scholarly journals Effects of insulin in vitro on protein turnover in rat epitrochlearis muscle

1983 ◽  
Vol 210 (2) ◽  
pp. 323-330 ◽  
Author(s):  
W S Stirewalt ◽  
R B Low
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Nitrogen Balance ◽  
Protein Metabolism ◽  
Serum Insulin ◽  
Specific Radioactivity ◽  
Physiological Concentration ◽  
Rat Serum ◽  
The Third

Rates of protein synthesis and degradation were measured in the isolated rat epitrochlearis muscle by radiotracer techniques, by using the specific radioactivity of tRNA-bound amino acid as precursor for protein synthesis. The tissue maintained linear rates of protein synthesis for 3 h of incubation in the presence of amino acids and glucose and in the absence of insulin. Under these conditions, however, the muscles were in negative nitrogen balance, with rates of protein degradation exceeding rates of protein synthesis. Under steady-state conditions of labelling, the specific radioactivities of tRNA-bound leucine, phenylalanine and valine were significantly less than their respective values in the incubation medium, at concentrations in the medium varying from 1 to 10 times those in normal rat serum. Insulin caused a dose- and time-dependent increase in tRNA-based protein synthesis rates, more than doubling rates at 5 and 50 ng of insulin/ml. At the lower, physiological, concentration of insulin, the stimulation of protein synthesis was not observed until the third hour of incubation with the hormone, whereas the rate of protein synthesis at the higher concentration was elevated during the second hour. There were no delays in the stimulation by insulin of glucose conversion into glycogen. The delayed stimulatory effects of insulin on the rate of protein synthesis brought the tissue to a nitrogen balance near zero. The presence of the hormone also prevented the increase in the rate of protein degradation seen in the third hour of incubation in the absence of the hormone. These studies demonstrate the viability of the incubated rat epitrochlearis muscle with respect to protein metabolism and sensitivity to the protein anabolic effects of physiological concentrations of insulin, and indicate that the preparation is a suitable experimental model for the study of the control of protein metabolism in fast-twitch skeletal muscle.

A proinflammatory tumor that activates protein degradation sensitizes rats to catabolic effects of endotoxin

2005 ◽  
Vol 289 (4) ◽  
pp. E527-E533 ◽  
Author(s):  
Michelle L. Mackenzie ◽  
Nathalie Bedard ◽  
Simon S. Wing ◽  
Vickie E. Baracos
Keyword(s):  
Protein Degradation ◽  
Nitrogen Balance ◽  
Protein Metabolism ◽  
Muscle Protein ◽  
Ring Finger ◽  
Whole Body ◽  
Proteolytic Pathway ◽  
Before And After ◽  
Muscle Protein Degradation

Chronic or acute inflammation may participate in the etiology of cancer cachexia. To investigate the interaction between tumor and a secondary inflammatory stimulus on muscle wasting, rats with and without tumors (Yoshida ascites hepatoma) received low doses of endotoxin (LPS, 400 μg/kg sc) or saline. Nitrogen balance was measured 24 h before and after LPS/saline. Epitrochlearis muscle was used to measure in vitro protein metabolism, and gastrocnemius muscle was used for quantification of the mRNA for components of the ubiquitin proteolytic pathway. The YAH reduced muscle mass ( P = 0.002), increased muscle protein degradation ( P = 0.042), and elevated mRNA expression of components of the ubiquitin proteolytic pathway ( P < 0.01) including ubiquitin, ubiquitin-conjugating enzyme E214k, and ubiquitin ligases muscle RING Finger 1 and atrogin-1. Although the selected low dose of LPS had no impact on protein metabolism in control rats, LPS in rats bearing YAH caused weight loss ( P = 0.0007), lowered nitrogen balance ( P = <0.0001), and increased muscle protein degradation ( P = 0.0336). In conclusion, the presence of a tumor can potentiate whole body and muscle-specific catabolic losses of protein in response to a stimulus that is not catabolic in healthy animals. This effect might be dependent on the inflammatory nature of the tumor.

Protein metabolism by rat lung: influence of fasting, glucose, and insulin

1977 ◽  
Vol 43 (3) ◽  
pp. 463-467 ◽  
Author(s):  
L. A. Thet ◽  
M. D. Delaney ◽  
C. A. Gregorio ◽  
D. Massaro
Keyword(s):  
Protein Synthesis ◽  
Protein Content ◽  
Protein Metabolism ◽  
Specific Radioactivity ◽  
Rat Lung ◽  
Synthetic Process ◽  
In Vitro System ◽  
Other Substances

We studied protein metabolism by rat lung slices. We found that phenylalanine is not metabolized to other substances by the lung and that the rate of incorporation of L-[U-14C]phenylalanine into protein, calculated using its intracellular specific radioactivity, reached a maximum within 20 min and remained stable for the rest of a 3-h incubation. The rate of protein degradation, determined using [12C]phenylalanine as a marker, was linear over a 3-h incubation. Fasting for 3 days slowed the increase in lung protein content of fasted compared to nonfasted rats; there was also a decrease in protein synthesis and an increase in proteolysis. In fed rats, glucose, insulin, and glucose plus insulin did not alter protein synthesis. Glucose, insulin alone, and glucose plus insulin decreased proteolysis. We conclude that the in vitro system reflected changes in the in vivo protein content of the lung. Fasting decreases protein synthesis and increases proteolysis. Glucose and insulin alone modulate protein metabolism in the lung by acting on the degradative rather than the synthetic process.

scholarly journals Regulation of protein metabolism by a physiological concentration of insulin in mouse soleus and extensor digitorum longus muscles. Effects of starvation and scald injury

1979 ◽  
Vol 184 (2) ◽  
pp. 323-330 ◽  
Author(s):  
K N Frayn ◽  
P F Maycock
Keyword(s):  
Protein Synthesis ◽  
Protein Metabolism ◽  
Extensor Digitorum Longus ◽  
Muscle Protein ◽  
Extensor Digitorum ◽  
Total Protein Content ◽  
Skin Thickness ◽  
Physiological Concentration ◽  
Scald Injury

1. Although high concentrations of insulin affect both synthesis and degradation of skeletal-muscle protein, it is not known to what extent these effects occur with physiological concentrations. The effects of a physiological concentration of insulin (100 mu units/ml) on muscle protein synthesis, measured with [3H]tyrosine, and on muscle protein degradation, measured by tyrosine release in the presence of cycloheximide, were studied in mouse soleus and extensor digitorum longus muscles in vitro. 2. Insulin significantly stimualated protein synthesis in both muscles, but an inhibition of degradation was seen only in the extensor digitorum longus. 3. Starvation for 24 h decreased the rate of protein synthesis and increased the rate of breakdown in the extensor digitorum longus. Sensitivity to insulin-stimulation of proteins synthesis in the soleus was increased by starvation. 4.;a 20%-surface-area full-skin-thickness dorsal scald injury produced a fall in total protein content in soleus and extensor digitorum muscles, maximal on the third day after injury. Soleus muscles 2 days after injury showed an impairment of protein synthesis; degradation was unaffected and neither synthesis nor degradation in vitro was significantly affected in the extensor digitorum longus. 5. The advantages and limitations of studies of protein metabolism in vitro are discussed.

Regulation of protein synthesis and degradation during in vitro cardiac work

1980 ◽  
Vol 238 (5) ◽  
pp. E431-E442 ◽  
Author(s):  
H. E. Morgan ◽  
B. H. Chua ◽  
E. O. Fuller ◽  
D. Siehl
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Nitrogen Balance ◽  
Cardiac Work ◽  
Amino Acid Availability ◽  
Intracellular Concentrations ◽  
Substrate Mixtures ◽  
Beta Hydroxybutyrate

Cardiac work increased protein synthesis in hearts supplied glucose (mixture 1), glucose-insulin-glucagon-lactate-beta-hydroxybutyrate (mixture 2) or palmitate-beta-hydroxybutyrate-glucose (mixture 3). In hearts provided mixture 1, acceleration of synthesis involved increased rates of peptide chain initiation. In these hearts intracellular concentrations of 5 amino acids decreased and 13 others were unchanged, indicating that faster protein synthesis did not depend on increased amino acid availability. In hearts supplied mixtures 2, 3, or 4 (lactate-glucose-insulin), intracellular concentrations of branched-chain amino acids were decreased by work, whereas intracellular levels of some acidic and neutral amino acids increased. Protein degradation was decreased by work in hearts supplied mixtures 1 and 2, but not mixtures 3 and 4. In hearts provided mixture 1, nitrogen balance was negative, but less so in working preparations. Nitrogen balance was zero or positive in working hearts provided mixtures 2 and 4. These studies indicated that in hearts supplied some, but not all, of the substrate mixtures, cardiac work maintained efficiently of protein synthesis and inhibited protein degradation. An improved method for perfusion of working hearts with albumin-containing buffer is described.

scholarly journals Leptin and leucine synergistically regulate protein metabolism in C2C12 myotubes and mouse skeletal muscles

2012 ◽  
Vol 110 (2) ◽  
pp. 256-264 ◽  
Author(s):  
Xiangbing Mao ◽  
Xiangfang Zeng ◽  
Zhimin Huang ◽  
Junjun Wang ◽  
Shiyan Qiao
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Metabolism ◽  
Skeletal Muscles ◽  
Receptor Expression ◽  
C2c12 Myotubes ◽  
Leucine Supplementation ◽  
Regulate Protein

Leucine and leptin play important roles in regulating protein synthesis and degradation in skeletal muscles in vitro and in vivo. However, the objective of the present study was to determine whether leptin and leucine function synergistically in regulating protein metabolism of skeletal muscles. In the in vitro experiment, C2C12 myotubes were cultured for 2 h in the presence of 5 mm-leucine and/or 50 ng/ml of leptin. In the in vivo experiment, C57BL/6 and ob/ob mice were randomly assigned to be fed a non-purified diet supplemented with 3 % l-leucine or 2·04 % l-alanine (isonitrogenous control) for 14 d. Ob/ob mice were injected intraperitoneally with sterile PBS or recombinant mouse leptin (0·1 μg/g body weight) for 14 d. In C57BL/6 mice, dietary leucine supplementation increased (P< 0·05) plasma leptin, leptin receptor expression and protein synthesis in skeletal muscles, but reduced (P< 0·05) plasma urea and protein degradation in skeletal muscles. Dietary leucine supplementation and leptin injection increased the relative weight of the gastrocnemius and soleus muscles in ob/ob mice. Moreover, leucine and leptin treatments stimulated (P< 0·05) protein synthesis and inhibited (P< 0·05) protein degradation in C2C12 myotubes and skeletal muscles of ob/ob mice. There were interactions (P< 0·05) between the leucine and leptin treatments with regard to protein metabolism in C2C12 myotubes and soleus muscles of ob/ob mice but not in the gastrocnemius muscles of ob/ob mice. Collectively, these results suggest that leptin and leucine synergistically regulate protein metabolism in skeletal muscles both in vitro and in vivo.

Increased Protein Synthesis by Human Platelets during Phagocytosis of Latex Particles in Vitro

1976 ◽  
Vol 35 (02) ◽  
pp. 350-357 ◽  
Author(s):  
Hana Bessler ◽  
Galila Agam ◽  
Meir Djaldetti
Keyword(s):  
Protein Synthesis ◽  
Fold Increase ◽  
Human Platelets ◽  
Polystyrene Latex ◽  
Latex Particles ◽  
The Third ◽  
Platelet Protein ◽  
Dose Dependent ◽  
Phagocytotic Activity

SummaryA three-fold increase of protein synthesis by human platelets during in vitro phagocytosis of polystyrene latex particles was detected. During the first two hours of incubation, the percentage of phagocytizing platelets and the number of latex particles per platelet increased; by the end of the third hour, the first parameter remained stable, while the number of latex particles per cell had decreased.Vincristine (20 μg/ml of cell suspension) inhibited platelet protein synthesis. This effect was both time- and dose-dependent. The drug also caused a decrease in the number of phagocytizing cells, as well as in their phagocytotic activity.

scholarly journals Effect of long-term refeeding on protein metabolism in patients with cirrhosis of the liver

1997 ◽  
Vol 77 (2) ◽  
pp. 197-212 ◽  
Author(s):  
Jens Kondrup ◽  
Klaus Nielsen ◽  
Anders Juul
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Metabolism ◽  
Cirrhosis Of The Liver ◽  
N Balance ◽  
Whole Body ◽  
Protein Requirement ◽  
Protein Utilization ◽  
Igf I

Patients with cirrhosis of the liver require an increased amount of protein to achieve N balance. However, the utilization of protein with increased protein intake, i.e. the slope from regression analysis of N balance v. intake, is highly efficient (Nielsen et al. 1995). In the present study, protein requirement and protein utilization were investigated further by measuring protein synthesis and degradation. In two separate studies, five or six patients with cirrhosis of the liver were refed on a balanced diet for an average of 2 or 4 weeks. Protein and energy intakes were doubled in both studies. Initial and final whole-body protein metabolism was measured in the fed state by primed continous [15N]glycine infusion. Refeeding caused a statistically significant increase of about 30% in protein synthesis in both studies while protein degradation was only slightly affected. The increase in protein synthesis was associated with significant increases in plasma concentrations of total amino acids (25%), leucine (58%), isoleucine (82%), valine (72%), proline (48%) and triiodothyronine (27%) while insulin, growth hormone, insulin-like growth factor (IGF)-I and IGF-binding protein-3 were not changed significantly. The results indicate that the efficient protein utilization is due to increased protein synthesis, rather than decreased protein degradation, and suggest that increases in plasma amino acids may be responsible for the increased protein synthesis. A comparison of the patients who had a normal protein requirement with the patients who had an increased protein requirement suggests that the increased protein requirement is due to a primary increase in protein degradation. It is speculated that this is due to low levels of IGF-I secondary to impaired liver function, since initial plasma concentration of IGF-I was about 25% of control values and remained low during refeeding.

Effect of glutamine-enriched total parenteral nutrition on septic rats

1991 ◽  
Vol 81 (2) ◽  
pp. 215-222 ◽  
Author(s):  
M. Salleh M. Ardawi
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Parenteral Nutrition ◽  
Protein Degradation ◽  
Total Parenteral Nutrition ◽  
Nitrogen Balance ◽  
Cumulative Percentage ◽  
Better Than

1. The effect of total parenteral nutrition with or without glutamine enrichment was studied in septic rats after 4 days of treatment. 2. Septic rats treated with glutamine-enriched total parenteral nutrition survived sepsis significantly better than other TPN-treated septic rats: the cumulative percentage of deaths over 4 days in septic rats treated with glutamine-enriched total parenteral nutrition was 25% compared with 55% in septic rats given total parenteral nutrition without glutamine and 70% in septic rats given glucose. 3. Glutamine-enriched total parenteral nutrition resulted in improved nitrogen balance in septic rats: the cumulative nitrogen balance over the 4 days of treatment was the least negative as compared with other groups of septic rats. 4. The rate of loss of intracellular glutamine in skeletal muscle was markedly decreased (P < 0.001) in response to glutamine-enriched total parenteral nutrition in septic rats. 5. The rate of protein synthesis was increased (21.2%) and the rate of protein degradation was decreased (35.5%) in response to glutamine-enriched total parenteral nutrition in septic rats. 6. It is concluded that the administration of glutamine-enriched total parenteral nutrition is beneficial to septic rats and possibly to septic patients.

scholarly journals Differential protein metabolism and regeneration in hypertrophic diaphragm and atrophic gastrocnemius muscles in hibernating Daurian ground squirrels

2019 ◽  
Author(s):  
Xia Yan ◽  
Xuli Gao ◽  
Xin Peng ◽  
Jie Zhang ◽  
Xiufeng Ma ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Muscle Regeneration ◽  
Protein Metabolism ◽  
Muscle Hypertrophy ◽  
Gastrocnemius Muscle ◽  
Fiber Type ◽  
Ground Squirrels ◽  
Diaphragm Muscle ◽  
Gastrocnemius Muscles

AbstractWhether differences in regulation of protein metabolism and regeneration are involved in the different phenotypic adaptation mechanisms of muscle hypertrophy and atrophy in hibernators? Two fast-type muscles (diaphragm and gastrocnemius) in summer active and hibernating Daurian ground squirrels were selected to detect changes in cross-sectional area (CSA), fiber type distribution, and protein expression indicative of protein synthesis metabolism (protein expression of P-Akt, P-mTORC1, P-S6K1, and P-4E-BP1), protein degradation metabolism (MuRF1, atrogin-1, calpain-1, calpain-2, calpastatin, desmin, troponin T, Beclin1, and LC3-II), and muscle regeneration (MyoD, myogenin, and myostatin). Results showed the CSA of the diaphragm muscle increased significantly by 26.1%, whereas the CSA of the gastrocnemius muscle decreased significantly by 20.4% in the hibernation group compared with the summer active group. Both muscles displayed a significant fast-to-slow fiber-type transition in hibernation. Our study further indicated that increased protein synthesis, decreased protein degradation, and increased muscle regeneration potential contributed to diaphragm muscle hypertrophy, whereas decreased protein synthesis, increased protein degradation, and decreased muscle regeneration potential contributed to gastrocnemius muscle atrophy. In conclusion, the differences in muscle regeneration and regulatory pattern of protein metabolism may contribute to the different adaptive changes observed in the diaphragm and gastrocnemius muscles of ground squirrels.

Reversal of the exercise-induced increase in muscle permeability to glucose

1987 ◽  
Vol 253 (4) ◽  
pp. E331-E335 ◽  
Author(s):  
D. A. Young ◽  
H. Wallberg-Henriksson ◽  
M. D. Sleeper ◽  
J. O. Holloszy
Keyword(s):  
Protein Synthesis ◽  
Glucose Transport ◽  
Glycogen Synthesis ◽  
Carbohydrate Restriction ◽  
Rat Serum ◽  
Low Concentration ◽  
Carbohydrate Feeding ◽  
Exercise Induced

Exercise is associated with an increase in permeability of muscle to glucose that reverses slowly (h) in fasting rats during recovery. Previous studies showed that carbohydrate feeding speeds and carbohydrate restriction slows reversal of the exercise-induced increase in glucose uptake. This study was designed to evaluate the roles of glucose transport, glycogen synthesis, and protein synthesis in the reversal process in rat epitrochlearis muscle. In contrast to recovery in vivo, when muscles were incubated without insulin in vitro, the exercise-induced increase in muscle permeability to sugar reversed rapidly regardless of whether glucose transport or glycogen synthesis occurred. Inhibition of protein synthesis did not prevent the reversal. Addition of 33% rat serum or a low concentration of insulin to the incubation medium markedly slowed reversal in vitro. We conclude that 1) prolonged persistence of the increased permeability of mammalian muscle to glucose after exercise requires a low concentration of insulin, and 2) reversal of the increase in permeability does not require glucose transport, glycogen synthesis, or protein synthesis.

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