The influence of abdominal surgical trauma on the exchange of blood-borne amino acids in the human leg

Glutamine appearance rate in plasma is not increased after gastrointestinal surgery in humans

The metabolic response to surgical stress is characterized by muscle protein breakdown and mobilization of amino acids and has been postulated to furnish glutamine and other amino acids to the immune system, gut and liver. The present study was undertaken to investigate whether the whole body appearance rate (R(a))(3) of glutamine in plasma is increased after major elective surgery. Fourteen patients (8 males, 6 females) were measured prior to laparotomy and on the second postoperative day. Patients received a primed continuous 6-h infusion of L-[5-(15) N]glutamine and L-[1-(13)C]leucine, and arterial blood samples and muscle biopsies were taken for concentration and enrichment measurements. As expected, the metabolic response to surgery was characterized by a rise in whole body protein breakdown (n = 14, P < 0.001) and a decreased concentration of glutamine in plasma (n = 14, P < 0.001) and muscle (n = 8, P < 0.01). However, these catabolic changes were not reflected by an increase in the plasma R(a) of glutamine: 246 +/- 8 micromol. kg(-1). h(-1) before surgery vs. 241 +/- 10 micromol. kg(-1). h(-1) on the second postoperative day. We conclude that the whole body R(a) of glutamine in plasma is not increased 2 d after elective gastrointestinal surgery. Further studies are warranted to establish whether the lack of an increase in plasma glutamine R(a) provides a rationale for glutamine supplementation.

Application of proton NMR spectroscopy to measurement of whole-body RNA degradation rates: effects of surgical stress in human patients

The urinary catabolites, N2,N2-dimethylguanosine (DMG), pseudouridine (PSU) and 7-methylguanine (m7-Gua) are formed from post-transcriptional methylation of RNA bases and are not reincorporated into RNA upon its degradation. Their quantitative urinary excretion may be used to determine rates of whole body degradation of individual RNA species since DMG occurs exclusively in tRNA, PSU occurs in rRNA and tRNA and m7-Gua occurs in all RNA species. Conventional HPLC analysis has several drawbacks since pre-analytical steps may involve selective losses and, under certain conditions, other urinary analytes may co-elute. In the present paper, we report analysis of these compounds by high-field 1H-nuclear magnetic resonance (1H-NMR) spectroscopy. Urinary concentrations of these metabolites were found to be in agreement with previously published HPLC and ELISA determinations. However, NMR analysis required minimal sample preparation (other than lyophilisation and reconstitution) and was capable of the simultaneous determination of other relevant analytes such as creatinine. This technique was therefore applied to urine samples from patients who had undergone surgical stress and insulin-like growth factor-1 (IGF-I) therapy. Surgical stress increased the excretion of DMG and m7-Gua. Degradation rates for tRNA and mRNA were also higher in surgically stressed subjects when compared with controls but degradation rates of rRNA decreased by approx. 30%. However, injection of IGF-I (40 micrograms/kg s.c.) had no significant effect on the excretion of these nucleosides. These data indicated that IGF-I therapy has no marked effects on RNA turnover following trauma. We suggest that this technique can be applied to study of RNA metabolism in any surgical or medical condition. Furthermore, since only 0.6 ml of urine is required, studies in neonates seem to be feasible.

A descriptive study of skeletal muscle metabolism in critically ill patients: free amino acids, energy-rich phosphates, protein, nucleic acids, fat, water, and electrolytes

OBJECTIVE

To characterize biochemical changes in skeletal muscle in critically ill patients.

DESIGN

Survey of critically ill patients.

SETTING

Intensive care unit (ICU) at a university hospital.

PATIENTS

Critically ill patients (n = 20) subjected to trauma, surgical complications, and/or bacteremia who were treated in the ICU and showed no risk of bleeding complications were included. Reference groups of metabolically healthy volunteers and patients served as the control/reference groups.

INTERVENTIONS

Percutaneous muscle biopsy was obtained from both patients and healthy volunteers.

MEASUREMENTS AND MAIN RESULTS

Total free amino acids in skeletal muscle decreased 59% (p < .001) and skeletal muscle glutamine concentration decreased 72% (p < .001) in the critically ill patients. Basic amino acids decreased 49% (p < .001). Branch-chain amino acids increased 39% (p < .01), and aromatic amino acids increased 88% (p < .001) in the patients. Adenosine triphosphate (ATP) was reduced by 12% (p < .01). Total creatine concentration increased by 26% (p < .001) due to an 80% increase in free creatine (p < .001). The phosphorylated creatine fraction of total creatine decreased 22% (p < .001) in the patients. Alkali-soluble protein/DNA decreased 24% (p < .01) and fat free solid/DNA decreased 21% (P <.01) in patients sampled on or after ICU day 5 compared with the reference group. Muscle water increased 10% due to a doubling of the extracellular water fraction.

CONCLUSIONS

Although critically ill patients are a very heterogeneous group from a clinical point of view, there is a remarkable homogeneity in many of the biochemical parameters regardless of the severity of illness and the length of the ICU admission. The three most consistent differences were the skeletal muscle low glutamine concentration, the decrease in protein content, and the increase in extracellular water in the patients.

Muscle protein synthesis rate decreases 24 hours after abdominal surgery irrespective of total parenteral nutrition

BACKGROUND

Muscle protein synthesis rate is known to decrease postoperatively as a part of the catabolic response to trauma. Conventional total parenteral nutrition (TPN) in the postoperative period does not seem to counteract the decrease in protein synthesis. However, it is still unclear if ongoing TPN given continuously after surgery would inhibit this fall in muscle protein synthesis.

METHODS

The rate of protein synthesis in skeletal muscle was determined before and 24 hours after open cholecystectomy, used as a standardized human model of trauma. Patients (n = 14) were randomized to receive either TPN continuously throughout the postoperative period or saline as postoperative fluid therapy. The protein synthesis rate was calculated from the increase in enrichment of labeled phenylalanine in protein after an IV flooding dose of [2H5] phenylalanine, 45 mg/kg body weight.

RESULTS

The fractional synthesis rate decreased by 31% from 1.74 +/- 0.13% to 1.15 +/- 0.10% per 24 hours in the saline group (p < .02) and by 23% from 1.59 +/- 0.10% to 1.22 +/- 0.07% per 24 hours in the group receiving TPN (p < .01), showing no significant difference between the two groups.

CONCLUSION

A continuous and ongoing infusion of conventional TPN started immediately after surgery did not counteract the obligatory decline of muscle protein synthesis, observed 24 hours postoperatively.

Long-term effect of glycyl-glutamine after elective surgery on free amino acids in muscle

In order to evaluate the long-term effect of total parenteral nutrition supplemented with glutamine after surgery, patients (n = 17) undergoing elective abdominal surgery were randomized into two groups and studied for 30 days after surgery. During the 3 days immediately after surgery, one group (n = 8) was given total parenteral nutrition including a conventional amino acid solution (control group). The other group (n = 9) was given isocaloric and isonitrogenous total parenteral nutrition including the same amino acid solution supplemented with the dipeptide, glycyl-glutamine (GLN group). Oral food intake started on the third postoperative day and was gradually increased at will. The concentration of free amino acids in percutaneous muscle biopsy specimens was determined preoperatively and on days 3, 10, 20, and 30 after the operation. Free glutamine decreased in skeletal muscle in the control group on days 3 and 10 by 32.2 +/- 5.4% (p < .01) and 20.1 +/- 6.9% (p < .05), respectively. In the glycyl-glutamine group, the decrease in glutamine was delayed until day 10 when it was 22.1 +/- 8.1% (p < .05). The glutamine levels were restored on days 20 and 30 in both groups. Total parenteral nutrition supplemented with glutamine maintained the free glutamine levels in skeletal muscle after surgery, but when treatment was discontinued, the glutamine concentration in muscle dropped, despite a normal enteral dietary intake.

The independent metabolic effects of halothane and isoflurane anaesthesia

Twelve healthy, unpremedicated women scheduled for total abdominal hysterectomy were given either isoflurane (n = 6) or halothane (n = 6) anaesthesia. They all received general anaesthesia for a period of 3 h, with surgery being carried out only in the last hour. The anaesthesia consisted of thiopentone, pancuronium and a mixture of oxygen-enriched air (FiO2 = 34%) supplemented with 1 MAC of either isoflurane or halothane. The patients were maintained normothermic, and with an arterial SaO2 above 95% throughout the period of the study. The following measurements were made before, during and after anaesthesia (with and without surgery): oxygen consumption (VO2), carbon dioxide production (VCO2); circulating concentrations of various hormones (insulin, growth hormone and cortisol); various metabolites; selected amino acids and albumin; forearm arterio-venous concentration difference of glucose, lactate, free fatty-acids and selected amino acids (four patients in each group). Whole body VO2 decreased significantly by over 20% during anaesthesia (with or without surgery), P < 0.05). Although the circulating concentration of most amino acids showed little or no change during anaesthesia alone, there was a tendency for the flux of most metabolites to decrease, and this persisted during surgery (P < 0.05). During anaesthesia alone there was a twofold reduction in the plasma cortisol concentration (P < 0.05), and a decrease in albumin concentration (P < 0.01). With the onset of surgery, plasma cortisol concentration increased rapidly (in association with several other hormones and metabolites) but hypoalbuminemia persisted.

Glutamine-synthesizing activity in lungs of fed, starved, acidotic, diabetic, injured and septic rats

The maximal catalytic activity of glutamine synthetase was measured in lung homogenates of the rat (being 5.46 +/- 0.29 mumol/min per g wet wt. or 31.70 +/- 2.62 nmol/min per mg of protein at 37 degrees C, in fed animals). The activity is similar to that of liver, but 16-fold higher than that in quadriceps muscles. Chronic (NH4Cl-induced) or acute (HCl-induced) metabolic acidosis had no effects on enzyme activity, but there was a marked increase in the activity of glutamine synthetase in starved (30-40%), streptozotocin-diabetic (17%), dexamethasone-treated (18-22%), laparotomized (25-27%) and septic rats (24-45%).

Effects of physiological and pathological levels of glucocorticoids on skeletal muscle glutamine metabolism in the rat

The effects of physiological and pathological concentrations of glucocorticoids were investigated using the glucocorticoid antagonist RU486 and the synthetic glucocorticoid dexamethasone, respectively. The effects of these treatments on the concentrations of glutamine and other amino acids in skeletal muscle and plasma and on the rates of release of glutamine and alanine from incubated preparations of skeletal muscle of the rat were investigated. Dexamethasone treatment increased the concentration of glutamine and the rate of release of this amino acid from incubated soleus muscle preparations. This treatment decreased the concentration of glutamine in both gastrocnemius and EDL muscles, but was without effect on the rate of glutamine release from EDL muscles. In contrast, administration of the glucocorticoid antagonist RU486 decreased the rate of glutamine release from muscle. It is concluded that glucocorticoids have marked effects on the metabolism of glutamine by skeletal muscle per se and that these hormones may be important in the control of the rate of glutamine release from muscle in both physiological and pathological conditions.

The effect of glutamine concentration on the activity of carbamoyl-phosphate synthase II and on the incorporation of [3H]thymidine into DNA in rat mesenteric lymphocytes stimulated by phytohaemagglutinin

The maximum catalytic activities of carbamoyl-phosphate synthase II, a limiting enzyme for pyrimidine nucleotide synthesis, are very much less than those of glutaminase, a limiting enzyme for glutamine utilization, in lymphocytes and macrophages; and the flux through the pathway for pyrimidine formation de novo is only about 0.4% of the rate of glutamine utilization by lymphocytes. The Km of synthase II for glutamine is about 16 microM and the concentration of glutamine necessary to stimulate lymphocyte proliferation half-maximally is about 21 microM. This agreement suggests that the importance of glutamine for these cells is provision of nitrogen for biosynthesis of pyrimidine nucleotides (and probably purine nucleotides). However, the glutamine concentration necessary for half-maximal stimulation of glutamine utilization (glutaminolysis) by the lymphocytes is 2.5 mM. The fact that the rate of glutamine utilization by lymphocytes is markedly in excess of the rate of the pathway for pyrimidine nucleotide synthesis de novo and that the Km and 'half-maximal concentration' values are so different, suggests that the glutaminolytic pathway is independent of the use of glutamine nitrogen for pyrimidine synthesis.

Skeletal muscle glutamine metabolism during sepsis in the rat

1. The effect of sepsis, induced by caecal ligation plus puncture (CLP) or endotoxin injection, on glutamine metabolism was studied in rat skeletal muscle. 2. The concentration of glutamine in muscle was decreased by CLP or after 24 or 48 hr after injection of endotoxin. However, the concentration was increased 3 hr after injection of endotoxin. 3. The plasma glutamine concentration was decreased by CLP, but it was unchanged after injection of endotoxin. 4. The rate of glutamine release from incubated stripped soleus muscles was increased in the muscles removed from animals subjected to CLP or from animals injected with endotoxin. 5. It is concluded that sepsis results in marked changes in skeletal muscle glutamine metabolism, which may be used as an early indicator of the septic state. During sepsis there is likely to be an increased demand for glutamine by the immune system, kidney and intestine. 6. This study provides evidence that during sepsis the rate of release of glutamine from the skeletal muscle per se is increased to a sufficient extent to satisfy this increased requirement.

Peripheral, visceral and body nitrogen balance of catabolic patients, without and with parenteral nutrition

The effect of major trauma and sepsis on skeletal muscle, central tissue and whole body nitrogen (N) metabolism was investigated in 5 patients before and during TPN (30 kcal, 0.30 g N kg-1 day-1). Fasting 3-methylhistidine (MEH) urinary excretion was elevated (407.9 +/- 67.6 mumol m-2 day-1), muscle and body N balances (NB) were markedly negative (-28.2 +/- 4.6 g m-2 day-1 and -15.7 +/- 3.1 g m-2 day-1), while central tissue NB was positive (13.0 +/- 2.4 g m-2 day-1). TPN effected a reduction in MEH excretion (261.8 +/- 27.5 mmol m-2 day-1 - p less than 0.05) and decreased the release of almost all amino acids from muscle tissue, some of them acting as catabolic markers. Muscle (-7.2 +/- 1.2 g m-2 day-1 - p less than 0.01) as well as body NB (-4.8 +/- 1.4 g m-2 day-1 - p less than 0.01) improved, whilst central tissue NB worsened, even though still positive (3.1 +/- 1.6 g m-2 day-1 - p less than 0.05). Gathering fasting and TPN data MEH excretion was significantly related to both body (r = 0.89) and muscle (r = 0.73) NB, that were highly related to each other (r = 0.93), being muscle always worse than body NB. In conclusion, the anticatabolic activity of TPN is confirmed, although our setting did not achieve muscle NB, it was consistently improved and seems to be the major determinant of body NB, in contrast central NB and central N utilization (46.4% +/- 5.4 vs 15.8% +/- 8.4 - p less than 0.05) worsened.

The influence of epidural analgesia on the splanchnic exchange of amino acids during upper abdominal surgery

Splanchnic turnover of plasma amino acids was studied in 10 patients given thoracic epidural analgesia combined with general anaesthesia for elective cholecystectomy. Ten other patients given only general anaesthesia for cholecystectomy served as a control group. All patients received an infusion of glucose during the investigation. The total concentration of amino acids in arterial plasma did not change in the patients given epidural analgesia but decreased by approximately 15% in the non-epidural group. In both groups splanchnic uptake of amino acids increased during surgery and was found to be more than doubled in the early postoperative period. The addition of epidural analgesia to general anaesthesia did not modify the splanchnic uptake of amino acids during surgery and in the immediate (2 h) postoperative period.