谷氨酰胺和生长激素对术后病人肌肉代谢的影响

目的许多研究表明,给予生长激素和谷氨酰胺能减少手术后肌肉蛋白的分解(术后肌蛋白分解表现在肌蛋白合成减少、谷氨酰胺水平降低和氮丢失增加)。本研究目的是联合使用生长激素和胰岛素样生长因子((IGF-I,一种能解释生长激素部分作用效果的生长因子)及添加生长激素和谷氨酰胺对术后肌肉代谢的影响。     

Anabolic steroids support postoperative gut/liver amino acid metabolism

The effects of an anabolic steroid (nandrolone decanoate, 5 mg/kg) on postoperative splanchnic fuel metabolism were studied in order to gain further understanding of the regulation of the altered gut/liver amino acid metabolism that occurs following catabolic illness. In addition to studying glutamine and alanine, which together transport 60% of whole blood amino acid nitrogen, we determined the fluxes of glutamate and glucose across the gastrointestinal tract and liver in 12 postoperative dogs. Substrate exchange (flux) was calculated by multiplying bloodflow by the arterial-venous concentration difference for each substrate. Arterial glutamine, glutamate, and alanine were significantly increased in dogs receiving the anabolic steroid (AS) compared to control animals (p less than 0.05). Intestinal bloodflow was unchanged, but gut glutamine uptake doubled in dogs receiving steroids (1.4 +/- 0.3 mumol/kg/min in controls vs 2.8 +/- 0.7 in AS, p less than 0.05). Simultaneously, gut alanine release was augmented by 100% in dogs receiving steroids (p less than 0.05). Control dogs demonstrated net glutamate release by the gut, while dogs treated with the anabolic steroid demonstrated glutamate balance (p less than 0.05). Liver bloodflow remained unchanged in AS dogs, but hepatic alanine uptake nearly tripled (p less than 0.01) and hepatic glucose production increased by 60% (p less than 0.05). Anabolic steroids appear to support postoperative splanchnic fuel metabolism by increasing blood amino acid levels, enhancing gut/liver amino acid uptake and processing, and augmenting hepatic gluconeogenesis.     

Hepatic glutamine metabolism during endotoxemia in neonatal rats

OBJECTIVES: The liver plays a central role during endotoxemia. We investigated the biochemical changes that occur in neonatal liver during early stages of endotoxemia. METHODS: Twenty neonatal rats (10 to 15 d; n = 10/group) were studied. Endotoxemic rats received intraperitoneal injections of 300 microg/kg of 12.5 mg/L of lipopolysaccharide and control rats received isovolemic normal saline. Two hours after injection, all lipopolysaccharide-injected animals exhibited signs of endotoxemia. Livers were removed and extracted into 12% perchloric acid. 1H and 31P magnetic resonance spectroscopy measured hepatic levels of glutamine, glutamate, alanine, lactate, glucose, beta-hydroxybutyrate, adenosine triphosphate, and adenosine diphosphate. Unpaired t test compared groups. RESULTS: No mortality occurred during the first 2 h after injection. Endotoxemia significantly decreased hepatic levels of glutamine (P < 0.001), glucose (P = 0.047), and beta-hydroxybutyrate (P < 0.001). There was no difference in hepatic levels of glutamate (P = 0.050), alanine (P = 0.165), lactate (P = 0.478), adenosine triphosphate (P = 0.165), and adenosine diphosphate (P = 0.136) between groups. CONCLUSIONS: Early endotoxemia caused significant changes in the hepatic metabolism of glutamine, glucose, and beta-hydroxybutyrate. These findings increase our understanding of the pathophysiology of neonatal endotoxemia.     

Plasma and jejunal glutamine levels after extensive small bowel resection in dogs

Recent studies have demonstrated that glutamine may be required for mucosal growth and that it is widely utilised by the intestinal tract after surgery. This study has evaluated the effect of massive small bowel resection on plasma and jejunal glutamine and related amino-acids level evolution after surgery. Transection was performed in 6 dogs (control group) and enterectomy in 10 dogs leaving 25cm of jejunum, associated with colectomy (group 1). Plasma glutamine levels decreased on D2 (p = 0.03) in the resected group while a significant decrease of plasma alanine levels was observed on D2 (p = 0.002), D4, D6 and D8 (p < 0.001). Intestinal mucosa glutamic acid content was increased on D8 in this group (p < 0.001). No changes were observed in the control group. These results suggest that glutamine is a required substrate after massive small bowel resection which could improve the intestinal adaptation encountered after enterectomy.     

More severe impairment of oral than intravenous glucose tolerance in rats after eating a high fat diet

Glucose and insulin responses to oral and intravenous glucose (1 g/kg body weight) were measured after consumption of a high fat (HF) or low fat (LF) diet for 3 wk in conscious rats with implanted intravenous and intra-arterial catheters. The HF diet resulted in impaired glucose tolerance and insulin resistance after both oral and intravenous glucose; the effect was more pronounced after oral glucose. In an attempt to understand the basis of the impairment of glucose tolerance after consuming the HF diet, the activity of hepatic glucokinase and the rate of intestinal glucose uptake were also measured. The more severe impairment of glucose tolerance by oral rather than intravenous administration was not explained by an increased rate of intestinal glucose uptake. Indeed, there was a small but significant reduction in the rate of jejunal glucose uptake in the HF rats. However, the greatly reduced activity of hepatic glucokinase in the HF rats was consistent with a reduced capacity for hepatic glucose uptake, which may have contributed significantly to the impaired glucose tolerance. The effects of the HF diet on the insulin response to glucose were much more pronounced after oral rather than intravenous glucose administration. This indicated that the HF diet may have stimulated the enteroinsular axis. However, it is also possible that the particularly high circulating insulin levels, resulting from oral glucose in the HF rats, were a direct response to hyperglycemia, secondary to reduced glucose removal.     

Response of glutamine metabolism to glutamine-supplemented parenteral nutrition

BACKGROUND: Increasing evidence suggests that glutamine is important for the function of many organ systems and supports the use of glutamine-enriched total parenteral nutrition (TPN) during severe illness. However, the effect of prolonged glutamine supplementation on glutamine kinetics has not been studied. OBJECTIVE: We investigated the effect of 8-10 d of TPN enriched with glutamine dipeptides on glutamine kinetics. DESIGN: Twenty-three preoperative patients were randomly allocated to receive either TPN enriched with glutamine dipeptides (60 micromol glutamine*kg body wt(-1)*h(-1)) or isonitrogenous, isoenergetic, glutamine-free TPN. A primed, continuous, 6-h intravenous infusion of L-[5-(15)N]glutamine and L-[1-(13)C]leucine was given before (baseline) and 8-10 d after the TPN solutions were administered. Baseline measurements were performed after a 40-h administration of a standard solution of glucose and amino acids (no glutamine). RESULTS: Glutamine-enriched TPN increased the total appearance rate of glutamine (P: < 0.05) but did not inhibit or increase the endogenous appearance rate. The standard TPN solution also increased the glutamine appearance rate (P: < 0.05), but the change was much smaller than in the glutamine-supplemented group (P: < 0.01). The plasma glutamine concentration did not rise significantly during either treatment, suggesting increased tissue glutamine utilization, especially in the glutamine-supplemented group. CONCLUSION: In view of the enhanced glutamine requirements in response to trauma and disease by tissues such as those of the gut, the immune system, and the liver, increased glutamine availability during glutamine-enriched TPN may be beneficial preoperatively in patients with gastrointestinal disease.     

Effects of norepinephrine on hepatic amino acid metabolism in isolated perfused rat liver

The effects of norepinephrine (NE) on hepatic amino acid exchanges were studied in the isolated perfused rat liver using a recirculating system with a medium containing amino acids at twice physiologic concentrations. Norepinephrine induced a significant decrease (25%) in portal blood flow at a concentration of 2 ng/ml (10(-8) M). The hormone also increased total hepatic amino acid uptake, essentially through a switch from glutamine release to net uptake. There was no modification in free intracellular amino acids, but glycogen was slightly decreased, and glucose production was increased. Taken as a whole, these results suggest that NE modulates hepatic protein balance.     

谷氨酰胺联合生长激素在肝移植病人术后应用的临床研究

目的:探讨谷氨酰胺(Gln)联合生长激素(GH)对肝移植术后病人的蛋白质合成、免疫功能、感染和急性排斥反应等的影响.方法:将60例肝移植病人前瞻性随机分为强化营养组(添加Gln+GH)和对照组.术后第2天开始,给予等热量83.68～104.6 kJ(20～25 kcal)/(kg·d)、等氮量0.16 g/(kg·d)...     

Effect of glutamine dipeptide on hepatic regeneration in partially hepatectomized malnourished rats

Glutamine promotes hepatic regeneration in nourished (N) rats. The aim of the present study was to evaluate the effects of glutamine-enriched total parenteral nutrition (TPN) on liver regeneration in malnourished (MN) rats.Seventy-two male Wistar rats ( congruent with 270 g) were assigned to one of two groups: N and MN. Each group was then subdivided into three groups: the first underwent partial hepatectomy (PH) and received standard TPN enriched with L-alanyl-L-glutamine (Ala-Gln); the second also underwent PH and received standard TPN, but enriched with a solution containing proline and alanine (Ala-Pro); and the third underwent no surgical procedure (control group). All experimental groups received isocaloric (188 kcal. kg(-1). d(-1)) and isonitrogenous (1.12 g of nitrogen. kg(-1). d(-1)) TPN for 96 h. All animals were injected with bromodeoxyuridine 2 h before death. The hepatic regeneration index (HRI), hepatic growth percentage (HG) and hepatic morphology were analyzed.In MN rats, HRI and HG were higher with glutamine enrichment (HRI = 81 and HG = 190) than with proline-containing TPN (HRI = 66 and HG = 154; P < 0.05) and HRI was 100 times higher in animals that underwent PH than in control animals. Morphologic analysis of hepatic tissue showed no difference among the six groups.Glutamine-enriched TPN promoted growth of the remnant liver in MN rats after PH, maintained cellular proliferation in the various experimental groups after surgery, and maintained hepatic morphology of MN rats after surgery.     

Administration of glutamine after hemorrhagic shock restores cellular energy, reduces cell apoptosis and damage, and increases survival

BACKGROUND: Hemorrhagic shock causes a rapid depletion of adenosine triphosphate (ATP) and an increase of the terminal metabolite xanthine. Free radicals generated from xanthine oxidase play a major role in cell injury. Programmed cell death, apoptosis, is a major pathway causing reperfusion injury. During apoptosis, cytosolic cytochrome-c is released from damaged mitochondria, and it further initiates activation of apoptosis as evidenced by the appearance of caspase-3. The bcl-2 protein serves as an antiapoptosis found on the mitochondrial membrane. Glutamine has been known as a conditionally essential nutrient and seems to have beneficial effects in critically ill patients. The hypothesis of the present study is that glutamine administered during resuscitation following hemorrhagic shock would restore the depletion of hepatic ATP, reduce cellular apoptosis, and increase survival. METHODS: Male Sprague-Dawley rats were randomly assigned to 3 groups for resuscitation after the same pattern of hemorrhagic shock: Ringer's lactate (LR 21 ml/kg); Alanine-glycine (LR with alanine 0.15 gm/kg and glycine 0.18 gm/kg); and glutamine (LR with glutamine 0.3 gm/kg). Hepatic ATP and xanthine was measured at different time periods. Hepatic apoptosis was measured and the levels of cytosolic cytochrome-c, caspase-3 and bcl-2 were analyzed. Another group of rats were used for survival study. RESULTS: Glutamine administered during resuscitation following hemorrhagic shock partially restored the depletion of hepatic ATP, reduced cellular apoptosis, and increased survival. CONCLUSIONS: Glutamine administration during resuscitation significantly protected the liver from tissue damage caused by hemorrhagic shock. Glutamine supplementation may offer opportunities for therapeutic intervention during and after shock.     

Metabolic response of muscle to alanine,glutamine, and valine supplementation during severe illness

BACKGROUND: Alanine and glutamine are released from muscle in response to critical illness. Subsequent depletion of glutamine from muscle is proposed as a principal factor in the limitation of muscle protein synthesis in severely ill patients. The objective of this study was to assess the peripheral metabolic response to enteral supplementation of alanine, glutamine, and valine in critically ill patients. METHODS: Isotopic tracers of alanine, glutamine, and phenylalanine were given IV to 6 critically ill patients and 6 healthy volunteers. Blood sampling from the femoral artery and vein along with muscle biopsies provided assessment of leg (ie, muscle) kinetics. Measurements were obtained during enteral nutrition alone and then with combined alanine (11.25 g), glutamine (7.5 g) and valine (11.25 g) supplementation for 3 hours. RESULTS: Compared with healthy volunteers, critically ill patients had significantly reduced concentrations of alanine and glutamine in arterial plasma (p < .05), which increased significantly with amino acid supplementation. Muscle glutamine concentrations were significantly less in the patients and were not significantly affected by supplementation. Alanine and glutamine transport into and out of muscle and the rates of alanine and glutamine incorporation into and production from muscle were not affected by supplementation. Phenylalanine kinetics, as a marker of muscle protein metabolism, were not significantly altered by alanine, glutamine, and valine intake. CONCLUSIONS: These results demonstrate that alanine, glutamine, and valine administration fails to significantly affect muscle glutamine availability or muscle protein metabolism. These findings suggest that accelerated muscle catabolism in critically ill patients is not in response to any deficiency in alanine or glutamine availability.     

Effects of growth hormone administration on skeletal muscle glutamine metabolism in severely traumatized patients: preliminary report

We have investigated the effects of 24 h human recombinant growth hormone (hGH) administration on leg muscle glutamine exchange and protein kinetics in severely traumatized patients. Muscle amino acid exchange and protein balance were evaluated using the leg arteriovenous balance technique, whereas changes in skeletal muscle free amino acid concentrations were evaluated in biopsy specimens. hGH infusion decreased phenylalanine release from protein degradation by 56 +/- 14%, and the rate of branched chain amino acid catabolism by 51 +/- 10%. Glutamine release from leg muscle was suppressed by 58 +/- 12%. This latter effect was completely accounted for by a hGH-mediated suppression of glutamine synthesis in skeletal muscle. In conclusion, growth hormone administration in trauma patients may restrain protein and amino acid catabolism in skeletal muscle. However, the growth hormone-mediated suppression of glutamine production we have observed in this study could decrease the systemic availability of this amino acid. During growth hormone treatment, this potential side-effect could be prevented by an exogenous glutamine administration.     

Oxygen consumption and metabolite flux of bovine portal-drained viscera and liver

Oxygen (O2) uptake and net metabolite flux by portal-drained viscera (PDV) and hepatic (HEP) tissues have been quantitated in vivo by measuring blood flow and arteriovenous concentration differences in cattle with chronic indwelling catheters in appropriate blood vessels. Results from use of this technique show that PDV of cattle account for 8-10% of body tissue, but 18-25% of whole animal O2 consumption. Similarly, HEP tissues account for 1-2% of body tissues, but more of whole animal O2 consumption than PDV. Glucose, volatile fatty acids (VFA), glutamate and glutamine are used as substrates by PDV; ketones, alanine and glycine are major products of PDV metabolism that are transported to HEP tissues along with absorbed VFA, ammonia, amino acids and other products of digestion. Most amino acids, L-lactate, propionate and butyrate and ammonia in blood from PDV are removed by HEP tissues, which in turn release glucose, glutamate, branched-chain amino acids, ketones, acetate and urea to peripheral blood. Net HEP flux of glucose measured by this technique is compatible with glucose requirements for lactation and other metabolism; similarly, HEP uptake of ammonia and alpha-amino N can account for 95% of HEP release of urea N. The technique is a powerful tool for quantitation of intermediary metabolism.     

Nutrient utilisation in muscle and in the whole body of patients receiving total parenteral nutrition

Forearm metabolite exchange was assessed by the arterio-venous catheterization technique in 5 parenterally fed patients (weight 55.22 kg +/- 4.18 kg; height 1.71 m +/- 0.04 m), who received an 'all-in-one' nutrition regimen whilst in remission from Crohn's disease. All patients received 12.8 g N, 4725 kJ from carbohydrate and 4200 kJ from fat (10416 kJ total energy). The exchanges were related to nutrient oxidation and nutrient balances in the whole body as assessed by indirect calorimetry and nitrogen excretion. At rest, the subjects were found to be in positive balances for carbohydrate (+0.78 +/- 0.13 kJ/min), fat (+1.85 +/- 0.26 kJ/min) and protein (+0.240 +/- 0.04 kJ/min). Resting forearm muscle was also in positive amino acid balance and positive carbohydrate balance. Despite the large estimated uptake of glucose by forearm muscle (+1860 +/- 84 nmol/100 ml tissue/min) there was no net release of pyruvate and lactate. Glutamate and the branched chain amino acids (BCAA) were the dominant amino acids taken up by muscle (26% and 30% of total uptake respectively) and glutamine was the dominant amino acid carrying nitrogen out of muscle (78% of total amino acid nitrogen release). The energy taken up by muscle as non-esterified fatty acids, triacylglycerol and ketone bodies was small relative to that associated with glucose uptake. The results suggest that during the hypercaloric parenteral nutrition regimen, a) increased peripheral glucose uptake is not necessarily associated with increased release of glycolytic products, b) in the absence of glutamine intake for at least 10 days, muscle retains enough capacity to synthesise and release sufficient quantities of glutamine so that it remains the dominant amino acid carrying nitrogen out of muscle, c) despite the use of the intravenous route for administration of nutrients, and unusual amino acid composition of the regimen, the overall pattern of forearm metabolism bears many similarities to that which occurs after a mixed meal in normal subjects.     

Relation between glutamine, branched-chain amino acids, and protein metabolism

The branched-chain amino acids (BCAAs; valine, isoleucine, and leucine) are the major nitrogen source for glutamine and alanine synthesis in muscle. Synthesis of glutamine, alanine, and BCAA use is activated in critical illnesses such as in sepsis, cancer, and trauma. The use of glutamine often exceeds its synthesis, resulting in the lack of glutamine in plasma and tissues. In critical illness, resynthesis of BCAA from branched-chain keto acids is activated, particularly in hepatic tissue. The BCAA released to circulation may be used for protein synthesis or synthesis of alanine and glutamine. Glutamine and/or alanine infusion has an inhibitory effect on the breakdown of body proteins and decreases BCAA catabolism in postabsorptive control, endotoxemic, and irradiated rats. Decreased protein breakdown also was observed when glutamine synthesis was activated by ammonia infusion. In conclusion some favorable effects of BCAA supply can be explained by its role in the synthesis of glutamine and some positive effects of glutamine exogenous supply can be explained by its effect on metabolism of BCAA.     

Tumor regulation of hepatic glutamine metabolism.

Fast-growing tumors are major glutamine consumers and may alter host glutamine metabolism to benefit the tumor. Previous studies from our laboratory have demonstrated that the liver switches from an organ of glutamine balance to one of glutamine release with progressive malignant growth. However, the regulation of this change is unclear. This study examined tumor modulation of hepatic glutamine metabolism by determining the activities of glutaminase, the principle enzyme of glutamine degradation, and glutamine synthetase, the principal enzyme of glutamine synthesis. Hepatic glutamine content was also determined. Rats with a fast-growing subcutaneous fibrosarcoma (TBR) and pair-fed controls were studied at 2 and 3 weeks after tumor or sham implantation, when the tumors comprised approximately 5% and 20% of total body weight. Arterial glutamine fell with progressive tumor growth (608 +/- 26 mumol/L in controls vs 494 +/- 15 in TBR, p less than 0.005) and was not attributable to a diminished food intake. Hepatic glutamine content was increased 45% (p less than 0.01) in tumor rats at 2 weeks due in part to a 35% fall in liver glutaminase activity. At 3 weeks, glutamine synthetase activity increased by 43% (0.58 +/- 0.07 mumol/mg of protein/hr in controls vs 0.83 +/- 0.04 in TBR, p less than 0.01) whereas glutaminase remained depressed (2.68 +/- 0.12 mumol/mg of protein/hr in controls vs 2.22 +/- 0.15 in TBR, p less than 0.05) and glutamine content fell compared to 2 week tumor-bearing rats, consistent with accelerated hepatic glutamine release. Tumors may alter liver glutamine metabolism by modulating hepatic enzyme activity in order to provide circulating glutamine for the growing malignancy.     

Plasma glutamine response to enteral administration of glutamine in human volunteers (free glutamine versus protein-bound glutamine)

The goal of the present work was to compare the plasma glutamine response to exogenous glutamine administration in human volunteers; glutamine was provided as a free amino acid, bound to proteins, or in the form of peptides. Plasma glutamine concentrations were measured in eight human volunteers at 30, 60, 90, 120, and 240 min after receiving a drink containing 30 g of protein from one of the five different proteins tested (sodium caseinate, sodium caseinate + free glutamine, carob germ flour, carob protein concentrate, and carob protein hydrolysate). Peak plasma glutamine concentrations were 42% higher than postabsorptive basal values when exogenous glutamine was administered in the form of free glutamine added to caseinate (925.9 +/- 67.7 versus 651.3 +/- 44.0 micromol/L, respectively). In contrast, when glutamine was offered 100% bound to proteins (carob proteins), peak plasma glutamine concentration increased only between 18% and 23% from basal values, possibly because of the lower digestibility of carob proteins versus that of caseinate + free glutamine, to a different glutamine utilization at the gut level, or to a different response in endogenous glutamine kinetics to enteral administration of glutamine, depending on the molecular form of the glutamine source (free or protein bound).     

Coffee acutely modifies gastrointestinal hormone secretion and glucose tolerance in humans: glycemic effects of chlorogenic acid and caffeine

BACKGROUND: Accumulating evidence suggests that certain dietary polyphenols have biological effects in the small intestine that alter the pattern of glucose uptake. Their effects, however, on glucose tolerance in humans are unknown. OBJECTIVE: The objective was to investigate whether chlorogenic acids in coffee modulate glucose uptake and gastrointestinal hormone and insulin secretion in humans. DESIGN: In a 3-way, randomized, crossover study, 9 healthy fasted volunteers consumed 25 g glucose in either 400 mL water (control) or 400 mL caffeinated or decaffeinated coffee (equivalent to 2.5 mmol chlorogenic acid/L). Blood samples were taken frequently over the following 3 h. RESULTS: Glucose and insulin concentrations tended to be higher in the first 30 min after caffeinated coffee consumption than after consumption of decaffeinated coffee or the control (P < 0.05 for total and incremental area under the curve for glucose and insulin). Glucose-dependent insulinotropic polypeptide secretion decreased throughout the experimental period (P < 0.005), and glucagon-like peptide 1 secretion increased 0-120 min postprandially (P < 0.01) after decaffeinated coffee consumption compared with the control. Glucose and insulin profiles were consistent with the known metabolic effects of caffeine. However, the gastrointestinal hormone profiles were consistent with delayed intestinal glucose absorption. CONCLUSIONS: Differences in plasma glucose, insulin, and gastrointestinal hormone profiles further confirm the potent biological action of caffeine and suggest that chlorogenic acid might have an antagonistic effect on glucose transport. Therefore, a novel function of some dietary phenols in humans may be to attenuate intestinal glucose absorption rates and shift the site of glucose absorption to more distal parts of the intestine.     

Net hepatic gluconeogenic amino acid uptake in response to peripheral versus portal amino acid infusion in conscious dogs

These studies were conducted to determine the effect of route of gluconeogenic amino acid delivery on the hepatic uptake of the amino acids. After a sampling period with no experimental intervention (basal period), conscious dogs deprived of food for 42 h received somatostatin, intraportal infusions of insulin (3-fold basal) and glucagon (basal), and a peripheral infusion of glucose to increase the hepatic glucose load 1.5-fold basal for 240 min. A mixture of alanine, glutamate, glutamine, glycine, serine and threonine was infused intraportally at 7.6 micromol. kg(-1). min(-1) (PorAA group, n = 6) or peripherally at 8.1 micromol. kg(-1). min(-1) (PerAA, n = 6), to match the hepatic load of gluconeogenic amino acids in PorAA. During the infusion period, there were no differences in PerAA and PorAA, respectively, with regard to arterial plasma insulin (144 +/- 18 and 162 +/- 18 pmol/L), glucagon (51 +/- 8 and 47 +/- 11 ng/L), hepatic glucose load (199.8 +/- 22.2 and 210.9 +/- 16.6 micromol. kg(-1). min(-1)), net hepatic glucose uptake (2.8 +/- 2.2 and 2.2 +/- 1.7 micromol. kg(-1). min(-1)), hepatic load of amino acids (68 +/- 14 and 62 +/- 7 micromol. kg(-1). min(-1)), or net hepatic glycogen synthesis (11.1 +/- 2.2 and 8.9 +/- 2.2 micromol. kg(-1). min(-1)). The net hepatic uptake of glutamine (2.1 +/- 0.4 vs. 0.8 +/- 0.3 micromol. kg(-1). min(-1)) and the net hepatic fractional extractions of glutamine (0.11 +/- 0.02 vs. 0.05 +/- 0.02) and serine (0.41 +/- 0.03 vs. 0.34 +/- 0.02) were greater in PorAA than in PerAA (P < 0.05). We speculate that one or more of the amino acids in the mixture causes enhancement of the net hepatic uptake and fractional extraction of glutamine, and perhaps other gluconeogenic amino acids, during intraportal amino acid delivery.     

Local effect of burn injury on glucose and amino acid metabolism by skeletal muscle

Previous studies from our laboratory demonstrated that there is a difference in glucose metabolism by skeletal muscles from the burned versus unburned regions of the body. To further investigate the effect of proximity to the burn wound on muscle metabolism, in vitro glucose uptake as well as lactic and amino acid releases by soleus muscles, were studied 3 days following a 3-second scald burn on one hind limb of the rat. No differences in glucose uptake or lactic and amino acid releases were observed between soleus from the unburned limb of burned rats and that of controls. In comparison to these two groups, soleus from the burned limb took up 125% more glucose (p less than 0.001), and released 80% more lactic acid (p less than 0.01), 229% more alanine (p less than 0.001), 84% more glutamic acid (p less than 0.01), and over 36% more glutamine (p less than 0.05). The relatively enhanced release of lactic acid by soleus muscle from the burned limb was reduced but not eliminated by the omission of glucose from the medium. Simultaneously, the omission of glucose had no effect on the release of alanine, glutamic acid, and glutamine by the burned limb soleus. The data indicate that a mild thermal injury stimulates glucose utilization and enhances amino acid release by skeletal muscle from the burned region. Since such an effect is absent in muscle from the contralateral unburned region of the same animal, the changes are not likely to be mediated by systemic alterations in the metabolic and endocrine environment. The persistence of an enhanced amino acid release in the presence of varying glycolytic rates suggests that the burn-induced local alterations in amino acid metabolism by skeleton muscle are independent of coincident changes in glucose utilization.