Differential effects of cooked common bean (Phaseolus vulgaris) and lentil (Lens esculenta puyensis) feeding on protein and nucleic acid contents in intestines, liver and muscles in rats

AIM: Our aim was to investigate the influence of legume feeding on the protein and nucleic acid content of intestinal tissues and muscles. METHODS: Growing male Wistar rats were fed ad libitum on balanced diets containing cooked common bean or lentil as the unique protein source (180 g.kg(-1) dry matter) for 20 days. The control group was pair-fed with an iso-energetic, iso-nitrogenous balanced casein diet. RESULTS: Intestinal tissues were heavier in the legume-fed groups and higher relative mass (g per 100 g body mass) of protein, RNA and DNA were found in these tissues as compared to those of the control groups. In liver protein and RNA masses were significantly lower in the bean group than in the control group but the DNA content was not different in the legume and in the control groups. In gastrocnemius and soleus muscles, there was no significant effect of legume feeding on the fresh mass and on the protein and RNA contents, but the DNA content of the m. gastrocnemius was significantly lower in both legume groups than in their control group. The ribosomal capacity of intestines, liver and muscles was not significantly affected by legume feeding. CONCLUSION: Legume feeding had a trophic effect on both proximal and distal intestinal tissues; dietary fiber appears to be the main cause of this effect.     

Osmotic diarrhoea and skeletal muscle protein synthesis in vivo.

The pathogenic nature of the wasting seen in diarrhoea is unknown. This study measured protein synthesis in an established model of diarrhoea using lactose for seven days. Comparisons were also made with data obtained from rats fed an identical diet in which lactose was replaced by isocaloric glucose ad libitum (that is, the control diet). To account for diarrhoea induced anorexia, a third group of rats were included, which were fed identical amounts of the control diet as the rats with diarrhoea inducing diet. Comparisons of the diarrhoea induced group with rats fed the control diet ad libitum showed that diarrhoea caused a significant reduction in body weights. Type I and type II muscles showed significant reductions in protein, RNA, and DNA contents, as well as a fall in the derived parameters, RNA/DNA, protein/DNA, and RNA/protein. Fractional rates of protein synthesis (ks) were also reduced. However, synthesis rates of type I and II muscles relative to RNA (kRNA) were unchanged in these muscles in diarrhoea induced rats compared with ad libitum fed controls. In the jejunum there was an increase in the RNA/DNA ratio, and reductions in ks and kRNA. Comparisons were also made between rats with diarrhoea and rats pair fed the control diet. There were no changes in total muscle protein, RNA or DNA contents. This suggests that an important feature of body wasting in diarrhoea is the element of anorexia, which induces severe metabolic changes. The comparison between rats with diarrhoea and the pair fed group showed that histological features of the plantaris were not overtly changed, though diarrhoea caused significant reductions in RNA/DNA, protein/DNA, ks, and kRNA. Similar changes were seen for the soleus; though the reduction in ks failed to attain statistical significance. In the jejunum a comparison of diarrhoea induced rats with pair fed controls, showed increases in the ratios of RNA/DNA and protein/DNA.     

Fiber type- and fatty acid composition-dependent effects of high-fat diets on rat muscle triacylglyceride and fatty acid transporter protein-1 content

Intramuscular triacylglyceride (TAG) is considered an independent marker of insulin resistance in humans. Here, we examined the effect of high-fat diets, based on distinct fatty acid compositions (saturated, monounsaturated or n-6 polyunsaturated), on TAG levels and fatty acid transporter protein (FATP-1) expression in 2 rat muscles that differ in their fiber type, soleus, and gastrocnemius; the relationship to whole body glucose intolerance was also studied. Compared with carbohydrate-fed rats, the groups subjected to any one of the high-fat diets consistently exhibited enhanced body weight gain and adiposity, elevated plasma free fatty acids and TAG in the fed condition, hyperinsulinemia, and glucose intolerance. TAG content was consistently higher in soleus than in gastrocnemius, but was only significantly elevated by the n-6 polyunsaturated-based diet. FATP-1 levels in soleus were double those in gastrocnemius muscle in carbohydrate-fed animals. High-fat diets caused an elevation in FATP-1 protein content in soleus, but a reduction in gastrocnemius. In conclusion, the hyperinsulinemic hyperlipidemic condition upregulates FATP-1 expression in soleus and downregulates that of gastrocnemius. Hypercaloric saturated, monounsaturated, or n-6 polyunsaturated lipid diets cause equivalent whole body insulin resistance in rats, but only an n-6 polyunsaturated acid-based diet triggers intramuscular TAG accumulation.     

Response to trauma of protein, amino acid, and carbohydrate metabolism in injured and uninjured rat skeletal muscles

Soft tissue injury to one hindlimb produced trauma in rats without affecting their food intake or weight gain. Histologic examination showed damage to the soleus and gastrocnemius muscles but not to the extensor digitorum longus muscle. The protein content of the injured soleus muscle was lower than that of the contralateral soleus at one day after injury, and was reflected in vitro by a faster rate of protein degradation. The injured soleus also showed greater rates of protein synthesis, glucose uptake, glycolysis, oxidation of glucose, pyruvate, and leucine, and de novo synthesis of alanine. During three days after the injury, urinary nitrogen excretion increased progressively and was paralleled by a faster rate of protein degradation in uninjured muscles incubated with glucose, insulin, and amino acids. In these muscles, the inhibition of protein degradation by insulin diminished, while its stimulation of protein synthesis was unaffected. This insensitivity of proteolysis to insulin in trauma can explain the increased rate of this process. The oxidation of glucose and pyruvate were lower in the diaphragms of traumatized than of normal rats incubated with leucine, while glycolysis and uptake of 2-deoxyglucose did not differ. The degradation of leucine and isoleucine was greater in the diaphragms of traumatized animals and was associated with a faster de novo synthesis of alanine. For the uninjured soleus muscles of the traumatized rats, the slower rates of oxidation of glucose, glycolysis, and uptake of 2-deoxyglucose in the presence of insulin showed an insensitivity of glucose metabolism to this hormone. In contrast, no differences were seen in these various metabolic processes between the extensor digitorum longus muscles of traumatized and normal rats. These data suggest that the response of skeletal muscles to trauma may depend on their physiologic and biochemical characteristics.     

Denervation stimulates apoptosis but not Id2 expression in hindlimb muscles of aged rats

Inhibitors of differentiation (Id) proteins are repressors of myogenic regulatory factors and have been implicated in apoptosis and muscle atrophy during aging. Indeed, we have previously found that Id levels are elevated in muscles from old rodents, possibly as a consequence of loss of alpha-motoneurons during senescence. To determine if Id2 proteins increase after denervation and if this is accompanied by increased apoptosis in aged as compared with adult animals, the gastrocnemius and soleus muscles were denervated in 1 limb of Fischer 344 x Brown Norway rats aged 9 months (adult, n = 12) and 33 months (aged, n = 9), while the contralateral limb served as the intra-animal control. After 14 days, the muscles in each limb were removed. The levels of Id1, Id2, and Id3 mRNA and protein were significantly greater in muscles of old as compared with young adult rats. Denervation, however, did not significantly increase Id1, Id2, and Id3 mRNA in soleus or gastrocnemius muscles from either young or old rats. Also Id2 protein levels were similar in denervated and control muscles from young adult and old rats. In young adult rats only, denervation induced an increase in Id1 and Id3 protein levels in both the soleus (Id1 113%; Id3 900%) and gastrocnemius (Id1 86%; Id3 80%). Denervation induced a significant increase in caspase 8 in both soleus and gastrocnemius muscles from young (101% and 147%, respectively) and old rats (167% and 190%, respectively). Bax protein levels, as estimated by western blots, increased by 726% and 1087% after denervation in the soleus and by 368% and 49% in the gastrocnemius muscles of young and old rats, respectively. The data suggest that the denervation-induced muscle loss was at least partly due to apoptosis as indicated by elevated caspase 8 and Bax levels in denervated muscles. While Id2 may have a role in aging-induced sarcopenia, Id2 does not appear to directly regulate apoptosis during denervation. The elevated Id expression in muscles from aged animals is therefore not a direct consequence of loss of alpha-motoneurons during senescence.     

The influence of age and chronic restricted feeding on protein synthesis in the small intestine of the rat.

Rates of protein synthesis (measured in vivo) and growth of the small intestine were studied as a function of age in ad libitum fed (control) and chronic dietary-restricted rats. At weaning, the fractional rates of synthesis in the mucosal and muscularis externa and serosal layers of the small intestine of control animals were similarly high (90-100% per day). Although these rates subsequently declined with age in the muscularis externa and serosa, they remained constant in the mucosa. Restricted feeding (50% reduced intake), when imposed from weaning onwards, significantly extends the maximum life span of rodents. However, the change in nutritional status slows the accumulation of protein, RNA, and DNA in both layers of the small intestine. Although underfeeding did not prevent the age-related fall in muscularis externa and serosal protein synthesis, significantly higher rates (both fractional and per ribosome) were found when compared age for age with controls. Mucosal fractional synthetic rates were similarly increased by the reduced food intake. These changes in protein turnover in the small intestine are consistent with the higher rates of whole body turnover previously observed in chronically underfed rats.     

Regulation of initiation of protein synthesis by insulin in skeletal muscle

Protein synthesis is impaired in skeletal muscle and heart from diabetic rats. In muscles composed primarily of slow-twitch fibres (e.g. heart or soleus), the inhibition of protein synthesis can be accounted for entirely by a decrease in the amount of RNA. In contrast, in muscles of mixed fibre composition (e.g. gastrocnemius or psoas), the inhibition of protein synthesis is associated with an impairment in peptide-chain initiation. We have found that the inhibition of peptide-chain initiation that occurs in muscles composed of mixed fast-twitch fibres involves eukaryotic initiation factor 2B (eIF-2B). Thus, eIF-2B activity is inhibited in gastrocnemius and psoas but not heart or soleus from diabetic rats. In other systems eIF-2B activity is regulated by phosphorylation of the -subunit of a second initiation factor, eIF-2. However, we have found no change in the phosphorylation state of eIF-2 in either fast-or slow-twitch muscles from diabetic compared to control animals. Instead, the available evidence suggests that eIF-2B activity may be modulated by an alternate mechanism such as a change in the extent of phosphorylation of the 82,000M _r subunit of the factor or a change in the NADPH/NADP⁺ ratio.     

Effect of exercise on protein turnover in muscles of lean and obese mice

Summary The effect of work-induced hypertrophy on skeletal muscle protein metabolism was studied in lean mice and in mice rendered obese with goldthioglucose. After tenotomy of the gastrocnemius muscle, the adaptative growth of soleus muscle was less pronounced in obese than in lean mice. Protein turnover was studied in the isolated soleus muscle 4 days after the operation. Tyrosine incorporation in total proteins and tyrosine release in the incubation medium (indices of protein synthesis and degradation) were increased by 3- and 2-fold in overloaded (i. e. work-induced hypertrophied) muscles of lean and obese mice, respectively, compared to the control muscles isolated from the non-operated leg. The qualitative modifications in the pattern of proteins synthetized from ³⁵S-methionine were identical in both groups of mice. This increase in protein turnover in overloaded muscles results from an increased rate of polypeptide chain initiation (3-fold in lean mice, 2.2-fold in obese mice) without any modification of peptide chain elongation rates. Work-induced hypertrophy was also able to reverse the defect in amino acid uptake which is present in soleus muscles of GTG-obese mice. These results suggest that the work-induced increase of skeletal muscle protein turnover is diminished in obese mice.     

Response of protein synthesis to hypercapnia in rats: independent effects of acidosis and hypothermia

Acute metabolic acidosis has been shown to inhibit muscle protein synthesis, although little is known on the effect of acidosis of respiratory origin. The aim of this study was to investigate the effect of acute respiratory acidosis on tissue protein synthesis. Rats (n = 8) were made acidotic by increasing the CO2 content of inspired air to 12% for 1 hour. Similar rats breathing normal air served as controls (n = 8). Muscle and liver protein synthesis rates were then measured with L-[ 2H5 ]phenylalanine (150 micromol per 100 g body weight, 40 mol%). The results show that protein synthesis is severely depressed in skeletal muscle (-44% in gastrocnemius, -39% in plantaris, and -24% in soleus muscles, P < .01) and liver (-20%, P < .001) in acidotic animals. However, because breathing CO2 -enriched air was found to lower body temperature by approximately 2 degrees C, in a second experiment (n = 10), the difference in body temperature between treated and control animals was minimized by gently wrapping rats breathing CO2 -enriched air in porous cloths. This second experiment confirmed that respiratory acidosis depresses protein synthesis in muscle (-22% in gastrocnemius, P < .001; -19% in plantaris, P < .01; and -4% in soleus, P = NS). However, no effect on liver protein synthesis could be detected, suggesting that liver protein synthesis may be sensitive to changes in body temperature but is not affected by acute respiratory acidosis for 1 hour. The results show that respiratory acidosis inhibits protein synthesis in skeletal muscle and indicates that acidosis, whether of metabolic or respiratory origin, may contribute to loss of muscle protein in patients with compromised renal or respiratory function.     

Carbonyl levels in type I and II fiber-rich muscles and their response to chronic ethanol feeding in vivo and hydroxyl and superoxide radicals in vitro

BACKGROUND: Chronic alcoholic myopathy is characterized by selective reductions in the size of Type II skeletal muscle fibers (i.e., glycolytic, anaerobic fast-twitch). Type I (i.e., oxidative, aerobic, slow twitch) fibers are relatively resistant. It is possible that reactive oxygen species may preferentially damage the Type II fibers because the concentrations of several antioxidant enzymes are lower in Type II compared with Type I fibers. METHODS: To test the hypothesis, we measured protein carbonyl levels in Type I (i.e., soleus) and Type II (i.e., plantaris) fiber-rich muscles of rats subjected to chronic alcohol dosage with the Lieber-DeCarli regimen. Muscles were also exposed to hydroxyl or superoxide radicals in vitro. RESULTS: The Type I fiber-predominant soleus of control animals had less carbonyl than the Type II fiber-predominant plantaris. In rats that were fed ethanol for 6 weeks, the weights of the plantaris muscle were preferentially reduced but changes in soleus weight did not achieve significance. However, carbonyl levels were not significantly altered in any muscle in response to alcohol feeding. Calculation of the data in terms of total carbonyl per whole muscle showed decreases in both soleus and plantaris at the end of the 6-week alcohol feeding period. In response to hydroxyl radical (OH*) generation in vitro, protein carbonyl increased substantially in both soleus and plantaris muscles, but more so in the soleus. The increase in carbonyl in control soleus muscles in response to OH* was significantly lower than in soleus muscles from alcohol-fed animals. The increase in control plantaris muscle was not significantly different from the increase in carbonyl in corresponding muscles from ethanol-fed rats in response to OH*. In response to superoxide radicals, carbonyl in control soleus increased, an effect similar to that recorded in the soleus from ethanol-fed rats. In control plantaris, carbonyl increased in response to superoxide radicals, an effect not significantly different to the increase in plantaris from alcohol-fed rats. CONCLUSIONS: Using increased carbonyl concentrations as an indicator of muscle damage by reactive oxygen species, we concluded (1) there is no evidence of enhanced reactive oxygen species-induced damage to mixed muscle proteins in either Type I or Type II muscles in response to alcohol feeding; (2) Type II muscles have a greater capacity than Type I muscles to protect against damage (as indicated by carbonyl formation) by both hydroxyl and superoxide radicals in vitro; (3) alcohol reduces the capacity of Type I muscle to resist hydroxyl radical-induced protein damage, a mechanism that may arise through impairment of other antioxidant systems or other process not yet elucidated.     

Accelerated intramyocellular triglyceride synthesis in skeletal muscle of high-fat-induced obese rats

OBJECTIVE: To test the hypothesis that the synthesis of intramyocellular triglycerides (imcTG) in skeletal muscle is increased in obese rats in which the content of imcTG is known to be abnormally high. ANIMALS: Sprague-Dawley male lean and high-fat-induced obese rats were studied at the age of 4, 8 and 12 months after an overnight fast, awake. MEASUREMENTS: [U-(14)C]glycerol was continuously infused intravenously for 2 h followed by muscle biopsies, and intracellular glycerol incorporation into imcTG was determined. imcTG content, intramyocellular free glycerol concentration and specific activity, systemic glycerol flux and plasma glycerol, free fatty acid (FFA) and glucose concentrations were also determined. RESULTS: The rates of incorporation of intramyocellular glycerol into imcTG (nmol/g wet muscle/h) were markedly accelerated in obese rats compared to their lean littermates at all ages: 66+/-12 vs 12+/-2 (P=0.02) for gastrocnemius and 74+/-29 vs 31+/-7 (P=0.09) for soleus when 4 months old; 223+/-29 vs 58+/-27 (P=0.001) for gastrocnemius, 224+/-28 vs 70+/-21 (P=0.001) for soleus and 294+/-78 vs 49+/-22 (P=0.02) for tibialis anterior when 8 months old; and 25+/-4 vs 11+/-2 (P=0.01) for gastrocnemius and 22+/-8 vs 8.4+/-3 (P=0.04) for soleus when 12 months old. As expected, this was accompanied by a higher imcTG content in virtually all muscles at all ages tested. CONCLUSION: The synthesis of imcTG in skeletal muscle is grossly increased in obese rats, which likely contributes to abnormal imcTG accumulation.     

Deprivation of dietary nucleotides decreases protein synthesis in the liver and small intestine in rats

BACKGROUND & AIMS: Dietary nucleotides are reported to influence the growth and functioning of the liver and small intestine. The aim of this study was to examine the mechanism by which nucleotides exert their effects in these tissues by assessing protein synthesis activity and related parameters in the presence or absence of dietary nucleotides. METHODS: Rats were fed a purified diet with or without nucleotides for 10 days. Fractional protein synthesis rate, RNA and DNA concentrations, polysome size distribution, and number of ribosomes were assessed. RESULTS: Fractional protein synthesis rates of the liver and small intestine were lower in the nucleotide-deprived group than in the control group. In the liver, RNA concentration was also lower in the nucleotide-deprived group, but values in the small intestine were similar in the two groups. In the liver, deprivation of nucleotides resulted in a reduction in the number of ribosomes and in polysome breakdown. Protein and DNA concentrations did not vary in the liver; however, the concentration of DNA was lower in the small intestine of the nucleotide-deprived group than in the control group. CONCLUSIONS: Dietary nucleotides can modulate protein synthesis in the liver and small intestine as a result of tissue-specific nucleic acid changes. (Gastroenterology 1996 Jun;110(6):1760-9)     

Response of muscle, liver and whole-body protein turnover to two different sources of protein in growing rats

A significant impairment in growth rate, food efficiency and weight of the gastrocnemius muscle was observed in rats fed a raw legume as the source of protein compared to casein-fed animals. No appreciable differences in chemical composition of the carcass were found. The source of dietary protein did not influence the ratio protein/DNA, DNA concentration or protein-synthesizing capacity (RNA/protein). The slower weight gain of animals fed the legume diet was attributed to a lower muscle protein synthesis, mediated by a depression of muscle RNA activity (grams protein synthesized/gram RNA) rather than changes in myofibrillar protein breakdown. In contrast liver protein synthesis appeared to be slightly increased in the legume-fed animals.     

Albumin-synthesizing capacity of hepatocytes isolated from rats fed diets differing in protein and energy content

The rate of albumin synthesis has been estimated in hepatocytes prepared from groups of rats maintained on diets of different protein content. These diets were fed either ad libitum or at 50% restriction of ad libitum consumption. The data show that the physiological capacity of hepatocytes to synthesize albumin varies with dietary intake. Albumin production by cells prepared from animals fed ad libitum was directly related to the protein energy:total energy ratio of the food. Restricting consumption of the control diet to 50% of ad libitum intake did not reduce albumin synthesis rates, and similar restriction of the low protein diets ameliorated some of the depression in albumin production observed in hepatocytes isolated from animals fed the same diets ad libitum. The results are discussed with reference to the occurrence of hypoalbuminaemia in children with protein-energy malnutrition.     

Development of Wistar rat model of insulin resistance

AIM: To establish a simplified and reliable animal model of insulin resistance with low cost in Wistar rats. METHODS: Wistar rats were treated with a high fat emulsion by ig for 10 d. Changes of the diets, drinking and body weight were monitored every day and insulin resistance was evaluated by hyperinsulinemic-euglycemic clamp techniques and short insulin tolerance test using capillary blood glucose. Morphologic changes of liver, fat, skeletal muscles, and pancreatic islets were assessed under light microscope. mRNA expressions of GLUT2 and α-glucosidase in small intestine epithelium, GLUT4 in skeletal muscles and Kir6.2 in beta cell of islets were determined by in situ hybridization. RESULTS: KITT was smaller in treated animals (4.5±0.9) than in untreated control Wistar rats (6.8±1.5), and so was glucose injection rate. Both adipocyte hypertrophy and large pancreatic islets were seen in high fat fed rats, but no changes of skeletal muscles and livers were observed. mRNA levels of GLUT2, α-glucosidase in small intestinal epithelium and Kir6.2 mRNA in beta cells of islets increased, whereas that of GLUT4 in skeletal muscles decreased in high fat fed group compared with normal control group. CONCLUSION: An insulin resistance animal model in Wistar rats is established by ig special fat emulsion.     

Effect of chronic ethanol ingestion on hepatic and intestinal acyl coenzyme a:cholesterol acyltransferase and 3-hydroxy-3-methylglutaryl coenzyme a reductase in the rat

Two groups of rats were pair-fed diets in which 36% of the calories were provided by either ethanol or dextrimaltose. After 60 days on these liquid diets, rats fed ethanol were significantly smaller than control rats fed dextrimaltose. Serum cholesterol levels in ethanol-fed animals were 20% higher than control rats. Cholestasis was not observed histologically, and serum alkaline phosphatase and bilirubin levels were the same in both groups. The livers of animals ingesting ethanol accumulated triglycerides and cholesterol. The increase in cholesterol was due to an increase in cholesteryl esters. The cholesterol content of liver microsomes, however, was unchanged by ethanol feeding. A small increase in unesterified cholesterol was observed in intestinal microsomes prepared from animals receiving ethanol. Microsomal fatty acids in liver and intestine were unchanged by the ethanol diet. Chronic ingestion of ethanol in these animals failed to change acyl coenzyme A:cholesterol acyltransferase or 3-hydroxy-3-methylglutaryl-coenzyme A reductase activities in the intestine. In contrast, the activities of acyl coenzyme A:cholesterol acyltransferase and 3-hydroxy-3-methylglutaryl-coenzyme A reductase were significantly increased in the livers of rats receiving ethanol. Thus, the chronic ingestion of ethanol caused a marked accumulation of hepatic cholesteryl esters. This was associated with a significant increase in the activities of enzymes that control the rates of both cholesterol synthesis and cholesterol esterification in the liver. These observed changes in enzyme activities may contribute to the lipid accumulation which occurs in these livers. Chronic ethanol consumption did not alter cholesterol metabolism in the intestine.     

Free radical changes in rat muscle tissue after exercise

Intense exercise accompanied by a manifold increase in oxygen utilization over resting conditions has been shown to elevate the probability of the appearance of free radicals. One of the effects of free radicals appears to be the peroxidation of cell membrane lipids resulting in malondialdehyde formation, which is detrimental to cell function. A common method for the measurement of malondialdehyde involves a reaction with thiobarbituric acid. The aim of this study was to evaluate the influence of exercise on concentrations of thiobarbituric acid-reactive substances (TBARS) in the gastrocnemius and soleus muscles of rats. Thirty male rats were used in this study. Soleus and gastrocnemius muscle biopsies were performed and TBARS levels were studied in these two muscles. The rats were randomly assigned to three groups of ten each. Group A was the control group and did not perform exercise. In group B, gastrocnemius and soleus muscle biopsies were performed immediately after exercise, and in group C muscle biopsies were performed on the 2nd postexercise day. The exercise resulted in a significant increase in TBARS in the gastrocnemius muscle. In the soleus, TBARS also increased, but this was not statistically significant. In conclusion, exercise-induced free radical changes may depend on the muscle type studied.     

Skeletal Muscle Ribonuclease Activities in Chronically Ethanol-Treated Rats

Alcoholic myopathy occurs in up to two thirds of alcohol misusers and is characterized by selective atrophy of type II (anaerobic, fast-twitch) fibers; type I (aerobic, slow twitch) fibers are relatively unaffected. Both clinical and animal studies have indicated that skeletal muscle RNA content is reduced in response to ethanol exposure, and contributes to impaired protein synthesis. We hypothesized that the reduction in muscle RNA may be due to raised ribonuclease (RNase) activities that enhance RNA catabolism. To test this hypothesis, we measured the total tissue and plasma RNase activities as well as the activities of general (RNase A) and specific or “restriction” RNases (T₁L, T₂L) in ethanol-treated rats. Chronically treated rats were fed a nutritionally complete liquid diet with 35% of calories as ethanol. Weight-matched controls were pair-fed with isocaloric glucose. Rats were killed at time-points up to 6 weeks. For comparative purposes, the effect of acute (24 hr) starvation was also analyzed in a second group of rats relative to a group of control rats allowed free access to food and water over 24 hr. Results showed that the type II fiber-predominant plantaris muscle exhibited a significant increase in total RNase, RNase A and RNase T₁L activities (increases ranged from +59% to +196%; P-values between 0.025 and 0.01) concomitant with large falls in RNA and protein content. In contrast, none of the RNase activities measured in the type 1 fiber-predominant soleus muscles were significantly affected; compositional changes were also smaller in the soleus. This effect was independent of reduced nutrition. In conclusion, the raised total RNase, RNase A and RNase T₁L activities may contribute to the type II fiber-specific reduction in total RNA in chronically ethanol-treated rats. In turn, this may contribute to the alterations in cellular protein metabolism seen under these treatments.     

Influence of sepsis in rats on muscle protein turnover in vivo and in tissue incubated under different in vitro conditions

We studied the influence of sepsis on muscle protein synthesis and degradation in vivo and in muscles, incubated flaccid or at resting length. Sepsis was induced in rats by cecal ligation and puncture (CLP). Control rats were sham-operated. A flooding dose of 14C-phenylalanine was used to determine muscle protein synthesis rate in vivo, and protein breakdown was calculated from the difference between protein synthesis and growth rates. Protein synthesis rate in vitro was assessed by determining incorporation of 14C-phenylalanine into protein in incubated extensor digitorum longus (EDL) and soleus (SOL) muscles. Total and myofibrillar protein breakdown rates were determined from release into incubation medium of tyrosine and 3-methylhistidine (3-MH), respectively. Muscle protein synthesis rate in vivo was reduced by 35%, similar to the reduction observed in muscles incubated flaccid or at resting length. The calculated protein breakdown rate in vivo was increased by 31% in septic rats. In incubated muscles, the increase in total protein breakdown (ie, tyrosine release) during sepsis was almost identical in muscles incubated flaccid or at resting length, ie, 83% to 88% in EDL and 47% to 49% in SOL. Myofibrillar protein degradation in vitro (ie, 3-MH release) was increased approximately 10-fold in EDL muscles incubated flaccid or at resting length, but was not significantly affected by sepsis in SOL. Results suggest that sepsis-induced changes in protein synthesis observed in muscles incubated either flaccid or at resting length reflect changes in vivo. Changes in protein breakdown were qualitatively similar in vivo and in vitro, but results in incubated muscles may overestimate the increase in muscle proteolysis caused by sepsis.