Rates Of Body Protein Synthesis Research Articles

Post‐prandial protein handling following ingestion of different amounts of protein during post‐exercise recovery in older males

PurposeThe age‐related decline in skeletal muscle mass is, at least partly, attributed to anabolic resistance to food intake. Resistance‐type exercise sensitizes skeletal muscle tissue to the anabolic properties of amino acids. Data are warranted to define the amount of ingested protein needed to maximize post‐exercise myofibrillar protein synthesis rates in older individuals.MethodsIn a parallel group design, forty‐eight healthy older men (66±1 y) were randomly assigned to ingest 0, 15, 30 or 45 g milk protein concentrate (MPC80) after performing a single bout of resistance type exercise. Post‐prandial protein digestion and absorption kinetics, whole body protein metabolism and myofibrillar protein synthesis rates were assessed using primed, continuous infusions of L‐[ring‐2H5]‐phenylalanine and L‐[ring‐2H2]‐tyrosine combined with the ingestion of intrinsically L‐[1‐13C]‐phenylalanine labeled milk protein.ResultsA total of 76±2% (11.4±0.3 g), 63±3% (18.9±0.9 g) and 60±3% (26.8±1.2 g) of the protein derived amino acids were released in the circulation during 6 h after ingesting 15, 30 or 45 g protein (P<0.01). Ingestion of 15, 30 and 45 g protein resulted in higher whole‐body protein synthesis when compared to the control treatment (0.61±0.01, 0.64±0.01 and 0.67±0.02 vs 0.53±0.02 μmol·Phe·kg−1·min−1, respectively; P<0.01). Whole body protein breakdown rates were lower after ingestion of 45 g when compared with 0 g (0.45±0.01 vs 0.52±0.02 μmol·Phe·kg−1·min−1; P<0.01). Whole‐body protein oxidation rates were increased after ingestion of 45 g when compared with 15 g and 0 g protein (0.061±0.003 vs 0.050±0.003 and 0.046±0.002 μmol Phe·kg−1·min−1, respectively; P<0.05). Whole‐body protein balance increased in a dose‐dependent manner after the ingestion of 0, 15, 30 and 45 g protein (0.02±0.0, 0.11±0.0, 0.16±0.01, and 0.22±0.01 μmol·Phe·kg−1·min−1, respectively; P<0.001). Muscle tissue analyses are currently being performed.ConclusionsDietary protein ingested after resistance‐type exercise is rapidly digested and absorbed, with 60–75% of the protein derived amino acids being released into the circulation within 6 h after ingestion. Whole body protein synthesis rates and net protein balance are increased in a dose‐dependent manner following the ingestion of 15, 30 and 45 g milk protein in older males.

Energy Expenditure and Protein Requirements After Traumatic Injury

Traumatic injury induces hypermetabolism. The degree of hypermetabolism can be variable, depending on the type of injury, the degree of inflammation, body composition, age, and treatment regimens. To estimate metabolic rate in some types of injury, predictive equations have been published. Some of these equations have been tested in validation studies. For other types of injury, equations do not exist. Some expert panels have recommended measuring in lieu of estimating metabolic rate, though studies have not been performed to determine whether clinical outcome is affected by the method used to determine energy requirements. Traumatically injured patients are usually catabolic, but protein needs after traumatic injury continue to be debated. Some suggest that 1.5 g protein per kg body weight is adequate and that any additional protein is simply oxidized, adding to the nitrogen load to be excreted. Alternately, protein intake >2.0 g/kg body weight increases the absolute rate of body protein synthesis, and achievement of nitrogen balance has been associated with survival. Thus, provision of high-protein feeding to achieve nitrogen balance might be worthwhile, even if that balance is achieved at the cost of additional nitrogen production.

Demonstration of a reduction in postoperative body protein breakdown using the Clinitron fluidized bed with an ambient temperature of 32°C

Patients managed at an elevated ambient temperature after major surgery have a less pronounced rise in postoperative urinary nitrogen excretion. To investigate the mechanism involved, body protein breakdown was assessed, using a tracer dose of labelled amino acid, in patients following aorto-bifemoral bypass surgery nursed on either a Clinitron fluidized bed at 32 degrees C or a hospital bed at 22 degrees C and correlated with urinary total nitrogen excretion. Results showed a small reduction in measured body protein breakdown on the second postoperative day in patients managed on the Clinitron fluidized bed at 32 degrees C (2.92 +/- 0.91 versus 3.23 +/- 0.84 g protein kg-1 day-1; mean +/- s.d.), which was equivalent to the mean protein sparing (0.29g protein kg-1 day-1) demonstrated by the significant improvement in urinary total nitrogen excretion (9.20 +/- 2.0 versus 12.48 +/- 3.9 g N day-1; mean +/- s.d.: P less than 0.05). Urinary total nitrogen excretion (N) and body protein breakdown (B) showed a weak though significant positive correlation (B = 1.25 + 13.13N; r = +0.55: P = 0.05), whereas no correlation existed between urinary total nitrogen excretion and the derived rate of body protein synthesis. There was also a significant decrease in postoperative stress, measured during the isotope infusion, in patients managed on the Clinitron fluidized bed at 32 degrees C (12.3 +/- 2.2 versus 16.1 +/- 3.2 per cent activity incorporated into plasma proteins; mean +/- s.d.: P less than 0.05). These results show the beneficial effect of managing postoperative patients on a Clinitron fluidized bed at 32 degrees C in conserving body nitrogen through a reduction in body protein breakdown, probably as a consequence of decreased postoperative stress.

Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects

The present study was designed to determine postexercise muscle protein synthesis and whole body protein balance following the combined ingestion of carbohydrate with or without protein and/or free leucine. Eight male subjects were randomly assigned to three trials in which they consumed drinks containing either carbohydrate (CHO), carbohydrate and protein (CHO+PRO), or carbohydrate, protein, and free leucine (CHO+PRO+Leu) following 45 min of resistance exercise. A primed, continuous infusion of L-[ring-13C6]phenylalanine was applied, with blood samples and muscle biopsies collected to assess fractional synthetic rate (FSR) in the vastus lateralis muscle as well as whole body protein turnover during 6 h of postexercise recovery. Plasma insulin response was higher in the CHO+PRO+Leu compared with the CHO and CHO+PRO trials (+240 +/- 19% and +77 +/- 11%, respectively, P < 0.05). Whole body protein breakdown rates were lower, and whole body protein synthesis rates were higher, in the CHO+PRO and CHO+PRO+Leu trials compared with the CHO trial (P < 0.05). Addition of leucine in the CHO+PRO+Leu trial resulted in a lower protein oxidation rate compared with the CHO+PRO trial. Protein balance was negative during recovery in the CHO trial but positive in the CHO+PRO and CHO+PRO+Leu trials. In the CHO+PRO+Leu trial, whole body net protein balance was significantly greater compared with values observed in the CHO+PRO and CHO trials (P < 0.05). Mixed muscle FSR, measured over a 6-h period of postexercise recovery, was significantly greater in the CHO+PRO+Leu trial compared with the CHO trial (0.095 +/- 0.006 vs. 0.061 +/- 0.008%/h, respectively, P < 0.05), with intermediate values observed in the CHO+PRO trial (0.0820 +/- 0.0104%/h). We conclude that coingestion of protein and leucine stimulates muscle protein synthesis and optimizes whole body protein balance compared with the intake of carbohydrate only.

Reducing plasma HIV RNA improves muscle amino acid metabolism.

We reported (Yarasheski KE, Zachwieja JJ, Gischler J, Crowley J, Horgan MM, and Powderly WG. Am J Physiol Endocrinol Metab 275: E577-E583, 1998) that AIDS muscle wasting was associated with an inappropriately low rate of muscle protein synthesis and an elevated glutamine rate of appearance (Ra Gln). We hypothesized that high plasma HIV RNA caused dysregulation of muscle amino acid metabolism. We determined whether a reduction in HIV RNA (> or =1 log) increased muscle protein synthesis rate and reduced R(a) Gln and muscle proteasome activity in 10 men and 1 woman (22-57 yr, 60-108 kg, 17-33 kg muscle) with advanced HIV (CD4 = 0-311 cells/microl; HIV RNA = 10-375 x 10(3) copies/ml). We utilized stable isotope tracer methodologies ([13C]Leu and [15N]Gln) to measure the fractional rate of mixed muscle protein synthesis and plasma Ra Gln in these subjects before and 4 mo after initiating their first or a salvage antiretroviral therapy regimen. After treatment, median CD4 increased (98 vs. 139 cells/microl, P = 0.009) and median HIV RNA was reduced (155,828 vs. 100 copies/ml, P = 0.003). Mixed muscle protein synthesis rate increased (0.062 +/- 0.005 vs. 0.078 +/- 0.006%/h, P = 0.01), Ra Gln decreased (387 +/- 33 vs. 323 +/- 15 micromol.kg fat-free mass(-1).h(-1), P = 0.04), and muscle proteasome chymotrypsin-like catalytic activity was reduced 14% (P = 0.03). Muscle mass was only modestly increased (1 kg, P = not significant). We estimated that, for each 10,000 copies/ml reduction in HIV RNA, approximately 3 g of additional muscle protein are synthesized per day. These findings suggest that reducing HIV RNA increases muscle protein synthesis and reduces muscle proteolysis, but muscle protein synthesis relative to whole body protein synthesis rate is not restored to normal, so muscle mass is not substantially increased.

Protein kinetics in stable heart failure patients.

Heart failure (HF) is a slow progressive syndrome characterized by low cardiac output and peripheral metabolic, biochemical, and histological alterations. Protein loss and reduced protein turnover occur with aging, but the consequences of congestive HF (CHF) superimposed on the normal aging response are unknown. This study has two objectives: 1) to determine whether there was a difference between older age-matched controls and those with stable HF (i.e., ischemic pathology) in whole body protein turnover and 2) to determine whether protein metabolism in liver and skeletal muscle protein turnover is impacted by CHF. We measured the whole body protein synthesis rate with a U-(15)N-labeled algal protein hydrolysate in 10 patients with CHF and in 10 age-matched controls. Muscle fractional synthesis rate of lateral vastus muscle was determined with [U-(13)C]alanine on muscle biopsies obtained by a standard percutaneous needle biopsy technique. Fractional synthesis rates of five plasma proteins of hepatic origin (fibrinogen, complement C-3, ceruloplasmin, transferrin, and very low-density lipoprotein apoliprotein B-100) were determined by using (2)H(5)-labeled l-phenylalanine as tracer. Results showed that whole body protein synthesis rate was reduced in CHF patients (3.09 +/- 0.19 vs. 2.25 +/- 0.71 g protein x kg(-1) x day(-1), P < 0.05) as was muscle fractional synthesis rate (3.02 +/- 0.58 vs. 1.33 +/- 0.71%/day, P < 0.05) and very low-density lipoprotein apoliprotein B-100 (265 +/- 25 vs. 197 +/- 16%/day, P < 0.05). CHF patients were hyperinsulinemic (9.6 +/- 3.1 vs. 47.0 +/- 7.8 microU/ml, P < 0.01). The results were compared with those found with bed rest patients. In conclusion, protein turnover is depressed in CHF patients, and both skeletal muscle and liver are impacted. These results are similar to those found with bed rest, which suggests that inactivity is a factor in depressed protein metabolism.

Effects of temperature on specific dynamic action and protein synthesis rates in the Baltic isopod crustacean, Saduria entomon

The mean rate of oxygen consumption in fasted Saduria entomon increased between 4°C and 13°C with a Q 10 of 2.33. After feeding, rates of oxygen uptake increased significantly by two- to threefold at both temperatures. However, the magnitude of the ‘specific dynamic action of food’ (SDA) response varied with temperature. At 4°C, the magnitude was 45.5±4.2 μmol, while at 13°C, magnitude was significantly higher at 62.8±6.5 μmol. In contrast, the duration of the response did not vary significantly with temperature in Saduria, with the consequence that the duration at 4°C was considerably shorter than that measured at this temperature from an Antarctic isopod in a parallel study, and the duration at 13°C was considerably longer than published values for temperate crustaceans at similar temperatures. Fasted rates of ammonia excretion increased with a Q 10 of 4.74 between 4°C and 13°C. The increase after feeding was sevenfold at 4°C but only 2.6-fold at 13°C. Fasted O/N ratios for Saduria at 4°C were about twice those at 13°C. Fasted whole body protein synthesis rates ( k S) increased with a Q 10 of 2.61 between 4°C and 13°C. Whole body k S, measured at the peak of the SDA response, showed significant 2.7-and 1.9-fold increases at 4°C and 13°C, respectively, compared to fasted values, although the factorial rise at 13°C was reduced compared to 4°C. Alterations in k S rates after feeding at both temperatures resulted from significant increases in RNA activity ( K RNA) alone. However, the increase in k S between 4°C and 13°C was accompanied by increases in both K RNA and RNA/protein ratio, a measure of the capacity for protein synthesis ( C S).

Free amino acids in plasma of neonatal calves are influenced by feeding colostrum for different durations or by feeding only milk replacer1

Introduction Newborn development is characterized by high protein synthesis and nitrogen (N) turnover rates in many tissues, especially in the gastrointestinal (GI) tract (G oldspink and K elly 1984; Y oung et al. 1988; S immen et al. 1990; X u 1996). Colostrum provides particularly large amounts of nutrients (especially proteins) and immunoglobulins as well as non‐nutrient growth‐promoting factors; it therefore plays a major role in the development of the neonatal gut, especially protein synthesis, and other organs, as shown in several species including cattle (B erseth et al. 1983; P atureau M irand et al. 1990; C ampana and B aumrucker 1995; O dle et al. 1996; X u 1996; B urrin et al. 1997). Rates of body protein synthesis and N turnover were greater during enteral than during parenteral feeding, indicating considerable involvement of the GI tract in protein metabolism (D uffy and P encharz 1986).Protein components in colostrum provided about 35% of amino acids (AA) in newborn lambs, suggesting that amounts of ingested protein with colostrum greatly influence the AA status of the neonate (Y von et al. 1993). Glutamine and glutamate are the most abundant AA in bovine milk protein (M eijer et al. 1993) and glutamine is of special interest for postnatal gut development (S ouba 1991; K imura 1996; H eird 1998). The glutamine:glutamate ratio was markedly changed in neonatal calves (D emign&amp; eacute; and R&amp; eacute; m&amp; eacute; sy 1979) after colostrum intake.Recently, we have demonstrated that gut growth and absorptive capacity of the intestine, as well as metabolic and endocrine changes in newborn calves, are greatly dependent on amounts of ingested colostrum (H ammon and B lum 1997, 1998; B&amp; uuml; hler et al. 1998). Based on that AA absorption, metabolism and status may be influenced by amounts of fed colostrum. Therefore in this study we have tested the hypothesis that feeding colostrum for different durations, or feeding only milk replacer, affects plasma protein and free AA concentrations during the first week of life in calves.

Protein kinetics during and after long-duration spaceflight on MIR.

Human spaceflight is associated with a loss of body protein. Bed rest studies suggest that the reduction in the whole body protein synthesis (PS) rate should be approximately 15%. The objectives of this experiment were to test two hypotheses on astronauts and cosmonauts during long-duration (>3 mo) flights on MIR: that 1) the whole body PS rate will be reduced and 2) dietary intake and the PS rate should be increased postflight because protein accretion is occurring. The 15N glycine method was used for measuring whole body PS rate before, during, and after long-duration spaceflight on the Russian space station MIR. Dietary intake was measured together with the protein kinetics. Results show that subjects lost weight during flight (4.64 +/- 1.0 kg, P < 0.05). Energy intake was decreased inflight (2,854 +/- 268 vs. 2,145 +/- 190 kcal/day, n = 6, P < 0.05), as was the PS rate (226 +/- 24 vs. 97 +/- 11 g protein/day, n = 6, P < 0.01). The reduction in PS correlated with the reduction in energy intake (r2 = 0.86, P < 0.01, n = 6). Postflight energy intake and PS returned to, but were not increased over, the preflight levels. We conclude that the reduction in PS found was greater than predicted from ground-based bed rest experiments because of the shortfall in dietary intake. The expected postflight anabolic state with increases in dietary intake and PS did not occur during the first 2 wk after landing.

Effect of spaceflight on human protein metabolism.

Nitrogen balance and the whole body protein synthesis rate were measured before, during, and after a 9.5-day spaceflight mission on the space shuttle Columbia. Protein synthesis was measured by the single-pulse [15N]glycine method. Determinations were made 56, 26, and 18 days preflight, on flight days 2 and 8, and on days 0, 6, 14, and 45 postflight. We conclude that nitrogen balance was decreased during spaceflight. The decrease in nitrogen balance was greatest on the 1st day when food intake was reduced and again toward the end of the mission. An approximately 30% increase in protein synthesis above the preflight baseline was found for flight day 8 for all 6 subjects (P < 0.05), indicating that the astronauts showed a stress response to spaceflight.

Effect of growth hormone and resistance exercise on muscle growth in young men

The purpose of this study was to determine whether growth hormone (GH) administration enhances the muscle anabolism associated with heavy-resistance exercise. Sixteen men (21-34 yr) were assigned randomly to a resistance training plus GH group (n = 7) or to a resistance training plus placebo group (n = 9). For 12 wk, both groups trained all major muscle groups in an identical fashion while receiving 40 micrograms recombinant human GH.kg-1.day-1 or placebo. Fat-free mass (FFM) and total body water increased (P less than 0.05) in both groups but more (P less than 0.01) in the GH recipients. Whole body protein synthesis rate increased more (P less than 0.03), and whole body protein balance was greater (P = 0.01) in the GH-treated group, but quadriceps muscle protein synthesis rate, torso and limb circumferences, and muscle strength did not increase more in the GH-treated group. In the young men studied, resistance exercise with or without GH resulted in similar increments in muscle size, strength, and muscle protein synthesis, indicating that 1) the larger increase in FFM with GH treatment was probably due to an increase in lean tissue other than skeletal muscle and 2) resistance training supplemented with GH did not further enhance muscle anabolism and function.

Whole body protein synthesis: studies with different amino acids in the rat.

These studies were undertaken to determine to what extent constant infusion measurements and plasma sampling could provide sensible answers for rates of whole body protein turnover and also which amino acid would be the most representative probe of whole body protein turnover. Whole body protein synthesis rates were estimated in 70-g rats with L-[U-14C]threonine, L-[U-14C]lysine, L-[U-14C]tyrosine, L-[U-14C]phenylalanine, and L-[1-14C]leucine by either simultaneous tracer infusion of four amino acids or by injections of large quantities of 14C-labeled amino acids. In the infusion experiment, indirect estimates of whole body protein turnover based on free amino acid specific radioactivity and stochastic modeling were compared with direct measurement of the incorporation of the tracer into proteins. These two methods of analysis provided similar results for each amino acid, although in each case fractional synthesis rates were lower (by between 26 and 63%) when calculations were based on plasma rather than tissue specific radioactivity. With the flooding-dose method, whole body fractional protein synthesis rates were 41.4, 25.6, 31.1, and 31.4% with threonine, lysine, phenylalanine, and leucine, respectively. These values were similar to those obtained by the continuous infusion method using tissue specific radioactivity for threonine and lysine. For leucine, however, the flooding-dose method provided an intermediate value between the two estimates derived either from the plasma or the tissue specific radioactivity in the infusion method.(ABSTRACT TRUNCATED AT 250 WORDS)

Methodic recommendations for the determination of whole body protein synthesis rates in tracer studies

Methodical recommendations are suggested--predominantly for laboratory and small animals (rats and young chickens)--for the determination of parameters of the protein metabolism of the whole body after single doses of a mixture of 15N labelled amino acids by means of the determination of the temporal course of cumulative 15N excretion in urine and the assessment of the tracer kinetic data in a compartment model. These recommendations are to make it possible to carry out purposefully such experiments under comparable conditions. The advantages of this method are: the non-invasive character of the method; the possibility of repeating the experiment with the same animal; the adaptability to other methods of investigation (e.g. measuring energy metabolism); the relatively low expenditure of labour and requirement of test animals; the relatively good reproducibility of the method. Thus this method is a good supplement to the flooding and permanent infusion methods and should be used wherever the determination of parameters of the protein metabolism of the total body is sufficient.

Kinetic parameters of protein metabolism in rats on protein-free diets

16 male rats of 100 g live weight were given 50 mg of a mixture containing 15N labelled amino acids as a single dose within a protein-free feeding period. Following this the 15N excretion in faeces and urine as well as the development of the 15N excess in different organs and tissues were estimated over 3 days by slaughtering the animals within given 7 time intervals. Using a 3 pool model and the computer program for the interpretation of 15N tracer experiments by Töwe et al. (1984), kinetic parameters such as the rate of protein synthesis, protein breakdown and the rate of reutilization were calculated. Despite a negative N balance (-41.8 mg N/d) under protein-free conditions the protein metabolism of the rat shows high dynamics characterized by a high flux rate (225 mg N/d) and a high rate of body protein synthesis (181 mg/d). The reutilization was 85%. Depending on time the 15N excess in the tested organs and tissues showed significant differences and seems to demonstrate that under these conditions protein synthesis mainly takes place in the most important organs (e.g. intestinal tract, liver). Under protein-free feeding conditions protein synthesis and protein breakdown of the whole body seems to be slightly increased in comparison to N balanced feeding conditions.

The effect of increasing total parenteral nutrition on protein metabolism.

We asked the question, if the amount of nutrients given parenterally is progressively increased, does the rate of whole body protein synthesis rate increase correspondingly and how does the protein breakdown rate change? Eight malnourished patients requiring total parenteral nutrition (TPN) were studied. We measured their whole body protein synthesis and breakdown rate four times at intervals of 3 days using 15N glycine as the tracer. The first study was done pre-TPN. The 2nd, 3rd, and 4th studies were done at increasing TPN rates. The rates were TPN 1, 1440 kcal/day and 7.9 g/N/day; TPN 2, 2160 kcal/day and 11.9 g/N/day; TPN 3, 2880 kcal/day and 15.8 g/N/day. The protein synthesis rate initially increased as the amount of TPN was increased, but increasing the rate from TPN-2 to TPN-3 did not result in further increase. Increasing the rate of TPN above a certain level does not lead to a concomitant increase in the protein synthesis rate.

Nutrition, protein turnover, and physical activity in young women

The whole body protein synthesis rate was measured in four groups of young women by giving a single pulse of 15N glycine and determining the 15N enrichment in the urinary ammonia excreted over the next 10 h. The groups were: Ia, normals, with normal dietary intake; Ib, competition swimmers, normal intake; IIa, normal activity but low intake; and IIb, high physical activity, low intake. The results indicated that the protein synthesis rate was lower in the two low intake groups. It did not correlate with a program of vigorous physical activity, while physical activity, but not nutritional status or the protein synthesis rate correlated with menstrual cycle irregularities.

Prehepatic total parenteral nutrition in the chair-adapted primate.

The relative efficacy of prehepatic and central venous infusion of total parenteral nutrition (TPN) was evaluated in a chair-adapted primate model. Four adult male monkeys (Macaca fascicularis) underwent surgical placement of a silastic catheter in both the portal vein (PV) and superior vena cava (SVC). Following recovery (10 days), each animal received two courses of TPN (100 kcal and 4 g of protein/kg/day) for 10 days each via the PV and SVC in an alternating crossover manner. The prehepatic (PV) infusion of TPN in the well nourished, chair-adapted primate results in maintenance of weight (PV: delta - 0.07 kg; SVC:delta - 0.07 kg), nitrogen equilibrium (PV:+ 0.8 g N/day; SVC: + 0.7 g N/day), and trends in serum albumin (PV:delta - 0.35 g %; SVC: delta - 0.38 g %), and total iron binding capacity (PV:delta + 44 mg %; SVC:delta + 8.67 mg %) comparable to the SVC route. No significant abnormalities in liver enzyme production were observed with either route of infusion. Whole body protein synthesis rates using 15N-glycine tracer were likewise comparable (PV = 2.05 g N/kg/day; SVC = 2.18 g N/kg/day). Prehepatic delivery and primary hepatic modulation of substrates does not substantially improve the efficacy of parenteral nutrient administration. Intestinal modification of substrates may be the most important contributing factor in the supposed superiority of enteral alimentation.

Energy expenditure and whole body protein synthesis in very low birth weight (VLBW) infants.

To examine the rates of whole body protein synthesis and energy expenditure during the rapid growing period, premature infants of very low birth weight (VLBW) (less than 1500 g), appropriate for gestational age were kept under standard thermoneutrality conditions and received a formula diet providing 110 kcal/kg.d metabolisable energy (ME) and 3.3 g protein/kg.d. Their energy expenditure was measured by open circuit indirect calorimetry. Nitrogen turnover and whole body protein synthesis and catabolism were determined using repeated oral administration of 15N-glycine for 60-72 h followed by the analysis of 15N-enrichment in urinary urea. These VLBW infants grew at an average rate of 15 g/kg.d. About half of the ME intake (i.e. 50 kcal/kg.d) was invested in weight gain while the remainder (i.e. 60 kcal/kg.d) was oxidised. The energy equivalent of the weight gain (i.e. the amount of energy stored per g weight gain) and the N balance indicated that lean tissue made up approximately 2/3 of the weight gained and fat tissue the remaining 1/3. The plateau value for 15N enrichment reached on the third day of administration allowed us to calculate a rate of protein synthesis of 14 g/kg.d and protein breakdown of 12 g/kg.d in five VLBW fed a formula diet. The elevated energy expenditure of the very low birth weight infant seems to be related to its rapid rate of weight gain which is accompanied by a high rate of body protein synthesis. More than 20% of the total energy expenditure of the VLBW infants was accounted for by whole body protein synthesis.

Whole Body Protein Synthesis and Turnover in Normal Man and Malnourished Patients With and Without Known Cancer

Plateau enrichment of 15N-ammonia following 24 hour continuous intravenous infusion of 15N-glycine was used to measure total body protein turnover and synthesis in normal volunteers and malnourished patients, with and without cancer. The mean postabsorptive total body protein synthesis rate in three normal controls was 2.5 g protein/kg/day. Protein synthesis and turnover decreased by a mean of 23% following one week of fasting, and returned to baseline levels following one week of refeeding. In three malnourished patients without known tumor, whole body protein synthesis and turnover was similar to controls; following seven to ten days of total parenteral nutrition (TPN) in the nontumor-bearing patients whole body protein synthesis and turnover decreased by 18%. Three of seven malnourished patients with known tumors had marked elevations in total body protein synthesis and turnover; TPN increased protein turnover in five of seven patients with known cancer. This study suggests that some malignant tumors can increase whole body protein synthesis and turnover in both the malnourished and fed state. This increase in protein turnover may represent a direct effect of the tumor, or reflect concomitant illness.

Whole body protein synthesis and turnover in normal man and malnourished patients with and without known cancer.

Plateau enrichment of 15N-ammonia following 24 hour continuous intravenous infusion of 15N-glycine was used to measure total body protein turnover and synthesis in normal volunteers and malnourished patients, with and without cancer. The mean postabsorptive total body protein synthesis rate in three normal controls was 2.5 g protein/kg/day. Protein synthesis and turnover decreased by a mean of 23% following one week of fasting, and returned to baseline levels following one week of refeeding. In three malnourished patients without known tumor, whole body protein synthesis and turnover was similar to controls; following seven to ten days of total parenteral nutrition (TPN) in the nontumor-bearing patients whole body protein synthesis and turnover decreased by 18%. Three of seven malnourished patients with known tumors had marked elevations in total body protein synthesis and turnover; TPN increased protein turnover in five of seven patients with known cancer. This study suggests that some malignant tumors can increase whole body protein synthesis and turnover in both the malnourished and fed state. This increase in protein turnover may represent a direct effect of the tumor, or reflect concomitant illness.