scholarly journals Dietary protein intake and skeletal-muscle protein metabolism in rats. Studies with salt-washed ribosomes and transfer factors

1972 ◽  
Vol 128 (3) ◽  
pp. 521-530 ◽  
Author(s):  
S. D. Alexis ◽  
S. Basta ◽  
Vernon R. Young
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Protein Diet ◽  
Low Protein Diet ◽  
Skeletal Muscle Protein ◽  
Transfer Factors ◽  
Low Protein ◽  
Enzyme Fraction

1. Aspects of skeletal muscle protein synthesis in vitro were studied in young rats given a low-protein diet for up to 10 days and during re-feeding with an adequate diet. 2. Partially purified muscle transfer factors (transferases I and II), crude and purified (NH4Cl-washed) ribosomes and a pH5 enzyme fraction were prepared for this purpose. 3. A marked decrease in the capacity of crude ribosomes to carry out cell-free polypeptide synthesis occurred within 4 days of feeding the low-protein diet. 4. The capacity of salt-washed ribosomes to promote amino acid polymerization, in the presence of added transfer factors and aminoacyl-tRNA, was only slightly decreased by the dietary treatment. 5. However, the capacity of salt-washed ribosomes to bind 14C-labelled aminoacyl-tRNA was decreased by feeding the low-protein diet. 6. The capacity of the pH5 enzyme fraction to promote amino acid incorporation in a complete cell-free system was decreased within 2 days of feeding the low-protein diet. There is no evidence that the change is associated with aminoacyl-tRNA synthetase or binding enzyme activities of the pH5 fractions. 7. These changes are discussed in relation to the diminished rate of protein synthesis in the intact muscle cell when rats are given a low-protein diet.

scholarly journals Testosterone injection stimulates net protein synthesis but not tissue amino acid transport

1998 ◽  
Vol 275 (5) ◽  
pp. E864-E871 ◽  
Author(s):  
Arny A. Ferrando ◽  
Kevin D. Tipton ◽  
David Doyle ◽  
Stuart M. Phillips ◽  
Joaquin Cortiella ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Acid Transport ◽  
Skeletal Muscle Protein ◽  
Net Protein

Testosterone administration (T) increases lean body mass and muscle protein synthesis. We investigated the effects of short-term T on leg muscle protein kinetics and transport of selected amino acids by use of a model based on arteriovenous sampling and muscle biopsy. Fractional synthesis (FSR) and breakdown (FBR) rates of skeletal muscle protein were also directly calculated. Seven healthy men were studied before and 5 days after intramuscular injection of 200 mg of testosterone enanthate. Protein synthesis increased twofold after injection ( P < 0.05), whereas protein breakdown was unchanged. FSR and FBR calculations were in accordance, because FSR increased twofold ( P < 0.05) without a concomitant change in FBR. Net balance between synthesis and breakdown became more positive with both methodologies ( P< 0.05) and was not different from zero. T injection increased arteriovenous essential and nonessential nitrogen balance across the leg ( P < 0.05) in the fasted state, without increasing amino acid transport. Thus T administration leads to an increased net protein synthesis and reutilization of intracellular amino acids in skeletal muscle.

Combined effects of hyperaminoacidemia and oxandrolone on skeletal muscle protein synthesis

2000 ◽  
Vol 278 (2) ◽  
pp. E273-E279 ◽  
Author(s):  
Melinda Sheffield-Moore ◽  
Robert R. Wolfe ◽  
Dennis C. Gore ◽  
Steven E. Wolf ◽  
Dennis M. Ferrer ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Compartment Model ◽  
Acid Mixture ◽  
Skeletal Muscle Protein ◽  
Amino Acid Infusion

We investigated whether the normal anabolic effects of acute hyperaminoacidemia were maintained after 5 days of oxandrolone (Oxandrin, Ox)-induced anabolism. Five healthy men [22 ± 3 (SD) yr] were studied before and after 5 days of oral Ox (15 mg/day). In each study, a 5-h basal period was followed by a 3-h primed-continuous infusion of a commercial amino acid mixture (10% Travasol). Stable isotopic data from blood and muscle sampling were analyzed using a three-compartment model to calculate muscle protein synthesis and breakdown. Model-derived muscle protein synthesis increased after amino acid infusion in both the control [basal control (BC) vs. control + amino acids (C+AA); P < 0.001] and Ox study [basal Ox (BOx) vs. Ox + amino acids (Ox+AA); P < 0.01], whereas protein breakdown was unchanged. Fractional synthetic rates of muscle protein increased 94% (BC vs. C+AA; P = 0.01) and 53% (BOx vs. Ox+AA; P < 0.01), respectively. We conclude that the normal anabolic effects of acute hyperaminoacidemia are maintained in skeletal muscle undergoing oxandrolone-induced anabolism.

scholarly journals The regulation of protein synthesis in the liver of rats. Mechanisms of dietary amino acid control in the immature animal

1968 ◽  
Vol 107 (5) ◽  
pp. 615-623 ◽  
Author(s):  
R. W. Wannemacher ◽  
W. K. Cooper ◽  
M. B. Yatvin
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Specific Radioactivity ◽  
Protein Diet ◽  
Low Protein Diet ◽  
Deficient Diet ◽  
Low Protein ◽  
Rna Content ◽  
Cytoplasmic Rna

Weanling (23-day-old) rats were fed either on an amino acid-deficient diet (6% of casein, which in effect represents an ‘amino acid-deficient’ diet) or on a diet containing an adequate amount of protein (18% of casein) for 28 days. The hepatic cells from the animals fed on the low-protein diet were characterized by low amino acid content, almost complete inhibition of cell proliferation and a marked decrease in cell volume, protein content and concentration of cytoplasmic RNA compared with cells from control rats. The lower concentration of cytoplasmic RNA was correlated with a decreased ribosomal-RNA content, of which a larger proportion was in the form of free ribosomes. The protein-synthetic competence and messenger-RNA content of isolated ribosomes from liver cells of protein-deprived animals were 40–50% of those noted in controls. At 1hr. after an injection of radioactive uridine, the specific radioactivity of liver total RNA was greater in the group fed on the low-protein diet, but the amount of label that was associated with cytoplasmic RNA or ribosomes was significantly less than that noted in control animals. From these data it was concluded that dietary amino acids regulate hepatic protein synthesis (1) by affecting the ability of polyribosomes to synthesize protein and (2) by influencing the concentration of cytoplasmic ribosomes. It is also tentatively hypothesized that the former process may be directly related to the concentration of cellular free amino acids, whereas the latter could be correlated with the ability of newly synthesized ribosomal sub-units to leave the nucleus.

Endotoxemia reduces skeletal muscle protein synthesis in neonates

2002 ◽  
Vol 283 (5) ◽  
pp. E909-E916 ◽  
Author(s):  
Renan A. Orellana ◽  
Pamela M. J. O'Connor ◽  
Hanh V. Nguyen ◽  
Jill A. Bush ◽  
Agus Suryawan ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Interleukin 1 ◽  
Amino Acid Mixture ◽  
Acid Mixture ◽  
Skeletal Muscle Protein ◽  
Skeletal Muscle Protein Synthesis

Protein synthesis in skeletal muscle is reduced by as much as 50% as early as 4 h after a septic challenge in adults. However, the effect of sepsis on muscle protein synthesis has not been determined in neonates, a highly anabolic population whose muscle protein synthesis rates are elevated and uniquely sensitive to insulin and amino acid stimulation. Neonatal piglets ( n = 10/group) were infused for 8 h with endotoxin [lipopolysaccharide (LPS), 0 and 10 μg · kg−1 · h−1]. Plasma amino acid and glucose concentrations were kept at the fed level by infusion of dextrose and a balanced amino acid mixture. Fractional protein synthesis rates were determined by use of a flooding dose of [3H]phenylalanine. LPS infusion produced a septic-like state, as indicated by an early and sustained elevation in body temperature, heart rate, and plasma tumor necrosis factor-α, interleukin-1, cortisol, and lactate concentrations. Plasma levels of insulin increased, whereas glucose and amino acids decreased, suggesting the absence of insulin resistance. LPS significantly reduced protein synthesis in longissimus dorsi muscle by only 11% and in gastrocnemius by only 15%, but it had no significant effect in masseter and cardiac muscles. LPS increased protein synthesis in the liver (22%), spleen (28%), kidney (53%), jejunum (19%), diaphragm (21%), lung (50%), and skin (13%), but not in the stomach, pancreas, or brain. These findings suggest that, when substrate supply is maintained, skeletal muscle protein synthesis in neonates compared with adults is relatively resistant to the catabolic effects of sepsis.

scholarly journals Response of skeletal muscle protein synthesis to insulin in suckling pigs decreases with development

1998 ◽  
Vol 275 (4) ◽  
pp. E602-E609 ◽  
Author(s):  
Diane Wray-Cahen ◽  
Hanh V. Nguyen ◽  
Douglas G. Burrin ◽  
Philip R. Beckett ◽  
Marta L. Fiorotto ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Whole Body ◽  
Skeletal Muscle Protein ◽  
Protein Deposition ◽  
Skeletal Muscle Protein Synthesis ◽  
Elevated Rate

The elevated rate of muscle protein deposition in the neonate is largely due to an enhanced stimulation of skeletal muscle protein synthesis by feeding. To examine the role of insulin in this response, hyperinsulinemic-euglycemic-amino acid clamps were performed in 7- and 26-day-old pigs. Pigs were infused with 0, 30, 100, or 1,000 ng ⋅ kg−0.66 ⋅ min−1of insulin to mimic the plasma insulin levels observed under fasted, fed, refed, and supraphysiological conditions, respectively. Whole body amino acid disposal was determined from the rate of infusion of an amino acid mixture necessary to maintain plasma essential amino acid concentrations near their basal fasting levels. A flooding dose ofl-[4-3H]phenylalanine was used to measure skeletal muscle protein synthesis. Whole body amino acid disposal increased progressively as the insulin infusion rate increased, and this response was greater in 7- than in 26-day-old pigs. Skeletal muscle protein synthesis was stimulated by insulin, and this response was maximal at a low insulin infusion rate (30 ng ⋅ kg−0.66 ⋅ min−1). The stimulation of muscle protein synthesis by insulin was also greater in 7- than in 26- day-old pigs. These data suggest that muscle protein synthesis is more sensitive to insulin than whole body amino acid disposal. The results further suggest that insulin is a central regulatory factor in the elevated rate of muscle protein deposition and the increased response of skeletal muscle protein synthesis to feeding in the neonate.

Response of rat heart and skeletal muscle protein in vivo to insulin and amino acid infusion

1993 ◽  
Vol 264 (6) ◽  
pp. E958-E965 ◽  
Author(s):  
P. H. McNulty ◽  
L. H. Young ◽  
E. J. Barrett
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Skeletal Muscle Protein ◽  
Acid Infusion ◽  
Amino Acid Infusion

Whether insulin, at physiological concentrations, stimulates net muscle protein synthesis in vivo remains unresolved. To examine this, we infused either saline, insulin (2.8 mU.kg-1.min-1, euglycemic clamp), an amino acid solution, or insulin plus amino acids for 4 h into awake overnight-fasted rats. Heart and skeletal muscle protein synthesis was measured by either a continuous tracer infusion method, using L-[1-14C]leucine, L-[2,5-3H]leucine, or L-[ring-2,6-3H]phenylalanine or by injection of L-[ring-2,6-3H]phenylalanine with a pool-flooding bolus of unlabeled phenylalanine. In heart, synthesis rates obtained using the arterial plasma specific activity of [3H]phenylalanine administered as either a tracer infusion or flooding bolus were comparable in saline-treated rats (range 10.9 +/- 1.2 to 12.2 +/- 0.9%/day) and were not affected by infusion of insulin or amino acids. Estimates using continuous infusion of L-[1-14C]leucine were significantly lower (P < 0.001), except when unlabeled amino acids were given also. In skeletal muscle, rates estimated using the flooding bolus (6.7 +/- 0.8%/day) were also not affected by insulin or amino acids. Estimates using continuous infusion of [3H]leucine (2.6 +/- 0.3%/day) or [3H]phenylalanine (2.8 +/- 1.0%/day) were lower and were still lower using [14C]leucine (1.6 +/- 0.6%/day), but increased toward those estimated with the flooding bolus during amino acid infusion. We conclude that, in heart muscle of the mature rat in vivo, neither insulin nor amino acids affect protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

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