Glutamine metabolism by the intestinal tract

In vivo inter-organ protein metabolism of the splanchnic region and muscle during trauma, cancer and enteral nutrition

The study of protein kinetics has entered a new era by the recognition that whole body protein turnover only poorly reflects the true events occurring in several organs and with regard to the multitude of proteins present in the body. It is also increasingly recognized that the simultaneous synthesis and degradation of proteins is important in regulation and adaptation during several metabolic conditions like starvation, feeding, after trauma, and during exercise. Especially important is the recognition that the kinetics of individual proteins may change in opposite directions, thereby leading to fluxes of alpha-amino-nitrogen that serve to adapt to and survive a changing environment. At present, much emphasis is put upon molecular biological regulation. However, it is important that the metabolic processes that occur in the intact organism are still poorly defined. New technology allows the exploration of these processes, which should therefore prompt the initiation of further research in this area.

Glutamine protects function and improves preservation of small bowel segments

BACKGROUND

Improved organ preservation is essential for the success of small bowel transplantation. Small bowel is usually preserved in UW (University of Wisconsin) solution which does not contain glutamine (Gln), the principal fuel for the enterocyte. We hypothesized that Gln-supplemented UW would improve mucosal function and structure of cold preserved small intestine.

MATERIALS AND METHODS

Jejunum (40 cm) was harvested from Lewis rats and preserved for 18 hr at 4 degrees C in saline; UW solution only; UW with 1, 2, or 4% Gln; and UW containing 1, 2, or 4% isonitrogenous balanced nonessential amino acids (NEAA). 14C glucose transport, mucosal protein, mucosal maltase and alkaline phosphatase, jejunal villous height, and histologic damage were measured.

RESULTS

UW with 2% Gln significantly increased glucose transport and mucosal protein when compared to the 2% NEAA and UW-only groups. Two percent Gln significantly decreased histologic damage of jejunum following cold preservation. Increasing Gln to 4% did not significantly increase its efficacy when compared to the UW with 2% Gln group. There were no significant differences in the activities of mucosal maltase and alkaline phosphatase among the various treatment groups.

CONCLUSIONS

The addition of Gln, optimally provided at a concentration of 2%, to UW solution may protect the preserved small bowel segments from cold ischemic injury and improve mucosal function.

The effects of short-term parenteral nutrition on human liver protein and amino acid metabolism during laparoscopic surgery

BACKGROUND

This study was undertaken to elucidate the specific effects of short-term artificial nutrition on human liver protein metabolism.

METHODS

Thirty patients undergoing elective laparoscopic cholecystectomy were studied: a control group (n = 16) and a group that received total parenteral nutrition (TPN; n = 14). The nutrition consisted of a balanced i.v. solution of nutrients (17.5 nonprotein kcal/kg body wt, 50% fat, 50% carbohydrates, and 0.1 gN/kg) that was discontinued when the investigation was finished, after a total infusion time of 8.6 +/- 1.0 hours. A liver biopsy specimen was taken as soon as possible after surgery was started, for the determination of the free hepatic amino acid concentrations. In 16 of the patients, L[2H5]phenylalanine was given by i.v. to determine the fractional synthesis rate of total liver protein in a second liver biopsy specimen taken approximately 30 minutes later.

RESULTS

The fractional synthesis rate of total liver protein was 15.2% +/- 4.7%/d in the TPN group (n = 7), which was not different from that of the control group (17.7% +/- 3.8%/d, n = 9). However, the free hepatic concentrations of alanine (p < .05) and the essential amino acids increased (p < .001) in the TPN group, whereas the total hepatic amino acid concentrations were comparable between the groups.

CONCLUSION

Thus short-term TPN induced specific changes of the free hepatic amino acid concentrations, whereas total liver protein synthesis remained unaffected by the nutrition.

Effect of epidermal growth factor on glutamine metabolic enzymes in small intestine and skeletal muscle of parenterally fed rats

Exogenous epidermal growth factor (EGF) markedly increases the in vivo uptake of glutamine by small intestine during total parenteral nutrition (TPN). Since glutamine is the major oxidative fuel for the small intestine and is synthesized mainly in skeletal muscle, we investigated whether EGF would induce changes in the activity of the enzymes that mediate glutamine degradation (glutaminase) and synthesis (glutamine synthetase) in the two tissues. Male Sprague Dawley rats were randomized into three groups: group I (chow) were fed rat chow and water and libitum, group II (TPN) received a standard formula of TPN, and group III (TPN-EGF) received the same TPN as group II and injections of EGF (0.1 microgram/ gm body weight (bw)) subcutaneously twice daily. TPN was given for 2 wk; when EGF was administered along with TPN, the glutaminase activity of intestinal mucosa and the glutamine synthetase activity of skeletal muscle were increased, respectively, by 25% and 24% (P < 0.05, versus TPN group). These data suggest a mechanism whereby EGF enhances the intestinal utilization of glutamine by changing the activities of glutamine metabolic enzymes in the small intestine and skeletal muscle during TPN.

Glutamine dipeptides in clinical nutrition

Glutamine is a conditional indispensable amino acid during stress. However, limited solubility and instability of glutamine prevent its addition to presently available nutritional preparations. To overcome these drawbacks, we propose the dipeptide concept by which stable and highly soluble synthetic glutamine containing dipeptides are used. The synthetic dipeptides fulfill all chemical/physical properties to be considered as parenteral substrates. Numerous experimental studies show rapid clearance of parenteral supplied glutamine containing dipeptides without accumulation in tissues; the loss via the urine being inconsequential. Differences related to the dipeptide structure are not observed. There is overwhelming evidence existent that a nutritional support with supplemental glutamine dipeptide positively influences nitrogen excretion, immune status, gut integrity, morbidity, rehabilitation and outcome. Consequently, omission of glutamine from conventional TPN and its subsequent administration should be considered as a replacement of a deficiency rather than a supplementation. It might thus be conceivable that the beneficial effects observed with glutamine nutrition are simply a correction of disadvantages produced by an inadequacy of conventional amino acid solutions. The availability of stable glutamine containing preparations will certainly facilitate an adequate amino acid nutrition in routine clinical setting during episodes of stress and malnutrition.

Metabolic support of the gastrointestinal tract: potential gut protection during intensive cytotoxic therapy

BACKGROUND

Potentially curative options involving cytoablative therapies are now available for the treatment of almost all human tumors, but major toxicities represent the rate-limiting step in achieving a cure with these therapies. With successful hematoprotective strategies now in use, it is apparent that the gastrointestinal tract will be the rate-limiting organ system that prevents further dose escalation in many cancer patients.

METHODS

A review of the English language literature was conducted. Paperchase, a computer-based application that reviews the data bases of the National Library of Medicine and the National Cancer Institute, was used to obtain pertinent literature.

RESULTS

A variety of gut-protective nutrients and growth factors were identified. These substances may be useful in preventing dose-limiting gastrointestinal symptoms. Animal studies and some patient data suggest that the amino acid glutamine stimulates mucosal growth and promotes gut health. When nutrient administration is coupled with growth factors, such as growth hormone, insulin-like growth factor-1, glucagon-like peptide-2, and interleukin-11, a high level of bowel protection should be attained.

CONCLUSIONS

Therapy is evolving that may be useful in protecting the intestinal mucosa and preventing dose-limiting gastrointestinal symptoms.

Human growth hormone induces system B transport in short bowel syndrome

BACKGROUND

After massive enterectomy, remnant intestine undergoes compensatory adaptation. A combination of human growth hormone (hGH) and a glutamine-enriched modified diet induces further adaptation in patients with short bowel syndrome (SBS) on long-term total parenteral nutrition. The specific actions of each component, however, are not well-defined.

METHODS

New Zealand White rabbits were randomized to control, sham operation, or SBS (70% midjejunoileal resection) groups and treated with either hGH or saline. Sodium-dependent uptake of glucose, glutamine, alanine, leucine, and arginine into brush border membrane vesicles was quantitated. Serum insulin-like growth factor-I (IGF-I) levels were determined by immunoradiometric assay. Mucosal mRNA expression of IGF-I and IGF binding protein 4 (IGFBP-4) was evaluated by northern blot analysis using rat cDNA probes.

RESULTS

Glutamine and leucine transports were 33 and 39% greater, respectively, in the hGH-treated versus saline-treated SBS group (P < 0.05), supporting induction of system B amino acid transport. This upregulation was due, in part, to an 88% increase in glutamine carrier capacity (Vmax) with no change in carrier affinity (Km). Both hGH treatment and SBS increased serum IGF-I levels without direct correlation with increased nutrient transport. IGFBP-4 mRNA expression in small bowel mucosa of saline-treated SBS animals was significantly greater than saline-treated unoperated control values. Mucosal IGFBP-4 mRNA was not significantly altered from control in the other study groups. IGF-I mRNA expression was not detected in mucosa, but weak hybridization was noted in rabbit liver.

CONCLUSIONS

Human growth hormone accelerates early adaptation in SBS by upregulation of system B carrier capacity. Serum IGF-I levels and mucosal IGF-I and IGFBP-4 mRNA expression did not directly correlate with this enhanced nutrient transport, suggesting that hGH might exert its adaptive effects by mechanisms that are independent from the IGF system in this model.

Glutamine-supplemented tube feedings versus total parenteral nutrition in children receiving intensive chemotherapy

Although enteral nutrition is generally advocated in the care of children with cancer, those patients receiving intensive chemotherapy alone or in combination with bone marrow transplantation often require total parenteral nutrition (TPN). Two patients are presented illustrating some differences between enteral and parenteral feedings in children receiving intensive chemotherapy. Nasogastric glutamine-supplemented tube feedings were well tolerated both in the hospital and at home. The cost of care for the enterally supported child was less than one third of the TPN-supported child. Although TPN appears to be beneficial in some patients with cancer, it is expensive and is associated with several significant disadvantages. Among these are an increased incidence of both gram-positive and gram-negative infections and an increased incidence of gastrointestinal symptoms. Enteral nutrition is less costly than TPN and maintains the structural and functional integrity of the intestinal mucosa. The addition of certain substrates such as glutamine, arginine and omega-3 fatty acids may improve the body's immune response as well. We hypothesize that early glutamine supplemented tube feedings in children receiving intensive chemotherapy alone or in combination with bone marrow transplantation will result in improved nutrition with fewer infections and lower cost than TPN-supplemented patients. In addition, a shorter hospital stay and improved quality of life are anticipated.

Enteral administration of ornithine alpha-ketoglutarate or arginine alpha-ketoglutarate: a comparative study of their effects on glutamine pools in burn-injured rats

OBJECTIVES

Ornithine alpha-ketoglutarate has proved to be an efficient nutritional support in trauma situations, especially after burn injury. To determine whether the action of ornithine alpha-ketoglutarate is due to its alpha-ketoglutarate moiety (as a glutamine precursor), we studied the effects of alpha-ketoglutarate administered to rats as ornithine alpha-ketoglutarate, or in combination with arginine salt (arginine alpha-ketoglutarate), as the two closely related amino acids have similar metabolic behavior.

DESIGN

Prospective, randomized trial.

SETTING

Animal laboratory.

SUBJECTS

Forty-six male Wistar rats, weighing approximately 90 g.

INTERVENTIONS

Rats were burned over 20% of their body surface area, starved for 24 hrs, with water ad libitum, and then enterally refed for 48 hrs using Osmolite (210 kcal/kg/day, 1.2 g of nitrogen/kg/day), supplemented with one of the following: a) an amount of glycine isonitrogenous to ornithine alpha-ketoglutarate (group 1); b) 5 g of monohydrated ornithine alpha-ketoglutarate/kg/day (group 2); c) an amount of arginine alpha-ketoglutarate isonitrogenous to ornithine alpha-ketoglutarate (group 3); or d) an amount of arginine alpha-ketoglutarate isomolar to ornithine alpha-ketoglutarate (group 4).

MEASUREMENTS AND MAIN RESULTS

We measured amino acid concentrations in plasma, muscle, and liver, and plasma urea concentration. At refeeding, ornithine alpha-ketoglutarate increased plasma glutamine concentration (p < .05 vs. the three other groups), and counteracted the increase in plasma phenylalanine concentration. In muscle, although the three alpha-ketoglutarate combinations induced similar increases in the glutamate pool, ornithine alpha-ketoglutarate induced the highest increase in glutamine (7.0 +/- 0.3 vs. 5.4 +/- 0.3 micromol/g in group 3, 6.3 +/- 0.3 in group 4, and 4.6 +/- 0.2 in group 1, p < .01 between group 2 and groups 3 or 1). Also, only ornithine alpha-ketoglutarate increased liver glutamine concentration. Finally, isomolar arginine alpha-ketoglutarate increased plasma urea concentration (+50% vs. the three other groups, p < .01).

CONCLUSIONS

Our results demonstrate, for the first time, the following: a) the action of ornithine alpha-ketoglutarate as a glutamine precursor cannot solely be ascribed to alpha-ketoglutarate since arginine alpha-ketoglutarate combinations did not exhibit this effect to the same extent; and b) the action of ornithine alpha-ketoglutarate is not due to its nitrogen content since isonitrogenous arginine alpha-ketoglutarate did not reproduce the effects of ornithine alpha-ketoglutarate.

Alanyl-glutamine-supplemented total parenteral nutrition improves survival and protein metabolism in rat protracted bacterial peritonitis model

BACKGROUND

The effects of glutamine-enriched total parenteral nutrition (TPN) solution on survival, and protein turnover in the whole body and in individual organs were investigated in a rat protracted peritonitis model.

METHODS

Twenty-three rats underwent venous catheter insertion. Osmotic pumps were implanted in the peritoneal cavity to allow continuous delivery of Escherichia coli (4 x 10(8) CFU/d). The conventional TPN group received a conventional amino acid solution. The Ala-Gln TPN group received an alanyl-glutamine-enriched TPN solution. The two TPN solutions were isocaloric and isonitrogenous.

RESULTS

Over the 5 days of TPN treatment, the survival rate of the Ala-Gln group was significantly higher than that of the conventional group. The Ala-Gln group tended to have increased whole-body protein turnover compared with the conventional group. Fractional protein synthetic rates (FSR) in the liver and gastrocnemius muscle of the Ala-Gln group were significantly higher than those of the conventional group. The serum glutamine concentration correlated positively with the FSR of both liver and muscle. The Ala-Gln group showed significantly greater mucosal height and mitoses per crypt, in the small intestine, than did the conventional group.

CONCLUSIONS

Our results suggested that, in comparison with standard glutamine-free TPN, Ala-Gln-supplemented TPN increases protein synthesis in the liver and skeletal muscle, protects the morphology of the intestinal mucosa, and improves survival in protracted bacterial peritonitis. Ala-Gln supplementation may be useful in septic patients.

Effects of the amino acid glutamine on frequency of chromosomal aberrations induced by gamma radiation in Wistar rats

The radiotherapy treatment of human cancer is often limited by the side effects and complications induced in normal surrounding tissues. The use of therapeutic strategies that could protect normal tissues while permitting the death of malignant neoplasm would be advantageous. Some studies have suggested that the amino acid glutamine (GLN) can serve as a conditionally essential nutrient in patients in a catabolic condition. The objective of this study was to evaluate the possible radioprotection of GLN on the frequency of chromosomal aberrations, number of metaphases with chromosomal aberrations and mitotic index in bone marrow cells of Rattus norvegicus. In this in vivo test system, GLN was administered by gavage at concentrations of 300 and 600 mg/kg body weight, in acute treatments, 30 min or 24 h before exposure to 3 Gy of whole-body gamma radiation. The results obtained in these experiments showed that GLN did not alter significantly the frequency of chromosome aberrations induced by gamma radiation under the experimental conditions used in the present study.

Ornithine alpha-ketoglutarate counteracts thymus involution and glutamine depletion in endotoxemic rats

This work studied the action of ornithine a-ketoglutarate (OKG) supplementation in an experimental model of endotoxemia in the rat. Male Wistar rats were injected intraperitoneally with lipopolysaccharide (LPS) from Escherichia coli (0127:B8). They were fasted for 24 h, then refed for 48 h with an enteral diet supplemented with either OKG (66 mg N x kg(-1) x d(-1)) or glycine, isonitrogenous to the OKG group. A control (sham) group was also studied. LPS treatment induced a decrease in thymus and muscle weights compared to controls, and a decrease in glutamine and arginine concentrations in the anterior tibialis muscle. Supplementation with OKG restored thymus weight and muscle arginine level and increased muscle glutamine concentration, when compared to controls. We conclude that OKG counteracts the thymic involution that occurs with endotoxemia, and restores the muscular content of glutamine and arginine, both of which are involved in the regulation of immune function.

Influence of glutamine-supplemented parenteral nutrition on intestinal amino acid metabolism in rats after small bowel resection

Glutamine (Gln)-supplemented total parenteral nutrition (TPN) has been shown to improve mucosal adaptation after massive small bowel resection (SBR); however, its influences on intestinal amino acid metabolism remain unknown. In this study, intestinal amino acid flux, circulating plasma aminogram, mucosal glutaminase activity and protein, and DNA content were measured 7 days after massive SBR in rats receiving either standard (Std) or Gln-supplemented TPN. Sham-operated rats and rats fed chow after enterectomy served as controls. The uptake of Gln and the release of citrulline (Cit) by the remaining intestine was significantly decreased, with reduced mucosal glutaminase activity after SBR in the Chow and Std-TPN groups. Glutamine supplementation resulted in significantly increased gut Gln uptake compared with Std-TPN (P < 0.01). Mucosal glutaminase activity, mucosal protein, and DNA content was also increased by Gln; however, the gut release of Cit remained unchanged (P > 0.05). The subsequent decrease in circulating arginine (Arg) in the Gln-TPN group compared with the Std-TPN group (P < 0.05) was attributed to an insufficient exogenous supply. These findings show that Gln-supplemented TPN improves mucosal growth and gut Gln uptake after SBR. However, the intestinal production of Cit, which remained low in both TPN groups, may lead to an insufficiency of endogenous Arg synthesis. Thus, both Gln and Arg may be essential amino acids after SBR.

Nutrition and the immune system

Malnutrition frequently contributes to the immunocompromise seen in hospitalized patients. Nutritional support corrects malnutrition and can reverse the associated immunocompromise. Developing an understanding of nutritional needs and the role of nutrition in immune function is essential to prevention and treatment of nutrition-related immunocompromise. Current research is defining the role of specific nutrients in immune function. Recent evidence also suggests that the route (enteral versus parenteral) of providing nutritional support can affect immune competence. Intervention trials may show a role of key nutrients in not only maintaining normal immune competence, but also in modulating immunologic outcomes in critically ill patients.

Metabolic response to radiation therapy in patients with cancer

The effect of radiation therapy on substrate metabolism was evaluated in five patients with head and neck or lung cancer. Stable isotope tracer methodology was used to determine urea, amino acid, glucose, and lipid kinetics during postabsorptive conditions before initiation, near the midpoint (after receiving 2,672 +/- 36 rads), and at completion (after receiving 6,072 +/- 307 rad) of a 6- to 8-week course of radiation therapy. Nutritional status was maintained throughout the treatment period by providing supplemental enteral feedings as needed. Postabsorptive plasma insulin, catecholamine, and amino acid concentrations did not change during the course of treatment. Before radiation therapy was initiated, values for the plasma rate of appearance (Ra) of urea (3.35 +/- 0.33 micromol x kg(-1) x min(-1)), alpha-ketoisocaproate ([alpha-KIC] 2.16 +/- 0.19 micromol x kg(-1) x min(-1)), phenylalanine (0.59 +/- 0.052 micromol x kg(-1) x min(-1)), and glucose (10.56 +/- 1.31 micromol x kg(-1) x min(-1)) were in the normal range. However, glycerol and palmitate Ra values (3.11 +/- 0.30 and 2.01 +/- 0.33 micromol x kg(-1) x min(-1), respectively) were 25% higher than values observed previously in normal subjects. Substrate flux did not change during radiation therapy, and measurements obtained during the midpoint and at completion of treatment were similar to initial values. These results demonstrate that large doses of radiation therapy, administered over 6 to 8 weeks to the upper body, do not cause significant metabolic stress.

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.

Isocaloric glutamine-free diet and the morphology and function of rat small intestine

BACKGROUND

The importance of L-glutamine as metabolic fuel for enterocytes and its role in prevention of mucosal atrophy during total parenteral nutrition is well documented. No data are available to date that document whether a glutamine-free complete enteral diet, requiring full energy expenditure for hydrolysis and absorption, is associated with changes in the morphology and function of the small intestine. Our aim was to examine the effect of such a diet during a 4-week period on the morphology and function of the small intestine of rats.

METHODS

Three isocaloric solid rat food, containing 0%, 4%, and 8% of glutamate, respectively, were fed to three groups of rats. On the 7th and 28th days the morphology of the jejunum, the subcellular structure of enterocytes on transmission electron microscopy, enzyme activities, blood, and muscle glutamine were examined and compared in the three groups.

RESULTS

The rats on the glutamine-free diet had significantly lower mucosal wet weight, protein and DNA content, and number of intraepithelial lymphocytes on the 7th day, whereas the number of mitoses in the Lieberkuhn's crypts was significantly less on the 28th day. The height of the enterocytes and villi was 20% higher on average in the glutamine-free group. Electron microscopy revealed either early (swelling of cristae) or terminal (swelling of matrix) mitochondrial degenerative changes, homogenization of apical cytoplasm, and degeneration and fragmentation of microvilli with loss of their rootlets. The Na+, K(+)-ATPase activity was markedly decreased in the glutamine-free group compared with that of the other groups, most likely because of a diminished energy supply. Among brush border membrane enzymes, lactase activity decreased markedly (p < .05) in the first week. The glutamine-free diet resulted in an increase of the lung glutamine synthetase activity and decrease in muscle glutamine content by the 28th day of the diet.

CONCLUSIONS

Our study shows for the first time that a complete enteral diet, deficient only in glutamine, is associated with significant early morphologic and functional changes in the small intestine. The precise effect on intracellular events and the time of onset of these changes needs to be clarified in the future.

High protein diets are associated with increased bacterial translocation in septic guinea pigs

During sepsis, body protein stores are decreased due to an increase in protein catabolism. The utilization of nutritional support with high-protein diets has been used as a solution to the problem of sepsis-induced protein loss. Work from our laboratory, however, has shown that diets low in protein (5% of total calories) improve survival in septic animals as compared to high protein (20%) diets. The present study investigated the relationship between low-protein diets and improved survival by determining whether septic animals receiving high-protein diets have increased bacterial translocation. Sepsis was induced in guinea pigs by the implantation of an osmotic minipump into the peritoneal cavity containing an equal mixture of Escherichia coli (10(8)) and Staphylococcus aureus (10(8)) or saline. On Day 3 postlaparotomy, the animals were randomized to one of four groups. The groups consisted of septic and nonseptic animals that received a diet with 5 or 20% of total calories as protein. Following 4 days of diet all animals received an instillation of 14C labeled E. coli (10(10)). Four hours later the animals were sacrificed and blood, mesenteric lymph nodes, spleen, lungs, and liver were removed for determination of radionuclide counts. Results indicated that the septic animals that received the high protein diet had more bacterial translocation, as indexed by higher radionuclide counts in the MLN, liver, lung and blood. These findings suggest that a low protein, enterally fed diet may improve survival in septic patients by decreasing the incidence of bacterial translocation.

Alanyl-glutamine dipeptide-supplemented parenteral nutrition improves intestinal metabolism and prevents increased permeability in rats

OBJECTIVE

The authors determined the effects of alanyl-glutamine-supplemented total parenteral nutrition (TPN) on mucosal metabolism, integrity, and permeability of the small intestine in rats.

METHODS

Male Sprague-Dawley rats were randomized to receive TPN supplemented with a conventional amino acids mixture (STD group) or the same solution supplemented with alanyl-glutamine; both solutions were isocaloric and isonitrogenous. On the seventh day of TPN, D-xylose and fluorescein isothiocyanate (FITC)-dextran were administered orally. One hour later, superior mesenteric vein (SMV) D-xylose and plasma FITC-dextran concentration were measured. Intestinal blood flow and calculated intestinal substrates flux were measured with ultrasonic transit time flowmetery.

RESULTS

Plasma FITC-dextran increased significantly in the STD group. Intestinal blood flow and SMV D-xylose concentration did not differ between the groups. Mucosa weight, villus height, mucosal wall thickness, mucosal protein, and DNA and RNA content in jejunal mucosa were significantly increased in the alanyl-glutamine group. Jejunal mucosal glutaminase activity and net intestinal uptake of glutamine (glutamine flux) were significantly higher in the alanyl-glutamine group as compared with the STD group.

CONCLUSION

Addition of alanyl-glutamine dipeptide to the TPN solution improves intestinal glutamine metabolism and prevents mucosal atrophy and deterioration of permeability.

Enteral glutamate is almost completely metabolized in first pass by the gastrointestinal tract of infant pigs

We studied the absorption of enteral glutamate and phenylalanine using isotopic tracer and arteriovenous difference techniques. Six piglets, implanted with portal, carotid, and gastric catheters and an ultrasonic portal flow probe received a 6-h intragastric infusion of [U-13C] glutamate and [2H] phenylalanine, with a high-protein diet offered one time each hour. Amino acid concentrations and the isotopic enrichments of all mass isotopomers of glutamate, glutamine, and phenylalanine were measured in portal and arterial blood over the last hour. There was significant (P<0.025) net absorption of the indispensable amino acids as well as arginine, proline, serine, and alanine. There was no portal uptake of glutamate, aspartate, and glycine, and arterial glutamine was removed by the portal drained viscera (P<0.05). At isotopic steady state, 72% of the [2H] phenylalanine but only 5% of the [U-13C] glutamate tracer appeared in the portal blood. We conclude that, in fed infant pigs, the gut metabolizes virtually all of the enteral glutamate during absorption. Therefore, glutamate and glutamine in the body as a whole must derive almost entirely from synthesis de novo.

Glutamine deficiency as a cause of human immunodeficiency virus wasting

Tissue wasting often occurs during human immunodeficiency virus infection and acquired immune deficiency syndrome. While weight-loss in the human immunodeficiency virus-infected individual can be seen as an isolated symptom, catabolism during acquired immune deficiency syndrome is usually associated with complications such as diarrhea, malabsorption, fever and secondary infection. Glutamine is an amino acid central to many important metabolic pathways and recent findings suggest that glutamine depletion may explain the progression of tissue wasting during human immunodeficiency virus infection.

Small bowel preservation using a cavitary two-layer (University of Wisconsin solution/perfluorochemical) cold storage method

Preservation of the small bowel by a cavitary two-layer (University of Wisconsin solution [UW]/perfluorochemical) cold storage method was evaluated in the heterotopic rat segmental small bowel transplant model. Simple cold storage UW was effective only for 24-hr preservation. However, the cavitary two-layer method using UW made it possible to prolong preservation time up to 48 hr. Furthermore, without oxygen bubbling, the cavitary two-layer method was not effective for 48-hr preservation. Histologic studies of grafts preserved by the cavitary two-layer method for 48 hr at 7 days after transplantation showed normal architecture of the intestinal mucosa. This study demonstrates that the oxygenation of the small bowel during preservation by the cavitary two-layer method using UW makes it possible to extend preservation time up to 48 hr in the heterotopic rat segmental small bowel transplant model.

Early enteral feeding in the pediatric intensive care unit

BACKGROUND

The purpose of this study was to evaluate the feasibility and safety of early enteral feedings of critically ill pediatric patients.

METHODS

The subject population of 42 critically ill patients ranged in age from 5 days to 18 years (mean 5.8 years), mean weight 17 kg. Transpyloric nasoenteric tubes were placed in all patients by a nonfluoroscopic bedside technique. All subjects were mechanically ventilated; 32 (76%) were on one or more vasoactive medications. Six (15%) patients were fed for more than 13 days while on vasoactive support and pharmacological paralysis.

RESULTS

There were no documented complications of early enteral feeding, including aspiration. All patients were able to achieve caloric goals within 48 hours of beginning enteral feedings. All patients developed regular stool patterns despite periodic absence of bowel sounds. Enteral feedings replaced 256 days of total parenteral nutrition. Estimated patient charge savings averaged $425 for each day of enteral feedings.

CONCLUSIONS

Early enteral feedings are feasible, well tolerated, and cost effective in critically ill pediatric patients.

Ammonia and glutamine metabolism during liver insufficiency: the role of kidney and brain in interorgan nitrogen exchange

BACKGROUND

During liver failure, urea synthesis capacity is impaired. In this situation the most important alternative pathway for ammonia detoxification is the formation of glutamine from ammonia and glutamate. Information is lacking about the quantitative and qualitative role of kidney and brain in ammonia detoxification during liver failure.

METHODS

This review is based on own experiments considered against literature data.

RESULTS AND CONCLUSIONS

Brain detoxifies ammonia during liver failure by ammonia uptake from the blood, glutamine synthesis and subsequent glutamine release into the blood. Although quantitatively unimportant, this may be qualitatively important, because it may influence metabolic and/or neurotransmitter glutamate concentrations. The kidney plays an important role in adaptation to hyperammonaemia by reversing the ratio of ammonia excreted in the urine versus ammonia released into the blood from 0.5 to 2. Thus, the kidney changes into an organ that netto removes ammonia from the body as opposed to the normal situation in which it adds ammonia to the body pools.

Topical glutamine therapy in experimentalinflammatory bowel disease

This study investigated the effects of glutamine and steroid enemas on disease activity in an animal model of colitis. Colitis was induced in male Wistar rats by intracolonic instillation of 30 mg trinitrobenzenesulphonic acid in 50% ethanol (TNBS/E). Controls were given an isovolumetric bolus of normal saline. After 24 h, animals were randomised to receive enemas (1 mL twice daily) of prednisolone (200 mg/L), or L-glutamine (500 g/L) or the suspending agent (placebo). On day 8, the colon was weighed and the degree of inflammation assessed using a colon macroscopic score (CMS). Thymic weight, splenic weight, percentage gain in body weight (%GBW), food intake, plasma interleukin-6 (IL6) and plasma alpha(2)-macroglobulin (alpha(2)M) were also determined. There was a significant increase in CMS, colon weight, splenic weight, IL6 and alpha(2)M in TNBS/E animals compared to controls (P< 0.01). There was also a significant decrease in %GBW, food intake and thymic weight in TNBS/E animals (P< 0.01). The therapeutic enema of prednisolone reduced colonic inflammation (CMS, colon weight), improved thymic weight, %GBW and food intake, and reduced plasma IL6 concentrations (P< 0.05). In contrast administration of glutamine enemas was associated with an exaggerated acute phase protein (alpha(2)M) response (P< 0.05) and failed to improve the colonic and systemic inflammatory response in this experimental model of colitis.

Growth hormone, glutamine, and a modified diet enhance nutrient absorption in patients with severe short bowel syndrome

BACKGROUND

Massive loss of intestinal surface area results in the short bowel syndrome characterized by malabsorption of fluid, electrolytes, and other nutrients. Although the remaining bowel undergoes morphological and functional adaptation, often these changes are inadequate to support the individual by enteral feedings, and parenteral nutrition is required to prevent dehydration, electrolyte disturbances, and malnutrition. Substances such as growth hormone, glutamine, and fiber exert bowel-specific trophic effects and either directly or indirectly influence nutrient absorption. This study was undertaken to determine whether the co-administration of exogenous growth hormone, supplemental glutamine, and a modified fiber-containing diet could enhance nutrient absorption in patients who had undergone massive intestinal resection.

METHODS

Ten patients (5 men, 5 women, aged 43 +/- 4 years) with short bowel syndrome were studied 6 +/- 1 years after surgical resection. All patients were admitted to the Clinical Research Center for a 28-day period; the first week served as a control period when nutritional (enteral and parenteral) and medical management simulated usual home therapy. Thereafter, eight patients received exogenous growth hormone, supplemental glutamine, and a modified high-carbohydrate, high-fiber diet. Two patients were treated with the modified diet alone. The efficiency of net nutrient absorption (percent absorbed) for total calories, protein, fat, carbohydrate, water, and sodium was calculated from the measured nutrient intake and stool losses.

RESULTS

Three weeks of treatment with growth hormone, glutamine, and a modified diet increased total caloric absorption from 60.1 +/- 6.0% to 74.3 +/- 5.0% (p < or = .003), protein absorption from 48.8 +/- 4.8% to 63.0 +/- 5.4% (p < or = .006), and carbohydrate absorption from 60.0 +/- 9.8% to 81.5 +/- 5.3% (p < or = .02). Fat absorption did not change (61.0 +/- 5.3% to 60.3 +/- 7.9%, p = NS). Water and sodium absorption increased from 45.7 +/- 6.7% to 65.0 +/- 7.3% (p < or = .002) and from 49.0 +/- 9.8% to 69.6 +/- 6.5% (p < or = .04), respectively. These absorptive changes resulted in a decrease in stool output (1,783 +/- 414 g/d control period vs 1,308 +/- 404 g/d third week of treatment, p < or = .05). Treatment with diet alone did not influence nutrient absorption or stool output.

CONCLUSIONS

The combined administration of growth hormone, glutamine, and a modified diet enhanced nutrient absorption from the remnant bowel after massive intestinal resection. These changes occurred in a group of patients that had previously failed to adapt to the provision of enteral nutrients. This therapy may offer an alternative to long-term dependence on total parenteral nutrition for patients with severe short bowel syndrome.

Intestinal amino acid content in critically ill patients

BACKGROUND

The purpose of the study was to determine the concentrations of free amino acids and the total protein content of the human intestinal mucosa during critical illness.

METHODS

The free amino acid and protein concentrations in endoscopically obtained biopsy specimens from the duodenum and the distal colonic segments were determined on 19 critically ill patients. The free amino acids were separated by ion exchange chromatography and detected by fluorescence, and the protein content was quantified by the method of Lowry.

RESULTS

In general, the typical amino acid pattern of the intestinal mucosa was seen, with very high levels of taurine, aspartate and glutamic acid. The main difference, as compared to a reference series of healthy subjects, was the elevated glutamine concentration of the duodenal mucosa. This amino acid was unaltered in the descending colon and depressed in the rectum. At the same time, the glutamatic acid concentrations were unaltered, suggesting that the degradation of glutamine was not increased in the septic state of the majority of the patients studied. Phenylalanine and the two branched-chain amino acids, valine and leucine, were elevated in the duodenal mucosa, and in the colonic mucosa, methionine and phenylalanine were elevated; otherwise, all the other individual amino acids were unaltered or depressed.

CONCLUSIONS

The alterations seen in mucosal free amino acid and protein concentrations in connection with critical illness are different in many respects and contrast with the findings seen after starvation or moderate surgical trauma.

Localization of rat small intestine glutamine synthetase using immunofluorescence and in situ hybridization

Glutamine is an important energy source for small intestinal epithelial enterocytes and serves as a key precursor for de novo synthesis of purines and pyrimidines in these rapidly dividing cells. Although glutamine synthetase (GS) is known to be the major enzyme of glutamine biosynthesis, the precise localization of this enzyme in the small intestine is not known. Because glutamine is an important precursor for nucleic acids biosynthesis, we hypothesized that GS is preferentially expressed in the crypt region, which contains the rapidly proliferating cells in the small intestine. Accordingly, immunofluorescence with a specific polyclonal antibody and in situ hybridization using a riboprobe were performed to localize GS protein and mRNA, respectively, in adult rats. Both GS protein and GS mRNA were detected primarily in the crypt region. This finding suggests that GS is located in the region with the highest nucleotide synthesis and cell proliferation. This finding is in support of the use of parenteral glutamine in patients with severe mucosal injury affecting the crypts.

Interrelation of intracellular proteases with total parenteral nutrition-induced gut mucosal atrophy and increase of mucosal macromolecular transmission in rats

Total parenteral nutrition (TPN) is known to induce mucosal atrophy and to increase macromolecular transmission of the small intestine. The potential participation of various proteases in that process was investigated. Male Wistar rats were randomly divided into two groups: the TPN group (n = 11) received a standard TPN (250 kcal/kg per day, 1.78 g nitrogen/kg per day) and the FED group (n = 10) received a standard rat food for 1 week. This was followed by an examination of gut macromolecular transmission of fluorescein isothiocyanate dextran 70,000 (FITC-dextran) after intragastric injection and of the activities of gut mucosal cathepsins B, H, and L and of proteasome. Mucosal wet weight and protein content decreased significantly by TPN for 1 week. In both groups, the activities of all proteases in the ileum were significantly greater than in the jejunum. In the TPN group, cathepsin L and H activities in the ileum, and cathepsin B activity in both the jejunum and the ileum, were greater than those in the FED group. The portal concentration of FITC-dextran was higher than arterial and venous concentrations in the both groups. In the TPN group, the portal FITC-dextran concentration increased significantly compared with the FED group. In conclusion, active proteolysis is not associated with TPN-induced mucosal atrophy. Cathepsins activities in the ileum increase as a result of TPN. Interrelationship is implicated between increase of lysosomal protease activity and the deterioration of the intestinal barrier function, which permits macromolecular transmission.

Intense nutritional support in inflammatory bowel disease

The value of intense nutritional support in inflammatory bowel disease is still debated. Claims have been made that total enteral nutrition is as effective as total parental nutrition. In this review, the use of parenteral and enteral nutritional support as primary therapy in patients with inflammatory bowel disease has been critically evaluated. Most studies have been uncontrolled and nonrandomized with short-term follow-up. The literature does suggest, however, that intense nutritional support may have an adjunctive role to drug therapy in achieving remission in Crohn's disease, especially in corticosteroid-refractory patients. Nutritional support has a lesser role in chronic ulcerative colitis, except for assistance in pre- and postoperative management. The data do not support one variety of nutritional support over another, although enteral support should be used if possible, as it is less costly and potentially less complicated.

Effect of glutamine on tumor and host growth

BACKGROUND

Oral glutamine supplementation has been found to support gastrointestinal mucosal growth and increase intestinal and systemic toxicity after chemotherapy and radiation therapy. Glutamine is also an important nutrient for rapidly proliferating tumor cells. However, it is not clear whether long-term glutamine supplementation in the tumor-bearing host has a selective benefit for host growth or tumor cell proliferation.

METHODS

To study the effect of glutamine in tumor-bearing animals, 30 Lewis/Wistar rats with subcutaneous mammary tumor implants (MAC-33) were randomized to receive a 3% glutamine- or 3% glycerine-enriched (control) diet for 25 days.

RESULTS

No significant difference was found in carcass weight, primary tumor weight, or spontaneous pulmonary metastasis with glutamine supplementation. Tumor cell cycle kinetics (aneuploidy, %S and %S [synthetic] + G2/M [growth fraction]) were similar between glutamine-supplemented and control animals. A trophic effect of glutamine on distal ileal mucosa was seen with increased DNA content (344 +/- 68 vs. 184 +/- 38 micrograms/100 mg tissue) (p < 0.05) and RNA content (435 +/- 44 vs. 335 +/- 30 micrograms/100 mg tissue) (p = 0.06) compared with control animals. No detectable differences were observed in liver or muscle, or in tumor DNA, RNA, or protein content.

CONCLUSIONS

These findings confirm the trophic effect of glutamine on small intestinal mucosa and suggest that glutamine can be administered to the tumor-bearing host over a long period of time without significantly stimulating tumor growth kinetics or metastasis.

[Consequences of surgery on nutritional status]

Trauma and surgery induce extensive physiological changes, commonly denominated the acute phase reaction (APR). This APR is activated by various kinds of stimuli, namely nociceptive stimulations, tissue injury, tissue ischaemia and reperfusion as well as by haemodynamic disturbances which occur commonly in such patients. APR is mainly characterised by the release of counter-regulatory hormones, complex metabolic changes and by the hepatic synthesis of numerous acute phase factors (C-reactive protein, haptoglobin, complement protein, etc). In addition, fever is typically present and there is a resistance to the nutritional support. The intensity of APR is variable, according to the extent of surgery, the subsequent course, occurrence of complications and to various factors related to the patient and its treatment. In patients with non complicated surgery and low or moderate severity trauma, the metabolic changes are minor and self-limited. In such a condition, there is no need for nutritional support. Conservely, in patients with complicated surgery or major trauma, there is an extensive APR, which can be very prolonged. This results in important and sustained metabolic changes, leading to extensive catabolism and progressive loss of body cell mass. The latter is amplified by the decreased body ability to adapt to starvation and by the resistance to the nutritional support that typically occur in complicated postoperative and trauma patients. Total parenteral nutrition does not prevent from metabolic changes occurring in surgical patients. By contrast, several experimental and human studies have shown that early enteral nutrition may alleviate both the endocrine and metabolic responses in such conditions. Regional anaesthesia, particularly by the epidural route, may also decrease but not abolish the extent of APR.

Oral glutamine decreases bacterial translocation and improves survival in experimental gut-origin sepsis

BACKGROUND

Glutamine has been shown to be an important dietary component for the maintenance of gut metabolism. The purpose of this study was to assess the potential benefit of glutamine-enriched diets on experimental gut-derived sepsis.

METHODS

BALB/c mice were fed either 2% glutamine-supplemented or 1% glycine-supplemented (near-isonitrogenous control) AIN-76A diets. Control mice received either nonsupplemented AIN-76A or regular Purina Rodent Laboratory Mouse Chow 5001 diets. After 10 days of feeding, the mice were transfused with allogeneic blood (from C3H/HeJ mice), and the feeding protocols were continued for an additional 5 days. The mice then underwent gavage with 10(10) Escherichia coli labeled with either indium-111 oxine or [14C]glucose followed immediately by a 20% burn injury. Some mice were observed 10 days postburn for survival rates. Others were killed 4 hours after burn, and the mesenteric lymph nodes, liver, and spleen were harvested to determine radionuclide and bacterial colony counts. The percentages of viable translocated E coli were also calculated.

RESULTS

Mice fed glutamine-enriched diets had a lower degree of translocation (as measured by both radionuclide and bacterial counts) to the tissues than did the other groups and had an improvement in the ability to kill translocated E coli (as measured by the percentage of viable bacteria). Survival was significantly higher in the group fed 2% glutamine (81%) compared with the groups fed 1% glycine (36%), AIN-76A (35%), and Purina Rodent Laboratory Mouse Chow 5001 (36%) diets (p < .004).

CONCLUSIONS

Glutamine-supplemented enteral diets may exert important benefits in preventing gut-origin sepsis after trauma.

Sepsis stimulates nonlysosomal, energy-dependent proteolysis and increases ubiquitin mRNA levels in rat skeletal muscle

We tested the role of different intracellular proteolytic pathways in sepsis-induced muscle proteolysis. Sepsis was induced in rats by cecal ligation and puncture; controls were sham operated. Total and myofibrillar proteolysis was determined in incubated extensor digitorum longus muscles as release of tyrosine and 3-methylhistidine, respectively. Lysosomal proteolysis was assessed by using the lysosomotropic agents NH4Cl, chloroquine, leupeptin, and methylamine. Ca(2+)-dependent proteolysis was determined in the absence or presence of Ca2+ or by blocking the Ca(2+)-dependent proteases calpain I and II. Energy-dependent proteolysis was determined in muscles depleted of ATP by 2-deoxyglucose and 2.4-dinitrophenol. Muscle ubiquitin mRNA and the concentrations of free and conjugated ubiquitin were determined by Northern and Western blots, respectively, to assess the role of the ATP-ubiquitin-dependent proteolytic pathway. Total and myofibrillar protein breakdown was increased during sepsis by 50 and 440%, respectively. Lysosomal and Ca(2+)-dependent proteolysis was similar in control and septic rats. In contrast, energy-dependent total and myofibrillar protein breakdown was increased by 172% and more than fourfold, respectively, in septic muscle. Ubiquitin mRNA was increased severalfold in septic muscle. The results suggest that the increase in muscle proteolysis during sepsis is due to an increase in nonlysosomal energy-dependent protein breakdown, which may involve the ubiquitin system.

Clinical applications of enteral nutrition

Clinical and experimental evidence confirms that delivery of nutrients via the gastrointestinal tract reduces septic morbidity in critically injured patients. Early enteral feeding seems to maintain mucosal integrity and to support the gut as an important immunologic organ that may affect other areas of the body. There is increasing evidence to suggest that specific nutrients are especially beneficial in maintaining intestinal host-defense function in times of critical illness and injury.

Growth retardation in children receiving long-term total parenteral nutrition: effects of ornithine alpha-ketoglutarate

We evaluated the effect of ornithine ketoglutarate (OKG) in reversing abnormal growth in six prepubertal children receiving total parenteral nutrition (TPN) for 5-10 y. They were 1-4 SDs below their expected 50th percentile for height. The energy and nitrogen intakes were unchanged from 8 mo before the beginning of the study until its completion. Two consecutive periods of 5 mo each were studied. OKG (15 g) was added to the parenteral solution during the first period (OKG+) but not during the second period (OKG-). Height velocity (HV) increased (P < 0.05) from a median of 3.8 cm/y to 6.45 cm/y (range 1.8-6.7) during the OKG+ period, and decreased (P < 0.05) to a median of 3.65 cm/y in the OKG- period. Plasma concentrations of insulin-like growth factor 1 (IGF1), glutamine, and glutamate increased (P < 0.05) during the OKG+ period. Variations of IGF1 concentrations correlated with HV variations (r = 0.82, P < 0.005) during both periods. This study demonstrates that OKG is associated with statural growth acceleration and increased IGF1 concentrations.

Muscle ammonia and glutamine exchange during chronic liver insufficiency in the rat

The aim of this study was to investigate the role of skeletal muscle in ammonia and glutamine metabolism during chronic hyperammonemia induced by liver insufficiency. The hindquarter ammonia and amino acid fluxes and muscle tissue concentrations were studied in two rat models of chronic liver insufficiency, portacaval shunting and portacaval shunting plus bile-duct ligation, as well as in sham-operated animals, 7 and 14 days after surgery, and in normal, unoperated rats. To reduce nutritional influences, portacaval-shunted rats and sham-operated rats were pair-fed to portacaval shunt biliary obstruction rats. Arterial ammonia levels were elevated in both liver insufficiency groups. In the portacaval shunting plus bile-duct ligation group, arterial glutamine levels were elevated compared with sham-operated controls. No net hind-quarter ammonia uptake was observed in any of the groups, despite hyperammonemia in the chronic liver insufficiency groups. Hindquarter glutamine release was always increased in the liver insufficiency groups compared with sham-operated controls, despite similar muscle glutamine levels in the sham-operated and hyperammonemic groups, suggesting enhanced muscle glutamine synthesis in the latter groups. Muscle ammonia levels were always increased and muscle glutamate decreased in the hyperammonemic groups, probably indicating glutamate consumption by enhanced glutamine synthesis. The increased phenylalanine tissue concentrations and efflux in portacaval shunt/biliary obstruction rats suggest that enhanced net muscle protein breakdown, amino acid catabolism and transamination, rather than ammonia uptake from the blood furnish amino acids and ammonia for enhanced glutamine synthesis. These experiments suggest that nutritional factors are important in explaining altered muscle metabolism during chronic liver insufficiency.

Effect of free glutamine and alanyl-glutamine dipeptide on mucosal proliferation of the human ileum and colon

BACKGROUND/AIMS

Glutamine (Gln) is considered a trophic factor for small intestinal epithelia, which is important during severe illness. Its use in parenteral nutrition is precluded by its instability, a problem that may be overcome by use of the stable dipeptide L-alanyl-L-glutamine (Ala-Gln). The hypothesis was tested that Gln or Ala-Gln may stimulate cell proliferation not only in the ileum but also in the proximal and distal colon and, thus, may contribute to the gut barrier function.

METHODS

Biopsy samples from the normal human ileum, proximal colon, and rectosigmoid were incubated for 4 hours with Gln (2 mmol/L), Ala-Gln (2 mmol/L), and saline (control). Cells in S phase were labeled with bromodeoxyuridine. In longitudinal crypt sections labeled and quiescent cells were counted.

RESULTS

Gln as well as Ala-Gln stimulated crypt cell proliferation in the ileum, proximal colon, and rectosigmoid colon. In ileal specimens, labeling was greater in the entire crypt, whereas in both colonic regions, the trophic effect was confined to the basal crypt compartments.

CONCLUSIONS

Gln and Ala-Gln have trophic effects not only in the ileum, but also in the proximal and distal colon. This could be important during parenteral nutrition when mucosal atrophy may weaken the gut barrier.

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.