Protein synthesis in the whole body,liver, skeletal muscle and kidney cortex of lambs infected by the nematode Trichostrongylus colubriformis

Jones W. O. and Symons L. E. A. 1982. Protein synthesis in the whole body, liver, skeletal muscle and kidney cortex of lambs infected by the nematode Trichostrongylus colubriformis. International Journal for Parasitology12: 295–301. Tyrosine flux and the synthesis of protein in the whole body, liver, skeletal muscle and kidney cortex and of albumin in lambs infected with Trichostrongylus colubriformis and uninfected lambs fed ad libitum or pair-fed with the infected group, were measured by constant infusion of ¹⁴C-l-tyrosine. Live weight gain was lower in the infected than in pairfed lambs, but rates of whole body protein synthesis were similar in both groups. On the other hand, compared with control lambs, there was a faster rate of protein synthesis per unit of protein consumed in infected but not in pair-fed lambs. Rates of protein synthesis per unit of body weight in infected were higher than in pair-fed lambs, but similar to the rate in control lambs. The fractional synthetic rates (FSR) of albumin and liver proteins and the amount of liver protein synthesized per day were increased by infection. The FSR and amount of protein synthesized per day were depressed in skeletal muscle and kidney cortex. Anorexia did not explain any of these changes. Infection caused a loss of protein from each of these tissues, but this loss was due to anorexia in only the liver. There was generally good correlation between concentration of RNA per g fresh weight or per mg nitrogen and the FSR of protein. However, although the $\text{RNA}\text{DNA}$ ratio correlated well with synthesis in skeletal muscle, it was poorly correlated for liver proteins. The relationship between the rate of growth and protein synthesis in infected lambs is discussed.     

Acute effects of corticosterone on tissue protein synthesis and insulin-sensitivity in rats in vivo.

The effect of corticosterone treatment on the sensitivity of muscle protein synthesis to insulin infusion was assessed in post-absorptive young rats. To select the optimal time period for corticosterone treatment, protein synthesis was measured by injection of L-[2,6-3H]phenylalanine (1.5 mmol/kg body weight) 1, 4, 12 or 24 h after injection of corticosterone (5 mg/kg body wt.). Muscle protein synthesis was significantly decreased at 4 h and the effect was maximal by 12 h; liver protein synthesis was elevated at 12 h and 24 h. The dose-response of muscle protein synthesis to a 30 min infusion with 0-150 munits of insulin/h was then compared in rats pretreated with corticosterone (10 mg/100 g body wt.) or vehicle alone. When no insulin was infused, corticosterone inhibited protein synthesis in gastrocnemius muscle. High doses of insulin stimulated protein synthesis, but the inhibition by corticosterone was similar to that in the absence of insulin. At intermediate doses of insulin there was an increased requirement for insulin to elicit an equivalent response in muscle protein synthesis. Plantaris muscle responded in a manner similar to that of gastrocnemius, but neither soleus muscle nor liver responded significantly to insulin. These data suggest that corticosterone has two modes of action; one which is independent from and opposite to that of insulin, and a second which causes insulin-resistance through a decrease in sensitivity rather than a change in responsiveness.     

In vivo rates of protein synthesis in brain,muscle, and liver of five vertebrate species

To compare cerebral protein metabolism rates in vivo, protein synthesis rates of three organs of five vertebrate species were measured after a single i.p. injection of a flooding dose of [1-¹⁴C]valine. In muscle, brain, and liver, the respective average protein synthesis rates, expressed as percent of total protein-bound valine replaced per hour, that is, percent synthesis per hour, in goldfish at 22°C body temperature, were 0.07, 0.23, and 0.57%; in the bullfrog at 20°C, 0.06, 0.18, and 0.55%; in the white Leghorn chicken at 39°C, 0.24, 0.70, and 2.17%; and in the mouse at 38°C, 0.22, 0.65, and 2.0%. In the Tokay lizard at different body temperatures, the synthesis rates were 0.04, 0.13, and 0.43% at 26°C; 0.05, 0.20, and 0.63% at 32°C; and 0.07, 0.27, and 0.81% at 38°C. The results demonstrate differences in protein synthesis rates in organs of the various species examined. The differences among the species seem to be due, to a major extent, to differences in body temperature; rates in lizard are below those in other species at temperatures tried. Protein synthesis rates in brain in all species are almost three times lower than those in liver and almost three times higher than those in muscle.     

Dietary protein and lactose increase translation initiation factor activation and tissue protein synthesis in neonatal pigs

Protein synthesis and eukaryotic initiation factor (eIF) activation are increased in muscle and liver of pigs parenterally infused with amino acids and insulin. To examine the effects of enteral protein and carbohydrate on protein synthesis, pigs (n = 42, 1.7 kg body wt) were fed isocaloric milk diets containing three levels of protein (5, 15, and 25 g x kg body wt(-1) x day(-1)) and two levels of lactose (low = 11 and high = 23 g x kg body wt(-1) x day(-1)) from 1 to 6 days of age. On day 7, pigs were gavage fed after 4-h food deprivation, and tissue protein synthesis rates and biomarkers of mRNA translation were assessed. Piglet growth and protein synthesis rates in muscle and liver increased with dietary protein and plateaued at 15 g x kg body wt(-1) x day(-1) (P < 0.001). Growth tended to be greater in high-lactose-fed pigs (P = 0.07). Plasma insulin was lowest in pigs fed 5 g x kg body wt(-1) x day(-1) protein (P < 0.0001). Plasma branched-chain amino acids increased as protein intake increased (P < 0.0001). Muscle (P < 0.001) and liver (P < or = 0.001) ribosomal protein S6 kinase-1 and eIF4E-binding protein phosphorylation increased with protein intake and plateaued at 15 g x kg body wt(-1) x day(-1). The results indicate that growth and protein synthesis rates in neonatal pigs are influenced by dietary protein and lactose intake and might be mediated by plasma amino acids and insulin levels. However, feeding protein well above the piglet's requirement does not further stimulate the activation of translation initiation or protein synthesis in skeletal muscle and liver.     

Brain protein synthesis rates are not sensitive to elevated GABA,taurine, or glycine

The effects of elevated levels of GABA, glycine, or taurine on the rate of protein synthesis in plasma, brain, liver, and muscle of adult mice were measured in in vivo experiments after a flooding dose of labeled valine. Elevation of these amino acids caused hypothermia; keeping the animals in an incubator maintained physiological body temperature. The increase in GABA or glycine did not affect the rate of protein synthesis in these tissues to a significant degree. The increase in taurine levels caused inhibition of valine incorporation in plasma, liver, and muscle, while brain protein synthesis was unaffected. When glycine was increased in brain, the uptake of labeled free valine in the brain was greater.     

Respective influences of age and weaning on skeletal and visceral muscle protein synthesis in the lamb.

1. The influences of age and weaning on muscle protein synthesis were studied in vivo, by injecting a large dose of [3H]valine into 1-, 5- and 8-week-old suckling or 8-week-old weaned lambs. 2. The fractional rates of protein synthesis, in red- and white-fibre-type skeletal muscles or striated and smooth visceral muscles, were in 8-week-old suckling animals 24-37% of their values at 1 week of age. This developmental decline was related to decreased capacities for protein synthesis, i.e. RNA/protein ratios. 3. At 8 weeks of age, suckling and weaned lambs had similar fractional synthesis rates, capacities for protein synthesis and efficiencies of protein synthesis (i.e. rates of protein synthesis relative to RNA) in skeletal muscles. 4. In contrast, visceral-muscle fractional synthesis rates were lower in 8-week-old suckling lambs than in weaned animals, owing to decreased efficiencies of protein synthesis. It was concluded that developmental factors and the change to a solid diet, or weaning in itself, or both, affect differently skeletal and visceral muscle protein synthesis in the immature lamb.     

Protein metabolism in the newborn lamb. IV. Consequences of amino acid and lactose ingestion

A study was made on protein metabolism and hormonal changes following birth in newborn lambs fed amino acids alone or in combination with lactose. Eight newborn lambs taken from their mother immediately after birth were fed hourly for 8 h, either with a solution of peptides and free amino acids obtained by mild hydrolysis of whey proteins (4 lambs; diet AP) or with the same solution + lactose (4 lambs; diet APL). L-[4,5-3H] leucine was continuously perfused into a jugular vein for 6 h when the lambs were 2 h 30 min old. Plasma glucose and insulin levels increased after birth in APL lambs whereas they decreased in the AP; these differences were significantly different. Plasma cortisol levels remained unchanged throughout the experiment. Free essential amino acid levels did not vary when lambs were older than 4.5 h; they depended on the corresponding amino acid intakes. Plasma free threonine, valine, isoleucine, leucine, tyrosine and lysine were lower in APL than in AP lambs. The plasma leucine irreversible loss and leucine oxidation were higher in AP than in APL lambs. The plasma flux of leucine from whole body protein breakdown was lower in APL than in AP lambs inasmuch as the plasma flux of dietary leucine may be estimated by the amounts of leucine ingested in both cases. No significant difference was found for the fractional synthesis rates of tissue proteins such as liver, skin, skeletal muscle, lung, brain and whole body. These rates for skin, muscle and whole body were close to those previously measured in colostrum fed lambs. The increase in whole body protein accretion resulting from lactose feeding in combination with amino acids seemed to result from a decreased protein breakdown that could be mediated by the insulin response.     

Synergism of triiodothyronine and corticosterone on muscle protein breakdown

The concerted effect of triiodothyronine (T3) and corticosterone on muscle protein synthesis and breakdown was studied. Thyroidectomized young male rats were treated with T3 (1.5 microgram/100 g body weight per day), corticosterone (10 mg/100 g body weight per day) and both T3 and corticosterone for 4 days. On the 3rd day of the experiment urine was collected to measure N tau-methylhistidine excretion as an index of muscle protein breakdown. On the last day of the experiment, the rates of protein synthesis in skeletal muscles were measured by the large-dose [3H]phenylalanine method. N tau-Methylhistidine excretion was slightly increased by T3 treatment and it was increased about 3-times by corticosterone treatment. When both T3 and corticosterone were administered, it was increased about 6-fold. The rate of muscle protein breakdown calculated from the difference between the rate of protein synthesis and the growth rate was consistent with these findings. The rate of muscle protein synthesis was increased by T3, and it was decreased by corticosterone. The rate was the same as that of the thyroidectomized control group when the animals were given T3 and corticosterone, showing that T3 restrained the inhibiting effect of corticosterone on muscle protein synthesis. The results indicate that a physiological level of T3 enhances the catabolic action of pharmacological doses of glucocorticoids on muscle protein breakdown.     

MEASUREMENTS OF IN VIVO RATES OF PROTEIN SYNTHESIS IN BRAIN, SPINAL CORD, HEART AND LIVER OF YOUNG VERSUS ADULT RATS, INTACT VERSUS HYPOPHYSECTOMIZED RATS

Abstract— In vivo protein synthesis rates in rats were estimated by single i.p. injections of large quantities of [1-¹⁴C]valine. This method gives reliable estimates of the precursor specific activity and average protein synthesis rates. In the brain, spinal cord, heart and liver, the average rates for adults were 0.65, 0.42, 0.49 and 1.92% replacement of protein-bound amino acid per h. In the brain and liver of 10-day olds the average rates were estimated to be 1.46 and 3.12% per h respectively. Hypophysectomy decreased synthesis rates by 25% or more in all tissues studied. The disadvantages of the method are that applying large amounts of valine i.p. appeared to constitute a stress and that the valine solution required for injection was hypertonic, causing withdrawal of body fluids of the animal.     

Endotoxemia reduces skeletal muscle protein synthesis in neonates

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 microg. 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 [(3)H]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-alpha, 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.     

In vivo protein synthesis in different tissues and the whole body of rainbow trout (Salmo gairdnerii R.). Influence of environmental temperature

The fractional protein synthesis rate (FSR) of tissue (liver, digestive tract, muscle and whole fish) proteins was measured in rainbow trout acclimated to 9 and 18 degrees C after a pulse injection of [U-14C] L-leucine. In each of the tissues two FSRs were calculated based on a different estimate of the specific radioactivity of leucine in the precursor compartment for protein synthesis. Whole fish protein synthesis (WFPS) was estimated to be 7 and 7.6 g protein per kg body weight and per day respectively at 10 and 18 degrees C. Muscle and digestive tract contributed the most (more than 30%) to WFPS. The rate of protein turnover in whole fish was very low, as in the muscle, when compared to liver and digestive tract.     

Influence of the gut microflora on protein synthesis in tissues and in the whole body of chicks.

1. The influence of the gut microflora on protein synthesis in individual tissues and in the whole body of young chicks was investigated by the large-dose injection of [3H]phenylalanine. 2. Growth of germ-free chicks was significantly better than that of conventional controls. Wet weights of liver, spleen, duodenum, jejunum + ileum and caeca were heavier in conventional birds than in germ-free counterparts. 3. Fractional rates of protein synthesis were higher in jejunum + ileum and whole body of conventional birds than in those of germ-free birds. Amounts of protein synthesized were larger in liver, jejunum + ileum and caeca in the presence of the gut microflora. 4. When tissues were classified into gut + liver and the remainder of the carcass, in the presence of the gut microflora an enhanced protein synthesis in fractional and absolute rate was found in the gut + liver, which is in direct contact or in close association with micro-organisms, whereas virtually no effect of the gut micro-organisms was detected in the remainder of the carcass. 5. The contribution of protein synthesis of gut + liver to that of the whole body was larger in conventional chicks than in germ-free birds, whereas the reverse was true for the remainder of the carcass.     

Brief fasting decreases protein synthesis in the brain of adult rats

The influence of starvation on protein synthesis in the adult rat brain was studied in vivo by an intravenous injection of a flooding dose of unlabeled valine including a tracer dose ofL-[3,4(n)-³H]valine. Brief starvation (24 hours) induced a 20% decline in fractional and absolute rates of brain protein synthesis. This decline resulted from a 20% decrease in the efficiency of protein synthesis (g protein synthesized per day per g RNA) whereas the capacity for protein synthesis (g RNA per mg protein) was maintained. Prolonged starvation (5 days) was marked by no further significant changes in the fractional rate, absolute rate and efficiency of protein synthesis, whereas the capacity for protein synthesis cecreased slightly. The relative contribution of brain to wholebody body protein synthesis increased during fasting, and neither the protein nor the RNA brain content did change during the experiment. These results clearly indicate that brain proteins are spared in response to brief and prolonged food deprivation, and that brain protein synthesis is very sensitive to short-term fasting.     

Muscle and liver protein synthesis and degradation in growing rats fed a raw field bean (Vicia faba L.) diet

Body weight gain, food intake, gastrocnemius muscle and liver weight, protein and RNA content, as well as the fractional rates of muscle and liver protein synthesis (ks, according to the method of constant infusion of L-[14C]tyrosine), growth (kg) and degradation (kd), along with RNA activity (g of protein synthesized per day/g RNA) of both organs, were determined in growing male rats fed ad libitum over a period of 10 days on 18.7% protein diets containing either casein (5% of methionine added) (control) or the raw legume field bean (Vicia faba L.) as the sole sources of protein. It has been found that as compared to control rats, those fed the raw legume diet exhibited a significant reduction in the rate of growth, muscle RNA, ks, kg, kd and RNA activity, and a significant increase in liver ks, kd and RNA activity. All differences were statistically significant at least at the 5% level. The possible nature of these findings is discussed.     

Acute metabolic acidosis inhibits muscle protein synthesis in rats

In this study, we investigated the effect of acute metabolic acidosis on tissue protein synthesis. Groups of rats were made acidotic with intragastric administration of NH(4)Cl (20 mmol/kg body wt every 12 h for 24 h) or given equimolar amounts of NaCl (controls). Protein synthesis in skeletal muscle and a variety of different tissues, including lymphocytes, was measured after 24 h by injection of l-[(2)H(5)]phenylalanine (150 micromol/100 g body wt, 40 moles percent). Results show that acute acidosis inhibits protein synthesis in skeletal muscle (-29% in gastrocnemius, -23% in plantaris, and -17% in soleus muscles, P < 0.01) but does not affect protein synthesis in heart, liver, gut, kidney, and spleen. Protein synthesis in lymphocytes is also reduced by acidosis (-8%, P < 0.05). In a separate experiment, protein synthesis was also measured in acidotic and control rats by a constant infusion of l-[(2)H(5)]phenylalanine (1 micromol.100 g body wt(-1).h(-1)). The results confirm the earlier findings showing an inhibition of protein synthesis in gastrocnemius (-28%, P < 0.01) and plantaris (-19%, P < 0.01) muscles but no effect on heart and liver by acidosis. Similar results were also observed using a different model of acute metabolic acidosis, in which rats were given a cation exchange resin in the H(+) (acidotic) or the Na(+) (controls) form. In conclusion, this study demonstrates that acute metabolic acidosis for 24 h depresses protein synthesis in skeletal muscle and lymphocytes but does not alter protein synthesis in visceral tissues. Inhibition of muscle protein synthesis might be another mechanism contributing to the loss of muscle tissue observed in acidosis.     

Effect of litter size and bacitracin administration on tissue protein synthesis of lactating rabbit does

Bacitracin is an antibiotic used in rabbit husbandry to control microbial digestive pathologies. Collateral effects on absorption and mucosal development have been reported and these may impact on protein metabolism. This study aims to analyse the effect of the antibiotic on protein synthesis in lactating does because mammary gland metabolism and milk output should provide a sensitive index of any undesirable action of bacitracin. Rates of protein synthesis were measured in mammary gland, liver, intestinal mucosa and muscle of lactating rabbits does by injecting a flooding dose of [(2)H(5)]phenylalanine into the auricular artery of two groups (each n = 8) of New Zealand White does fed different experimental diets. The control group (C) received the basal diet and the bacitracin group (B) ingested the same diet but supplemented with bacitracin (100 mg/kg). Animals received the experimental diet from day 28 of pregnancy until day 26 of lactation when they were slaughtered. Just after birth, litter size was adjusted by cross-fostering either to five or nine pups (four does per dietary treatment). The relative weight of the liver tended to be greater in those females receiving the B diet (27 v. 22.5 g/kg BW; P < 0.07), while diet did not affect mammary gland weight (255.7 ± 10.59 g). Fractional protein synthesis rate (FSR) was higher for intestinal mucosa (duodenum; 51.7% ± 2.09%/day) followed by mammary gland and liver (38.29 ± 2.62%/day and 40.2 ± 1.98%/day, respectively), and the lowest value was observed in muscle (2.92 ± 0.26%/day; P < 0.0001). Bacitracin treatment lowered FSR in the mammary gland by 23% (P = 0.024) and this was independent of litter size. Conversely, FSR in the duodenum was not affected by antibiotic treatment but reduced by 15% (P = 0.021) for the larger litter size.     

Effect of dietary lysine on muscle protein turnover in growing chickens.

Day-old male chickens were fed ad libitum isoenergetic diets containing 20% crude protein but differing in their lysine content (from 6.5 up to 11.3 g/kg). At 3 weeks of age, protein fractional synthesis rates in the pectoralis major muscle were determined using a large dose injection of 120 mumol per kg body weight of L-[4-3H] phenylalanine. Protein gain in the pectoralis major was measured between 19 and 23 days of age. Protein breakdown was obtained by calculating the difference between protein synthesis and deposition. Weight gain varied curvilinearly with dietary lysine intake and was maximum for 11.3 g lysine/kg of diet. In birds fed an adequate lysine intake (10.1-11.3 g/kg) protein fractional synthesis and breakdown rates were 23.6-25.9 and 17.8-19.8%/d respectively. Increasing lysine supplementation in the diet resulted in an impairment of protein fractional breakdown rates. By contrast, protein fractional synthesis rates remained unchanged owing mainly to an improvement in the synthesis efficiency (kRNA), until birds were fed an adequate lysine intake. These data suggest that the growth rate reduction of chickens fed lysine deficient diets was due to alterations in both rates of protein synthesis and breakdown in skeletal muscle. A maximum protein deposition is achieved when kRNA was optimal, ie for a dietary lysine content of about 9 g/kg, a value close to the requirement.     

Pharmacologic effects of 4-chlorophenol in rats: comparison to clofibrate

4-Chlorophenol (4-CP) is an identified trace contaminant in commercial clofibrate preparations and the pharmacologic effects of 4-CP have not yet been widely established. We have examined the dose-dependent effects of oral 4-CP and clofibrate administration on selected hepatic parameters and on serum glucose, cholesterol, and triglyceride concentrations in male rats. 4-CP treatment (0.00125-0.08 mmol/kg, twice a day) of rats for 2 weeks increased hepatic microsomal protein (20-30%) and cytochrome P-450 (20-190%) contents without changing liver/body weight ratios. Both 4-CP (0.0025 mmol/kg body wt, twice a day) and CPIB (0.4 mmol/kg body wt, twice a day) treatment to rats for 2 weeks caused significant elevations in microsomal cytochrome P-450 content and in the maximal activities of ethylmorphine, aminopyrine, and benzphetamine N-demethylase, but not in the activity of zoxazolamine 6-hydroxylase. With the same dose of 4-CP, time-dependent increases in hepatic microsomal protein, cytochrome P-450, and the activity of benzphetamine N-demethylase were observed for a 4-week period, and the induction of hepatic microsomal benzphetamine N-demethylase activity by 4-CP was associated with an increased enzyme synthesis. 4-CP treatment produced a marked morphologic change in liver cell ultrastructure, including a proliferation of mitochondria and endoplasmic reticulum at lower 4-CP doses. A clustering of intracellular organelles (mitochondria and endoplasmic reticulum) and a foamy cytoplasm were seen at doses greater than 0.01 mmol/kg, twice a day for 2 weeks, and at 0.0025 mmol/kg, twice a day for greater than 4 weeks. The effects of 4-CP and clofibrate on fasting blood glucose and fasting serum lipid levels were also monitored throughout an 8-week period. Both 4-CP (0.005 mmol/kg body wt, twice a day) and clofibrate (0.2 mmol/kg body wt, twice a day) produced significant elevations in fasting serum glucose levels, but this dosage of 4-CP did not alter serum lipid and lipoprotein parameters, whereas clofibrate significantly reduced serum total cholesterol and high density lipoprotein cholesterol levels. These results lead us to conclude that 4-CP does not contribute to the antilipidemic effects of clofibrate.     

Modulation of muscle protein synthesis by insulin is maintained during neonatal endotoxemia

Sepsis promotes insulin resistance and reduces protein synthesis in skeletal muscle of adults. The effect of sepsis on insulin-stimulated muscle protein synthesis has not been determined in neonates, a highly anabolic population that is uniquely sensitive to insulin. Overnight fasted neonatal pigs were infused for 8 h with endotoxin [lipopolysaccharide (LPS), 0 and 10 mug.kg(-1).h(-1)]. Glucose and amino acids were maintained at fasting levels, insulin was clamped at either fasting or fed (2 or 10 muU/ml) levels, and fractional protein synthesis rates were determined at the end of the infusion. LPS infusion induced a septic-like state, as indicated by a sustained elevation in body temperature, heart rate, and cortisol. At fasting insulin levels, LPS reduced fractional protein synthesis rates in gastrocnemius muscle (-26%) but had no effect on the masseter and heart. By contrast, LPS stimulated liver protein synthesis (+28%). Increasing insulin to fed levels accelerated protein synthesis rates in gastrocnemius (controls by +38%, LPS by +60%), masseter (controls by +50%, LPS by +43%), heart (controls by +34%, LPS by +40%), and diaphragm (controls by +54%, LPS by +29%), and the response to insulin was similar in LPS and controls. Insulin did not alter protein synthesis in liver, kidney, or jejunum in either group. These findings suggest that acute endotoxemia lowers basal fasting muscle protein synthesis in neonates but does not alter the response of protein synthesis to insulin.     

Protein synthesis in skeletal muscle measured at different times during a 24 hour period

Six groups of 5 male rats (starting body weight 109 g) were allowed free access to a conventional rat diet. At 4 hourly intervals, starting at 10.00 h muscle protein synthesis was measured. By relating the weights of the gastrocnemius and soleus muscles to the initial body weights of the animals (i.e., at 09.30, day 1), a linear increase in muscle weight throughout the day was demonstrated. The fractional rate of muscle protein synthesis varied from 16.8% per day to 20.3% per day in gastrocnemius muscle and from 17.9% per day and 22.1% per day in the soleus. It was calculated that the maximum error incurred in estimating daily muscle protein synthesis by extrapolation of the value at any one time was 6% in gastrocnemius and 9% in soleus. It is concluded that calculations of the average rate of muscle protein degradation based on the difference between the rates of synthesis and deposition are generally valid in rats allowed free access to an adequate diet.