scholarly journals The effect of protein depletion and repletion on muscle-protein turnover in the chick

1981 ◽  
Vol 194 (3) ◽  
pp. 811-819 ◽  
Author(s):  
M L MacDonald ◽  
R W Swick
Keyword(s):  
Protein Synthesis ◽  
Protein Turnover ◽  
Muscle Protein ◽  
Control Diet ◽  
Breast Muscle ◽  
Synthesis Rate ◽  
Protein Depletion ◽  
Protein Mass ◽  
Fractional Rate

Rates of growth and protein turnover in the breast muscle of young chicks were measured in order to assess the roles of protein synthesis and degradation in the regulation of muscle mass. Rates of protein synthesis were measured in vivo by injecting a massive dose of L-[1-14C]valine, and rates of protein degradation were estimated as the difference between the synthesis rate and the growth rate of muscle protein. In chicks fed on a control diet for up to 7 weeks of age, the fractional rate of synthesis decreased from 1 to 2 weeks of age and then changed insignificantly from 2 to 7 weeks of age, whereas DNA activity was constant for 1 to 7 weeks. When 4-week-old chicks were fed on a protein-free diet for 17 days, the total amount of breast-muscle protein synthesized and degraded per day and the amount of protein synthesized per unit of DNA decreased. Protein was lost owing to a greater decrease in the rate of protein synthesis, as a result of the loss of RNA and a lowered RNA activity. When depleted chicks were re-fed the control diet, rapid growth was achieved by a doubling of the fractional synthesis rate by 2 days. Initially, this was a result of increased RNA activity; by 5 days, the RNA/DNA ratio also increased. There was no evidence of a decrease in the fractional degradation rate during re-feeding. These results indicate that dietary-protein depletion and repletion cause changes in breast-muscle protein mass primarily through changes in the rate of protein synthesis.

Skeletal and heart muscle protein turnover during long-term exposure to high environmental temperatures in young rats

2000 ◽  
Vol 78 (7) ◽  
pp. 557-564 ◽  
Author(s):  
S E Samuels ◽  
T A McAllister ◽  
J R Thompson
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Muscle Mass ◽  
Protein Turnover ◽  
Muscle Protein ◽  
Control Group ◽  
Skeletal Muscle Protein ◽  
Protein Mass ◽  
Fractional Rate

A study was undertaken to determine the long-term effects of a hot environment on protein turnover in skeletal and cardiac muscles of young homeothermic animals. Three groups of 36 male 28 day old rats were housed at 35°C (hot group), 25°C (control group), or 25°C but pair-fed to the intake of the hot group (pair-fed group). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. By day 20, soleus and gastrocnemius (skeletal muscle) protein masses were 7 and 14% lower in the hot group and 31 and 21% lower in the pair-fed group compared with the control group (P < 0.05). The fractional rate of protein synthesis (ksyn) was on average 11% lower (P < 0.05) in the hot group compared with control rats and was not different from pair-fed rats. The fractional rate of skeletal muscle protein degradation (kdeg) in hot rats was slightly lower than in control rats; kdegwas on average 18% higher (P < 0.05) in the pair-fed group compared with the hot group and this difference appeared to be most prominent on day 5. In heart, by day 20, protein mass was 30% lower in the hot group and 40% lower in the pair-fed group compared with control rats (P < 0.05). ksynwas on average 19% lower (P < 0.05) in the hot group compared with the control group, but not different from pair-fed rats. In the heart there were no differences in kdegamong treatments. Plasma triiodothyronine (T3) concentration was lower in the hot group, but not in the pair-fed group, compared with controls. In conclusion, chronic exposure to hot environments was associated with lower skeletal and cardiac muscle mass and protein turnover; lower protein mass in this tissue was due to decreased ksyn; this is consistent with lower plasma T3concentrations. In pair-fed rats, ksynwas also reduced, but interestingly kdegwas not, resulting in a greater loss of skeletal muscle mass. These results suggest that heat exposure invokes physiological adaptations to preserve skeletal muscle mass despite decreased food intake. In the heart, loss of protein was a result of decreased ksyn, which can be primarily ascribed to lower food intake.Key words: protein synthesis, protein metabolism, acclimation, heat stress.

scholarly journals The diurnal response of muscle and liver protein synthesis in vivo in meal-fed rats

1973 ◽  
Vol 136 (4) ◽  
pp. 935-945 ◽  
Author(s):  
P. J. Garlick ◽  
D. J. Millward ◽  
W. P. T. James
Keyword(s):  
Protein Synthesis ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Specific Radioactivity ◽  
Whole Body ◽  
Rat Tissues ◽  
Liver Protein ◽  
Protein Mass ◽  
Fractional Rate

1. The rate of protein synthesis in rat tissues was measured by constant intravenous infusion of [14C]tyrosine. A modification has been developed for the method of calculating the rate of protein synthesis in individual tissues from the specific radioactivity of the free and protein-bound amino acid in tissue at the end of the infusion. This technique gives greater accuracy and allows a greater choice of labelled amino acids. The specific radioactivity of free tyrosine in plasma was used to calculate the plasma tyrosine flux, an index of the rate of protein synthesis in the whole body. 2. Young male Wistar rats were allowed access to food for only 4h in every 24h. The tyrosine flux and the rate of protein synthesis in liver and muscle at different periods of time after a single feed were estimated. 3. The tyrosine flux did not alter after feeding nor even after starvation for 48h. 4. The average fractional rate of protein synthesis in muscle was 7.2%/day, i.e. the proportion of the protein mass which is replaced each day. The rate rose after eating and declined during starvation for 48h. In addition the rate of muscle protein synthesis correlated with the growth rate of the rat. 5. In liver the average fractional rate of protein synthesis was 50%/day. There was no change in the rate after eating nor after starvation for 48h. In contrast with muscle this suggests that the changes in protein mass were accompanied by changes in the rate of protein breakdown rather than synthesis.

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.

Chronic effects of β2 agonists on body composition and protein synthesis in the rat

1984 ◽  
Vol 4 (1) ◽  
pp. 83-91 ◽  
Author(s):  
P. W. Emery ◽  
N. J. Rothwell ◽  
M. J. Stock ◽  
P. D. Winter
Keyword(s):  
Protein Synthesis ◽  
Muscle Protein ◽  
Binding Capacity ◽  
Body Weight Gain ◽  
Muscle Protein Synthesis ◽  
Body Protein ◽  
Fractional Rate ◽  
Brown Adipose ◽  
Β2 Agonists

Chronic treatment of rats with the β2-adrenergic agonists clenbuterol and fenoterol over 16–19 d raised energy intake, expenditure, and body weight gain but did not affect fat or energy deposition, and body protein gain was increased by 50 and 18%, respectively. Both drugs increased the protein content and mitochondrial GDP-binding capacity of brown adipose tissue. Clenbuterol did not affect plasma insulin, growth hormone, or triiodothyronine levels, although insulin levels were reduced by fenoterol. Both drugs caused hypertrophy of skeletal muscle (gastrocnemius), and muscle protein synthesis in vivo (fractional rate) was elevated by 34 and 26% in clenbuterol and fenoteroltreated rats, respectively.

Attenuated responses of muscle protein synthesis to fasting and insulin in adult female rats

1992 ◽  
Vol 262 (1) ◽  
pp. E1-E5 ◽  
Author(s):  
A. G. Baillie ◽  
P. J. Garlick
Keyword(s):  
Protein Synthesis ◽  
Adult Female ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Fiber Type ◽  
Female Rats ◽  
Adult Rats ◽  
Fractional Rate ◽  
The Individual

One-year-old adult female rats were fasted for 12 or 36 h followed by a 30-min infusion of insulin. The responses of the fractional rate of protein synthesis (Ks) in the individual muscles (measured in vivo) to fasting were small and mostly nonsignificant. After 12 h of fasting, only the epitrochlearis muscle (ET) showed a significant decrease in Ks, and, even after 36 h of fasting, a significant decrease in Ks was seen in only ET, extensor digitorum longus, and tensor fasciae latae (TFL). After the 36-h fast, infusion of insulin restored the fed Ks in all muscles except TFL. The fiber-type composition of the individual muscles appeared to influence the muscles' responsiveness to the fasting, since the highly glycolytic TFL was the most sensitive (particularly after 36 h of fasting), whereas the highly oxidative adductor longus and soleus muscles were unaffected by either fasting or insulin. In a second experiment, refeeding of fasted adult rats also had little effect on Ks, consistent with the low sensitivity to fasting shown by the first experiment. The parallel results in the two experiments confirmed that the low responsiveness to fasting and insulin infusion in these adult rats was not a result of failure to absorb in “fed” animals or insufficient levels of insulin during insulin infusions. In contrast, a third experiment showed that muscle protein synthesis in the gastrocnemius muscle from young adult (5-mo-old) female rats was significantly reduced after only 12 h of fasting.

Alterations of protein turnover underlying disuse atrophy in human skeletal muscle

2009 ◽  
Vol 107 (3) ◽  
pp. 645-654 ◽  
Author(s):  
S. M. Phillips ◽  
E. I. Glover ◽  
M. J. Rennie
Keyword(s):  
Protein Synthesis ◽  
Muscle Mass ◽  
Protein Turnover ◽  
Cultured Cells ◽  
Muscle Protein ◽  
Human Muscle ◽  
Muscle Loss ◽  
Disuse Atrophy ◽  
In Vivo Measurements

Unloading-induced atrophy is a relatively uncomplicated form of muscle loss, dependent almost solely on the loss of mechanical input, whereas in disease states associated with inflammation (cancer cachexia, AIDS, burns, sepsis, and uremia), there is a procatabolic hormonal and cytokine environment. It is therefore predictable that muscle loss mainly due to disuse alone would be governed by mechanisms somewhat differently from those in inflammatory states. We suggest that in vivo measurements made in human subjects using arterial-venous balance, tracer dilution, and tracer incorporation are dynamic and thus robust by comparison with static measurements of mRNA abundance and protein expression and/or phosphorylation in human muscle. In addition, measurements made with cultured cells or in animal models, all of which have often been used to infer alterations of protein turnover, appear to be different from results obtained in immobilized human muscle in vivo. In vivo measurements of human muscle protein turnover in disuse show that the primary variable that changes facilitating the loss of muscle mass is protein synthesis, which is reduced in both the postabsorptive and postprandial states; muscle proteolysis itself appears not to be elevated. The depressed postprandial protein synthetic response (a phenomenon we term “anabolic resistance”) may even be accompanied by a diminished suppression of proteolysis. We therefore propose that most of the loss of muscle mass during disuse atrophy can be accounted for by a depression in the rate of protein synthesis. Thus the normal diurnal fasted-to-fed cycle of protein balance is disrupted and, by default, proteolysis becomes dominant but is not enhanced.

Changes in protein turnover in rat uterus during pregnancy

1986 ◽  
Vol 250 (2) ◽  
pp. E114-E120 ◽  
Author(s):  
A. J. Morton ◽  
D. F. Goldspink
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Turnover ◽  
Cathepsin D ◽  
Cell Loss ◽  
Protein Breakdown ◽  
Rat Uterus ◽  
Fractional Rate ◽  
Uterine Growth

The adaptive growth and protein turnover of the rat uterus were studied during the 21 days of gestation and up to 3 days after parturition. Despite large increases (13-fold) in uterine size during gestation, the fractional rate of protein synthesis (measured in vivo) remained unchanged when compared with nonpregnant tissue values of 44 +/- 5%/day. However, decreases were found in the rate of protein breakdown after implantation (i.e., 75% on day 7 and 28% on day 11) and in the activity of cathepsin D (i.e., 33 and 85% on days 8 and 16 of gestation). Changes in the degradative processes would therefore appear to be primarily responsible for the massive uterine growth during pregnancy. In contrast to the uterus the fractional rates of synthesis in the placenta and fetus progressively decreased during gestation. After parturition the uterus rapidly returned to its normal size by a combination of cellular atrophy and cell loss. After 2 days, a complementary decrease in the fractional rate of synthesis (30%) and an increase in protein degradation (2-fold) explained the process of involution.

Gastrointestinal tract protein synthesis and mRNA levels for proteolytic systems in adult fasted rats

1996 ◽  
Vol 271 (2) ◽  
pp. E232-E238 ◽  
Author(s):  
S. E. Samuels ◽  
D. Taillandier ◽  
E. Aurousseau ◽  
Y. Cherel ◽  
Y. Le Maho ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Small Intestine ◽  
Gastrointestinal Tract ◽  
Mrna Levels ◽  
Protein Mass ◽  
Fractional Rate ◽  
Intestinal Protein ◽  
Critical Components ◽  
Fasted Rats

We studied protein turnover in the gastrointestinal tract of adult fasted rats, since the mechanisms responsible for protein wasting in these tissues are poorly understood. Protein mass of stomach, small intestine, and colon decreased by 14-29 and 21-49% after 1 and 5 days of fasting, respectively. The fractional rate of in vivo protein synthesis (ks) was approximately 34% lower in the stomach after 1 and 5 days of fasting due to decreased capacity for protein synthesis (Cs). In small intestine and colon, ks was not different after 1 day, but was approximately 26% lower on day 5, mainly because of a reduction in Cs. Thus protein wasting in the stomach is primarily mediated by decreased protein synthesis but not in small intestine and colon during short-term fasting. To determine which proteolytic systems may be activated in the gut, we measured mRNA levels for critical components of the lysosomal (cathepsins B and D), Ca(2+)-activated (m-calpain), and ubiquitin-dependent (ubiquitin, 14-kDa ubiquitin-conjugating enzyme E2, and C8, and C9 proteasome subunits) proteolytic pathways. mRNA levels for most of these components increased during fasting, suggesting that a coordinated activation of multiple proteolytic systems contributed to intestinal protein wasting.

The use of doubly labeled milk protein to measure postprandial muscle protein synthesis rates in vivo in humans

2014 ◽  
Vol 117 (11) ◽  
pp. 1363-1370 ◽  
Author(s):  
Nicholas A. Burd ◽  
Naomi M. Cermak ◽  
Imre W. K. Kouw ◽  
Stefan H. Gorissen ◽  
Annemie P. Gijsen ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Continuous Infusion ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Constant Infusion ◽  
Synthesis Rate ◽  
Mole Percent ◽  
Precursor Pool ◽  
The Impact

We aimed to determine the impact of precursor pool dilution on the assessment of postprandial myofibrillar protein synthesis rates (MPS). A Holstein dairy cow was infused with large amounts of L-[1-13C]phenylalanine and L-[1-13C]leucine, and the milk was collected and fractionated. The enrichment levels in the casein were 38.7 and 9.3 mole percent excess, respectively. In a subsequent human experiment, 11 older men (age: 71 ± 1 y, body mass index: 26 ± 0.1 kg·m−2) received a primed constant infusion of L-[ring-2H5]phenylalanine and L-[1-13C]leucine. Blood and muscle samples were collected before and after the ingestion of 20-g doubly labeled casein to assess postprandial MPS based on the 1) constant tracer infusion of L-[ ring-2H5]phenylalanine, 2) ingestion of intrinsically L-[1-13C]phenylalanine-labeled casein, and 3) constant infusion of L-[1-13C]leucine in combination with the ingestion of intrinsically L-[1-13C]leucine-labeled casein. Postprandial MPS was increased ( P < 0.05) after protein ingestion (∼70% above postabsorptive values) based on the L-[1-13C]leucine tracer. There was no significant stimulation of postprandial MPS (∼27% above postabsorptive values) when the calculated fractional synthesis rate was based on the L-[ring-2H5]phenylalanine ( P = 0.2). Comparisons of postprandial MPS based on the primed continuous infusion of L-[1-13C]leucine or the ingestion of intrinsically L-[1-13C]phenylalanine-labeled casein protein demonstrated differences compared with the primed continuous infusion of L-[ ring-2H5]phenylalanine ( P > 0.05). Our findings confirm that the postprandial MPS assessed using the primed continuous tracer infusion approach may differ if tracer steady-state conditions in the precursor pools are perturbed. The use of intrinsically doubly labeled protein provides a method to study the metabolic fate of the ingested protein and the subsequent postprandial MPS response.

scholarly journals Rates of protein turnover in vivo and in vitro in ventricular muscle of hearts from fed and starved rats

1984 ◽  
Vol 222 (2) ◽  
pp. 395-400 ◽  
Author(s):  
V R Preedy ◽  
D M Smith ◽  
N F Kearney ◽  
P H Sugden
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Protein Turnover ◽  
Synthesis Rate ◽  
Protein Synthesis Rate ◽  
Ventricular Muscle ◽  
Degradation Rates ◽  
Perfused Hearts

Starvation of 300 g rats for 3 days decreased ventricular-muscle total protein content and total RNA content by 15 and 22% respectively. Loss of body weight was about 15%. In glucose-perfused working rat hearts in vitro, 3 days of starvation inhibited rates of protein synthesis in ventricles by about 40-50% compared with fed controls. Although the RNA/protein ratio was decreased by about 10%, the major effect of starvation was to decrease the efficiency of protein synthesis (rate of protein synthesis relative to RNA). Insulin stimulated protein synthesis in ventricles of perfused hearts from fed rats by increasing the efficiency of protein synthesis. In vivo, protein-synthesis rates and efficiencies in ventricles from 3-day-starved rats were decreased by about 40% compared with fed controls. Protein-synthesis rates and efficiencies in ventricles from fed rats in vivo were similar to values in vitro when insulin was present in perfusates. In vivo, starvation increased the rate of protein degradation, but decreased it in the glucose-perfused heart in vitro. This contradiction can be rationalized when the effects of insulin are considered. Rates of protein degradation are similar in hearts of fed animals in vivo and in glucose/insulin-perfused hearts. Degradation rates are similar in hearts of starved animals in vivo and in hearts perfused with glucose alone. We conclude that the rates of protein turnover in the anterogradely perfused rat heart in vitro closely approximate to the rates in vivo in absolute terms, and that the effects of starvation in vivo are mirrored in vitro.

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