Protein and substrate metabolism during starvation and parenteral refeeding

Protein and energy metabolism response to the initial dose of infliximab in children with Crohn's disease

BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) may contribute to the alterations in protein and energy metabolism present in children with Crohn's disease (CD), who frequently suffer from growth disturbance. We hypothesized that anti-TNF-alpha therapy would reduce protein losses, due to decreased proteolysis and increased protein synthesis, and that anti-TNF-alpha therapy would decrease resting energy expenditure.

METHODS

Children with active CD underwent metabolic assessment immediately before and 2 weeks following initial infliximab infusion. Using the stable isotopes [d5] phenylalanine and [1-13C] leucine, 2 independent measures of protein metabolism were determined during fasting and in response to parenteral nutrition. Energy expenditure, determined by indirect calorimetry, was measured in fasting and parenterally fed states.

RESULTS

Fifteen children completed the study. Following infliximab therapy, significant reductions in proteolysis (P < 0.05) were noted in the fasting state (8%-11%) and during parenteral nutrition infusion (10%-12%). Phenylalanine utilization for protein synthesis decreased significantly (8%-13%) following infliximab (P < 0.05). Protein balance was not significantly altered. No significant changes in energy expenditure were observed following infliximab in fasting or parenterally fed states. Supplementation with parenteral nutrition resulted in significantly decreased proteolysis (8%-21%; P < 0.05), increased protein synthesis (37%-45%; P < 0.01), and improved protein balance (P < 0.01) compared to the fasting state.

CONCLUSIONS

Following the initial infliximab infusion in children with CD, proteolysis and protein synthesis were significantly reduced in the fasting and parenterally fed states. Supplementation with parenteral nutrition resulted in significant improvements in protein metabolism compared to the fasting state both before and after infliximab therapy.

Growth hormone effects on protein metabolism

Growth hormone (GH) has a pivotal role in regulating in vivo protein metabolism. GH enhances protein anabolism at the wholebody level, mainly by stimulating protein synthesis. It remains incompletely understood whether this important GH effect on protein synthesis occurs in all tissues. This effect of GH may be different with acute versus chronic administration. These differences in the GH exposure may have different effects based not only on direct GH stimulation of protein synthesis but also the variable effects at the level of gene transcription that ultimately affect protein metabolism. Other GH effects are likely to be mediated by changes in various metabolites and hormones that also likely differ based on the duration of GH administration.

The end-product method of measuring whole-body protein turnover: a review of published results and a comparison with those obtained by leucine infusion

The present review summarizes the results of all published papers on whole-body protein turnover in man measured by [15N]glycine and the end-product method using both urea and ammonia. It begins with a short account of the underlying assumptions and the justification for the use of [15N]glycine. The results are then compared with those of a large sample of measurements by the 'gold standard' precursor method with continuous infusion of [13C]leucine. The pros and cons of the two methods are compared and it is suggested that there is a place for further work by the less invasive end-product method, particularly for population studies of the genetic, environmental and functional determinants of whole-body rates of protein synthesis.

Epidural blockade improves substrate utilization after surgery

The purpose of this study was to test the hypothesis that epidural blockade with local anesthetic improves the anticatabolic effects of glucose after colorectal surgery. Sixteen patients were randomly assigned to undergo a 6-h stable isotope infusion study (3 h fasted, 3 h glucose infusion at 4 mg. kg(-1). min(-1)) on the second postoperative day with or without perioperative epidural blockade. Protein synthesis, breakdown and oxidation, and glucose production and clearance were assessed by L-[1-(13)C]leucine and [6, 6-(2)H(2)]glucose. Epidural blockade did not affect protein and glucose metabolism in the fasted state. Glucose infusion increased glucose clearance (P < 0.05), accompanied by an increase in the respiratory quotient (P < 0.05) and a decrease in leucine oxidation (P < 0.05) only in the presence of epidural blockade. An inverse correlation (r = -0.74, P < 0.05) between changes in glucose clearance and leucine oxidation was observed. In conclusion, epidural blockade facilitates whole body glucose uptake and inhibits endogenous protein oxidation after abdominal surgery, indicating a shift from a protein to a more glucose-dominated substrate utilization.

Addition of tyrosyl-arginine to parenteral nutrition is anabolic in unstressed rats

To determine whether the addition of tyrosine and arginine (Arg), as tyrosyl-arginine (TyrArg), to parenteral nutrition (PN) can promote anabolism, rats were assigned to: 1) PN (1.20 MJ. kg body weight [BW](-1) x d(-1) and 1.22 gN x kgBW(-1) x d(-1); PN control group, n = 5), 2) PN plus TyrArg (2.6 mmol. kgBW(-1) x d(-1); TyrArg group, n = 6), or 3) PN plus Arg (2.6 mmol. kgBW(-1). d(-1); Arg group, n = 5). Results from these three groups were compared with an unoperated chow-fed reference group (chow control group, n = 5). The BW gain during PN and the proportion of lipid in the total body after 14 d of PN was greater for the TyrArg group than for the PN group (P<0.01). Although the differences in weight gain, body water, lipid, and protein between the TyrArg and Arg groups were not significant, the mean weight gain throughout PN was greater in the TyrArg group than in the Arg group. The proportion of protein in the small intestine, colon, and gastrocnemius muscle was greater in the TyrArg and Arg groups than in the PN group (P<0.01). A distinct requirement for tyrosine has not been demonstrated in this model, and additional studies in stressed animals are required. In contrast, arginine had tissue-specific anabolic activity.

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.

A nitrogen-free hypocaloric diet and recombinant human growth hormone stimulate postoperative protein synthesis: fasted and fed leucine kinetics in the surgical patient

Twelve otherwise healthy patients undergoing elective surgery for resection of rectosigmoid adenocarcinoma were randomly allocated to two groups: one group receiving intravenous dextrose 5% 600 to 800 kcal.d-1 (DX, n = 6) and the other group receiving the same amount of dextrose intravenously plus recombinant human growth hormone (DX + rGH, n = 6). Supplementation with rGH started on the day of surgery and continued postoperatively for 5 days. No nitrogen was provided in the diet. This regimen was started 3 days before surgery and continued for 5 days after surgery. Protein kinetics were studied over a period of 8 hours in all patients. Following an overnight fast, a primed constant infusion of L-[1-13C]leucine was maintained for 4 hours (fasted state) and continued for a further 4 hours (fed state) during which 5% beet dextrose (low 13C content) with or without rGH was administered. The isotope studies were performed on the day before surgery and 6 days after surgery. Other measurements included urinary nitrogen excretion, gaseous exchange, and plasma concentrations of insulin, GH, and insulin-like growth factor-I (IGF-I). Addition of rGH to the dextrose diet had a significant positive effect on protein synthesis (P = .02). Surgery was responsible for a significant increase in postoperative whole-body protein breakdown and synthesis and leucine oxidation (P < .01), although lesser changes were observed in the DX group. An interaction between rGH and surgery was associated with a significant increase in protein synthesis (P = .009), but not with changes in either protein breakdown or leucine oxidation. Carbohydrate provision in the form of beet dextrose during the fed state of the isotopic study did not attenuate the significant decrease in protein synthesis (P = .01) or breakdown (P = .003) either before or after surgery, probably reflecting the absence of nitrogen in the diet. No significant interaction was found between rGH and feeding. These results of leucine kinetics indicate that addition of rGH to a low-dextrose intake in the absence of dietary nitrogen can actually promote protein synthesis. The low levels of leucine oxidation could be explained by the fact that amino acids resulting from protein degradation were directed preferentially toward resynthesis of new proteins rather than to oxidative pathways. There was a significant increase in plasma insulin and GH in the group receiving rGH (P < .05). The postoperative plasma concentration of IGF-I did not change in the latter group compared with the DX group, in which IGF-I concentration decreased significantly (P < .05) as part of the response to combined surgery and dietary restriction. Although both IGF-I and insulin are independently capable of stimulating protein synthesis, elevated levels of either hormone or GH itself may primarily modulate protein synthesis, even with a low intake of carbohydrates.

Nutritional assessment and the role of preoperative parenteral nutrition in the colon cancer patient

Hospital-based malnutrition is prevalent, especially among patients with gastrointestinal malignancy. Colorectal cancers produce malnutrition through impairment of gastrointestinal function and the liberation of cytokines. Malnourished patients who undergo operation have an increased likelihood of perioperative morbidity and mortality. The performance of a nutritional assessment will aid in the recognition of such patients and provide a risk assessment profile. Preoperative parenteral nutrition is a major expense and delays surgical intervention. Studies to document the efficacy of preoperative parenteral nutrition suffer from design flaws and small sample sizes. Studies that exclusively address patients with cancer of the colon and rectum are absent; therefore results must be extrapolated from the existing literature. Cumulative evidence suggests that a 7-10 day period of parenteral nutrition repletion in the severely malnourished patient will diminish the incidence of postoperative septic complications and mortality. The preoperative treatment of lesser degrees of malnutrition remain controversial. Once the decision has been made to institute preoperative parenteral alimentation, attention to the details of protein requirements and caloric needs should be stressed. The endpoint of therapy is poorly defined. The role of glutamine, arginine, omega-3 fatty acids, and growth hormone in the preoperative repletion process provide an exciting arena for future research.

Anabolic therapy with growth hormone accelerates protein gain in surgical patients requiring nutritional rehabilitation

OBJECTIVE

The authors investigated the effects of exogenous growth hormone (GH) on protein accretion and the composition of weight gain in a group of stable, nutritionally compromised postoperative patients receiving standard hypercaloric nutritional therapy.

SUMMARY BACKGROUND DATA

A significant loss of body protein impairs normal physiologic functions and is associated with increased postoperative complications and prolonged hospitalization. Previous studies have demonstrated that standard methods of nutritional support enhance the deposition of fat and extracellular water but are ineffective in repleting body protein.

METHODS

Fourteen patients requiring long-term nutritional support for severe gastrointestinal dysfunction received standard nutritional therapy (STD) providing approximately 50 kcal/kg/day and 2 g of protein/kg/day during an initial 7-day equilibrium period. The patients then continued on STD (n = 4) or, in addition, received GH 0.14 mg/kg/day (n = 10). On day 7 of the equilibrium period and again after 3 weeks of treatment, the components of body weight were determined; these included body fat, mineral content, lean (nonfat and nonmineral-containing tissue) mass, total body water, extracellular water (ECW), and body protein. Daily and cumulative nutrient balance and substrate oxidation studies determined the distribution, efficiency, and utilization of calories for protein, fat, and carbohydrate deposition.

RESULTS

The GH-treated patients gained minimal body fat but had significantly more lean mass (4.311 +/- 0.6 kg vs. 1.988 +/- 0.2 kg, p < or = 0.03) and more protein (1.417 +/- 0.3 kg vs. 0.086 +/- 0.1 kg, p < or = 0.03) than did the STD-treated patients. The increase in lean mass was not associated with an inappropriate expansion of ECW. In contrast, patients receiving STD therapy tended to deposit a greater proportion of body weight as ECW and significantly more fat than did GH-treated patients (1.004 +/- 0.3 kg vs. 0.129 +/- 0.2 kg, p < 0.05). GH administration altered substrate oxidation (respiratory quotient = 0.94 +/- 0.02 GH vs. 1.17 +/- 0.05 STD, p < or = 0.0002) and the use of available energy, resulting in a 66% increase in the efficiency of protein deposition (13.37 +/- 0.8 g/1000 kcal vs. 8.04 g +/- 3.06 g/1000 kcal, p < or = 0.04).

CONCLUSIONS

GH administration accelerated protein gain in stable adult patients receiving aggressive nutritional therapy without a significant increase in body fat or a disproportionate expansion of ECW. GH therapy accelerated nutritional repletion and, therefore, may shorten the convalescence of the malnourished patient requiring a major surgical procedure.

Substrate efficacy in early nutrition support of critically ill multiple trauma victims

The metabolic consequences of excessive nutrition support in patients have been increasingly recognized in recent years. Time-dependent optimal nutrition support is desired for an early and uncomplicated recovery after severe injury or illness. Metabolic effects of adding balanced amino acids to glucose infusion during total parenteral nutrition were investigated in 18 patients after major trauma (injury severity score 32 +/- 2). Two studies were conducted on each subject, one in the early "flow" phase of injury (40-60 hours postinjury) in the basal state without any dietary intake and then after 4 to 6 days of intravenous nutrition provided solely as glucose (24 +/- 2 kcal/kg per day, 80% resting energy expenditure, n = 8) or isocaloric glucose (28 +/- 3 kcal/kg per day) with amino acids (275 +/- 28 mg of nitrogen per kilogram per day, n = 10). Whole-body fuel substrate kinetics were studied for energy metabolism (indirect calorimetry), protein kinetics (primed-constant infusion of 15N glycine), and lipid mobilization (two-stage infusion of 10% glycerol). Injury-induced hypoaminoacidemia was equally modulated whether the glucose-based nutrition had amino acids or not. The negative nitrogen balance is reduced similarly in both groups. Protein breakdown rate is significantly (p = .025) decreased in both groups and it is more so (30% vs 18%) in patients receiving total parenteral nutrition. Intravenous nutrition could not stimulate protein synthesis. Whole-body lipolysis rate as well as net fat oxidation rate are suppressed more when glucose alone is given, and this also results in less reesterification. Provision of intravenous glucose alone, not to exceed the resting energy expenditure, seems to be superior to isocaloric glucose with amino acids during this early catabolic flow phase of injury because the injured body could not assimilate this exogenous amino acid.

The effect of fuel source on amino acid metabolism in critically ill patients

The ideal energy substrate for critically ill patients receiving total parenteral nutrition (TPN) remains controversial. While glucose has been proved to have nitrogen sparing properties in postoperative patients, critically ill patients tolerate glucose loads poorly and fat appears to be an obligatory fuel in sepsis. Furthermore, it is not yet certain whether the changes in whole body protein metabolism induced by critical illness are influenced by the nature of the TPN provided. This study was conducted on patients admitted to a surgical intensive care unit (SICU) who fulfilled the criteria of requiring TPN and mechanical ventilation for at least four days. Patients were randomized to receive either glucose (G) or equicaloric proportions of glucose and lipid (GF) as an intravenous energy source. TPN was commenced early, within 24-48 hr of trauma or surgery and admission to the ICU. Nonprotein calorie intake was 125% of calculated basal energy expenditure. Nitrogen balance was calculated from 24-hr urinary urea excretion. Protein synthesis, turnover, and catabolism were measured on Day 4 of the study using an established radiolabeled C14-leucine technique. Degree of sepsis and illness were calculated using published scores. Fifty patients entered the trial but 32 were excluded by Day 4. Of the 18 patients completing an initial four day study, eight went on to complete a second study on the alternative regimen--a total of 26 studies (14 G, 12 GF). Net protein synthesis was achieved in 18 studies (12 G, 6 FG) and positive nitrogen balance by Day 4 in 22 studies. Four patients on the G regimen were withdrawn due to glucose intolerance while none of the patients on GF developed glucose intolerance or hyperlipidaemia. Both whole body protein synthesis and catabolism correlated significantly with degree of sepsis. The type of TPN fuel used, G and GF, did not appear to influence whole body protein dynamics, both regimens achieving greatly improved whole body protein kinetics.

Glucose infusion improves endogenous protein synthesis efficiency in multiple trauma victims

Metabolic costs of excessive nutritional support in stressed patients have been increasingly recognized. The decreased endogenous protein synthesis efficiency (PSE) following major injury has been attributed to the predominant need of amino acid precursors for gluconeogenesis. The present study tested the hypothesis that provision of glucose alone, not to exceed the resting energy expenditure (REE), for the first 4 to 5 days after trauma would be enough to restore PSE and stimulate the injured body to accept full nutrition. Eight severely injured, adult, hypermetabolic, and highly catabolic patients admitted to the Trauma Intensive Care Unit (TICU) served as our subjects. Integrated measurements of whole body fuel-substrate kinetics were obtained for energy metabolism (indirect calorimetry), protein kinetics (primed constant infusion of 15N-glycine), and glucose kinetics (labeled glucose infusions). Two studies were conducted on each same subject, one in the early flow phase of injury (48 to 60 hours after trauma) and a second after 4 to 5 days of hypertonic glucose (4.1 +/- 0.5 mg/kg/min; 80% REE calories) infusion with electrolytes, trace elements, and minerals. Significant (P less than .05) increases in PSE (14%, 65% +/- 2% to 74% +/- 2%), plasma growth hormone and insulin levels, and respiratory quotient (RQ) (31%, 0.74 +/- 0.03 to 0.97 +/- 0.04), and decreases in endogenous glucose appearance rate (55%, 3.1 +/- 0.5 to 1.4 +/- 0.1 mg/kg/min), and negative N balance (48%, 219 +/- 26 to 114 +/- 15 mgN/kg/d) were observed. The results suggest that hypertonic glucose infusion alone may be sufficient for physiological adaptation in the immediate posttrauma days. This therapy restores normal PSE, which should protect the labile protein pool.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of surgical injury and intraoperative hypothermia on whole body protein metabolism

Whole body protein turnover and urinary nitrogen and 3-methyl-L-histidine (3-MH) excretion were measured before and after cardiac surgery using cardiopulmonary bypass in 20 male patients randomized to an intraoperative blood temperature of 28 or 20 degrees C. Rates of whole body protein synthesis (WBPS) and breakdown (WBPB) were determined from the 15N isotopic enrichment of urinary urea, ammonium, and from a calculated end-product average (EPA) after a primed 24-h infusion of [15N]glycine. In the postoperative period, there was a 40% increase in median nitrogen excretion in the 28 degrees C group (P less than 0.03) and a 22% increase in the 20 degrees C group (P = 0.10). There was a 79% increase in the median postoperative 3-MH excretion in the 28 degrees C group (P = 0.01) and a 66% increase in the median postoperative 3-MH excretion in the 20 degrees C group (P less than 0.01). Postoperatively, there was a 23% fall in the median value of WBPS in the 28 degrees C group (P less than 0.01) and an 11% fall in the 20 degrees C group [not significant (NS)] measured by 15N enrichment of urinary urea. In contrast, when WBPS was measured from isotopic enrichment of urinary ammonium, there was an increase in the median value of the postoperative rates of WBPS in both groups, by 20% in the 28 degrees C group (P = NS) and 29% in the 20 degrees C group (P = 0.03). There was no significant change in the rate of WBPS and WBPB, judged by the postoperative EPA in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic effects of cachectin/tumor necrosis factor are modified by site of production. Cachectin/tumor necrosis factor-secreting tumor in skeletal muscle induces chronic cachexia, while implantation in brain induces predominantly acute anorexia

We have developed a murine model of wasting by injecting intracerebrally cells which continuously secrete h-cachectin/TNF (CHO-TNF) to: (a) determine the effects of cachectin/TNF produced continuously in the central nervous system (CNS), and (b) compare the metabolic effects of cachectin/TNF-secreting tumor in the brain to the cachexia caused by CHO-TNF tumor in peripheral tissue (IM). Intracerebral CHO-TNF tumors produced increased serum h-cachectin/TNF levels with lethal hypophagia and weight loss (mean survival time of 11 d); these changes were not observed in association with nonsecretory control brain tumors. The metabolic consequences of intracerebral cachectin/TNF production were indistinguishable from acute, lethal starvation: whole-body lipid content was decreased significantly but protein was conserved. Although intramuscular cachectin/TNF-secreting tumors caused similar increases of serum h-cachectin/TNF levels, profound anorexia did not develop; wasting developed after a longer period of tumor burden (50 d) with classical signs of cachexia (i.e., anemia and depletion of both protein and lipid). These studies provide a reproducible animal model of site-specific cytokine production and suggest that, regardless of serum levels, cachectin/TNF produced locally in brain influences both the rate of development of wasting and its net metabolic effects.

Nutritional status affects renal 3-methylhistidine handling in humans

The plasma concentration of 3-methylhistidine (3MH) has been used in the assessment of nutritional status. Because urinary excretion is the sole route of elimination, and hence a potential determinant of the plasma concentration, 3MH renal handling was examined under different nutritional conditions. Ten obese women consumed a meat-free maintenance energy diet for 4 days before undergoing a 21-day total fast, after which they were assigned into two groups (n = 5) that received 7 days of hypocaloric feeding with 80 g of either milk protein or carbohydrate. 3MH excretion and plasma levels decreased in parallel during fasting and protein refeeding, suggesting that the plasma concentration accurately reflected a decrease of myofibrillar protein turnover, but carbohydrate refeeding was associated with a 31% increase in plasma 3MH (P less than .05) despite a concurrent 28% decrease in its excretion (P less than .05). This was due to a 41% decrease in 3MH renal clearance (P less than .05). Creatinine and urea clearances changed insignificantly in all diet periods. Plasma histidine (HIS) concentrations decreased with fasting and carbohydrate refeeding (P less than .05). 3MH clearance was found to be related to the plasma HIS/3MH concentration ratio (r = .60, P less than .001). Under some circumstances, an altered plasma HIS concentration appears to influence renal 3MH clearance and hence its plasma concentration.

The effect of amino acid infusion on leg protein turnover assessed by L-[15N]phenylalanine and L-[1-13C]leucine exchange

A stable isotope technique depending on the use of [15N]phenylalanine and [1-13C]leucine to assess exchange was utilized to measure the components of protein turnover of the human leg and the effects of amino acid infusion. Eight healthy subjects (28.5 +/- 2.5 years) were studied when post-absorptive in the basal state and again during infusion of a mixed amino acid solution (55 g l-1, 1.52 ml kg-1 h-1). During the basal period leucine oxidation by the leg was 4.4 +/- 2.0 nmol 100 g-1 min-1 and this increased threefold during amino acid infusion (13.6 +/- 3.1 nmol 100 g-1 min-1, mean +/- SEM, P = 0.003). Amino acid infusion abolished the net negative balance between incorporation of leucine into, and release from, protein (basal, -31.8 +/- 5.8; during infusion, +3.1 +/- 7.1 nmol 100 g-1 P = 0.001). Phenylalanine exchange showed a similar pattern (basal, -13.7 +/- 1.8; during infusion, -0.8 +/- 3.0 nmol 100 g-1 min-1, P = 0.003). Basal entry of leucine into leg protein (i.e. protein synthesis) was 70.0 +/- 10.8 nmol 100 g-1 min-1 and this increased during amino acid infusion to 87.3 +/- 14.1 nmol 100 g-1 min-1 (P = 0.11). Phenylalanine entry to protein also increased with amino acid infusion (29.1 +/- 4.5 vs. 38.3 +/- 5.8 nmol 100 g-1 min-1, P = 0.09). Release from protein of leucine (101.8 +/- 9.1 vs. 84.2 +/- 9.1 nmol 100 g-1 min-1, P = 0.21) and of phenylalanine (42.8 +/- 4.2 vs. 39.1 +/- 4.2 nmol 100 g-1 min-1, P = 0.50) was unchanged by amino acid infusion. The results suggest that, in the post-absorptive state in man, infusion of mixed amino acids, without additional energy substrates; reverses negative amino acid balance by a mechanism which includes stimulation of muscle protein synthesis but which does not alter protein breakdown. Interpretation of the results obtained concurrently on whole-body protein turnover suggests that the increase in muscle protein synthesis contributes substantially to the whole-body increase, but the fall in whole-body breakdown with exogenous amino acids is independent of changes in muscle.

Endogenous protein-synthesis efficiency in trauma victims

Hyperglycemia despite increased glucose oxidation and hypoaminoacidemia despite increased rate of protein breakdown are frequently seen in hypermetabolic and highly catabolic patients with major trauma. The extent of reutilization of endogeneously produced amino acids in the synthesis of new proteins (protein recycling) by the traumatized human is poorly understood. The protein synthesis efficiency was measured in ten multiple trauma patients during the early "flow" phase of injury, and these data were compared with normal and depleted patients. In acute trauma the synthetic efficiency of protein is significantly (P = .01) low (61% +/- 4%) compared with other pathologic states (78% +/- 1%). This suggests that the priority is preferentially set to meet the increased demands of glucose production, and a major portion of the amino acids are utilized for purposes other than synthesis of body proteins. This observation should be taken into account in the early management of acute trauma patients before the body adapts to accept the exogenous supply of amino acids.

Adjunctive therapy for nutritional support in hospitalized patients

It would be unrealistic to expect that a single adjuvant modality may be applicable to all patients receiving nutritional support, either IV or enterally. Further characterization of the optimal application of each adjuvant modality may establish the precise role of adjuvant anabolic stimulation throughout the clinical course. Better definition of IV formulas with addition of stable glutamine dipeptides may be of benefit in patients at high risk for sepsis and significant skeletal muscle wasting, while use of met-hGH may improve nitrogen retention and whole-body net protein accrual under these circumstances. Chronic, low- to moderate-intensity exercise may be applicable in a select group of patients, particularly patients at risk for developing complications after surgical intervention in whom aggressive nutritional support has been shown to improve operative outcome.

Recombinant growth hormone enhances muscle myosin heavy-chain mRNA accumulation and amino acid accrual in humans

A potentially lethal complication of trauma, malignancy, and infection is a progressive erosion of muscle protein mass that is not readily reversed by nutritional support. Growth hormone is capable of improving total body nitrogen balance, but its role in myofibrillar protein synthesis in humans is unknown. The acute, in situ muscle protein response to an infusion of methionyl human growth hormone was investigated in the limbs of nutritionally depleted subjects during a period of intravenous refeeding. A 6-hr methionyl growth hormone infusion achieved steady-state serum levels comparable to normal physiologic peaks and was associated with a significant increase in limb amino acid uptake, without a change in body amino acid oxidation. Myosin heavy-chain mRNA levels, measured by quantitative dot blot hybridization, were also significantly elevated after growth hormone administration. The data indicate that methionyl growth hormone can induce intracellular amino acid accrual and increased levels of myofibrillar protein mRNA during hospitalized nutritional support and suggest growth hormone to be a potential therapy of lean body wasting.