scholarly journals Estimation of tissue protein synthesis in sheep during sustained elevation of plasma leucine concentration by intravenous infusion

1986 ◽  
Vol 56 (1) ◽  
pp. 281-288 ◽  
Author(s):  
A. L. Schaefer ◽  
S. R. Davis ◽  
G. A. Hughson
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Intravenous Infusion ◽  
Infusion Rate ◽  
Specific Radioactivity ◽  
Precursor Pool ◽  
Fractional Rate ◽  
Tissue Protein Synthesis ◽  
Plasma Leucine

1. The fractional rate of protein synthesis (FSR) was determined in skeletal muscle, liver, rumen and cardiac muscle of wether sheep by continuous intravenous infusion of L–[4,5–3H]leucine accompanied by infusion of 0, 7.6, 15.2 or 22.8 mmol leucine/h (three sheep per treatment). FSR was calculated assuming plasma (ksp) or intracellular (ksi) leucine-specific radioactivity (SRA) was representative of the leucine precursor pool SRA for protein synthesis.2. Plasma leucine concentration (plateau) was linearly related to leucine infusion rate, 22.8 mmol/h evoking tenfold increase in plasma concentration.3. Difference between plasma leucine SRA and intracellular leucine SRA in all tissues diminished as plasma leucine concentration increased.4. There were significant differences between ksi and kap estimates for liver and rumen in control sheep.5. As leucine infusion rate increased, differences between kri and kag, diminished in all tissues. With increasing leucine infusion, in liver kst decreased and ksp was increased, in rumen kge decreased and ksp was stable, while in cardiac and skeletal muscle ksi and ksp both increased.6. At a leucine infusion rate of 22.8 mmol/h, mean kap, and kst respectively were: rumen 1 1 (SE 2), 13 (SE 1); liver 19 (SE 2), 21 (SE 2); cardiac muscle 3–6 (SE 0.4), 3.8 (SE 0.3); skeletal muscle 4.1 (SE 0.2), 4.5 (SE 0.5) and did not differ significantly in any tissue.

scholarly journals Acute IGF-I infusion stimulates protein synthesis in skeletal muscle and other tissues of neonatal pigs

2002 ◽  
Vol 283 (4) ◽  
pp. E638-E647 ◽  
Author(s):  
Teresa A. Davis ◽  
Marta L. Fiorotto ◽  
Douglas G. Burrin ◽  
Rhonda C. Vann ◽  
Peter J. Reeds ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Liver Protein ◽  
Tissue Protein ◽  
Neonatal Pigs ◽  
Igf I ◽  
Tissue Protein Synthesis ◽  
Insulin Replacement

Studies have shown that protein synthesis in skeletal muscle of neonatal pigs is uniquely sensitive to a physiological rise in both insulin and amino acids. Protein synthesis in cardiac muscle, skin, and spleen is responsive to insulin but not amino acid stimulation, whereas in the liver, protein synthesis responds to amino acids but not insulin. To determine the response of protein synthesis to insulin-like growth factor I (IGF-I) in this model, overnight-fasted 7- and 26-day-old pigs were infused with IGF-I (0, 20, or 50 μg · kg−1 · h−1) to achieve levels within the physiological range, while amino acids and glucose were clamped at fasting levels. Because IGF-I infusion lowers circulating insulin levels, an additional group of high-dose IGF-I-infused pigs was also provided replacement insulin (10 ng · kg−0.66 · min−1). Tissue protein synthesis was measured using a flooding dose ofl-[4-3H]phenylalanine. In 7-day-old pigs, low-dose IGF-I increased protein synthesis by 25–60% in various skeletal muscles as well as in cardiac muscle (+38%), skin (+24%), and spleen (+32%). The higher dose of IGF-I elicited no further increase in protein synthesis above that found with the low IGF-I dose. Insulin replacement did not alter the response of protein synthesis to IGF-I in any tissue. The IGF-I-induced increases in tissue protein synthesis decreased with development. IGF-I infusion, with or without insulin replacement, had no effect on protein synthesis in liver, jejunum, pancreas, or kidney. Thus the magnitude, tissue specificity, and developmental change in the response of protein synthesis to acute physiological increases in plasma IGF-I are similar to those previously observed for insulin. This study provides in vivo data indicating that circulating IGF-I and insulin act on the same signaling components to stimulate protein synthesis and that this response is highly sensitive to stimulation in skeletal muscle of the neonate.

scholarly journals Protein synthesis in tissues of growing lambs

1981 ◽  
Vol 46 (3) ◽  
pp. 409-419 ◽  
Author(s):  
S. R. Davis ◽  
T. N. Barry ◽  
G. A. Hughson
Keyword(s):  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Specific Radioactivity ◽  
Biceps Femoris ◽  
Whole Body ◽  
Tissue Homogenate ◽  
Body Protein ◽  
Tissue Protein ◽  
Biceps Femoris Muscle ◽  
Plasma Leucine

1. The fractional rate of protein synthesis (FSR) in tissues of nine growing lambs (4–5 months of age) was estimated following continuous infusion of L-[4,5–3H]leucine for a period of 7 h. Minimum and upper estimates of FSR were obtained assuming that the specific radioactivity (SRA) of leucine in blood plasma and tissue homogenate respectively defined that of leucyl tRNA.2. Mean upper estimates of tissue protein FSR (/d) were skin 0·35, longissimus dorsi muscle 0·05, biceps femoris muscle 0·04, liver 0·54, rumen 0·79, cardiac muscle 0·09. Minimum estimates of tissue protein FSR ranged from 0·03 (muscle) to 0·15 (liver).3. Plasma leucine flux was closely related to body protein content and dietary leucine absorption (r 0·94).4. The rate of whole-body protein synthesis (WBS) derived from plasma leucine flux corrected for oxidation and localized recycling of leucine into protein was similar to that calculated from the sum of daily protein synthesis in individual tissues using the upper estimate of FSR, i.e. 610 g/d v. 581 g/d.5. The estimate of WBS derived from plasma leucine flux directly (241 g/d) was similar to that calculated from the sum of minimum estimates of daily protein synthesis in individual tissues (214 g/d).6. The ratio, intracellular leucine SRA:plasma leucine SRA tended to increase with increasing dietary leucine absorption in all tissues although these factors were only significantly correlated (P < 0·05) in cardiac muscle, skin and rumen. Such relationships suggest an increased exchange of plasma leucine with intracellular leucine with increased food intake.7. It was estimated that the energy cost of protein synthesis accounted for approximately 42% of daily heat production.

Protein synthesis and RNA in tissues of the pig

1976 ◽  
Vol 230 (4) ◽  
pp. 1108-1112 ◽  
Author(s):  
PJ Garlick ◽  
TL Burk ◽  
RW Swick
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Metabolic Rate ◽  
Protein Content ◽  
Intravenous Infusion ◽  
Whole Body ◽  
Continuous Intravenous Infusion ◽  
Visceral Organs ◽  
Fractional Rate ◽  
Rna Concentration

The rate of protein synthesis in 75-kg pigs was measured by continuous intravenous infusion of [14C]tyrosine. In the whole body, over 600 g of protein were synthesized each day. In pigs, rats, and man the rate of protein synthesis in the whole body was related to metabolic rate. The fractional rate of synthesis of protein in the tissues was also measured. The proteins of visceral organs (liver kidney, lung, and spleen) were renewed at rates close to 20% per day, those of brain at 8% per day, heart 7% per day, and skeletal muscle 4% per day. A significant correlation was observed between the fractional rate of protein synthesis in the tissue and RNA concentration. Calculation of the total amount of protein synthesized in skeletal muscle of the pig (fractional rate of synthesis X protein content) shows that muscle contributes 42% of whole-body synthesis. By contrast, in the rat only 19% of whole-body synthesis occurs in muscle.

Aminoacyl-tRNA and tissue free amino acid pools are equilibrated after a flooding dose of phenylalanine

1999 ◽  
Vol 277 (1) ◽  
pp. E103-E109 ◽  
Author(s):  
Teresa A. Davis ◽  
Marta L. Fiorotto ◽  
Hanh V. Nguyen ◽  
Douglas G. Burrin
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Free Amino Acid ◽  
Free Amino ◽  
Specific Radioactivity ◽  
Isotopic Labeling ◽  
Precursor Pool ◽  
Free Amino Acid Pools

The flooding dose method, which is used to measure tissue protein synthesis, assumes equilibration of the isotopic labeling between the aminoacyl-tRNA pool and the tissue and blood free amino acid pools. However, this has not been verified for a phenylalanine tracer in an in vivo study. We determined the specific radioactivity of [3H]phenylalanine in the aminoacyl-tRNA and the tissue and blood free amino acid pools of skeletal muscle and liver 30 min after administration of a flooding dose of phenylalanine along with [3H]phenylalanine. Studies were performed in neonatal pigs in the fasted and refed states and during hyperinsulinemic-euglycemic-amino acid clamps. The results showed that, 30 min after the administration of a flooding dose of phenylalanine, there was equilibration of the specific radioactivity of phenylalanine among the blood, tissue, and tRNA precursor pools. Equilibration of the specific radioactivity of the three precursor pools for protein synthesis occurred in both skeletal muscle and liver. Neither feeding nor insulin status affected the aminoacyl-tRNA specific radioactivity relative to the tissue free amino acid specific radioactivity. The results support the assumption that the tissue free amino acid pool specific radioactivity is a valid measure of the precursor pool specific radioactivity and thus can be used to calculate protein synthesis rates in skeletal muscle and liver when a flooding dose of phenylalanine is administered.

scholarly journals Effects of experimental hyperthyroidism on protein turnover in skeletal and cardiac muscle as measured by [14C]tyrosine infusion

1982 ◽  
Vol 204 (1) ◽  
pp. 69-74 ◽  
Author(s):  
W J Carter ◽  
W S V W Benjamin ◽  
F H Faas
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Heart Muscle ◽  
Protein Turnover ◽  
Cardiac Myocyte ◽  
Muscle Protein ◽  
Muscle Growth ◽  
Protein Breakdown ◽  
Fractional Rate

The effect of T3 (3,3′,5-tri-iodothyronine) on protein turnover in skeletal and cardiac muscle was measured in intact rats by means of a 6 h [14C]tyrosine-infusion technique. Treatment with 25-30 micrograms of T3/100 g body wt. daily for 4-7 days increased the fractional rate of protein synthesis in skeletal muscle. Since the fractional growth rate of the muscle was decreased or unchanged, T3 treatment increased the rate of muscle protein breakdown. These findings suggest that increased protein degradation is an important factor in decreasing skeletal-muscle mass in hyperthyroidism. In contrast with skeletal muscle, T3 treatment for 7 days caused an equivalent increase in the rate of cardiac muscle growth and protein synthesis. This suggests that hyperthyroidism does not increase protein breakdown in heart muscle as it does in skeletal muscle. The failure of T3 to increase proteolysis in heart muscle may be due to a different action on the cardiac myocyte or to systemic effects of T3 which increase cardiac work.

Effect of intravenous glutamine on duodenal mucosa protein synthesis in healthy growing dogs

1999 ◽  
Vol 276 (4) ◽  
pp. E747-E753 ◽  
Author(s):  
J. Sérgio Marchini ◽  
Patrick Nguyen ◽  
Jack-Yves Deschamps ◽  
Pascale Maugère ◽  
Michel Krempf ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Intravenous Infusion ◽  
Duodenal Mucosa ◽  
Precursor Pool ◽  
Synthetic Rate ◽  
Intravenous Infusions ◽  
Appearance Rate ◽  
Fractional Synthetic Rate ◽  
Plasma Leucine ◽  
Glycine Level

To determine whether glutamine acutely stimulates protein synthesis in the duodenal mucosa, five healthy growing dogs underwent endoscopic biopsies of duodenal mucosa at the end of three 4-h primed, continuous intravenous infusions ofl-[1-13C]leucine on three separate days, while receiving intravenous infusion of 1) saline, 2)l-glutamine (800 μmol ⋅ kg−1 ⋅ h−1), and 3) isonitrogenous amounts of glycine. The three infusions were performed after 24 h of fasting, a week apart from each other and in a randomized order. Glutamine infusion induced a doubling in plasma glutamine level, and glycine caused a >10-fold rise in plasma glycine level. During intravenous infusions of [13C]leucine, the plasma leucine labeling attained a plateau value between 3.22 and 3.68 mole % excess (MPE) and [13C]ketoisocaproate ([13C]KIC) of 2.91–2.84 MPE; there were no significant differences between glutamine, glycine, and saline infusion days. Plasma leucine appearance rate was 354 ± 33 (SE), 414 ± 28, and 351 ± 35 μmol ⋅ kg−1 ⋅ h−1(not significant) during glycine, saline, and glutamine infusion, respectively. The fractional synthetic rate (FSR) of duodenal mucosa protein was calculated from the rise in protein-bound [13C]leucine enrichment in the biopsy sample, divided by time and with either plasma [13C]KIC or tissue free [13C]leucine as precursor pool enrichment. Regardless of the precursor pool used in calculations, duodenal protein FSR failed to rise significantly during glutamine infusion (65 ± 11%/day) compared either with saline (84 ± 18%/day) or glycine infusion days (80 ± 15%/day). We conclude that 1) plasma [13C]KIC and tissue free [13C]leucine can be used interchangeably as precursor pools to calculate gut protein FSR; and 2) short intravenous infusion of glutamine does not acutely stimulate duodenal protein synthesis in well-nourished, growing dogs.

scholarly journals Estimation of rate of protein synthesis by constant infusion of labelled amino acids in pigs

1978 ◽  
Vol 40 (2) ◽  
pp. 243-252 ◽  
Author(s):  
O. Simon ◽  
R. Münchmeyer ◽  
H. Bergner ◽  
Teresa Zebrowska ◽  
Lucyna Buraczewska
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Daily Intake ◽  
Specific Radioactivity ◽  
Growing Pigs ◽  
Constant Infusion ◽  
Fractional Rate ◽  
Liver And Pancreas ◽  
Infusion Method ◽  
Plasma Leucine

1. The fractional synthetic rates of tissue proteins were studied in growing pigs using the constant-infusion technique of tracer-labelled amino acids ([14C]leucine and [14C]lysine) and the mathetmatical model for calculation, employed in rats by Garlick, Millward & James (1973).2. During a 6 h infusion, samples were taken from blood and muscle and at the end of the infusion from liver, muscle, pancreas, heart, duodenum, jejunum, ileum, colon, and skin. The specific radioactivity of free and protein-bound leucine and lysine was estimated.3. A quasi-steady-state in the specific radioactivity of free plasma leucine and lysine was reached within approximately 2 h, the rate-constants being 35 and 48/d respectively.4. The specific radioactivity of free leucine and lysine in plasma was used to calculate the flux of these amino acids. It was found to be higher than the daily intake.5. The average fractional rate of protein synthesis in muscle and heart was 8.1 %/d, in small and large intestine the values were 50 and 33 %/d respectively and in liver and pancreas more than 100 %/d.6. The calculation of protein synthetic rate in pig tissue using the constant-infusion method of labelled amino acids seems to be a suitable tool for study of this species.

Skeletal and cardiac muscle protein turnover during cold acclimation in young rats

2000 ◽  
Vol 278 (3) ◽  
pp. R705-R711 ◽  
Author(s):  
T. A. McAllister ◽  
J. R. Thompson ◽  
S. E. Samuels
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Cold Acclimation ◽  
Protein Turnover ◽  
Muscle Protein ◽  
Muscle Protein Turnover ◽  
Protein Mass ◽  
The Absolute

The effect of long-term cold exposure on skeletal and cardiac muscle protein turnover was investigated in young growing animals. Two groups of 36 male 28-day-old rats were maintained at either 5°C (cold) or 25°C (control). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. Protein mass by day 20 was ∼28% lower in skeletal muscle (gastrocnemius and soleus) and ∼24% higher in heart in cold compared with control rats ( P < 0.05). In skeletal muscle, the fractional rates of protein synthesis ( k syn) and degradation ( k deg) were not significantly different between cold and control rats, although k syn was lower (approximately −26%) in cold rats on day 5; consequent to the lower protein mass, the absolute rates of protein synthesis (approximately −21%; P < 0.05) and degradation (approximately −13%; P < 0.1) were lower in cold compared with control rats. In heart, overall, k syn(approximately +12%; P < 0.1) and k deg(approximately +22%; P < 0.05) were higher in cold compared with control rats; consequently, the absolute rates of synthesis (approximately +44%) and degradation (approximately +54%) were higher in cold compared with control rats ( P < 0.05). Plasma triiodothyronine concentration was higher ( P < 0.05) in cold compared with control rats. These data indicate that long-term cold acclimation in skeletal muscle is associated with the establishment of a new homeostasis in protein turnover with decreased protein mass and normal fractional rates of protein turnover. In heart, unlike skeletal muscle, rates of protein turnover did not appear to immediately return to normal as increased rates of protein turnover were observed beyond day 5. These data also indicate that increased rates of protein turnover in skeletal muscle are unlikely to contribute to increased metabolic heat production during cold acclimation.

Gut mucosal protein synthesis in fed and fasted humans

1998 ◽  
Vol 274 (3) ◽  
pp. E541-E546 ◽  
Author(s):  
Corinne Bouteloup-Demange ◽  
Yves Boirie ◽  
Pierre Déchelotte ◽  
Pierre Gachon ◽  
Bernard Beaufrère
Keyword(s):  
Protein Synthesis ◽  
Intravenous Infusion ◽  
Young Men ◽  
Duodenal Mucosa ◽  
Liquid Diet ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Fed State ◽  
Precursor Pool ◽  
Mucosal Protein

Fractional protein synthesis rate (FSR) of duodenal mucosa was measured in two groups of six healthy young men, either in the fed state at the end of a 10-day standardized diet or after a 36-h fast. Protein synthesis rate was measured during a 9-h intravenous infusion of [13C]leucine and [2H5]phenylalanine. The fed group also received an intragastric tracer, [2H3]leucine, mixed with the liquid diet. At the end of the tracer infusion, an endoscopy was performed to take duodenal mucosal biopsies. The major results were that 1) duodenal mucosal protein synthesis was high, 48.0 ± 8.5% (SE)/day by use of intravenous leucine tracer and intracellular leucine enrichment; 2) it was not affected by feeding whatever the tracer or the precursor pool used for the calculations; 3) the two intravenous tracers gave different FSR values; and 4) with the intragastric tracer, FSR was 25–220% of the rate calculated with the intravenous tracer, depending on the precursor pool used for the calculation. Thus absolute values of FSR should be taken with caution, because they depend on the precursor pool chosen, the route of tracer administration, and the tracer itself. However, gut mucosal protein synthesis as assessed by an intravenous tracer is not affected by feeding in humans.

Regulation of eukaryotic initiation factor-2B activity in muscle of diabetic rats

1993 ◽  
Vol 264 (1) ◽  
pp. E101-E108 ◽  
Author(s):  
A. M. Karinch ◽  
S. R. Kimball ◽  
T. C. Vary ◽  
L. S. Jefferson
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Cardiac Muscle ◽  
Casein Kinase Ii ◽  
Diabetic Rats ◽  
Casein Kinase ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Fast Twitch

Peptide-chain initiation is inhibited in fast-twitch skeletal muscle, but not heart, of diabetic rats. We have investigated mechanisms that might maintain eukaryotic initiation factor (eIF)-2B activity, preventing loss of efficiency of protein synthesis in heart of diabetic rats but not in fast-twitch skeletal muscle. There was no change in the amount or phosphorylation state of eIF-2 in skeletal or cardiac muscle during diabetes. In contrast, eIF-2B activity was decreased in fast-twitch but not slow-twitch muscle from diabetic animals. NADP+ inhibited partially purified eIF-2B in vitro, but addition of equimolar NADPH reversed the inhibition. The NADPH-to-NADP+ ratio was unchanged in fast-twitch muscle after induction of diabetes but was increased in heart of diabetic rats, suggesting that NADPH also prevents inhibition of eIF-2B in vivo. The activity of casein kinase II, which can phosphorylate and activate eIF-2B in vitro, was significantly lower in extracts of fast-twitch, but not cardiac muscle, of diabetic rats compared with controls. The results presented here demonstrate that changes in eIF-2 alpha phosphorylation are not responsible for the effect of diabetes on eIF-2B activity in fast-twitch skeletal muscle. Modulation of casein kinase II activity may be a factor in the regulation of protein synthesis in muscle during acute diabetes. The activity of eIF-2B in heart might be maintained by the increased NADPH/NADP+.

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