Effect of Exercise on Tissue Protein Synthesis in Rats

The effect of exercise on the protein metabolism in skeletal muscles (gastrocnemius and soleus), liver and small intestine was investigated in rats. Treadmill treatment for 7 d resulted in atrophy of the liver and small intestine, which was associated with a reduction in protein content. The rates of protein synthesis in the liver and small intestine were significantly suppressed in rats subjected to exercise. The change in protein synthesis in the visceral organs was mediated by the change in RNA activity (protein synthesis per unit RNA) but not by the change in RNA concentration. The tissue weight and the rate of protein synthesis in the gastrocnemius and soleus muscles were not affected by exercise. The results suggest that these changes in protein synthesis in the liver and small intestine may explain, at least partly, the atrophy of these organs which was observed after 7 d of exercise.     

Protein turnover measured in vivo and in vitro in muscles undergoing compensatory growth and subsequent denervation atrophy.

The rapid growth (1-6 days) of the functionally overloaded soleus muscle, in response to tenotomy of the synergist gastrocnemius, was found to correlate with increases in both the protein synthetic and degradative rates, the change in the former being greater than that of the latter. These conclusions were drawn from two different methods used to measure (in vivo and in vitro) the average rates of protein synthesis and protein breakdown in these soleus muscles. Although the basal rates of synthesis were higher when measured in vivo, and the degradative rates higher in isolated muscle preparations incubated in vitro, both methods gave good agreement concerning the changes in protein turnover induced by tenotomy of the gastrocnemius. The possible involvement of passive stretch in inducing this additional growth is discussed. As an antagonist to the soleus, growth of the extensor digitorum longus muscle was decreased under the same conditions, presumably because of less usage. At 3 days after the cutting of the sciatic nerve, the previously normal or overloaded soleus muscles underwent rapid atrophy. Although in both cases RNA and protein were lost, while protein synthesis decreased and protein breakdown increased, denervation induced larger changes within these parameters of the formerly overloaded muscle. The slowing of growth in the tenotomized gastrocnemius, and its subsequent rapid atrophy after additional denervation, were explained by large increases in protein breakdown, with little or no change in the synthetic rate.     

Protein synthesis in skeletal muscle of the perfused rat hemicorpus compared with rates in the intact animal.

The rate of protein synthesis was measured in muscles of the perfused rat hemicorpus, and values were compared with rates obtained in whole animals. In gastrocnemius muscle of fed rats the rate of synthesis measured in the hemicorpus was the same as that in the whole animal. However, in plantaris, quadriceps and soleus muscles rates were higher in the hemicorpus than those in vivo. In the hemicorpus, starvation for 1 day decreased the rate of protein synthesis in gastrocnemius and plantaris muscles, in parallel with decreases in the RNA content, but the soleus remained unaffected. Similar effects of starvation were observed in vivo, so that the relationships between rates in vivo and in the hemicorpus were the same as those in fed rats. Proteins of quadriceps and plantaris muscles were separated into sarcoplasmic and myofibrillar fractions. The rate of synthesis in the sarcoplasmic fraction of the hemicorpus from fed rats was similar to that in vivo, but synthesis in the myofibrillar fraction was greater. In the plantaris of starved rats the rates of synthesis in both fractions were lower, but the relationships between rates measured in vivo and in the perfused hemicorpus were similar to those seen in fed rats. The addition of insulin to the perfusate of the hemicorpus prepared from 1-day-starved animals increased the rates of protein synthesis per unit of RNA in gastrocnemius and plantaris muscles to values above those seen in fed animals when measured in vivo or in the hemicorpus. Insulin had no effect on the soleus. Overall, the rates of protein synthesis in the hemicorpus differed from those in vivo. However, the effect of starvation when measured in the whole animal was very similar to that measured in the isolated rat hemicorpus when insulin was omitted from the perfusate.     

Hindlimb unloading-induced muscle atrophy and loss of function: protective effect of isometric exercise.

The primary objective of this study was to determine the effectiveness of isometric exercise (IE) as a countermeasure to hindlimb unloading (HU)-induced atrophy of the slow (soleus) and fast (plantaris and gastrocnemius) muscles. Rats were assigned to either weight-bearing control, 7-day HU (H7), H7 plus IE (I7), 14-day HU (H14), or H14 plus IE (I14) groups. IE consisted of ten 5-s maximal isometric contractions separated by 90 s, administered three times daily. Contractile properties of the soleus and plantaris muscles were measured in situ. The IE attenuated the HU-induced decline in the mass and fiber diameter of the slow-twitch soleus muscle, whereas the gastrocnemius and plantaris mass were not protected. These results are consistent with the mean electromyograph recordings during IE that indicated preferential recruitment of the soleus over the gastrocnemius and plantaris muscles. Functionally, the IE significantly protected the soleus from the HU-induced decline in peak isometric force (I14, 1.49 +/- 0.12 vs. H14, 1.15 +/- 0.07 N) and peak power (I14, 163 +/- 17 vs. H14, 75 +/- 11 mN.fiber length.s-1). The exercise protocol showed protection of the plantaris peak isometric force at H7 but not H14. The IE also prevented the HU-induced decline in the soleus isometric contraction time, which allowed the muscle to produce greater tension at physiological motoneuron firing frequencies. In summary, IE resulted in greater protection from HU-induced atrophy in the slow soleus than in the fast gastrocnemius or plantaris.     

Dose response of protein turnover in rat skeletal muscle to triiodothyronine treatment

Skeletal muscle protein turnover has been examined in thyroidectomized rats treated with 0, 0.3, 0.75, 2, 20 and 100 micrograms triidothyronine/day for 7 days by implanted osmotic minipump. Protein synthesis in gastrocnemius, plantaris and soleus muscle were measured in vivo by the constant infusion method and protein degradation estimated as the difference between gross and net rates of synthesis. Serum levels of triidothyronine (T3) and insulin were also measured in addition to oxygen consumption rates in some cases. Compared with untreated intact rats muscle growth rates were unchanged at 0.3, 0.75 and 2 micrograms T3/day and, judging by plasma T3 levels, 0.75 microgram T3/day was a replacement dose. Slowing of growth was evident in the untreated thyroidectomized rats mid-way through the 7 day experimental period (6-7 days after throidectomy). High doses of T3 (20 and 100 micrograms/day) promptly supressed growth but there was subsequent recovery. Protein synthesis and degradation were generally lower in the hypothyroid state and normal or elevated in the hyperthyroid state. The changes in protein synthesis were mediated by changes in both RNA concentration and RNA activity (protein synthesis per unit RNA). Gastrocnemius and plantaris muscles were most responsive in the hypothyroid range. Since protein synthesis is particularly depressed in these muscles in malnutrition, the fall in protein degradation induced by the lowered thyroid status in this condition will be an important adaptive response to conserve protein. The increased protein turnover in the hyperthyroid rats was most marked in the soleus muscle and it is argued that this is necessary to allow the changes in protein composition and metabolic character which occur in response to hyperthyroidism in this muscle.     

The effects of surgical stress and short-term fasting on protein synthesis in vivo in diverse tissues of the mature rat.

1. We measured fractional rates of protein synthesis, capacities for protein synthesis (i.e. RNA/protein ratio) and efficiencies of protein synthesis (i.e. protein-synthesis rate relative to RNA content) in fasted (24 or 48 h) or fasted/surgically stressed female adult rats. 2. Of the 15 tissues studied, fasting caused decreases in protein content in the liver, gastrointestinal tract, heart, spleen and tibia. There was no detectable decrease in the protein content of the skeletal muscles studied. 3. Fractional rates of synthesis were not uniformly decreased by fasting. Rates in striated muscles, uterus, liver, spleen and tibia were consistently decreased, but decreases in other tissues (lung, gastrointestinal tract, kidney or brain) were inconsistent or not detectable, suggesting that, in many tissues in the mature rat, protein synthesis was not especially sensitive to fasting. 4. In fasting, the decreases in fractional synthesis rate resulted from changes in efficiency (liver and tibia) or from changes in efficiency and capacity (heart, diaphragm, plantaris and gastrocnemius). In the soleus, the main change was a decrease in capacity. 5. Surgical stress increased fractional rates of protein synthesis in diaphragm (where there were increases in both efficiency and capacity) by about 50%, in liver by about 20%, in spleen by about 40%, and possibly also in the heart. In liver and spleen, capacities were increased. In other tissues (including the skeletal muscles), the fractional rates of protein synthesis were unaffected by surgical stress.     

AMP-activated protein kinase activation prevents denervation-induced decline in gastrocnemius GLUT-4.

This study was designed to determine whether the reductions in GLUT-4 seen in 3-day-denervated muscles can be prevented through chemical activation of 5'-AMP-activated protein kinase (AMPK). Muscle AMPK can be chemically activated in rats using subcutaneous injections with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). In this study, the tibial nerve was sectioned on one side; the other was sham operated but without nerve section. Acute injections of AICAR resulted in significantly increased AMPK activity in denervated gastrocnemius but not soleus muscles. Acetyl-CoA carboxylase activity, a reporter of AMPK activation, declined in both gastrocnemius and soleus in both denervated and contralateral muscles. Three days after denervation, GLUT-4 levels were significantly decreased by approximately 40% in gastrocnemius muscles and by approximately 30% in soleus muscles. When rats were injected with AICAR (1 mg/g body wt) for 3 days, the decline in GLUT-4 levels was prevented in denervated gastrocnemius muscles but not in denervated soleus muscles. The extent of denervation-induced muscle atrophy was similar in AICAR-treated vs. saline-treated rats. These studies provide evidence that some effects of denervation may be prevented by chemical activation of the appropriate signaling pathways.     

Effects of chronic exercise during aging on muscle and end-plate morphology in rats

Terminal sprouting, myofiber atrophy, and fiber type changes were studied in soleus and distal gastrocnemius muscles of 21- and 26-mo-old rats and in rats who performed treadmill running from 21 to 26 mo. End-plate structure and muscle fiber types were demonstrated by staining for acetylcholinesterase and myosin ATPase activity. Terminal sprouting was expressed as the percentage of end plates with growth configurations. Fiber atrophy was assessed as percentage of small-diameter fibers. In all three groups, the percentage of small-diameter fibers was significantly smaller and the percentage of growth configurations significantly larger in the soleus than in the gastrocnemius. The exercised-soleus group had a significantly higher percentage of growth configurations than the 26-mo controls, which had a higher percentage than the 21-mo controls. Percentages among gastrocnemius groups were not different. Fiber type was similar among gastrocnemius groups. However, the exercised-soleus had significantly more slow-twitch fibers than the controls. These data suggest that the soleus responds differently to chronic exercise during aging than does the gastrocnemius.     

Glycogen concentrations and endurance capacity of rats with chronic heart failure

The endurance capacities of rats with myocardial infarctions (MI) and of rats having undergone sham operations (SHAM) were tested during a submaximal exercise regimen that consisted of swimming to exhaustion. During this test, a decrement in the endurance capacity of the MI rat was demonstrated as the SHAM rat swam 25% longer than the MI rat (65 +/- 4 vs. 52 +/- 4 min). Glycogen concentrations were measured in the liver and the white gastrocnemius, plantaris, and soleus muscles of SHAM and MI rats that were randomly divided into four subgroups, which consisted of resting control, swim to exhaustion, swim to exhaustion + 24 h recovery, and swim to exhaustion + 24 h recovery + a second swim to exhaustion. The results demonstrated that the glycogen concentrations found in the liver, white gastrocnemius, plantaris, and soleus muscles of the SHAM and MI rats belonging to the resting control groups were similar. After swimming to exhaustion the glycogen concentrations in these tissues were significantly reduced compared with those found in the resting control groups of rats, and after 24 h of recovery the glycogen concentrations in these tissues were again similar to those found in the resting control groups of rats. Since the magnitude of the glycogen depletion in the liver and the white gastrocnemius, plantaris, and soleus muscles was similar in the SHAM and MI rats and because the SHAM rats consistently swam for longer periods of time in each of the experimental groups, it would be logical to assume that the rates of glycogen utilization for the various tissues may have been greater in the MI rat during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)     

Beneficial effects of melatonin on stroke-induced muscle atrophy in focal cerebral ischemic rats

MUSCLE ATROPHY IS THE RESULT OF TWO OPPOSING CONDITIONS THAT CAN BE FOUND IN PATHOLOGICAL OR DISEASED MUSCLES: an imbalance in protein synthesis and degradation mechanisms. Thus, we investigated whether exogenous melatonin could regulate muscle components in stroke-induced muscle atrophy in rats. Comparing muscle phenotypes, we found that long-term melatonin administration could influence muscle mass. Muscle atrophy-related genes, including muscle atrophy F-box (MAFbx) and muscle ring finger 1 (MuRF1) were significantly down-regulated in melatonin-administered rats in the gastrocnemius. However, only MAFbx at the mRNA level was attenuated in the soleus of melatonin-administered rats. Insulin-like growth factor-1 receptor (IGF-1R) was significantly over-expressed in melatonin-administered rats in both the gastrocnemius and soleus muscles. Comparing myosin heavy chain (MHC) components, in the gastrocnemius, expression of both slow- and fast-type isoforms were significantly enhanced in melatonin-administered rats. These results suggest that long-term exogenous melatonin-administration may have a prophylactic effect on muscle atrophy through the MuRF1/MAFbx signaling pathway, as well as a potential therapeutic effect on muscle atrophy through the IGF-1-mediated hypertrophic signaling pathway in a stroke animal model.     

Skeletal muscle IGF-binding protein-3 and -5 expressions are age,muscle, and load dependent

The purpose of the current study was to examine IGFBP-3, -4, and -5 mRNA and protein expression levels as a function of muscle type, age, and regrowth from an immobilization-induced atrophy in Fischer 344 x Brown Norway rats. IGFBP-3 mRNA expression in the 4-mo-old animals was significantly higher in the red and white portions of the gastrocnemius muscle compared with the soleus muscle. However, there were no significant differences in IGFBP-3 mRNA expression among any of the muscle groups in the 30-mo-old animals. There were no significant differences in IGFBP-5 mRNA expression in any of the muscle groups, whereas in the 30-mo-old animals there was significantly less IGFBP-5 mRNA expression in the white gastrocnemius compared with the red gastrocnemius muscles. Although IGFBP-3 and -5 proteins were detected in the type I soleus muscle with Western blot analyses, no detection was observed in the type II red and white portions of the gastrocnemius muscle. Aging from adult (18 mo) to old animals (30 mo) was associated with decreases in IGFBP-3 mRNA and protein and IGFBP-5 protein only in the soleus muscle. After 10 days of recovery from 10 days of hindlimb immobilization, IGFBP-3 mRNA and protein increased in soleus muscles from young (4-mo) rats; however, only IGFBP-3 protein increased in the old (30-mo) rats. Whereas there were no changes in IGFBP-5 mRNA expression during recovery, IGFBP-5 protein in the 10-day-recovery soleus muscle did increase in the young, but not in the old, rats. Because one of the functions of IGFBPs is to modulate IGF-I action on muscle size and phenotype, it is hypothesized that IGFBP-3 and -5 proteins may have potential modulatory roles in type I fiber-dominated muscles, aging, and regrowth from atrophy.     

Dietary conjugated linoleic acid has limited effects on tissue protein anabolism in sedentary and exercising adult rats

The effects of conjugated linoleic acid isomers (CLA) and endurance training on lean body mass are expected to result from their action on tissue protein metabolism. The aim of this study was to analyze their effects on protein metabolism in 2 muscles, the small intestine and liver of adult rats. Four-month-old male Wistar rats were fed diets containing either no CLA, cis-9, trans-11 CLA isomer (1 g.100 g(-1)), trans-10, cis-12 CLA isomer (1 g.100 g(-1)) or both isomers (1 g.100 g(-1) each) for 6 weeks. Half of the rats were subjected to endurance training by running on a treadmill. At the end of this period, the rats were injected with a flooding dose of (13)C-valine to determine protein synthesis rates in the post-absorptive (experiment 1) and in the post-prandial (experiment 2) states. No effect of CLA or endurance training were detected in the small intestine. Training reduced food intake and protein synthesis rates in the liver but no effect was found on the protein synthesis rates in muscles. In the post-absorptive state, protein synthesis rate was increased by feeding the trans-10, cis-12 CLA isomer alone in the liver (+9%) or in combination with the cis-9, trans-11 isomer in the gastrocnemius (+30%), mostly in sedentary rats. In the post-prandial state, the cis-9, trans-11 CLA isomer tended to reduce the protein synthesis rate in the gastrocnemius muscle. However, no effect of CLA was found on muscle protein amounts. In conclusion, CLA isomers would have limited but differential effects on tissue protein metabolism in adult rats.     

Differential effect of lentil feeding on proteosynthesis rates in the large intestine, liver and muscle of rats

The aim of this work was to test the hypothesis that the trophic effect of lentil feeding on large intestine results from a stimulation of protein synthesis and to determine whether it interferes with protein metabolism in other splanchnic or peripheral organs. Two groups of growing Sprague Dawley male rats were pair-fed iso-caloric iso-nitrogenous balanced diets containing either cooked lentils (Lens esculenta puyensis) or casein as unique protein source. Protein synthesis rates were measured in vivo, in large intestine, liver and gastrocnemius at the postprandial state. In large intestine, protein and ribonucleic acid contents were higher in the lentil-fed group than in the control group, and the amount of proteins synthesized was also higher (+57%). By contrast, liver protein and ribonucleic acid contents as well as protein synthesis rates were significantly lower in the lentil-fed group than in the control group. In the gastrocnemius muscle protein and ribonucleic acid contents were significantly lower and the amount of protein synthesized was also lower (-18%) in the lentil fed group than in the control group. This study suggests that stimulation of protein synthesis in the large intestine is compensated for by a decrease in liver and muscle.     

Adaptive response of hypertrophied skeletal muscle to endurance training

The response of hypertrophied soleus and plantaris muscle of rats to endurance training was studied. Hypertrophy was produced by bilateral extirpation of the gastrocnemius muscle. A 13-wk training program of treadmill running initiated 30 days after removal of the gastrocnemius muscle accentuated (P less than 0.01) the hypertrophy. Succinate dehydrogenase activities of the enlarged muscles of sedentary rats were similar to those of normal animals, as were the increases associated with training. Phosphorylase and hexokinase activities were unaltered as a result of the experimental perturbations. Rates of glycogen depletion during exercise were lower (P less than 0.01) in the liver and soleus and plantaris muscles of endurance-trained animals. No difference existed in the rate of glycogen depletion of normal and hypertrophied muscle within the sedentary or trained groups. These data demonstrate that extensively hypertrophied muscle responds to training and exercise in a manner similar to that of normal muscle.     

Effects of aging and denervation on the expression of uncoupling proteins in slow- and fast-twitch muscles of rats

We investigated the effects of aging and denervation on the gene expression of uncoupling proteins (UCPs) in slow-twitch soleus and fast-twitch gastrocnemius muscles. In a comparison between the control limbs of 6- and 24-month-old rats, the mRNA levels of UCP3, heart-type fatty acid binding protein (HFABP), and glucose transporter-4 (GLUT4) were considerably lower in the gastrocnemius muscles of the older rats, whereas no significant differences in the mRNA levels of those genes as well as UCP2 and cytochrome oxidase subunit IV (COX-IV) were observed in the soleus muscles of young and old rats. The UCP3 and COX-IV protein levels were also reduced considerably in the aged gastrocnemius muscles with atrophy. Denervation of the sciatic nerve caused an increase in UCP3 mRNA levels in both muscles, but the regulation of other genes contrasted between the two types of skeletal muscles. In spite of the increased mRNA level, a remarkable reduction in UCP3 protein was found in the denervated gastrocnemius muscles. These results indicate that the effects of aging and denervation on the gene expression of UCPs, HFABP, GLUT4, and COX-IV are different between the muscle types. The reduction in the mitochondrial UCP3 and COX proteins in aged fast-twitch muscles may have a negative effect on energy metabolism and thermogenesis in old animals.     

Effect of acute exercise on the content of free sphinganine and sphingosine in different skeletal muscle types of the rat.

It has previously been shown that prolonged exercise of moderate intensity reduces the content of ceramide in each type of skeletal muscle. This was accompanied by a reduction in the activity of neutral, Mg++-dependent sphingomyelinase (the major enzyme responsible for ceramide formation from sphingomyelin) in the soleus and red gastrocnemius, but not in the white gastrocnemius (A. Dobrzyń and J. Górski, Am. J. Physiol.: Endorcinol. Metab. 282: E277 - E285, 2002). No other data on regulation of ceramide metabolism in contracting muscles are available. The aim of the present study was to examine the content of sphinganine (a key precursor of ceramide on the de novo synthesis route) and the content of sphingosine (the main product of ceramide catabolism) in different skeletal muscle types after two kinds of acute exercise. The experiments were carried out on 30 male Wistar rats, 250 - 280 g of body weight. The rats were divided equally into three groups: 1 - control, 2 - run until exhaustion (1200 m/h, +10 degree incline), 3 - a group in which the sciatic nerve was stimulated 10 min with tetanic pulses (60 pulses/min). Samples were taken of the soleus and of the red and white section of the gastrocnemius. These muscles are composed mostly of the slow-twitch oxidative, fast-twitch oxidative-glycolytic and fast-twitch glycolytic fibers, respectively. Lipids were extracted with chloroform/methanol. Sphinganine and sphingosine were quantified by high-performance liquid chromatography. At rest, the content of sphinganine in the soleus was higher than in the red gastrocnemius (p < 0.05), and in the latter, it was higher than in the white gastrocnemius (p < 0.01). Prolonged exercise increased the content of sphinganine approximately 6-fold in each muscle. The resting content of sphingosine in the soleus and in the red gastrocnemius was similar--higher than in the white gastrocnemius (p < 0.001 and p < 0.01, respectively). The content of sphingosine increased over 3-fold in the soleus and nearly 2-fold in the red and white sections of the gastrocnemius. Stimulation of the sciatic nerve increased the content of both compounds approximately 2-fold in each muscle. We conclude that acute exercise increases both de novo synthesis and catabolism of ceramide in skeletal muscles. Accumulation of sphingosine in contracting muscles may contribute to the development of fatigue.     

Experimental investigations on hypokinesis of skeletal muscles with different function. IV. Changes in the sarcoplasmic proteins

The changes in the sarcoplasmic proteins of the m. gastrocnemius and m. soleus were examined by biochemical methods on the 5th, 7th, 14th and 28th days after plaster cast immobilization of the right hind limbs of adult rabbits. During 4 weeks the soluble/myofibrillar protein ratio increased from 0.47 to 0.75 in the m. gastrocnemius, and to 0.85 in the m. soleus. Evaluation of the relative quantities of the components identified after gel-electrophoresis separation led to the following results: (1) There was no, or no appreciable change in the glyceraldehyde-3-phosphate dehydrogenase, creatine kinase and enolase activities. (2) The enzymes lactate dehydrogenase, aldolase and the glycogenolytic enzymes showed a relative decrease in both muscles. (3) Phosphoglycerate kinase, phosphoglucose isomerase and pyruvate kinase increased in both muscles. (4) Changes of opposite directions were exhibited by myoglobin, myokinase and F-protein. These results provide new data on the biochemical characterization of these functionally different muscles, and on the mechanism of disuse atrophy.     

Changes in protein turnover in hypertrophying plantaris muscles of rats: effect of fenbufen--an inhibitor of prostaglandin synthesis

Plantaris muscle of the right hind limb of rats was subjected to hypertrophic stimulus by section of the tendons of the right gastrocnemius muscle. The RNA and protein content and the fractional rate of protein synthesis were elevated both 3 and 7 days after operation compared both with the unoperated left limb and with sham-operated control rats. The rate of protein degradation, calculated from the difference between the fractional rates of protein synthesis and protein gain of the muscles, was elevated in the plantaris 3-7 days after tenotomy. Dietary administration of the drug fenbufen reduced the RNA content and the ratio of RNA:protein in muscles from control animals. In one group of tenotomised rats administration of fenbufen commenced 3 days before tenotomy and resulted in a reduction in the ratio RNA:protein of the muscles of the left limb 3 days after the operation. Four days later, i.e. 7 days after tenotomy, both the ratio RNA:protein and the fractional rate of protein synthesis were significantly reduced in the fenbufen treated rats. In spite of these effects, fenbufen did not impair the ability of the plantaris to hypertrophy since the drug also reduced the rate of protein degradation.