Effects of food restriction on stretch induced muscle hypertrophy in chickens of various ages

1. The patagialis muscle of three groups of different aged chickens was subjected to passive stretch by placing an inflexible sleeve over the left wing, and the right wing served as the control. 2. Food was removed from the animals 2 days prior to applying passive stretch. After 6 days of passive stretch on young 7-week-old animals, the stretched muscle was 200% larger than the control. 3. During the restriction, control muscle lost 69% of its weight and the stretched muscle maintained its original weight. 4. Changes in muscle DNA and hydroxyproline content were similar to changes in muscle weight but hydroxyproline content lagged changes in muscle weight. 5. Restricted 10-month-old chickens responded to passive stretch with an absolute increase in muscle mass which was accompanied by increases in protein, DNA and hydroxyproline content. 6. Muscle from the 28-month-old chickens did not respond to either 11 days of restriction or passive stretch. 7. The results of the present study indicate that as the chicken grows older, the ability of the muscle to respond to stimuli, stretch and/or starvation, is reduced.     

The influence of passive stretch on the growth and protein turnover of the denervated extensor digitorum longus muscle

At 7 days after cutting the sciatic nerve, the extensor digitorum longus muscle was smaller and contained less protein than its innervated control. Correlating with these changes was the finding of elevated rates of protein degradation (measured in vitro) in the denervated tissue. However, at this time, rates of protein synthesis (measured in vitro) and nucleic acid concentrations were also higher in the denervated tissue, changes more usually associated with an active muscle rather than a disused one. These anabolic trends have, at least in part, been explained by the possible greater exposure of the denervated extensor digitorum longus to passive stretch. When immobilized under a maintained influence of stretch the denervated muscle grew to a greater extent. Although this stretch-induced growth appeared to occur predominantly through a stimulation of protein synthesis, it was opposed by smaller increases in degradative rates. Nucleic acids increased at a similar rate to the increase in muscle mass when a continuous influence of stretch was imposed on the denervated tissue. In contrast, immobilization of the denervated extensor digitorum longus in a shortened unstretched state reversed most of the stretch-induced changes; that is, the muscle became even smaller, with protein synthesis decreasing to a greater extent than breakdown after the removal of passive stretch. The present investigation suggests that stretch will promote protein synthesis and hence growth of the extensor digitorum longus even in the absence of an intact nerve supply. However, some factor(s), in addition to passive stretch, must contribute to the anabolic trends in this denervated muscle.     

In vivo lipogenesis in genetically fat and lean chickens of various ages

Lipogenesis was studied in vivo in genetically fat and lean male chickens at 2, 5 and 15 weeks of age using tritiated water. At 2 and 5 weeks of age, the liver was the major site of de novo fatty acid synthesis rather than the carcass. Per 100 g of tissue lipogenesis was greater in the carcass at 15 weeks of age than at 2 or 5 weeks. Lipogenesis in the liver did not vary according to age. At 15 weeks of age there was no observable exaggeration in the degree of fattening (as in genetically obese rodents) of fat line chickens. The regulation of fattening in fat line chickens, at least at the onset of sexual maturity, appears to be different to that in genetically obese rodents.     

Body temperature during fasting in chickens of various ages and body weight

Chickens of different ages will be submitted to periods of non-eating of 2 to 10 days. The non-eating causes a constant lowering of the body temperature which, in the 10 days old chickens, is 4-5 times higher than in the 3 months old ages. To an higher diminishing of the temperature it corresponds an higher loss percentage of weight. In normal conditions the temperature tends to increase from morning to evening, while during the non-eating period it diminishes. With repeated non-eating periods the colling increases. The difference between young and old animals would depend on differences in quantity of their basal metabolism (lower in the old aged) and on the different availability of energetic material in reserve (higher percentage in the old aged).     

Akt signaling in skeletal muscle: regulation by exercise and passive stretch

Akt/protein kinase B is a serine/threonine kinase that has emerged as a critical signaling component for mediating numerous cellular responses. Contractile activity has recently been demonstrated to stimulate Akt signaling in skeletal muscle. Whether physiological exercise in vivo activates Akt is controversial, and the initiating factors that result in the stimulation of Akt during contractile activity are unknown. In the current study, we demonstrate that treadmill running exercise of rats using two different protocols (intermediate high or high-intensity exhaustive exercise) significantly increases Akt activity and phosphorylation in skeletal muscle composed of various fiber types. To determine if Akt activation during contractile activity is triggered by mechanical forces applied to the skeletal muscle, isolated skeletal muscles were incubated and passively stretched. Passive stretch for 10 min significantly increased Akt activity (2-fold) in the fast-twitch extensor digitorum longus (EDL) muscle. However, stretch had no effect on Akt in the slow-twitch soleus muscle, although there was a robust phosphorylation of the stress-activated protein kinase p38. Similar to contraction, stretch-induced Akt activation in the EDL was fully inhibited in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas glycogen synthase kinase-3 (GSK3) phosphorylation was only partially inhibited. Stretch did not cause dephosphorylation of glycogen synthase on GSK3-targeted sites in the absence or presence of wortmannin. We conclude that physiological exercise in vivo activates Akt in multiple skeletal muscle fiber types and that mechanical tension may be a part of the mechanism by which contraction activates Akt in fast-twitch muscles.     

Respiration and lactate production in isolated frog skeletal muscle: effects of passive stretch

The effects of varying degrees of passive stretch on in vitro oxygen consumption and intracellular lactate efflux have been investigated in paired recti abdomini muscles from small male frogs. Oxygen consumption [mm3 (STP)/mg (dry wt)/hr] was found to be linearly related to load (r = 0.98), increasing from 1.57 +/- 0.11 (SE) at 2 g to 2.30 +/- 0.18 at 10 g, 2.89 +/- 0.16 at 20 g and 3.26 +/- 0.21 at 30 g. Lactate released into the medium [microM/g (dry wt)/hr] was inversely related to load (r = -0.52), increasing initially from 36.84 +/- 3.28 (SE) at 2 g to 108.55 +/- 12.9 at 10 g, then abruptly decreasing with additional loading (18.10 +/- 2.60 at 20 g and 11.71 +/- 2.80 at 30 g). Results suggest that as stretch-related oxidative energy metabolism increases, there is a lessening dependence on anaerobic energy-yielding processes.     

Lipase and alpha amylase of chick embryo pancreas and of chickens of various ages]

In chicken embryo pancreas on the 19th day the activity of alpha-amylase and especially of lipase is very low; it increases soon after until it reaches its highest level in 36 hours old chick. Then it falls considerably on the 2nd and 10th day of normal diet; finally it starts again: in fact in three months old chickens the activity of alpha-amylase is equal to thirty-six hours old chick's, while lipase's is lower than this last one.     

Glycogen utilization in isolated frog muscle: an effect of passive mechanical stretch

The effect of passive mechanical stretch on glycogen utilization and total protein maintenance in paired sartorii muscles from small male frogs has been investigated, in vitro. Glycogen content of stretched muscles decreased 72.6% over a 24-hr incubation period, compared to a 23.1% decline in unstretched control muscles. Stretched muscles retained 54.7% of their total protein content over a 24-hr period, compared to 38.4% in the unstretched control muscles. Unstretched muscles demonstrated a significant (11.1%) increase in wet weight following 24 hr of incubation, presumably due to increased water retention. There were no significant changes in the wet wts of stretched muscles.     

Effects of dietary fat source and subtherapeutic levels of antibiotic on the bacterial community in the ileum of broiler chickens at various ages

The effect of dietary fat source (soy oil or a mixture of lard and tallow) and dietary supplementation with antibiotics (a combination of avilamycin at 10 mg kg of feed(-1) and salinomycin at 40 mg kg of feed(-1)) on the bacterial community in the ileum of broiler chickens at different ages (7, 14, 21, and 35 days) was studied using PCR with denaturing gradient gel electrophoresis (DGGE) analysis and bacteriological culture. The bacterial origin of fragments in DGGE profiles was identified by sequencing. Bacterial enumeration results, together with PCR-DGGE profiles, showed that the composition of the microflora was age dependent and influenced by dietary fat source and antibiotic supplementation. An increased incidence of streptococci, enterobacteria, and Clostridium perfringens with age of the chickens was demonstrated. Lactobacilli and C. perfringens were the bacterial groups most strongly affected by the dietary treatments. Moreover, different strains (clonal variants of the alpha-toxin gene) of C. perfringens type A were detected in response to age, dietary fat source, and dietary supplementation with antibiotics.     

Effects of serum from human subjects of various ages on proliferation of human lung and skin fibroblasts

We carried out a study to determine whether serum from old human subjects inhibited cell proliferation. The results showed that serum from old subjects of either sex did not greatly inhibit the proliferation of human fetal lung fibroblast TIG-1 cells, even when serum from subjects in their 80s was used. The same results were obtained when the effects of serum on cell proliferation were examined up to a serum concentration of 50%. It was also found that serum from old subjects did not inhibit proliferation of human skin fibroblasts from a young adult to any greater degree than serum from young adult subjects, and that serum from young adult subjects did not stimulate proliferation of skin fibroblasts from an elderly donor to any greater degree than serum from old subjects.     

The contribution of muscle progenitor cells to maintaining morphological characteristics of unweighted rat soleus muscle during passive stretch

Skeletal muscle work hypertrophy is usually connected with muscle progenitor SC (satellite cells) activation with subsequent incorporation their nuclei into myofibers. Passive stretch of unloaded muscle was earlier established to prevent atrophic processes and be accompanied by enhanced protein synthesis. We hypothesized that elimination of SC proliferation capacity by gamma-irradiation would partly preavent stretched muscle fiber capability to maintain their size under condition of gravitational unloading. To assess the role of muscle progenitor (satellite) cells in development of passive stretch preventive effect SC proliferation was suppressed by local exposure to ionizing radiation (2500 Rad) and then subsequent hindlimb suspension or hindlimb suspension with concomitant passive stretch were carried out. Reduction of myofiber cross-sectional area and decrease in myo-nuclei number accompanying unloaded muscle atrophy were completely abolished by passive stretch both in irradiated and sham-treated animals. We concluded that satellite cells did not make essential contribution to passive stretch preventive action under condition of simulated weightlessness.     

Effects of a single session of prolonged muscle stretch on spastic muscle of stroke patients

The control of spasticity is often a significant problem in the management of patients with spasticity. The aim of this study was to evaluate the effect of a single session of prolonged muscle stretch (PMS) on the spastic muscle. Seventeen patients with spastic hemiplegia were selected to receive treatment. Subjects underwent PMS of the triceps surae (TS) by standing with the feet dorsiflexed on a tilt-table for 30 minutes. Our test battery consisted of four measurements including the modified Ashworth scale of the TS, the passive range of motion (ROM) of ankle dorsiflexion, the H/M ratio of the TS, and the F/M ratio of the tibialis anterior (TA). The results indicated that the passive ROM of ankle dorsiflexion increased significantly (p < 0.05) compared to that before PMS treatment. Additionally, PMS reduced motor neuron excitability of the TS and significantly increased that of the TA (p < 0.05). These results suggest that 30 minutes of PMS is effective in reducing motor neuron excitability of the TS in spastic hemiplegia, thus providing a safe and economical method for treating stroke patients.     

Enhanced stretch reflex excitability in the soleus muscle during passive standing posture in humans

The purpose of this study was to test whether the spinal reflex excitability of the soleus muscle is modulated as posture changes from a supine to a passive upright position. Eight healthy subjects (29.6 ± 5.4 yrs) participated in this study. Stretch and H-reflex responses were elicited while the subjects maintained passive standing (ST) and supine (SP) postures. The passive standing posture was accomplished by using a gait orthosis to which a custom-made device was mounted to elicit stretch reflex in the soleus muscle. This orthosis makes it possible to elicit stretch and H-reflexes without background muscle activity in the soleus muscle. The results revealed that the H-reflex amplitude in the ST was smaller than that in the SP condition, which is in good agreement with previous reports. On the other hand, the stretch reflex was significantly larger in the ST than in the SP condition. Since the experimental conditions of both the stretch and H-reflex measurements were exactly the same, the results were attributed to differences in the underlying neural mechanisms of the two reflex systems: different sensitivity of the presynaptic inhibition onto the spinal motoneuron pool and/or a change in the muscle spindle sensitivity.     

Mechanical stretch stimulates growth of vascular smooth muscle cells via epidermal growth factor receptor

We have studied whether activation of epidermal growth factor receptor (EGFR) is involved in stretch-induced extracellular signal-regulated kinase 1/2 (ERK1/2) activation and protein synthesis in cultured rat vascular smooth muscle cells (VSMC). Cyclic stretch (1 Hz) induced a rapid (within 5 min) phosphorylation of ERK1/2, an effect that was time and strength dependent and inhibited by an EGFR kinase inhibitor (AG-1478) but not by a platelet-derived growth factor receptor kinase inhibitor (AG-1296). The stretch rapidly (within 2 min) induced tyrosine phosphorylation of several proteins, among which 180-kDa protein was shown to be EGFR as revealed by blockade with AG-1478 as well as immunoprecipitation with anti-EGFR antibody coupled with immunoblotting with anti-phosphotyrosine antibody. The stretch rapidly (within 2 min) induced association of tyrosine-phosphorylated EGFR with adaptor proteins (Shc/Grb2) as revealed by coprecipitation with glutathione-S-transferase-Grb2 fusion protein coupled with immunoblotting with anti-phosphotyrosine, anti-EGFR, and anti-Shc antibodies. Transfection of a dominant-negative mutant of H-Ras also inhibited stretch-induced ERK1/2 activation. Treatment with a stretch-activated ion channel blocker (Gd(3+)) and an intracellular Ca(2+) antagonist (TMB-8) inhibited stretch-induced phosphorylation of EGFR and ERK1/2. Treatment with AG-1478 and a mitogen-activated protein kinase kinase inhibitor (PD-98059), but not AG-1296, blocked [(3)H]leucine uptake stimulated by a high level of stretch. These data suggest that ERK1/2 activation by mechanical stretch requires Ca(2+)-sensitive EGFR activation mainly via stretch-activated ion channels, thereby leading to VSMC growth.     

Effects of chronic heat exposure and protein intake on growth performance, nitrogen retention and muscle development in broiler chickens

The respective effects of ambient temperature, dietary crude protein and feed intake were investigated in finishing chickens and the consequence of protein supplementation under high temperature conditions was analysed in particular. Heat-related reduction in growth was associated with decreased nitrogen retention (-30 or -35% according to the diet), which could not be explained by the observed lower feed intake alone. Tissue samples performed in 5- to 6-week-old chicks showed varying effects of heat according to the muscles studied: at 32 degrees C, the proportion of Pectoralis major muscle (in percentage of body weight) appeared slightly reduced (reduction lower than 10%), whereas the proportion of two leg muscles were increased (+10 to +15% for the Sartorius muscle; +5% for the gastrocnemius muscle). At 32 degrees C, providing a high protein diet significantly (P < 0.05) increased weight gain and feed efficiency, and slightly improved whole body protein deposition.     

Effect of passive stretch on intracellular nitric oxide and superoxide activities in single skeletal muscle fibres: influence of ageing

Skeletal muscle is repeatedly exposed to passive stretches due to the activation of antagonist muscles and to external forces. Stretch has multiple effects on muscle mass and function, but the initiating mechanisms and intracellular signals that modulate those processes are not well understood. Mechanical stretch applied to some cell types induces production of reactive oxygen species (ROS) and nitric oxide that modulate various cellular signalling pathways. The aim of this study was to assess whether intracellular activities of ROS and nitric oxide were modulated by passive stretches applied to single mature muscle fibres isolated from young and old mice. We developed a novel approach to apply passive stretch to single mature fibres from the flexor digitorum brevis muscle in culture and to monitor the activities of ROS and nitric oxide in situ by fluorescence microscopy. Passive stretch applied to single skeletal muscle fibres from young mice induced an increase in dihydroethidium oxidation (reflecting intracellular superoxide) with no increase in intracellular DAF-FM oxidation (reflecting nitric oxide activity) or CM-DCFH oxidation. In contrast, in fibres isolated from muscles of old mice passive stretch was found to induce an increase in intracellular nitric oxide activities with no change in DHE oxidation.     

Role of muscle progenitor cells in maintaining morphological characteristics of rat soleus muscle during gravitational unloading by means of passive stretch

Working hypertrophy of skeletal muscle is usually coupled with activation of satellite cells with subsequent incorporation of their nuclei into muscle fibers. Earlier, it has been repeatedly shown that muscle stretching prevents the development of atrophic alterations and is accompanied by an intensification of protein synthesis. We suggested that the elimination of the proliferative abilities of progenitor cells by γ-irradiation would lead to a partial loss of the ability of muscle fibers to maintain their size. To evaluate the role of progenitor cells in the development of the preventive effect of passive stretching, an experiment was carried out with the 2500 rad local irradiation of a rat shin and subsequent hind-limb suspension or hind-limb suspension with stretch. Passive stretching during hind-limb suspension completely prevented atrophy, the transformation of fibers, and a decrease in the myonuclear number observed in the hind-limb-suspension group. Irradiation produced no action of the preventive effect of passive stretch. The conclusion is made that passive stretch preventive action is also realized in the absence of proliferating satellite cells.