Fast-twitch Oxidative-glycolytic Fibers Research Articles

Effect of dressing percentage on chemical composition, microstructure and quality traits of Pectoralis major muscle in female Japanese quail

Summary The experiment involved 40 female Japanese quail ( Coturnix japonica) slaughtered at 8 weeks of age. The study was arranged to determine slaughter traits, physicochemical properties and microstructure characteristics of Pectoralis major muscle as related to the different dressing percentages, and to examine the correlation between tested parameters. The results show that dressing percentage significantly affected carcass and Pectoralis major muscle weight, acidity and the content of crude fat, dry matter and soluble collagen. Dressing percentage did not influence the number of fast-twitch oxidative-glycolytic muscle fibres, cross-section area for slow-twitch oxidative fibres and aerobic index. Dressing percentage was positively and significantly correlated with the number of fibres and capillaries per bundle, the quantity of fast-twitch glycolytic fibres, cross-section area for fast-twitch oxidative-glycolytic fibres, anaerobic index and fat content in the muscle. Only in the case of the number of slow-twitch oxidative fibres the correlation coefficient was negative and the relationship with dressing percentage significant. It is concluded that it is possible to obtain high-quality meat with increased dressing percentage from 8-week-old female Japanese quail.

Exercise myopathy: changes in myofibrils of fast-twitch muscle fibres.

The purpose of the present study was to determine the relationships between the changes of myofibrils in fast-twitch oxidative-glycolytic (type IIA) fibres and fast-twitch glycolytic (type IIB) muscle fibres, protein synthesis and degradation rate in exercise-induced myopathic skeletal muscle. Exhaustive exercise was used to induce myopathy in Wistar rats. Intensity of glycogenolysis in muscle fibres during exercise, protein synthesis rate, degradation rate and structural changes of myofibrils were measured using morphological and biochemical methods. Myofibril cross sectional area (CSA) in type IIA fibres decreased 33% and type IIB fibres 44%. Protein degradation rate increased in both type IIA and IIB fibres, 63% and 69% respectively in comparison with the control group. According to the intensity of glycogenolysis, fast oxidative-glycolytic fibres are recruited more frequently during overtraining. Myofibrils in both types of fast-twitch myopathic muscle fibres are significantly thinner as the result of more intensive protein degradation. Regeneration capacity according to the presence of satellite cells is higher in type IIA fibres than in type IIB fibres in myopathic muscle.

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.

Relationship between histochemical, structural characteristics and oxidative stability of rhea limb muscles

Histochemical and structural characteristics were investigated in Gastrocnemius pars interna (GN) and Iliofiburalis (IF) limb muscles of Rhea americana. The average myofibre area cross-section was greater in GN than IF muscle (p<0.001), whereas the fibre density per section was higher in IF than GN muscle. The only type of myofibre found in both the rhea limb muscles analysed in this study was fast-twitch oxidative–glycolytic fibres (FOG). Immunolabelling analysis and ultrastructural observation of myofibres confirmed the contractile and metabolic characteristics of rhea myofibres, revealing the absolute fast isoform of myosin heavy chain and the abundance of glycogen and mitochondria inside the cells, mainly in IF muscle. These findings converged with previous results on the biochemical and physicochemical characteristics of rhea meat to provide further evidence that myofibre composition substantially influences the oxidative reactions of the muscle and therefore the meat quality, but more in-depth examination is needed to establish the links between myofibre characteristics, myofibre glycogen concentration and meat stability during storage.

Relationship between morphometric characteristics of fibre types and adipocytes in Cinta Senese pig

The research was carried out on 16 pigs of autochthonous (located breed of pig) genetic type Cinta Senese. The morphometric characteristics of the fibre types and their percentage were determined on Longissimus Dorsi (LD) and Psoas major (PM) muscles. The area, diameter, volume and thickness of adipocytes from internal and external layers of adipose tissue from pig backfat, shoulder, dorsal and loin regions were determined. Maximum shortening velocity and isometric tension were measured in single muscle fibres. The type slow twitch oxidative fibres (SO) was larger than fast twitch glycolytic fibres (FG) and fast twitch oxidative glycolytic fibres (FOG) (P<0.001), LD muscle was characterised by fibres larger than PM and males had fibres larger than females. As regards adipocytes the dorsal region had bigger adipocytes (P<0.05–0.001) and fat thickness, adipocyte diameter and volume were higher in the middle layer. Isometric tension values were higher in the fibres type FOG, the values of maximum shortening velocity were higher in the fibres type FG.

Effect of Age and Sex on Histomorphometrical Characteristics of Two Muscles of Laticauda Lambs

The aim of the present experiment was to determine the effect of sex and age on histochemical and morphometric characteristics of muscle fibres (myocytes) in lambs born by single, twin, triplet and quadruplet birth. Thirty lambs were slaughtered at 60 days of age; thirty were weaned at 60 days and fed until 120 days with flakes (60%) and food supplements, and then slaughtered. Muscle tissues were obtained from two muscles, namely m. semitendinosus and m. longissimus dorsi of all lambs. For each fibre type, area perimeter and diameter (maximum and minimum) were measured and slow-twitch oxidative fibres, fast-twitch glycolytic fibres, fast-twitch oxidative-glycolytic fibres were histochemically differentiated. The muscles were stained for myosin ATPase, and succinic dehydrogenase. At 60 days, females had fibres larger than males, whereas the opposite was observed at 120 days. Besides, at 60 days, the lambs born by single birth had fibres larger than those born by multiple birth, whereas the opposite was observed at 120 days. Single lambs were heavier than twin lambs and multiple lambs. Fast-twitch glycolytic fibres had the largest size, followed by slow-twitch oxidative and fast-twitch oxidative glycolytic fibres. The dimensions of fibre types in m. longissimus dorsi were larger than in m. semitendinosus (P &lt; 0.001).These muscle fibre characteristics are thought to be important factors influencing meat quality, which is often related to metabolic and contractile properties as determined by the muscle fibre type distribution.

New Insights into Muscle Fibre Types in Casertana Pig

Little is known about the Casertana pig. The aim of this study was to evaluate the effect of sex on histochemical and morphometrical characteristics of muscle fibres (myocytes) in this pure breed and to verify the presence of giant fibres as well as vascularity of the muscle. Finally, maximum shortening velocity and isometric tension were measured in single muscle fibres. Sixteen Casertana pigs (8 males, 8 females) from a farm in Campania (Italy) were slaughtered at one year of age. Muscle tissues were obtained from psoas minor, rhomboideus and longissimus dorsi. Myofibres were stained for myosin adenosine triphosphatase, succinic dehydrogenase, and α-amylase-periodic acid schiff. For all fibre types, the area and perimeter were measured. Slowtwitch oxidative fibres, fast-twitch glycolytic fibres and fast-twitch oxidative-glycolytic fibres were histochemically differentiated; an image-analyzing system was used. The results showed significant differences between the sexes in the size of all three fibre types. The psoas minor muscle had a high percentage of slow-twitch oxidative fibres and contained more capillaries per fibre and per mm2 than rhomboideus and longissimus dorsi, in which fast-twitch glycolytic fibres dominated. The cross-sectional area of all fibre types was larger in longissimus dorsi than in rhomboideus and psoas minor muscles; the giant fibres were present in the longissimus dorsi muscle only. Besides, isometric tension values were higher in fast-twitch glycolytic fibres than in the other ones. Variations in fibre type composition may contribute to meat quality.

Skeletal Myocyte Types and Vascularity in the Black Sicilian Pig

The objective of this study was to verify the presence of giant fibres in the Black Sicilian pig skeletal muscle and to evaluate the effect of sex on histochemical and morphometric characteristics of the myocytes (myofibres) as well as vascularity of the muscle. Twenty Black Sicilian pigs (10 males, 10 females) from a farm in Sicily (Italy) were slaughtered at two years of age. Muscle tissues were obtained from three muscles: psoas major, longissimus dorsi, and trapezius. Myofibres were stained for myosin ATPase, succinic dehydrogenase, and α-amylase-PAS. For all fibre types, area and perimeter were measured. Slow-twitch oxidative fibres, fast-twitch glycolytic fibres and fast-twitch oxidative-glycolytic fibres were histochemically differentiated; an image-analyzing system was used. The results showed no differences between males and females in percentage of the fibre types, but there were significant differences between sexes in size of all the three fibre types. Psoas major muscle had a high percentage of slow-twitch oxidative fibres and contained more capillaries per fibre and per mm2 than trapezius and longissimus dorsi, in which fast-twitch glycolytic fibres dominated. The cross-sectional area of all fibres types was larger in longissimus dorsi than in trapezius and psoas major muscles; the giant fibres were absent in all the muscles studied. Fibre type composition may contribute to the variation of meat quality.

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.

Impact of aging on muscle blood flow in chronic heart failure

Chronic heart failure (CHF) is manifested principally in the elderly population. Therefore, to understand the causes of exercise intolerance in CHF patients, it is imperative to resolve the effects of aging on muscle blood flow (BF) in CHF. To address this issue, we determined the muscle BF response to submaximal treadmill exercise (20 m/min, 5% grade) in young (Y(CHF): 6-8 mo, 412 +/- 11 g, n = 11) and old (O(CHF): 27-29 mo, 494 +/- 10 g, n = 8) Fischer 344 x Brown Norway rats with similar degrees of myocardial infarction-induced left ventricular (LV) dysfunction [resting LV end-diastolic pressure: Y(CHF) = 24 +/- 2, O(CHF) = 22 +/- 2 mmHg; derivative of LV pressure over time: Y(CHF) = 5,168 +/- 285; O(CHF) = 5,050 +/- 165 mmHg/s; lung weight normalized to body weight: Y(CHF) = 9.14 +/- 0.72; O(CHF) = 8.21 +/- 0.29 mg/g (all P > 0.05)]. The exercising heart rate response was blunted in O(CHF) compared with Y(CHF) rats (Y(CHF) = 454 +/- 8, O(CHF) = 395 +/- 9 beats/min; P < 0.05). BF (radiolabeled microspheres) to the total hindlimb musculature and to each of the 28 individual muscles examined was similar between Y(CHF) and O(CHF) rats under resting conditions. During exercise, BF to five of the hindlimb muscles that normally possess a majority of slow-twitch oxidative and fast-twitch oxidative glycolytic muscle fibers increased significantly less (-25 to -42%) for O(CHF) compared with Y(CHF) rats. In contrast, BF to 14 of the hindlimb muscles that normally possess a majority of fast-twitch glycolytic muscle fibers was increased (+22 to +337%) for O(CHF) vs. Y(CHF) rats, which contributed to a greater mass-specific total hindlimb BF response in O(CHF) rats (Y(CHF) = 78 +/- 5, O(CHF) = 100 +/- 11 ml.min(-1).100 g(-1); P < 0.05) and coincided with greater reductions in BF to the kidneys and splanchnic organs during exercise in O(CHF) vs. Y(CHF). In conclusion, there appears to be a profound age-related redistribution of BF from the highly oxidative to the highly glycolytic muscles of the hindlimb during exercise in O(CHF) compared with Y(CHF) rats. This phenomenon is qualitatively similar to that reported previously for healthy young and old rats.

Histochemical and morphometrical characterization and distribution of fibre types in four muscles of ostrich (Struthio camelus).

A staining procedure used for simultaneously determining three different fibre types in single sections bovine, porcine or ovine skeletal muscle was modified for use with ostrich skeletal muscle. The muscle fibres of gastrocnemius pars externa, tibialis cranialis caput tibiale, tibialis cranialis caput femorale and fibularis longus tendo caudalis were studied. The histochemical results revealed the presence of three types of fibre only in the gastrocnemius pars externa muscle: fast-twitch glycolytic fibres (FG), fast-twitch oxidative glycolytic fibres (FOG) and slow-twitch oxidative fibres (SO), while in the other muscles the FG fibres were absent. The percentage distribution of fibres types showed a higher incidence of SO fibres compared to FOG fibres in tibialis cranialis caput femorale and tibialis cranialis caput tibiale muscles, while it was opposite in the case of the fibularis longus tendo caudalis muscle. In the gastrocnemius pars externa muscle the FG fibres outnumber the other fibres, followed by the SO and FOG fibres. The results of the analysis of variance show significant interaction between muscle x fibre type for every morphometric parameter evaluated. Differences about value of fibres area exists between tibialis cranialis caput femorale and fibularis longus tendo caudalis muscles. Both fibre types in tibialis cranialis caput tibiale muscle have mean values of transversal section area smaller than tibialis cranialis caput femorale. The other morphometric parameters show a similar trend. The gastrocnemius pars externa muscle presents similar dimensions of muscle fibres for the FG and FOG types, and significantly smaller for the SO type.

Effect of plasma free fatty acid concentration on the content and composition of the free fatty acid fraction in rat skeletal muscles.

Skeletal muscles contain a fraction of free (unesterified) fatty acids. This fraction is very small, but important since it contributes to the creation of the plasma-myocyte free fatty acid concentration gradient. Maintenance of this gradient is necessary for blood-borne fatty acids to be transported into the cell. There are no data on the regulation of the content and composition of the free fatty acid fraction in the cell. The aim of the present study was to examine the effect of an elevation and a reduction in the plasma-borne free fatty acid concentration on the content and composition of the free fatty acid fraction in different skeletal muscle types. The experiments were carried out on male Wistar rats with 280 - 310 g body weight. They were divided into four groups - 1, control; 2, exercised 3 h on a treadmill moving with a speed of 1,200 m/h and set at + 10 degrees incline; 3, treated with heparin; and 4, treated with nicotinic acid. Samples of the soleus as well as the red and white sections of the gastrocnemius muscles were taken. These muscles are composed mostly of slow-twitch oxidative, fast-twitch oxidative-glycolytic and fast-twitch glycolytic fibres, respectively. Lipids were extracted from the muscle samples and from the blood; the free fatty acid fraction was isolated by means of thin-layer chromatography. The individual free fatty acids were identified and quantified using gas-liquid chromatography. The plasma concentration of free fatty acids was as follows: control group, 236.1 +/- 32.9; after exercise, 407.4 +/- 117.5; after heparin, 400.8 +/- 36.8; and after nicotinic acid, 102.5 +/- 26.1 micromol/l (p < 0.01 vs. control values in each case). The total content of the free fatty acid fraction in the control group was as follows: white gastrocnemius, 27.6 +/- 7.3; red gastrocnemius, 52.2 +/- 13.9; soleus, 72.3 +/- 10.2 nmol/g. Elevation in plasma free acid concentration during exercise increased the total content of free fatty acids in the white gastrocnemius (38.7 +/- 13.9) and in the soleus (103.4 +/- 15.9 nmol/g; rest-exercise: p < 0.05 and p < 0.01, respectively), but had no effect in the red gastrocnemius. Neither elevation in the plasma free fatty acid concentration with heparin nor reduction with nicotinic acid affected the total content of the free fatty acid fraction in the muscles examined. The ratio of plasma concentration of individual acid to muscle concentration for the same acid varied greatly, depending on acid, muscle type and experimental group. The ratio was positive (above unity) for each acid almost in all cases with the exception of certain acids in the nicotinic acid-treated group where it was below unity. We conclude that the skeletal myocytes maintain a stable level of free fatty acid fraction in the wide range of plasma free fatty acid concentrations.

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.

Palmitic acid incorporation into intramuscular acylglycerols depends on both total and unbound to albumin palmitic acid concentration.

Palmitic acid incorporation into the intramuscular acylglycerols in rat skeletal muscles of different fiber types was investigated at various total and unbound to albumin concentrations by means of the hind-limb perfusion technique. It was found that at simultaneously increasing total and unbound to albumin palmitic acid concentrations in the perfusion medium the incorporation of palmitic acid into acylglycerols increased. However, when the concentration of palmitic acid not bound to albumin was kept constant and the total palmitic acid concentration was increased, the incorporation also increased although markedly less than under former conditions. The increase was most apparent in the muscles composed of slow-twitch oxidative and fast-twitch oxidative-glycolytic fibers where fatty acid uptake is the greatest. These findings suggest that fatty acid incorporation into intramuscular acylglycerols depends not only on the unbound to albumin fatty acid concentration but also, to some extent, on the total fatty acid concentration.

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.

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.