain darkly for either succinic dehydrogenase or myosin ATPase activity), a fiber-type only occasionally seen in the other 23 species examined. Many species have a large proportion of either fast-twitch glycolytic (FG; e.g. sand lizards and Aspidoscelis) or fast-twitch oxidative-glycolytic (FOG) fibers (e.g. horned lizards), with the slow-oxidative proportion occupying only 1-17% of the iliofibularis. Importantly, the negative relationship between FG and FOG composition observed in Phrynosomatidae appears to be a characteristic of lizards in general, and could lead to functional trade-offs in aspects of locomotor performance, as has previously been reported for Lacertidae. Reconstruction of ancestral trait values by use of phylogenetically based statistical methods indicates especially large changes in fiber-type composition during the evolution of horned lizards.

Slow-tonic muscle fibers and their potential innervation in the turtle,Pseudemys (Trachemys)scripta elegans

A description is provided of the ratio of slow-tonic vs. slow- and fast-twitch fibers for five muscles in the adult turtle, Pseudemys (Trachemys) scripta elegans. The cross-sectional area of each fiber type and an estimation of the relative (weighted) cross-sectional area occupied by the different fiber types are also provided. Two hindlimb muscles (flexor digitorum longus, FDL; external gastrocnemius, EG) were selected on the basis of their suitability for future motor-unit studies. Three neck muscles (the fourth head of testo-cervicis, TeC4; the fourth head of retrahens capitus collique, RCCQ4; transversalis cervicis, TrC) were chosen for their progressively decreasing oxidative capacity. Serial sections were stained for myosin adenosine triphosphatase (ATPase), NADH-diaphorase, and alpha-glycerophosphate dehydrogenase (alpha-GPDH). Conventional fiber-type classification was then performed using indirect markers for contraction speed and oxidative (aerobic) vs. glycolytic (anaerobic) metabolism: i.e., slow oxidative (SO, including slow-twitch and possibly slow-tonic fibers), fast-twitch, oxidative-glycolytic (FOG), and fast-twitch glycolytic (Fg) fibers. Slow-tonic fibers in the SO class were then revealed by directing the monoclonal antibody, ALD-58 (raised against the slow-tonic fiber myosin heavy chain of chicken anterior latissimus dorsi), to additional muscle cross sections. All five of the tested muscles contained the four fiber types, with the ATPase-stained fibers including both slow-tonic and slow-twitch fibers. The extreme distributions of SO fibers were in the predominately glycolytic TrC vs. the predominately oxidative TeC4 muscle (TrC-SO, 9%; FOG, 20%; Fg, 71% vs. TeC4-SO, 58%: FOG, 16%; Fg, 25%). Across the five muscles, the relative prevalence of slow-tonic fibers (4-47%) paralleled that of the SO fibers (9-58%). TeC4 had the highest prevalence of slow-tonic fibers (47%). The test muscles exhibited varying degrees of regional concentration of each fiber type, with the distribution of slow-tonic fibers paralleling that of the SO fibers. In the five test muscles, fiber cross-sectional area was usually ranked Fg > FOG > SO, and slow-twitch always > slow-tonic. In terms of weighted cross-sectional area, which provides a coarse-grain measure of each fiber type's potential contribution to whole muscle force, all five muscles exhibited a higher Fg and lower SO contribution to cross-sectional area than suggested by their corresponding fiber-type prevalence. This was also the case for the slow-twitch vs. slow-tonic fibers. We conclude that slow-tonic fibers are widespread in turtle muscle. The weighted cross-sectional area evidence suggested, however, that their contribution to force generation is minor except in highly oxidative muscles, with a special functional role, like TeC4. There is discussion of: 1) the relationship between the present results and previous work on homologous neck and hindlimb muscles in other nonmammalian species, and 2) the potential motoneuronal innervation of slow-tonic fibers in turtle hindlimb muscles.

SELECTIVE CHANGES IN MUSCLE FIBER SIZE FOLLOWING BONE FRACTURE IN AGED RATS

PURPOSE The purpose of this study was to investigate the effect of bone fracture-induced muscle atrophy on the histochemical property of muscle fibers in aged rats. METHODS All experimental procedures were approved by the institutional Animal Care and Use Committee at Kyoto University. Ten male and female Wistar Kyoto rats (aged:88.7 □} 3.2 wk) were subdivided into four groups based upon gender and the presence of fractures or non-fractures of the metatarsal bone of the right hindlimb paw: …3) male fractur ed (M-FR, n=5); …) non-fractur ed (M-NFR, n=5); … μ) female fractured (F-FR, n=5); …¶) non-fractured (F-NFR, n=5). The soleus muscles were dissected from both hindlimbs and analyzed for histochemical properties. Myofibrillar adenosine triphosphatase (ATPase) histochemical staining procedure was used to determine muscle fiber type and calculate the percentage distribution and cross-sectional area (CSA) of each fiber type. RESULTS The wet weight of the soleus muscles of the leg with the fractured paw decreased by 9.6% in M-FR and decreased by 10.0% in F-FR compared to M-NFR and F-NFR, respectively (p > 0.05). However, the wet weight of the soleus muscle of the contralateral, nonfractured site of both M-FR and F-FR groups displayed a hypertrophic compensation and was increased by 12% in M-FR and increased by 3.3% in F-FR (p > 0.05). The CSA of the fast-twitch oxidative glycolytic (FOG) fibers hypertrophied by 40% (p < 0.05) in the soleus muscles of the leg with the fractured paw in the M-FR compared with M-NFR group. In contrast, there was no change in CSA of the FOG of soleus muscle between the female groups. CONCLUSION The data suggest that stress-induced increases in male androgen hormones upregulated the synthesis of contractile proteins of the fast twitch oxidative and glycolytic fibers.

Skeletal muscle ouabain binding sites are reduced in rats with chronic heart failure.

Intrinsic skeletal muscle abnormalities decrease muscular endurance in chronic heart failure (CHF). In CHF patients, the number of skeletal muscle Na(+)-K(+) pumps that have a high affinity for ouabain (i.e., the concentration of [(3)H]ouabain binding sites) is reduced, and this reduction is correlated with peak oxygen uptake. The present investigation determined whether the concentration of skeletal muscle [(3)H]ouabain binding sites found during CHF is related to 1) severity of the disease state, 2) muscle fiber type composition, and/or 3) endurance capacity. Four muscles were chosen that represented slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), fast-twitch glycolytic (FG), and mixed fiber types. Measurements were obtained 8-10 wk postsurgery in 23 myocardial infarcted (MI) and 18 sham-operated control (sham) rats. Eighteen rats had moderate left ventricular (LV) dysfunction [LV end-diastolic pressure (LVEDP) < 20 mmHg], and five had severe LV dysfunction (LVEDP > 20 mmHg). Rats with severe LV dysfunction had significant pulmonary congestion and were likely in a chronic state of compensated congestive failure as indicated by an approximately twofold increase in both lung and right ventricle weight. Run time to fatigue and maximal oxygen uptake (VO(2 max)) were significantly reduced ( downward arrow39 and downward arrow28%, respectively) in the rats with severe LV dysfunction and correlated with the magnitude of LV dysfunction as indicated by LVEDP (run time: r = 0.60, n = 21, P < 0.01 and VO(2 max): r = 0.93, n = 13, P < 0.01). In addition, run time to fatigue was significantly correlated with VO(2 max) (r = 0.87, n = 15, P < 0.01). The concentration of [(3)H]ouabain binding sites (B(max)) was significantly reduced (21-28%) in the three muscles comprised primarily of oxidative fibers [soleus: 259 +/- 14 vs. 188 +/- 17; plantaris: 295 +/- 17 vs. 229 +/- 18; red portion of gastrocnemius: 326 +/- 17 vs. 260 +/- 14 pmol/g wet tissue wt]. In addition, B(max) was significantly correlated with VO(2 max) (soleus: r = 0.54, n = 15, P < 0.05; plantaris: r = 0.59, n = 15, P < 0.05; red portion of gastrocnemius: r = 0.65, n = 15, P < 0.01). These results suggest that downregulation of Na(+)-K(+) pumps that possess a high affinity for ouabain in oxidative skeletal muscle may play an important role in the exercise intolerance that attends severe LV dysfunction in CHF.

Composition of myofiber types in the vocalis muscles involved in rapid closure of the glottis in Japanese macaques

Myofiber types of the medial thyroarytenoid (vocalis) muscle, lateral thyroarytenoid muscle, and cricothyroid muscle of the Japanese macaque were examined with enzyme-histochemical methods. For comparison, the semitendinosus muscle of the Japanese macaque and the thyroarytenoid (vocalis) muscle of cattle, sheep, and pig were examined with the same methods. The vocalis muscle of the Japanese macaque was composed exclusively of fast-twitch/oxidative/glycolytic (FOG) myofibers; it differed from the lateral thyroarytenoid, cricothyroid, and semitendinosus muscles of the Japanese macaque and from the vocalis muscles of the other animals, which consisted of slow-twitch/oxidative, FOG-, and fast-twitch/glycolytic myofibers or type IIC myofibers. The histochemical properties of the vocalis muscle of the Japanese macaque show that the vocalis muscle has a capacity to close the glottis rapidly and completely.

Comparative analysis of fiber‐type composition in the iliofibularis muscle of phrynosomatid lizards (Squamata)

The lizard family Phrynosomatidae comprises three subclades: the closely related sand and horned lizards, and their relatives the Sceloporus group. This family exhibits great variation in ecology, behavior, and general body plan. Previous studies also show that this family exhibits great diversity in locomotor performance abilities; as measured on a high-speed treadmill, sand lizards are exceptionally fast sprinters, members of the Sceloporus group are intermediate, and horned lizards are slowest. These differences are paralleled by differences in relative hindlimb span. To determine if muscle fiber-type composition also varies among the three subclades, we examined the iliofibularis (IF), a hindlimb muscle used in lizard locomotion, in 11 species of phrynosomatid lizards. Using histochemical assays for myosin ATPase, an indicator of fast-twitch capacity, and succinic dehydrogenase, denoting oxidative capacity, we classified fiber types into three categories based on existing nomenclature: fast-twitch glycolytic (FG), fast-twitch oxidative-glycolytic (FOG), and slow-twitch oxidative (SO). Sand lizards have a high proportion of FG fibers (64–70%) and a low proportion of FOG fibers (25–33%), horned lizards are the converse (FG fibers 25–31%, FOG fibers 56–66%), and members of the Sceloporus group are intermediate for both FG (41–48%) and FOG (42–45%) content. Hence, across all 11 species %FOG and %FG are strongly negatively correlated. Analysis with phylogenetically independent contrasts indicate that this negative relationship is entirely attributable to the divergence between sand and horned lizards. The %SO also varies among the three subclades. Results from conventional nested ANCOVA (with log body mass as a covariate) indicate that the log mean cross-sectional area of individual muscle fibers differs among species and is positively correlated with body mass across species, but does not differ significantly among subclades. The log cross-sectional area of the IF varies among species, but does not vary among subclades. Conversely, the total thigh muscle cross-sectional area does not vary among species, but does vary among subclades; horned lizards have slimmer thighs. Muscle fiber-type composition appears to form part of a coadapted suite of traits, along with relative limb and muscle sizes, that affect the locomotor abilities of phrynosomatid lizards. J. Morphol. 250:265–280, 2001. © 2001 Wiley-Liss, Inc.

Effects of nitric oxide synthase inhibition on vascular conductance during high speed treadmill exercise in rats.

To determine the functional role of nitric oxide (NO) in regulating vascular conductance during high intensity dynamic exercise in skeletal muscles composed of all major fibre types, female Wistar rats (277 +/- 4 g; n = 7) were run on a motor-driven treadmill at a speed and gradient (60 m min(-1), 10 % gradient) established to yield maximal oxygen uptake (V(O2,max)). Vascular conductance (ml min(-1) (100 g)(-1) mmHg(-1)), defined as blood flow normalised to mean arterial pressure (MAP), was determined using radiolabelled microspheres during exercise before and after NO synthase (NOS) inhibition with N (G)-nitro-L-arginine methyl ester (L-NAME; 10 mg kg(-1), I.A.). The administration of L-NAME increased MAP from pre-L-NAME baseline values, demonstrating that NOS activity is reduced. The administration of L-NAME also reduced vascular conductance in 20 of the 28 individual hindlimb muscles or muscle parts examined during high speed treadmill exercise. These reductions in vascular conductance correlated linearly with the estimated sum of the percentage of slow twitch oxidative (SO) and fast twitch oxidative glycolytic (FOG) types of fibres in each muscle (Deltaconductance = -0.0082(%SO + %FOG) - 0.0105; r = 0.66; P < 0.001). However, if the reduction in vascular conductance found in the individual hindquarter muscles or muscle parts was expressed as a percentage decrease from the pre-L-NAME value (%Delta = (pre-L-NAME conductance - post-L-NAME conductance)/ pre-L-NAME conductance x 100), then the reduction in vascular conductance was similar in all muscles examined (average %Delta = -23 +/- 2 %). These results suggest that NO contributes substantially to the regulation of vascular conductance within and among muscles of the rat hindquarter during high intensity exercise. When expressed in absolute terms, the results suggest that the contribution of NO to the regulation of vascular conductance during high intensity exercise is greater in muscles that possess a high oxidative capacity. In contrast, if results are expressed in relative terms, then the contribution of NO to the regulation of vascular conductance during high intensity exercise is similar across the different locomotor muscles located in the rat hindlimb and independent of the fibre type composition.

VASCULAR CONDUCTANCE DURING HIGH INTENSITY EXERCISE IN RATS

To determine the functional role of nitric oxide (NO) in regulating vascular conductance to skeletal muscle, female Wistar rats (277 ± 4 g; n = 7) were run at a speed established to yield VO2max (i.e., treadmill; 60 m/min, 10% grade). Regional vascular conductances (VC, ml/min/100g/mmHg) were measured using radiolabeled microspheres during exercise before and after NO synthase (NOS) inhibition with NG-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg i.a.). NOS inhibition increased (p < 0.05) mean arterial pressure from the pre-exercise baseline value of 137 ± 2 to 168 ± 5 mmHg and attenuated (p < 0.05) the vasodilator response to acetylcholine injections (10 mg/kg i.a.), demonstrating reduced NOS function. During exercise, NOS inhibition reduced VC to the kidneys and splanchnic organs. In addition, VC was reduced in 20 of the 28 individual hindlimb muscles or muscle parts (average −25 ± 2%, P < 0.05). Also, these reductions in VC were correlated linearly with the percentage of slow-twitch oxidative (SO) and fast-twitch oxidative glycolytic (FOG) fiber types found in each muscle [ΔVC = −0.0082(%SO + %FOG) - 0.0105, r = 0.66, P < 0.001], similar to that found previously for moderate intensity exercise (20 m/min, 10% grade). The reduction in VC for the total hindlimb musculature produced by NOS inhibition during high intensity exercise (ΔVC = −0.37 ± 0.06) was significantly greater (p < 0.05) than that found at rest (ΔVC = −0.15 ± 0.03) and during moderate intensity exercise (ΔVC = −0.28 ± 0.04 ml/min/100g/mmHg). These results suggest that during high intensity exercise NO contributes substantially to the regulation of VC within and among the muscles of the rat hindlimb with its relative contribution being greater in muscles that have a high oxidative capacity. Moreover, L-NAME reduces VC in an exercise intensity dependent manner. Supported in part by NIH-HL-50306, HL-57226, AG-11535

Recombinant bovine somatotropin (rbST) increases size and proportion of fast-glycolytic muscle fibers in semitendinosus muscle of creep-fed steers.

The objective of this study was to determine the effect of recombinant bovine somatotropin (rbST) on muscle fiber histology and histochemistry in creep-fed beef steers. Crossbred steer calves were assigned to one of two treatment groups: control (sham-injected; n = 12) or rbST-injected (0.09 mg x kg(-1) x d(-1); n = 12). Calves were injected every 14 d starting at d 28 of age until weaning at 205 d of age. Biopsies of the semitendinosus muscle were performed on d 100, and slaughter samples of semitendinosus muscle were collected for muscle fiber analyses on d 206. The rbST-treated calves had larger (P = 0.045) fast-twitch-glycolytic (FG) fibers [2,564 +/- 10 vs 2,351 +/- 11 microm2 cross-sectional area, respectively] than controls. No differences (P = 0.36) between rbST-treated and control steers in cross-sectional area were detected for slow-twitch-oxidative (SO) [1,192 +/- 20 vs 1,148 +/- 22 microm2, respectively] or fast-twitch-oxidative-glycolytic (FOG) fibers [1,484 +/- 35 vs 1,403 +/- 38 microm2, respectively]. The percentage distribution for FOG fibers was greater for control calves than for the rbST-treated calves (38.4 vs 34.9 +/- 0.1%, respectively; P = 0.014), whereas the percentage distribution for FG fibers was greater in the rbST-treated calves than for control calves (53.5 vs 48.4 +/- 0.2%, respectively; P = 0.03). The percentage distribution for SO fibers tended to be greater for the control calves than for the rbST-treated calves (13.1 vs 11.7 +/- 0.1%, respectively; P = 0.07). The percentage of FG fibers increased with age (45.4 vs 56.6 +/- 0.8%, respectively; P = 0.001), whereas the percentage distribution of SO (14.3 vs 10.5 +/- 0.5%, respectively) and FOG fibers (40.3 vs 32.9 +/- 0.7%, respectively) decreased (P = 0.001) from d 100 to d 206. The increased longissimus muscle area and dissectable lean tissue in rbST-treated calves are associated with a greater percentage of FG fibers, which possess larger cross-sectional areas than the other fibers.

Effects of growth-promoting implants on morphology of Longissimus and Semitendinosus muscles in finishing steers

Growth-promoting implants lead to increased muscle accretion in ruminants. To elucidate the effects at a cellular level, muscle fiber distribution and cross-sectional area (CSA) of longissimus (LM) and semitendinosus (ST) muscles were compared in implanted and control steers. Sixty-four Charolais steers were assigned to one of four treatments (16 steers/treatment): (1) no implant, (2) Synovex-S® (estradiol benzoate+progesterone), (3) Ralgro® (zeranol) or (4) Revalor-S® (trenbolone acetate+estradiol-17β). The experiment was carried out using four slaughter groups (SGRP). Sixteen steers each were slaughtered after 48, 104, 160 and 175 days (four steers/treatment) on trial. Steers on an implant treatment were first implanted at 15 months of age (day 0) and re-implanted at 56 and 112 days. Muscle fibers in the LM and ST (for both live biopsy and post-mortem samples) were characterized as either slow-twitch oxidative (SO), fast-twitch oxidative-glycolytic (FOG) and fast-twitch glycolytic (FG) fibers. Fiber distribution was minimally affected by SGRP in these physiologically mature steers. Implantation with Synovex did not alter fiber distribution in either muscle compared with control steers. Both Synovex-implanted and control steers showed a decrease of FG and an increase of FOG fibers in the LM from day 0 to SGRP 2 followed by an increase of FG and a decrease of FOG fibers. Ralgro- and Revalor-implanted steers had an almost constant fiber distribution in the LM throughout the experiment resulting in higher precentages of FG fibers in SGRP 2 ( P<0.05) than SYN or CON steers. Biopsy samples of the LM muscle which were excised 51 days (SGRP 1–3) or 65 days (SGRP 4) before slaughter proved to be suitable for the determination of fiber distribution in live animals. Fiber area increased in post-mortem samples of both muscles from SGRP 1–3 in all treatment groups followed by a plateau. Implantation with Revalor led to an additional increase in fiber area from SGRP 3 and 4 ( P<0.05). Synovex did not affect fiber area compared with control steers whereas Ralgro and Revalor implants led to larger fibers in SGRP 3 and 4, respectively. It can be concluded that some growth-promoting implants result in noticeable differences in muscle hypertrophic responses which coincide with their different effectiveness to enhance lean mass accretion.

Effect of hypobaric hypoxia on rat soleus muscle fibers and their innervating motoneurons: a review.

Mammalian skeletal muscle fibers are classified into three basic types based on their enzyme histochemical profiles: fast-twitch glycolytic (FG), fast-twitch oxidative glycolytic (FOG), and slow-twitch oxidative (SO) types. The type-shift of fibers from FOG to SO in the slow soleus muscle of rats occurs during postnatal growth. Our previous studies have demonstrated that hypoxic exposure inhibits a growth-related type-shift of fibers from FOG to SO in the rat soleus muscle, irrespective of the duration and age at which the animals are exposed to hypoxia. Our previous studies have also revealed that a high percentage of FOG fibers in the soleus muscle of the hypoxia-adapted rats is found only under hypoxic conditions. Furthermore, we have found that these adaptations in fibers of the rat soleus muscle correspond well with those in motoneurons at the ventral horn of the spinal cord that innervate the muscle fibers.

Histochemical study of the extensor digitorum longus and soleus muscles in alcoholic rats.

The extensor digitorum longus (EDL) and soleus (SOL) muscle fibres from albino rats submitted to experimental chronic alcoholism were evaluated in accordance with their metabolic and morphometric profiles. Twenty-seven male animals aged 4 months and weighing approximately 400 g were used. The animals were divided into three groups: control, isocaloric and alcoholic and sacrifices were carried out after 5, 10 and 15 months. The muscles were dissected, removed, cross-sectioned in a cryostat and submitted to the NADH (nicotinamide adenine dinucleotide) reaction. The SO (slow-twitch-oxidative), FG (fast-twitch-glycolytic) and FOG (fast-twitch-oxidative-glycolytic) muscle fibre types exhibited a polygonal, triangular or rounded shape and did not present noteworthy modifications in either muscles during the study. The cross-sectional areas of the fibres from the studied muscles did not present significant differences during the observations. Fibre area behaved similarly in the alcoholic animals up to the 10th month, i.e. it was decreased, as also observed in the other groups. At 15 months, however, all fibres were increased, with a predominance of FG fibres in the SOL muscle. Changes in fibre population were observed mainly in the SOL muscle of alcoholic animals: SO fibres were initially increased in number but decreased after the 10th month, and the opposite was observed for the population of FG fibres. FOG fibres increased linearly in number throughout the experiment. The statistical analysis showed nevertheless that the fibre population and cross-sectional area changes were not significant. In the alcoholic animals quantitative variations of muscle fibres were more evident in the SOL muscle, suggesting that the SOL muscle is more sensitive to the toxic action of ethanol. The results concerning the increased fibre diameter in alcoholic animals would be associated with muscle oedema induced directly or indirectly by the ethanol.

Correlation between histochemically assessed fiber type distribution and isomyosin and myosin heavy chain content in porcine skeletal muscles.

Highly sensitive enzyme assays developed to differentiate skeletal muscle fibers allow the recognition of three main fiber types: slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), and fast-twitch glycolytic (FG). Myosin, the predominant contractile protein in mammalian skeletal muscle, can be separated based on the electrophoretic mobility under nondissociating conditions into SM2, SM1, IM, FM3, and FM2 isoforms, or under dissociating conditions into myosin heavy chain (MHC) I, IIb, IIx/d, and IIa. The purpose of the present study was to determine whether the histochemical method of differentiation of fiber types is consistent with the electrophoretically identified isomyosin and MHC isoforms. These comparisons were made using serratus ventralis (SV), gluteus medius (GM), and longissimus muscles (LM) from 13 pigs. Two calculation methods for the histochemical assessed fiber type distribution were adopted. The first method incorporated the number of fibers counted for each fiber type and calculated a percentage of the total fiber number (fiber number percentage: FNP). The second method expressed the cross-sectional area of each fiber type as a percentage of the total fiber area measured per muscle (fiber area percentage: FAP). Independent of the calculation methods, correlation analyses revealed in all muscles a strong relation between SO fibers, the slow isomyosin (SM1 and SM2), and MHCI, as well as between the FG fibers, the fast isomyosin (FM3 and FM2), and MHCIIx/b content (P<.05). There were no correlations between FOG fiber population assessed by histochemical analysis and intermediate isoform (IM) or MHCIIa content. The present results did not provide conclusive evidence as to which of the calculation methods (FNP or FAP) was more closely related to myosin composition of skeletal muscles. Despite some incompatibility between the methods, the present study shows that histochemical as well as electrophoretic analyses yielded important information about the composition of porcine skeletal muscle. The combination of the two methods may be essential to accurately characterize porcine skeletal muscles.

Increase in oxidative capacity of pigeon pectoralis muscle before and after fledging

Using the pectoralis muscle of the pigeon (Columba livia), we previously showed that at fledging, both fast-twitch oxidative-glycolytic (FOG) and fast-twitch glycolytic (FG) fiber types retain a myosin isoform characteristic of the neonatal period, despite the birds being at adult body mass. Our aim here was to test the hypothesis that muscle fibers of the pigeon pectoralis increase their aerobic capacity both before and after fledging. Pigeons aged from 1 week after hatching through to adulthood were used. Adopting a microdensitometric technique from studies on mammalian muscle, the activity of succinate dehydrogenase (SDH) within individual fibers was quantified as optical density and used as an index of aerobic capacity. We demonstrate a strong linear correlation (r2 = 0.936) between optical density of FOG fibers and time exposed to the SDH incubation medium. Optical density of FG fibers, however, could not be discerned from background staining. SDH activity in FOG fibers increased logarithmically (r2 = 0.969) with the age of the birds, increasing 2.5-fold from 1 week through to adult. Thus, aerobic capacity did increase both before and after fledging. In addition, within FOG fibers, aerobic capacity and myosin content appear to have different timetables of development.

Expression of myosin heavy chain isoforms during development of domestic pigeon pectoralis muscle.

The pectoralis muscle of birds provides virtually all the power for the downstroke of the wing during flight. In adults it consists almost entirely of FOG (fast-twitch oxidative-glycolytic) and/or FG (fast-twitch glycolytic) fiber types. The aims of this study are to contrast MyHC (myosin heavy chain) transitions occurring within avian FG and FOG fibers during development, and to test the hypothesis that the pectoralis matures before the acquisition of flight. Pectoralis was obtained from pigeons (Columba livia) aged from 13 days in ovo to adult. Monoclonal antibodies generated against chicken MyHC isoforms were used with Western blots and immunocytochemistry. FG and FOG fibers were differentiated using a histochemical method demonstrating NADH (nicotinamide adenine dinucleotide), and "lesser fiber diameters" were quantified. Western blots confirm that the antibodies label pigeon MyHCs. A small number of the fibers are slow type in ovo, but these are quickly restricted in distribution and lost after hatching. In ovo fast-twitch fibers contain a ventricular isoform, and at least two embryonic-neonatal forms (designated E-N103 and E-N165). One week after hatching, fast-twitch fibers can be distinguished by NADH as FG or FOG. At fledging, four weeks after hatching, FG and FOG fibers are smaller than in older birds and E-N103 and E-N165 persist in both fibertypes. E-N103 wanes in all fibers shortly after fledging. E-N165 gradually disappears from FG fibers. Thus, despite pigeons being at adult body mass at fledging, their pectoralis is not fully mature.