Slow-twitch Oxidative Research Articles

The effect of breed and body weight at slaughter on histochemical muscle fiber characteristics and meat quality of longissimus lumborum and semitendinosus lamb muscles

Abstract. The skeletal muscles of mammals are composed of fibers of different morphological, metabolic and functional characteristics. The properties of muscle fibers may be determined genetically as well as by environmental factors such as the age of the animals, their physical activity, the level of nutrition, or the selection intensity. The present study was conducted to determine the influence of genotype (Polish Lowland vs. Polish Heath) and body weight at slaughter (23–25 kg vs. 35–40 kg) of lambs on histological characteristics of muscle fibers in musculus longissimus lumborum (LL) and musculus semitendinosus (ST) skeletal muscles and their impact on chosen meat quality features. Three types of muscle fibers were identified: slow-twitch oxidative (STO), fast-twitch oxidative (FTO) and fast-twitch glycolytic (FTG). Differences in the diameters of individual fiber types between the LL and ST muscles have been found in both investigated genotypes. The diameters of the analyzed types of fibers were usually larger in the ST muscle compared to the LL muscle. The lambs of the more primitive Polish Heath breed were characterized by a smaller diameter of all fiber types, especially in the LL muscle. The higher proportion of STO fibers and the lower proportion of FTO fibers have been found in the LL muscle of Polish Heath lambs in the group with lower body weight. The breed of lambs, muscle type and slaughter body weight had an impact on some meat quality characteristics, especially color, intramuscular fat content and expressed juice.

Systemic delivery of AAVrh74.tMCK.hCAPN3 rescues the phenotype in a mouse model for LGMD2A/R1

Limb girdle muscular dystrophy (LGMD) 2A/R1, caused by mutations in the CAPN3 gene and CAPN3 loss of function, is known to play a role in disease pathogenicity. In this study, AAVrh74.tMCK.CAPN3 was delivered systemically to two different age groups of CAPN3 knockout (KO) mice; each group included two treatment cohorts receiving low (1.17 × 1014 vg/kg) and high (2.35 × 1014 vg/kg) doses of the vector and untreated controls. Treatment efficacy was tested 20 weeks after gene delivery using functional (treadmill), physiological (in vivo muscle contractility assay), and histopathological outcomes. AAV.CAPN3 gene therapy resulted in significant, robust improvements in functional outcomes and muscle physiology at low and high doses in both age groups. Histological analyses of skeletal muscle showed remodeling of muscle, a switch to fatigue-resistant oxidative fibers in females, and fiber size increases in both sexes. Safety studies revealed no organ tissue abnormalities; specifically, there was no histopathological evidence of cardiotoxicity. These results show that CAPN3 gene replacement therapy improved the phenotype in the CAPN3 KO mouse model at both doses independent of age at the time of vector administration. The improvements were supported by an absence of cardiotoxicity, showing the efficacy and safety of the AAV.CAPN3 vector as a potential gene therapy for LGMDR1.

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.

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.

Sexual dimorphism in histological characteristics and contractility of the iliofibularis muscle in the lizardSceloporus torquatus

The iliofibularis is a hindlimb muscle used in lizard locomotion that is composed of at least three types of fibres: fast-twitch-glycolytic (FG), fast-twitch-oxidative-glycolytic fibre (FOG) and slow-twitch-oxidative (SO). The striated skeletal muscle is a highly plastic tissue undergoing phenotypic change in response to activity. The lizard Sceloporus torquatus has sexual differences associated with microhabitat use, which can be reflected in the physiology and anatomy of the muscle, and thus, in our study, we analysed the morphological and contractile characteristics of the iliofibularis muscle (IF) of S. torquatus males and females. We found a larger prevalence of FOG compared with FG and SO fibres in the muscle of both sexes. We also found that males show larger areas of the three types of fibres, develop greater strength but also faster fatigue than females, suggesting that strength is a key functional feature that enables males to perform faster movements (but for shorter periods), associated with the demands of territoriality.

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.

Mitochondrial respiratory activity in porcine longissimus muscle fibers of different pig genetics in relation to their meat quality

The pig genetics of Duroc, Pietrain (MHS homozygote negative, PiNN), Pietrain (MHS homozygote positive, PiPP) and a F2-Duroc-Pietrain cross-breed were analyzed. The animals had comparable (P>0.05) carcass weights, but the PiPP pigs had higher carcass yield and lean meat values (P<0.05). Considering the meat quality characteristics, the PiPP showed a faster pH drop and higher electrical conductivity, drip loss, shear force as well as lightness and redness values (P<0.05). The PiPP animals had less slow-twitch-oxidative (STO) and more fast-twitch-glycolytic (FTG) muscle fibers, whereas the results of the Duroc animals were converse (P<0.05). The STO and FTG fibers of the PiPP animals were larger than those of the other genetics (P<0.05). The analysis of the mitochondrial respiratory activity (MRA) using permeabilized longissimus muscle fibers resulted in no differences between the pig genetics before and immediately after slaughter. During chilling the MRA decreased in all pigs but to a higher extent in the PiPP pigs (P<0.05).

Influence of acorn intake on blood lipid profile and longisimus muscle characteristics of Black Slavonian pig

The beneficial effect of acorn on blood lipid level could be linked with presence of both high tannin content (70.10 g/kg DM) and high amounts of unsaturated fatty acids (more than 80%) such as linoleic (43.38%), oleic (30.52%) and alpha linolenic (4.58%) acid. In this study the influence of ad libitum acorn intake on blood lipid profile and longissimus muscle (MLD) composition of Black Slavonian pig were investigated and compared with the effects of commercial corn based diet. Acorn consumption in last three weeks of fattening period had a decreasing effect on triglyceride and total cholesterol concentration in blood without adverse effect on liver function. Compared with the intake of corn based diet, the intake of acorn resulted in 11% (0.22 mmol/l) lower total cholesterol (P &lt; 0.05) concentration and 48% lower (0.20 mmol/l) triglycerides concentration (P &lt; 0.01). In addition, there was no observed statistically significant differences (P &gt; 0.05) among finishing diets for any histochemical characteristics, except for diameter of intermediate fast-twitch oxidative-glycolytic (FOG) fiber types (58.10 μm and 51.67 μm in acorn and corn based fed pigs, respectively; P &lt; 0.01). The trend toward lower proportion (10.80 vs. 12.36%) and smaller diameter (59.36 vs. 64.57%) of red slow-twitch oxidative (SO) fiber types (P &lt; 0.08) was observed in acorn than in corn-based fed pigs.

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.

An association between genotypes at the porcine loci &amp;lt;i&amp;gt;MSTN (GDF8)&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;CAST&amp;lt;/i&amp;gt; and microstructural characteristics of &amp;lt;i&amp;gt;m. longissimus lumborum&amp;lt;/i&amp;gt;: a preliminary study

Abstract. The aim of the study was to evaluate the association between the microstructure characteristics of longissimus lumborum (LL) muscle and the genotype at porcine loci MSTN and CAST. The study was carried out on 132 unrelated pigs – 93 crosses of Pietrain and (Polish Large White x Polish Landrace) and 39 Stamboek castrated males. Crosses Pi x (PLW x PL), with an equal proportion of castrated males (n=46) and females (n=47), were of genotype CC or CT at the locus RYR1, whereas Stamboek pigs were of genotype CC at this locus. The diameters of slow-twitch oxidative (STO), fast-twitch oxidative (FTO) and fast-twitch glycolytic (FTG) fibers, their per cent share in a bundle and number of fibers per 1 mm2 were determined. Moreover, the analyses covered the frequency of occurrence of pathological fibers, including giant and angular fibers. The parameters examined, characterising the microstructure of LL muscle, were not found to be related to the presence of the C→T polymorphism in exon 3 of the MSTN gene, identified by enzyme TaqI. However, it was shown that the diameters of the STO, FTO and FTG fibres in the LL muscle were significantly smallest in the Stamboek pigs with genotype FF at locus CAST compared to both the remaining genotypes. Among the crosses Pi x (PLW x PL) this genotype was not observed. The content of FTG fibres in a bundle proved to be related to the CAST genotype in Stamboek pigs. The frequency of pathological fibres in the LL muscle was the lowest in pigs with genotype EE at the locus CAST, but only in the case of the crosses Pi x (PLW x PL) was this relation statistically significant. The studies should be continued to determine whether such relations occur in other pig breeds. The frequency of pathological fibres affects meat quality and thus the polymorphism of the CAST gene could be of importance in selection.

Effect of iron bioavailability on muscle fibre types and on quality and oxidative stability of grain-fed veal

The bioavailability of dietary iron can be reduced by using a chelator in the ration. In order to characterise the effects of supplementing veal calf rations with three doses of EDTA (0, 5 or 15 mg EDTA mg-1 Fe in the ration) for 8 or 18 wk, histochemical characteristics of the longissimus thoracis (LT) muscle and meat colour, composition, quality and stability were evaluated. Meat pH, colour, drip loss, cooking loss and shear forces were measured after a keeping period of 0, 7 and 14 d at 4°C, while lipid stability (thiobarbituric acid reactive substances) was measured on thawed ground meat stored for 1, 3 and 5 d at 4°C. EDTA treatments had no effect on dissectible tissue composition of the 9–11th rib section (P &gt; 0.05) or on the chemical composition of the LT muscle (P &gt; 0.05). EDTA dose had a quadratic effect (P &lt; 0.05) on the proportion of slow-twitch, oxidative (SO) fibres and a negative, linear effect (P &lt; 0.01) on the proportion of fast-twitch, oxidoglycolytic (FOG) fibres in the LT. The chelator was effective in enhancing paleness of veal, particularly with long-term administration of the highest dose (P &lt; 0.05). This interaction, however, had a negative effect on shear force and also on oxidative stability of the meat during storage (P &lt; 0.05). Key words: Veal quality, EDTA, fibre type, oxidative stability, TBARS

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.

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.

Attenuation of insulin resistance by chronic β 2-adrenergic agonist treatment Possible muscle specific contributions

A possible mechanism by which chronic clenbuterol treatment causes multiple physiological changes in skeletal muscle that leads to reduced insulin resistance in the obese Zucker rat ( fa/ fa) was investigated. Animals were gavaged with clenbuterol (CB) (0.8 mg·kg −1·day −1), terbutaline (TB) (1.0 mg·kg −1·day −1), or control (CT) vehicle for six weeks. Oral glucose tolerance and insulin responses were markedly improved in CB rats and impaired in TB rats. CB treatment caused a 24–34% gain in muscle mass in all muscle fiber types, and increases in 3-O-methyglucose transport (2-fold) and GLUT4 concentration (57%) in fast twitch glycolytic (FG) muscle. Oxidative capacity was reduced in both FG (47%) and fast twitch oxidative (FO) muscle (30%), but not in slow twitch oxidative (SO) muscle. Null model analysis for receptor occlusion demonstrated that most functional β-adrenoceptors were lost in FO (82%) and FG (89%) fibers, but not in SO fibers. We propose that hypertrophy is the result of continuous direct activation of β-adrenoceptors while loss in oxidative capacity may be the result of receptor down regulation. Improvements in insulin resistance may have been due, in part, to both increases in lean body mass and specific adaptations in FG muscle.

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.

Morphometric and Histochemical Study of the Human Vocal Muscle

The present study was conducted on vocal muscles removed at autopsy from adult individuals (10 men and 8 women, ages ranging from 48 to 78 years) with no laryngeal disease. Histologic analysis was performed with hematoxylin and eosin staining, and histochemical analysis was performed by nicotinamide-adenine-dinucleotide tetrazolium reductase, succinate dehydrogenase, and acid and alkaline myofibrillar adenosine triphosphatase reactions. The histochemical reactions showed that the muscle consists of slow-twitch oxidative (SO), fast-twitch glycolytic (FG), and fast-twitch glycolytic oxidative (FOG) fibers distributed in mosaic form. The frequencies of SO, FOG, and FG fibers were 40.50%, 54.75%, and 4.75%, respectively. The higher frequency of SO and FOG oxidative fibers characterizes the muscle as having aerobic metabolism, resistance to fatigue, and fast contraction. The mean minimum diameters were 31.37 microm for SO fibers and 36.46 microm for FOG and FG fibers.