Determinants of blood amino acid concentration after hemorrhage

Many mechanisms, including alterations in muscle metabolism, cellular damage, decreased blood volume, and hepatic disfunction, are influential in producing the observed progressive rise in the concentration of amino acids in arterial and venous blood during persisting hypovolemic shock. The rapid rise of venous and arterial concentrations of amino acids and the increase in venoarterial concentration difference suggest that hypovolemia causes a net release from muscle of a potential substrate for energy metabolism. The blood flow through peripheral tissues, however, is reduced to such an extent during hypovolemic shock that the net rate of release of amino acids is not greater than preshock release and may be less. Therefore, the homeostatic advantages served by the alteration in protein metabolism during the more chronic stresses of starvation or after injury may not obtain during acute hypovolemia.     

Protein sparing in skeletal muscle during prolonged starvation. Dependence on lipid fuel availability

Previous studies indicated that protein sparing in skeletal muscle during prolonged starvation depends on the availability of lipid fuels. To test this relationship further, fasted rats conserving protein were treated in vivo for 6-8 h with the antilipolytic agent nicotinic acid (NA) or with tetradecylglycidate (TDGD), an inhibitor of long-chain fatty acid oxidation. After treatment, protein synthesis and degradation in skeletal muscle were evaluated with the perfused rat hindquarter. NA treatment decreased plasma 3-hydroxybutyrate and free fatty acids and increased plasma urea and urine urea excretion, indicating increased breakdown of body protein. TDGD produced similar metabolic effects, except that plasma free fatty acids were markedly increased as a result of inhibition of fatty acid oxidation. NA and TDGD also decreased plasma insulin and increased plasma corticosteroid. Inhibition of lipid metabolism in vivo resulted in accelerated loss of protein from skeletal muscle due to decreased protein synthesis and increased protein breakdown. NA increased both total (i.e., tyrosine release) and myofibrillar (i.e., 3-methylhistidine release) protein breakdown, whereas TDGD increased the breakdown of only nonmyofibrillar proteins (i.e., 3-methylhistidine release by perfused hindquarter was not altered). These data indicate that lipid fuels may directly modulate protein metabolism in muscle during prolonged starvation and may prevent a rise in catabolic hormones. They also indicate that free fatty acids may directly attenuate the breakdown of myofibrillar proteins in muscle during prolonged starvation and that this may be unrelated to their oxidation.     

Amino acid metabolism in dogs with E. coli bacteremic shock.

In 10 fasting dogs receiving 10(9) viable E. coli bacteria per kilogram intravenously, mean systolic blood pressure decreased from 120.6 +/- 15.1 to 82.2 +/- 12.8 mm Hg. The association of hypoglycemia and increased arterial alanine and glycine with elevated plasma glucagon implied impaired gluconeogenesis. A rapid elevation of blood urea concentration, indicating increased ureagenesis, a fall of blood glucose, and an increase of net urea synthesis relative to that of glucose suggested that an increased proportion of the carbon residues derived from glucogenic amino acids is catabolized via pathways other than gluconeogenesis. In the bacteremic dogs the absolute net release from the leg of valine, isoleucine, and leucine and their net release relative to the net rate of proteolysis were decreased, suggesting increased oxidation of these amino acids in skeletal muscle. An increased net release of alanine relative to the net rate of protein catabolism in muscle was in agreement with this contention.     

Effect of catabolic hormone infusion on protein turnover and amino acid uptake in skeletal muscle

Increased plasma levels of the catabolic hormones glucagon, epinephrine, and cortisol have been implicated in mediating various metabolic alterations in trauma and sepsis. Their role in altered protein turnover and amino acid transport in skeletal muscle during sepsis, however, is not known. In the current study, rats were infused with a mixture of the catabolic hormones for 16 hours. Control animals were infused with vehicle solution. Protein synthesis and degradation rates were measured in incubated, intact soleus muscles as incorporation of 14C-phenylalanine into protein and release of tyrosine into incubation medium, respectively. Muscle amino acid uptake was determined by measuring the intracellular to extracellular ratio of [3H]-alpha-aminoisobutyric acid after incubation for 2 hours. Infusion of catabolic hormones for 16 hours resulted in elevated plasma glucose and lactate levels, reduced plasma concentrations of most amino acids, and accelerated muscle protein breakdown, similar to previous findings in septic rats. Protein synthesis rates and amino acid uptake in incubated muscles were not significantly different in control and hormone-infused rats. The current study suggests that increased muscle proteolysis in sepsis and severe injury may be mediated in part by catabolic hormones. In contrast, reduced muscle protein synthesis and amino acid uptake are probably signaled by other substances or mechanisms.     

大鼠严重烫伤早期血浆游离氨基酸浓度的变化

目的 探讨烫伤早期大鼠血浆游离氨基酸含量的变化规律,为研究烧伤后骨骼肌代谢机制异常提供依据。方法 以30％TBSAⅢ度烫伤大鼠为模型,随机分为正常对照组和烧伤后2、6、12和24h共5组,每组8只。用氨基酸自动分析仪的生理体液柱测定血浆游离氨基酸含量,同时测定血清丙氨酸氨基转移酶（ALT）、血清天冬氨酸氨基转移酶（AST）浓度、皮质醇、TNFα和IL－6含量。结果 烫伤后24h内各时相点血浆总氨基酸含量虽然无显性变化,但有不同程度降低趋势;支链氨基酸（BCAA）2h显降低,12h显升高;芳香族氨基酸（AAA）在12和24h显升高;BCAA／AAA比值无显性变化;苯丙氨酸／酪氨酸（Phe/Tyr)比值除伤后2h外,其余各时相点均显升高（P＜0．01）,伤后12h达峰值;血浆TNFα和IL－6含量均显上升（P＜0．01）;IL－6和皮质醇与3－MH和Phe/Tyr呈显正相关。结论 烫伤大鼠因浆氨基酸发生明显变化,其原因可能与早期炎性介质过度释放以及骨骼肌蛋白降解增强和肝功能受损有关,其机制有待进一步研究。     

Alanine metabolism in the skeletal muscle and plasma in endotoxemia

Utilizing a 24 hour fasting rabbit (N = 30), we measured free amino acids in the femoral artery and vein and the quadriceps femoris muscle. The endotoxin E. coli 026, 3.0mg/kg (LD100) was injected and free amino acid plasma levels were monitored for 6 hours. Changes in free amino acid plasma levels were variable and marked after endotoxin injection. By 360 min. after endotoxin injection: (a) the rate of increase in free amino acid levels in the femoral artery was 366 mumole/l of alanine, 162 mumole/l of glycine and 85 mumole/l of proline; (b) the rate of increase in free amino acid of the quadriceps femoris muscle was 1376 nmole/g of alanine, 156 nmole/g of glycine and 109 nmole/g of serine; and (c) the femoral arteriovenous difference was -225 nmole/l of alanine, -118 nmole/l of glycine and -77nmole/l of proline. Within 10 min. after endotoxin injection, alanine concentration was higher in the femoral vein. This change in concentration became significant by 60 min. The results show the following: Skeletal muscle appears to be an important source of amino acids for amino acid metabolism during endotoxemia, especially plasma alanine which is closely connected with alanine levels in skeletal muscle.     

The effect of metabolic acidosis on amino acid and keto acid metabolism in chronic renal failure

The effect of metabolic acidosis (MA) on amino acid and keto acid metabolism was studied in fourteen patients with chronic renal failure (CRF) under the low protein diet (0.6-0.8 g/kgBW). The comparative study of five patients with renal tubular acidosis was carried out. Each patient was investigated before [MA(+)period] and after correction with sodium bicarbonate administration lasting 10 days [MA(-)period]. The correction of MA improved nitrogen balance and elevated plasma branched-chain amino acids (BCAA), keto acids (BCKA), glutamine and alanine concentrations. No effect was however, observed in change of plasma insulin and glucagon. Oral administration of the keto-analogues of BCKA [0.1 g/kgBW of alpha-ketoisovalerates (KIV) and alpha-keto-isocaproic acid (KIC)] is made for the purpose of investigating the change in the metabolic conversion rate to amino acids. As a result, MA (+) suppressed an increase in plasma KIV and KIC concentrations. Moreover, an increase in plasma valine and leucine concentrations were suppressed by MA (+). These results suggested that MA stimulates BCKA oxidation and suppresses the protein sparing effect of leucine and KIC, and accelerates the catabolism in CRF under the low protein diet. The correction of MA is ineffective in severe renal failure (serum creatinine above 10.0 mg/dl), because the other uremic factors appear to be affecting protein and amino acid metabolism. Therefore, it might be concluded that MA should be corrected at an earlier stage of CRF.     

Influence of branched chain amino acid infusions on wound healing

Branched chain amino acids (BCAA) may serve as a major oxidative fuel for skeletal muscle during periods of starvation. This study compared the ability of protein-undernourished rats to heal musculo-aponeurotic wounds of the abdominal wall when they were infused with solutions containing 45% BCAA or 8% BCAA (conventional TPN). Although the provision of 45% BCAA tended to result in better nourished animals and significantly increased plasma glutamine concentrations, this was not associated with improved healing.     

Amino Acid and protein kinetics in renal failure: an integrated approach

Even apparently healthy patients on dialysis have significant loss of lean body mass. Patients with chronic renal failure without coexisting metabolic acidosis or inflammation have decreased protein turnover, with balanced reduction in protein synthesis and breakdown. However, regional and whole-body protein kinetic studies indicate that hemodialysis (HD) induces net increase in protein breakdown. Whole-body protein turnover studies show that HD is associated with decreased protein synthesis, but proteolysis is not increased. Muscle protein kinetics studies, however, identify enhanced muscle protein breakdown with inadequate compensatory increases in synthesis as the cause of the catabolism. Transmembrane amino acid-transport kinetics studies show that the outward transport is increased more than the inward transport of amino acids during HD. Altered intracellular amino acid transport kinetics and protein turnover during HD could be caused by the loss of amino acids in the dialysate or cytokine activation. Cytokines may be released from peripheral blood mononuclear cells and skeletal muscle during HD. Preliminary evidence indicates that intradialytic increase in cytokines activates the ubiquitin-proteasome pathway. An intradialytic increase in albumin and fibrinogen synthesis is facilitated by interleukin-6 and the constant supply of amino acids derived from skeletal muscle catabolism. Protein anabolism can be induced in end-stage renal disease patients by repletion of amino acids, and perhaps treatment with recombinant human insulin-like growth factor.     

脓毒症大鼠血浆游离氨基酸浓度的变化

目的 探讨脓毒症早期大鼠血浆游离氨基酸含量的变化与骨骼肌蛋白降解间的关系。方法 以腹腔注射内毒素建立大鼠脓毒症模型,将动物随机分为正常对照组和内毒素攻击后2、6、12、24h共5组,每组8只动物。用氨基酸自动分析仪的生理体液柱测定各组大鼠血游离氨基酸含量;用全自动生化分析仪测定血浆谷丙转氨酶（ALT）和谷草转氨酶（AST）浓度;用放射免疫分析（RIA）法测定血浆皮质醇含量;用酰联免疫吸附试验（ELISA）测定血浆TNF－α和IL－6含量。结果 内毒素攻击后各时相点大鼠血浆总氨基酸含量在正常范围内波动;支链氨基酸（BCAA）在2、6、12h降低,24h则出现显著升高,亮氨酸、异亮氨酸无显著怀变化,缬氨酸早期明显降低,后期则上升;芳香族氨基酸（AAA）在各时相点不同程度升高,2h和6h显著升高,酪氨酸12h降低,苯丙氨酸在各时相点均显著升高;苯丙氨酸／酪氨酸（Phe/Tyr)比值内毒素攻击后各时相点均出现显著增加;BCAA／AAA比值在2h和6h较正常显著较低;苏氨酸、谷氨酸、鸟氨酸、3－甲基组氨酸（3－MH）、组氨酸、丙氨酸早期升高或大多数时相点显著升高,赖氨酸、肌氨酸、胱氨酸和磷酸丝氨酸在内毒素攻击后无显著性变化,其它氨基酸均见不同程度的降低或显著降低。血浆ALT、AST浓度在内毒素攻击后各时相点显著升高（P＜0．01）,6h达峰值。血浆皮质醇含量在各时相点均显著升高（P＜0．01）,6h达峰值。血浆TNF－α和IL－6含量均上升（P＜0．01）,其中TNF-α于2h达峰值,IL－6于12h达峰值。结论 脓毒症大鼠血浆游离氨基酸浓度变化主要由于骨骼肌蛋白降解增强与肝脏代谢负担加重所致。     

Splanchnic amino acid and glucose metabolism during amino acid infusion in dogs

With the organ-balance technique, we studied amino acid and glucose metabolism by hepatic and extrahepatic splanchnic tissues in awake dogs in the postabsorptive state and during a 3-h intravenous amino acid infusion. Dogs received a high (1.4 g/kg body wt, n = 5) or low (0.7 g/kg body wt, n = 8) dose of amino acids. In four of the latter dogs, the dose was delivered into a mesenteric vein. During the basal period there was a net removal of gluconeogenic amino acids (particularly alanine), but not branched-chain amino acids, and a net production of glucose by the liver in all dogs. During this time there was a net removal of glucose and production of alanine by the extrahepatic splanchnic tissues. During either high- or low-dose amino acid infusion, net hepatic glucose release increased; despite this, arterial plasma glucose declined due to an increase in tissue glucose uptake at extrasplanchnic sites. The net amount of glucogenic amino acids removed by the liver during high-dose (9.1 +/- 1.0 mmol.kg-1.3 h-1) and low-dose (4.8 +/- 0.6 mmol.kg-1.3 h-1) infusion equaled or exceeded the infused load of these amino acids. In addition, the liver contributed to the net disposal of branched-chain amino acids during high-dose (536 +/- 147 mumol.kg-1.3 h-1) and low-dose (341 +/- 70 mumol.kg-1.3 h-1) infusion. During high-dose infusion, extrahepatic splanchnic tissues participated in the net removal of branched-chain amino acids (436 +/- 162 mumol.kg-1.3 h-1) but not glucogenic amino acids, and net alanine production continued (410 +/- 91 mumol.kg-1.3 h-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of catabolic hormone infusion on organ amino acid uptake

Elevated plasma levels of the so-called catabolic hormones (glucocorticoid, epinephrine, glucagon) have been observed in severely injured patients, and infusion of these hormones to normal subjects has reportedly simulated several metabolic aberrations characteristic of severe trauma and sepsis. We recently reported that amino acid uptake was reduced in soleus muscle, heart, and diaphragm, and increased in the liver, of septic rats. The purpose of the present study was to investigate organ amino acid uptake in nonseptic rats infused with catabolic hormones. Central venous catheters were placed in male Sprague-Dawley rats (100-150 g) and after 24 hr hormones (glucagon 5 micrograms/kg/hr, epinephrine 6 micrograms/kg/hr, corticosterone 4.2 mg/kg/hr) or vehicle (saline, ascorbic acid 1 mg/ml, albumin 3 mg/ml) was infused for 72 hr. Animals were housed in metabolic cages and allowed food and water ad lib. One hour prior to sacrifice, alpha-[3H]aminoisobutyric acid (AIB) (2.5 microCi), a nonmetabolized amino acid analog mainly transported by system-A, was injected intravenously. Animals were killed and organs were removed, weighed, and dissolved in tissue solubilizer for measurement of radioactivity. AIB uptake was significantly elevated in all organs of catabolic hormone-infused animals studied. The results suggest that catabolic hormones may be involved in the pathogenesis of increased amino acid uptake in the liver during sepsis. Inhibited amino acid uptake in skeletal muscle during sepsis, however, is probably not primarily mediated by catabolic hormones.     

Insulin decreases muscle protein loss after operative trauma in man

Seventy-two hours after major operative trauma, nine patients receiving a constant infusion of calories (1460 kcal/m2/day) and protein (75 gm of amino acid/m2/day) showed a negative nitrogen balance, increased muscle catabolism, as measured by 3-methylhistidine excretion, increased amino acid efflux from muscle, and decreased circulating levels of insulin. When 5 U of insulin/hr were added to the infusate, arterial insulin levels rose significantly from 39.7 +/- 4.1 microU/ml to approximately the pretrauma levels (74.6 +/- 7.7 microU/ml). Despite this normalization of insulin levels, excretion of nitrogen and 3-methylhistidine and the efflux of amino acids from forearm muscle fell but did not return to pretraumatic levels, suggesting some insulin resistance. Visceral gluconeogenesis from amino acids appeared to decrease, since insulin infusion decreased the efflux of alanine from skeletal muscle with no change in its arterial level. Insulin also significantly reduced the efflux of isoleucine, tyrosine, phenylalanine, glutamine, and total amino acid nitrogen from forearm muscle. These findings, along with the partial reduction in the excretion of 3-methylhistidine and nitrogen, suggest that insulin, in combination with infused calories and protein, decreases the loss of muscle protein after trauma.     

Lipid infusion impairs physiologic insulin-mediated capillary recruitment and muscle glucose uptake in vivo

Infusion of triglycerides and heparin causes insulin resistance in muscle. Because the vascular actions of insulin, particularly capillary recruitment, may contribute to the increase in glucose uptake by skeletal muscle, we investigated the effects of Intralipid/heparin infusion on the hemodynamic actions of insulin during clamp conditions. Saline or 10% Intralipid/heparin (33 U/ml) was infused into anesthetized rats at 20 microl/min for 6 h. At 4 h into the saline infusion, a 2-h hyperinsulinemic (3 mU. min(-1).kg(-1))-euglycemic clamp was conducted (Ins group). At 4 h into the lipid infusion, a 2-h saline control (Lip group) or 2-h hyperinsulinemic-euglycemic clamp (Lip + Ins group) was conducted. Arterial blood pressure, heart rate, femoral blood flow (FBF), hindleg vascular resistance, glucose infusion rate (GIR), hindleg glucose uptake (HGU), and muscle 2-deoxyglucose uptake (R'g) were measured. Capillary recruitment, as measured by metabolism of infused 1-methylxanthine (1-MX), was also assessed. When compared with either Lip or Lip + Ins, Ins had no effect on arterial blood pressure, heart rate, FBF, or vascular resistance but increased GIR, HGU, and R'g of soleus, plantaris, extensor digitorum longus, and gastrocnemius red muscles and hindlimb 1-MX metabolism. GIR, HGU, and R'g of soleus, plantaris, gastrocnemius red, and the combined muscles and 1-MX metabolism were less in Lip + Ins than in Ins rats. HGU correlated closely with hindleg capillary recruitment (r = 0.86, P < 0.001) but not total hindleg blood flow. In conclusion, acute elevation of plasma free fatty acids blocks insulin-mediated glucose uptake and capillary recruitment.     

Evidence for a major role of skeletal muscle lipolysis in the regulation of lipid oxidation during caloric restriction in vivo.

A lipolytic process in skeletal muscle has recently been demonstrated. However, the physiological importance of this process is unknown. We investigated the role of skeletal muscle lipolysis for lipid utilization during caloric restriction in eight obese women before and after 11 days of very low-calorie diet (VLCD) (2.2 MJ per day). Subjects were studied with indirect calorimetry and microdialysis of skeletal muscle and adipose tissue in order to analyze substrate utilization and glycerol (lipolysis index) in connection with a two-step euglycemic-hyperinsulinemic (12 and 80 mU/m(2). min) clamp. Local blood flow rates in the two tissues were determined with (133)Xe-clearance. Circulating free fatty acids and glycerol decreased to a similar extent during insulin infusion before and during VLCD, and there was a less marked insulin-induced reduction in lipid oxidation during VLCD. Adipose tissue glycerol release was hampered by insulin infusion to the same extent ( approximately 40%) before and during VLCD. Skeletal muscle glycerol release was not influenced by insulin before VLCD. However, during VLCD insulin caused a marked (fivefold) (P < 0.01) increase in skeletal muscle glycerol release. The effect was accompanied by a fourfold stimulation of skeletal muscle blood flow (P < 0.01). We propose that, during short-term caloric restriction, the reduced ability of insulin to inhibit lipids, despite a preserved antilipolytic effect of the hormone in adipose tissue, is caused by an augmented mobilization of fat from skeletal muscle, and that a physiological role of muscle lipolysis provides a local source of fatty acids.     

Mechanism of amino acid-induced skeletal muscle insulin resistance in humans

Plasma concentrations of amino acids are frequently elevated in insulin-resistant states, and a protein-enriched diet can impair glucose metabolism. This study examined effects of short-term plasma amino acid (AA) elevation on whole-body glucose disposal and cellular insulin action in skeletal muscle. Seven healthy men were studied for 5.5 h during euglycemic (5.5 mmol/l), hyperinsulinemic (430 pmol/l), fasting glucagon (65 ng/l), and growth hormone (0.4 microg/l) somatostatin clamp tests in the presence of low (approximately 1.6 mmol/l) and increased (approximately 4.6 mmol/l) plasma AA concentrations. Glucose turnover was measured with D-[6,6-(2)H(2)]glucose. Intramuscular concentrations of glycogen and glucose-6-phosphate (G6P) were monitored using (13)C and (31)P nuclear magnetic resonance spectroscopy, respectively. A approximately 2.1-fold elevation of plasma AAs reduced whole-body glucose disposal by 25% (P < 0.01). Rates of muscle glycogen synthesis decreased by 64% (180--315 min, 24 plus minus 3; control, 67 plus minus 10 micromol center dot l(-1) center dot min(-1); P < 0.01), which was accompanied by a reduction in G6P starting at 130 min (DeltaG6P(260--300 min), 18 plus minus 19; control, 103 plus minus 33 micromol/l; P < 0.05). In conclusion, plasma amino acid elevation induces skeletal muscle insulin resistance in humans by inhibition of glucose transport/phosphorylation, resulting in marked reduction of glycogen synthesis.     

Experimental study on metabolism of branched chain amino acids after partial hepatectomy

Metabolism of branched chain amino acids (BCAA) after partial hepatectomy was investigated. Total amino acids of the plasma in the rats undergone 70% partial hepatectomy increased significantly as compared with those of control animals. This increase was due to an increase of sum of all amino acids other than BCAA, whereas total amount of BCAA was unaffected. Both BCAA aminotransferase (BCAA-AT) and branched chain ketoacid dehydrogenase (BCKA-DH), the rate limiting enzymes in BCAA metabolism, increased in mitochondria of the liver and BCAA-AT increased in skeletal muscle homogenate. These increases of both enzymes might reduce the concentration of BCAA relatively. Mitochondrial respiration such as state 3 respiration, respiratory control index (RCI) and ATP synthesis in mitochondria of regenerating liver increased remarkably, when not only succinate but also alpha-ketoisocaproic acid was used as a substrate. ATP synthesis, however, was much higher and mitochondrial respiration was more coupled when alpha-ketoisocaproic acid was used as a substrate. These results suggest that BCAA metabolism was activated after partial hepatectomy and BCAA might serve as an appropriate substrate for regenerating liver.     

Adaptive regulation in skeletal muscle glutamine metabolism in endotoxin-treated rats.

The effects of a single dose of endotoxin (7.5 mg/kg BW) on skeletal muscle glutamine metabolism were studied in vivo in rats to gain further understanding of the altered glutamine metabolism that characterizes sepsis and other catabolic diseases. In endotoxin-treated animals the arterial glutamine concentration fell early initially and then increased compared with control values. Twelve hours after treatment, the arteriovenous concentration difference for glutamine across the hindquarter doubled, resulting in a significant increase in net muscle glutamine release in endotoxin-treated rats. As a consequence, the muscle glutamine concentration fell in the endotoxin-treated animals by 25%-40%, an event that was apparent as early as two hours after endotoxin treatment. Skeletal muscle glutaminase activity, the major enzyme of glutamine breakdown, was unchanged by endotoxemia, but expression of glutamine synthetase mRNA and glutamine synthetase specific activity increased in a time-dependent fashion. The glutamine depletion that develops in skeletal muscle during endotoxemia is caused by accelerated muscle glutamine release rather than an increase in intracellular degradation or a fall in intracellular biosynthesis. The adaptive increase in glutamine synthetase expression that occurs requires de novo RNA and protein synthesis and may be designed to prevent complete depletion of the intracellular glutamine pool.     

Insulin stimulates branched chain amino acid uptake and diminishes nitrogen flux from skeletal muscle of injured patients

Resistance to insulin-mediated glucose disposal occurs in uninjured skeletal muscle of trauma patients but the effect of insulin on the accelerated proteolysis of trauma is unknown. We examined the influence of insulin on forearm amino acid and substrate exchange in five normals and four trauma patients using the hyperinsulinemic glucose clamp technique. Forearm substrate and amino acid flux (Q, nM/100 ml tissue/min), the product of blood flow and arterial deep venous concentration difference, was calculated before and during insulin infusion. Total nitrogen release (NQ, nM/100 ml tissue/min) was calculated as the algebraic sum of all nitrogen groups contained in the amino acids released. Among normal subjects, total nitrogen release from the forearm did not change (581 +/- 197 nM/100 ml tissue/min to 1167 +/- 455) during insulin infusion nor did total branched chain amino acid flux (0 +/- 30 nM/100 ml/min to 106 +/- 36). Under conditions of hyperinsulinemia, neither glutamine nor alanine changed in control subjects. In trauma patients, total nitrogen release (3843 +/- 1383 nM/100 ml/min) was inhibited during insulin administration (819 +/- 314, P less than 0.05). Total branched chain amino acid flux went from a net release of 460 +/- 134 nM/100 ml/min to a net uptake of 10 +/- 82 (P less than 0.05). In patients, statistically significant (P less than 0.05) differences were seen in individual amino acids as well. Forearm nitrogen flux was directly related to total branched chain amino acid flux in patients (r2 = 0.89). Additional studies in normals (n = 4) at higher insulin infusion rates confirmed that these effects were unique to injured subjects and not an effect of the insulin dose. Insulin attenuates the accelerated release of skeletal muscle amino acid in trauma patients. This effect may be mediated in part by facilitated branched chain amino acid uptake. The manipulation of both insulin and branched chain amino acid concentrations may provide a method to reduce post-traumatic protein catabolism.     

Muscle and Plasma Amino Acids Following Injury: Influence of Intercurrent Infection

The present study was undertaken to determine intracellular amino acid patterns in patients with multiple trauma, whether or not complicated by sepsis and during convalescence. A percutaneous muscle biopsy was performed three to four days following major accidental injury in ten patients and analyzed for muscle free amino acids. Venous blood was drawn at the time of the biopsy and analyzed for plasma free amino acids. Five patients developed sepsis and a repeat biopsy was performed on days 8 to 11. In five of the patients a biopsy was performed during the late convalescent period (anabolic phase). A marked depletion of nonessential amino acids in muscle occurred in both injury and sepsis due to a decrease (50%) in glutamine, which was equally marked in both states. The essential amino acids in muscle increased in injury. During sepsis, a further increase was observed with a return toward normal in the convalescent period. In injury, the most marked rise was in the branched-chain amino acids, phenylalanine, tryosine and methionine. With sepsis, a further rise in muscle branched-chain amino acids, phenylalanine and tryosine occurred, while plasma levels remain unchanged. During convalescence, muscle glutamine, arginine, histidine and plasma branched-chain amino acids were below normal, whereas muscle phenylalanine and methionine were elevated. The muscle free amino acid pattern observed after major trauma was essentially the same as earlier described following elective operation. This suggests a common response of intracellular amino acids irrespective of the degree of injury, and may indicate that the pump settings which regulate amino acid transport follow the “all or none” rule. The high intracellular levels of branched-chain amino acids in sepsis suggest that the energy deficit of this state is due to an impairment of substrate use rather than intracellular availability. The high concentrations of the aromatic amino acids and methionine may be due to altered liver function. During the late convalescent period (anabolic phase) the low levels of certain key amino acids suggests inadequate nutrition. The difficulties in nourishing the injured or septic patient are well recognized. The period following these catabolic states may be an important period for the application of an optimal, aggressive nutritional regimen.