Maintenance of small bowel mucosa with glutamine-enriched parenteral nutrition

Renal metabolism of amino acids: its role in interorgan amino acid exchange

The kidneys play a role in the synthesis and interorgan exchange of several amino acids. The quantitative importance of renal amino acid metabolism in the body is not, however, clear. We review here the role of the kidney in the interorgan exchange of amino acids, with emphasis on quantitative aspects. We reviewed relevant literature by using a computerized literature search (PubMed) and checking relevant references from the identified articles. Our own data are discussed in the context of the literature. The kidney takes up glutamine and metabolizes it to ammonia. This process is sensitive to pH and serves to maintain acid-base homeostasis and to excrete nitrogen. In this way, the metabolism of renal glutamine and ammonia is complementary to hepatic urea synthesis. Citrulline, derived from intestinal glutamine breakdown, is converted to arginine by the kidney. Renal phenylalanine uptake is followed by stoichiometric tyrosine release, and glycine uptake is accompanied by serine release. Certain administered oligopeptides (eg, glutamine dipeptides) are converted by the kidneys to their constituent components before they can be used in metabolic processes. The kidneys play an important role in the interorgan exchange of amino acids. Quantitatively, for several important amino acids, the kidneys are as important as the gut in intermediary metabolism. The kidneys may be crucial "mediators" of the beneficial effects of specialized, disease-specific feeding solutions such as those enriched in glutamine dipeptides.

Indications for specific therapy in the rehabilitation of patients with the short-bowel syndrome

Diarrhoea, malabsorption and malnutrition characterize the short-bowel syndrome. Following the initial intestinal resection, complications such as fistulas and intra-abdominal abscesses may occur, but these usually resolve with appropriate surgical care. All residual intestine should be placed in continuity before serious attempts at rehabilitation with oral feedings are initiated. Small hourly oral feedings composed of food items high in complex carbohydrate and low in fat are started when appropriate and the diet is gradually increased as intestinal adaptation occurs. The goal during this process is to prevent diarrhoea and allow the formation of semiformed stools. With time, parenteral nutrition (PN) can be reduced, and the time required depends on both length of residual bowel and the particular anatomy involved-for example, the presence or absence of the colon. A programme of optimal diet plus growth hormone (0.1 mg/kg) and oral glutamine (30 g/day) enhances the adaptive process and allows many patients independence from PN. However, those with extremely short segments of jejuno-ileum (<50 cm) and no colon have excessive fluid and electrolyte losses, and intestinal transplantation may be the only therapy which allows such patients to be independent of PN.

Glutamine supplementation in vitro and in vivo, in exercise and in immunodepression

In situations of stress, such as clinical trauma, starvation or prolonged, strenuous exercise, the concentration of glutamine in the blood is decreased, often substantially. In endurance athletes this decrease occurs concomitantly with relatively transient immunodepression. Glutamine is used as a fuel by some cells of the immune system. Provision of glutamine or a glutamine precursor, such as branched chain amino acids, has been seen to have a beneficial effect on gut function, on morbidity and mortality, and on some aspects of immune cell function in clinical studies. It has also been seen to decrease the self-reported incidence of illness in endurance athletes. So far, there is no firm evidence as to precisely which aspect of the immune system is affected by glutamine feeding during the transient immunodepression that occurs after prolonged, strenuous exercise. However, there is increasing evidence that neutrophils may be implicated. Other aspects of glutamine and glutamine supplementation are also addressed.

Modulation of intestinal protein synthesis and protease mRNA by luminal and systemic nutrients

Route of nutrient supply is important in regulation of intestinal protein metabolism, because total parenteral nutrition, compared with enteral feeding, leads to profound atrophy. Participation of the fractional rate of protein synthesis (Ks), their degradation in regulation of gut protein balance, and their possible modulation by specific nutrients are the focus of our work. We developed an in situ experimental system that allows controlled exposure of intestinal mucosa to nutrients systemically, luminally, or both. We examined the effects of systemic glucose and amino acid (AA) infusion in overnight-fasted piglets. Jejunal segments within each piglet were simultaneously, luminally perfused with solutions containing various AAs or glucose. Intravenous infusion of glucose increased mucosal Ks by 16% (P < 0.05), whereas intravenous infusion of AA had no effect on Ks. Systemic glucose infusion had no effect on mRNA levels for components of the ubiquitin-proteasome proteolytic pathway. However, levels of these mRNA were reduced by intravenous or luminal AA supply. This effect was greatest (-50%) when highest tissue concentrations of AAs were achieved by the simultaneous infusion of AA by both routes (P < 0.05). Our findings suggest that not only is the modulation of protein balance in the intestine in response to nutrients in part attributable to anabolic stimulation of protein synthesis initiated by the systemic appearance of glucose, but a fall in protein degradation is also a likely contributor. AAs appear to be a key factor required to reduce expression of genes connected with proteolysis.

Phase III double-blind study of glutamine versus placebo for the prevention of acute diarrhea in patients receiving pelvic radiation therapy

PURPOSE

A phase III, randomized, double-blind study was conducted by the North Central Cancer Treatment Group to determine the efficacy and toxicity of oral glutamine for the prevention of acute diarrhea in patients receiving pelvic radiation therapy (RT).

PATIENTS AND METHODS

All 129 patients enrolled from 14 institutions between February 1998 and October 1999 were eligible. Patients received 4 g of glutamine or placebo orally, twice a day, beginning with the first or second day of RT and continuing for 2 weeks after RT. During treatment, patients were assessed weekly for toxicity, and a bowel function questionnaire was administered. The primary measures of treatment efficacy were diarrhea levels measured by maximum grade of diarrhea, incidence of diarrhea, and average diarrhea score. After completion of RT, the bowel function questionnaire was administered weekly for 4 weeks and at 12 and 24 months. Toxicity was measured by National Cancer Institute common toxicity criteria.

RESULTS

The median age of patients was 69 years (range, 34 to 86 years). The two treatment arms were balanced with respect to all baseline factors. There were no significant differences in toxicity by treatment. Quality-of-life scores and the mean number of problems reported on the bowel function questionnaire were virtually identical for both treatment groups. The incidence of grade 3 or higher diarrhea was 20% for the glutamine arm and 19% for the placebo arm (P =.99). The maximum number of stools per day was 5.1 for the glutamine arm and 5.2 for the placebo arm (P =.99).

CONCLUSION

There is no evidence of a beneficial effect of glutamine during pelvic RT.

Role of the gut in the course of severe acute pancreatitis

INTRODUCTION

The pathogenesis of acute pancreatitis remains elusive. Sepsis and multiple organ failure continue to cause death (overall mortality rate, approximately 10%) despite immense improvements in supportive, radiologic, and surgical therapy. The gut appears to play a key role in the development of these complications.

AIM

To critically review the evidence implicating the gut in the pathogenesis of acute pancreatitis.

METHODS

Relevant English-language literature or abstracts cited in the MEDLINE database were reviewed.

RESULTS AND CONCLUSION

Gram-negative enteric organisms account for most infections of pancreatic necrosis and subsequent sepsis, which suggests the gut as a source. Intestinal permeability is increased early in patients with severe acute pancreatitis and correlates with endotoxemia, which suggests translocation as a possible mechanism. The pathogenesis of the deranged function of the gut mucosal barrier and the possible sites of increase in intestinal permeability are discussed. The gut also plays a role in priming neutrophils and the release of inflammatory cytokines, which initiate and propagate nearly all the detrimental consequences of severe inflammation and sepsis. Future research avenues and potential therapeutic measures that may restore and preserve gut barrier function are explored.

Nutraceuticals: a pharmaceutical viewpoint: I

PURPOSE OF REVIEW

To review pharmaceutical aspects of selected amino acids, antioxidants and related nutraceuticals, deemed to be important for clinical nutrition.

RECENT FINDINGS

New clinical applications of nutraceuticals are increasingly being reported, but there are fundamental differences between formulation, production and the evidence supporting clinical use. Nutraceuticals generally fall within the novel foods and ingredients regulations but their purity, dosage requirements and clinical consequences exceed those of most 'healthfoods'. Replacement of one nutrient or antioxidant is unlikely to correct the cascade of interconnected metabolic abnormalities associated with many diseases. However, it is difficult to ascertain whether the reported benefits of complex mixtures, with little published stability data, are due to one or more individual substrates or some in-vitro interaction between them. Many clinical studies have suffered from inconsistencies of dose, formulation discrepancies and unproven outcome. These contradictory results weaken any firm evidence base to substantiate their effectiveness.

SUMMARY

Nutraceuticals are destined to play an important role in future therapeutic developments but their success will be governed by control of purity, safety and efficacy without inhibiting innovation. The straightforward application of pharmaceutical standards, especially across national borders, is likely to be a difficult challenge and could effectively paralyse the industry. Nevertheless more standardized formulations, dosage forms and production controls are called for. A place for nutraceuticals in clinical practice is emerging, but important pharmaceutical and clinical issues need to be addressed by further research.

Glutamine supplementation and deprivation: effect on artificially reared rat small intestinal morphology

The mechanisms of how glutamine benefits critically ill patients have not been established. The purpose of this study was to determine the effects of dietary and endogenously produced glutamine on small intestinal morphology using light and transmission electron microscopy in artificially reared rat pups. It was hypothesized that deprivation of dietary glutamine leads to intestinal disease that is exacerbated by inhibition of glutamine synthetase by methionine sulfoximine (MS). Rat pups were placed into five different test groups: The first was a reference group that was reared by their mother. The other four groups were reared artificially and received a 10% Travasol amino acid solution at 5 g/kg per day, which does not contain glutamine, added to a mixture containing carbohydrates, lipids, and vitamins. This dose was chosen because it represents an approximation of the amount of glutamine these rats would be receiving in a normal rat diet (approximately 40 g/kg per day total protein, 10 to 15% of which is glutamine + glutamate). The glutamine was manipulated by adding glutamine (Q) or MS or both. The four groups were as follows: MS-Q-, MS-Q+, MS+Q-, and MS+Q+. Light microscopy revealed the greatest blunting of villus height in the ileum of rats from the MS+Q- group when compared with the MS-Q+ group (123 +/- 48.9 micro m versus 207 +/- 36 microm, p < 0.05). The other two groups exhibited intermediate villus heights, but all were shorter than the villi from the mother-reared animals. The number of villi per unit length of bowel was also lowest in the animals that were treated with MS and not provided with dietary glutamine. Transmission electron microscopy demonstrated breakdown of the epithelial junctions in the glutamine-deprived and glutamine synthetase-inhibited intestines. Glutamine-deprived animals also displayed sloughing of microvilli, decreased actin cores, and degeneration of the terminal web. In summary, these studies support the hypothesis that glutamine is involved with maintenance of intestinal epithelial integrity.

Interorgan ammonia metabolism in liver failure

In the post-absorptive state, ammonia is produced in equal amounts in the small and large bowel. Small intestinal synthesis of ammonia is related to amino acid breakdown, whereas large bowel ammonia production is caused by bacterial breakdown of amino acids and urea. The contribution of the gut to the hyperammonemic state observed during liver failure is mainly due to portacaval shunting and not the result of changes in the metabolism of ammonia in the gut. Patients with liver disease have reduced urea synthesis capacity and reduced peri-venous glutamine synthesis capacity, resulting in reduced capacity to detoxify ammonia in the liver. The kidneys produce ammonia but adapt to liver failure in experimental portacaval shunting by reducing ammonia release into the systemic circulation. The kidneys have the ability to switch from net ammonia production to net ammonia excretion, which is beneficial for the hyperammonemic patient. Data in experimental animals suggest that the kidneys could have a major role in post-feeding and post-haemorrhagic hyperammonemia.During hyperammonemia, muscle takes up ammonia and plays a major role in (temporarily) detoxifying ammonia to glutamine. Net uptake of ammonia by the brain occurs in patients and experimental animals with acute and chronic liver failure. Concomitant release of glutamine has been demonstrated in experimental animals, together with large increases of the cerebral cortex ammonia and glutamine concentrations. In this review we will discuss interorgan trafficking of ammonia during acute and chronic liver failure. Interorgan glutamine metabolism is also briefly discussed, since glutamine synthesis from glutamate and ammonia is an important alternative pathway of ammonia detoxification. The main ammonia producing organs are the intestines and the kidneys, whereas the major ammonia consuming organs are the liver and the muscle.

Enhancing bowel adaptation in short bowel syndrome

Malabsorption of both nonessential and essential nutrients, fluid, and electrolytes will, if not compensated for by increased intake, lead to diminished body stores and to subclinical and eventually clinical deficiencies. By definition, intestinal failure prevails when parenteral support is necessary to maintain nutritional equilibrium. After intestinal resection, adaptation, a progressive recovery from the malabsorptive disorder, may be seen. Research has focused on optimizing remnant intestinal function through dietary or pharmacologic interventions. In this review, factors responsible for the morphologic and functional changes in the adaptive processes are described. Results of clinical trials employing either growth hormone and glutamine or glucagon-like peptide-2 in short bowel patients are presented.

Effects of an alanyl-glutamine-based oral rehydration and nutrition therapy solution on electrolyte and water absorption in a rat model of secretory diarrhea induced by cholera toxin

OBJECTIVES

Recurring diarrhea and persistent diarrhea are commonly associated with malnutrition and long-term functional deficits. A beneficial approach would be to develop an alanyl-glutamine (AlaGln)-based oral rehydration and nutrition therapy (ORNT). We investigated the effect of an AlaGln-ORNT solution on electrolyte and water absorption in a rat model of secretory diarrhea induced by cholera toxin.

METHODS

Phenolsulfonphthalein (50 microg/mL) was used as a non-absorbable marker for calculation of net water and electrolyte transport. Solutions tested were Ringer's solution, a glutamine-based ORNT (Gln-ORNT) solution, and an AlaGln-ORNT solution. Cholera toxin (1 microg/mL) was injected into lumen of rat small intestinal segments and incubated for 18 h before the initiation of the perfusion.

RESULTS

Cholera toxin induced significant secretion of electrolyte and water in the control Ringer's solution. AlaGln-ORNT and Gln-ORNT solutions reduced the sodium secretory effect of cholera toxin by 128% and 36%, respectively. The net water secretion also was reduced by 95% and 60%, respectively, with the AlaGln-ORNT and Gln-ORTN solutions.

CONCLUSIONS

These results showed that AlaGln-ORNT solution can enhance water and electrolyte intestinal absorption even better than glutamine or glucose and thus provide a potential novel approach for ORNT to break the vicious cycle of diarrhea and malnutrition. Clinical trials are now needed in children and adults with diarrhea and malnutrition.

Protective nutrients and functional foods for the gastrointestinal tract

Epithelial and other cells of the gastrointestinal mucosa rely on both luminal and bloodstream sources for their nutrition. The term functional food is used to describe nutrients that have an effect on physiologic processes that is separate from their established nutritional function, and some of these nutrients are proposed to promote gastrointestinal mucosal integrity. We review the recent in vitro, animal, and clinical experiments that evaluated the role of several types of gastrointestinal functional foods, including the amino acids glutamine and arginine, the essential micronutrients vitamin A and zinc, and 2 classes of food additives, prebiotics and probiotics. Many of the data from preclinical studies support a strong role for enteral nutrients in gastrointestinal health; in comparison, the data from human studies are limited. In some cases, impressive data from in vitro and animal studies have not been replicated in human trials. Other clinical trials have shown positive health benefits, but some of those studies were plagued by flaws in study design or analysis. The methods available to detect important changes in human gastrointestinal function and structure are still limited, but with the development of more sensitive measures of gastrointestinal function, the effects of specific nutrients may be more easily detected. This may facilitate the development of phase 3 clinical trials designed to more rigorously evaluate the effects of a particular nutrient by focusing on valid and reliable outcome measures. Regulatory changes in the way in which health claims can be made for dietary supplements should also be encouraged.

Intestinal and hepatic response to combined partial hepatectomy and small bowel resection in mice

BACKGROUND

Both partial-hepatectomy (PHx) and massive small bowel resection (SBR) are strong mitogenic signals to the remnant liver and intestine, respectively. This study tested the hypothesis that PHx was an additive signal for intestinal adaptation after massive SBR.

METHODS

Male mice underwent either sham SBR or 50% proximal SBR. Mice from these two groups were then subjected to a 70% PHx or sham PHx. After 3 days, parameters of intestinal adaptation and liver regeneration were recorded in the remnant intestine and liver, respectively.

RESULTS

Intestinal adaptation following SBR occurred normally, but was not enhanced after concomitant PHx. On the other hand, SBR impaired the regenerative ability of the liver following PHx.

CONCLUSIONS

Intestinal adaptation after SBR takes priority over liver regeneration after PHx. These data implicate a hierarchy with regard to adaptive alterations to organ loss and endorse an important role for the intestinal mucosa in the regulation of hepatic regeneration.

Nutritional and metabolic support in patients undergoing bone marrow transplantation

Bone marrow transplantation (BMT) is a sophisticated procedure consisting of the administration of high-dose chemoradiotherapy followed by intravenous infusion of hemopoietic stem cells to reestablish marrow function when bone marrow is damaged or defective. BMT is used in the treatment of solid tumors, hematologic diseases, and autoimmune disorders. Artificial nutrition, total parenteral nutrition in particular, is provided to patients undergoing BMT to minimize the nutritional consequences of both the conditioning regimens (eg, mucositis of the gastrointestinal tract) and complications resulting from the procedure (eg, graft versus host disease and venoocclusive disease of the liver). Although artificial nutrition is now recognized as the standard of care for BMT patients, defined guidelines for the use of artificial nutrition in this clinical setting are lacking. During the past 2 decades, artificial nutrition in BMT patients has moved from simple supportive care to adjunctive therapy because of the possible benefits, not strictly nutritional, of specialized nutritional intervention. Although data exist documenting the beneficial role of special nutrients, such as lipids and glutamine, in the management of BMT recipients, the results obtained to date are controversial. The reasons for this controversy may reside in the heterogeneity of the patients studied and of the study designs. This review focuses on the need to correctly identify the different patterns of BMT to achieve reproducible and reliable data, which may in turn be used to devise precise guidelines for the use of specialized artificial nutrition in BMT patients.

The influence of L-glutamine on the depression of hepatic cytochrome P450 activity in male rats caused by total parenteral nutrition

Total parenteral nutrition (TPN) bypasses the gut leading to intestinal and hepatic dysfunction, including decreased hepatic cytochrome P450 (P450) activity. Glutamine prevents the TPN-associated changes in gut function and morphology. This study examined the effect of glutamine supplementation on hepatic P450 activities in male Sprague-Dawley rats receiving continuous TPN. Animals received continuous lipid-free TPN for 7 days with 0, 0.1, or 4.5% glutamine. Surgical controls were allowed free access to rat chow. The V(max)/K(m) ratios (intrinsic clearance) for the formation of 4-hydroxymidazolam (CYP3A) were 12.8, 14.6, and 27.7 microl/min/mg for TPN treatment with 0, 0.1%, or 4.5% glutamine, respectively, compared with a chow-fed control (37.1 microl/min/mg). The corresponding values for 1'-hydroxymidazolam formation (CYP3A) were 3.7, 6.1, 11.7, and 15.2 microl/min/mg, respectively. The addition of glutamine to TPN similarly affected the formation rates for 2beta- and 6beta-hydroxytestosterone (CYP3A), and these metabolite formation rates were highly correlated (r = 0.865; p < 0.001). The formation rates for 2alpha- and 16alpha-hydroxytestosterone (CYP2C) were also highly correlated (r = 0.892; p < 0.001). Parenteral glutamine modified the TPN-associated suppression of CYP3A and CYP2C activities in adult male rats receiving TPN.

Glutamine deficiency renders human monocytic cells more susceptible to specific apoptosis triggers

BACKGROUND

After major trauma and sepsis, patients frequently show a decreased blood glutamine (Gln) level. Gln deprivation has been shown to induce apoptosis in intestinal epithelial cells. In this study, we investigated whether the Gln level also affects the susceptibility of monocytic cells to apoptosis.

METHODS

Human monocytic U937 cells were suspended in a Gln-free medium, exposed for 20 minutes to either tumor necrosis factor alpha, Fas ligand, heat shock, or UV irradiation and allowed to recover for 4 hours or 24 hours. Apoptosis was measured by annexin-V assay and confirmed by nuclear condensation. The activation of caspase-3 was determined by Western blot.

RESULTS

When induced by tumor necrosis factor alpha, Fas ligand, or heat shock, the apoptosis rate was significantly lower (50%-60%) in the presence of Gln than in the absence of Gln (P <.02). However, Gln had no effect on UV irradiation-induced apoptosis. Caspase-3 was activated by all inducers and was independent of Gln.

CONCLUSIONS

This study shows that glutamine deprivation increases the susceptibility of monocytic cells to some but not all inducers of apoptosis. Because Gln has no effect on caspase-3 activation, we hypothesize that the selective anti-apoptotic effect of Gln occurs downstream of caspase-3. These results suggest that Gln serves as a selective immunomodulating factor.

Metabolic effects of intraportal nutrition in humans

OBJECTIVE

We investigated the metabolic effects of intravenous nutrition through a portal (PN) or systemic (SN) peripheral vein.

METHODS

Twenty patients were randomized to receive PN or SN nutrition after colorectal surgery. The daily regimen included 900 kcal and 100 g of amino acid (AA). Visceral proteins and hepatic enzymes were measured on days 0, 1, 3, 5, and 7, and plasma arterovenous differences and limb flux of AA were measured on days 0, 3, and 7; urinary nitrogen and 3-CH3-histidine were analyzed daily.

RESULTS

Serum albumin on day 7 was still depressed (P = 0.01) in SN and fully restored in PN patients. Prealbumin levels increased significantly (P = 0.05) in the PN group only. Plasma levels of glutamine and asparagine were higher in PN than in SN patients, and this difference was statistically significant (P = 0.05). SN patients had significantly more negative limb-muscle balance of valine and tyrosine, whereas PN patients had a higher muscle release of citrulline and taurine.

CONCLUSIONS

In conclusion, short-term PN is safe and has some metabolic benefits: it accelerates recovery from postoperative hypoalbuminemia and hypopnealbuminemia and is associated with a higher plasma level of glutamine and an AA plasma pattern that is closer to normal. PN blunts the catabolic response of the muscle, decreasing loss of proteins and release of some AA involved in hepatic gluconeogenesis.

Glutamine in the fetus and critically ill low birth weight neonate: metabolism and mechanism of action

Of all the amino acids, glutamine is the most versatile. Studies in the maternal-fetal-placental unit demonstrate that both glutamine and glutamate play an important role in fetal and placental metabolism. If an infant is born very prematurely, the supply of glutamine from the mother is suddenly interrupted. The infant is dependent on endogenous synthesis or an exogenous supply of glutamine to meet the challenges of the external environment and a tripling of body weight in the first 3-4 mo of life. Studies of glutamine supplementation in low birth weight infants and critically ill adults suggest benefits, especially in terms of decreased nosocomial infections. Two large multicenter trials are currently underway that are designed to address these potential benefits in very low birth weight infants. These trials will not explain the mechanism of action. This review raises hypotheses about the role of the amide nitrogen of glutamine for nucleotide and glucosamine synthesis in the small intestine and how this might relate to greater integrity of the intestinal mucosa, hence preventing bacterial translocation and/or the subsequent proinflammatory response that might lead to multiorgan failure.

The effect of glutamine supplementation in patients following elective surgery and accidental injury

The metabolic response to injury, whether a controlled elective surgical procedure or an accidental injury, is characterized by the breakdown of skeletal muscle protein and the translocation of the amino acids to visceral organs and the wound. At these sites, the substrate serves to enhance host defenses, and support vital organ function and wound repair. Glutamine (GLN) plays a major role in these processes, accounting for approximately one third of the translocated nitrogen. From available data, GLN-supplemented intravenous nutrition in patients undergoing elective surgery improves nitrogen balance, helps correct the decreased GLN concentration found in the free intracellular skeletal muscle amino acid pool and enhances net protein synthesis (particularly in skeletal muscle). Six randomized blind trials (two multicentered investigations) reported a decreased length in hospital stay in postoperative patients receiving GLN supplementation. After blunt trauma, GLN supplementation increased plasma concentrations, attenuated the immunosuppression commonly observed and decreased the rate of infection. Patients with burn injury have low GLN plasma and intramuscular concentrations; turnover and synthesis rate are accelerated, yet apparently inadequate to support normal concentrations. These data suggest that GLN supplementation has important effects in catabolic surgical patients, but the exact mechanisms to explain these events remain unknown, and more research is required to explain the apparent benefits of dietary GLN.

Nutrition in patients with acute pancreatitis

Acute pancreatitis is a disease with varying severity. Patients with the mild form do not require nutritional support because oral intake is resumed rapidly. Studies on nutritional support in acute pancreatitis have included patients with both mild and severe disease. In this heterogeneous group, total parenteral nutrition did not improve outcome compared with no nutrition at all. This is caused in part by an increase in septic complications during total parenteral nutrition. Likewise, no benefit from enteral nutrition was observed compared with no nutrition, probably because the group was heterogeneous or because nutritional goals were not achieved. Patients with severe acute pancreatitis become profoundly catabolic. This group undoubtedly requires nutritional support to treat undernutrition. The limited available data indicate that enteral nutrition, if well tolerated, is superior to parenteral nutrition for patients with severe acute pancreatitis. Based on current knowledge, a combination of early total parenteral nutrition and enteral nutrition is advisable as soon as enteral nutrition is tolerated. Monitoring of gut function is crucial in this situation.

Pharmacotherapy and growth factors in the treatment of short bowel syndrome

A review of the pharmacologic substances and growth factors that have been studied experimentally and administered clinically for the management of short bowel syndrome is presented. The medical management of short bowel syndrome is multifaceted. In the acute phase, efforts focus on fluid and electrolyte management and the reduction of gastric acid output. As enteral feeding is initiated, antimotility and antisecretory agents may be effective in reducing gastrointestinal losses. Additional modalities of management, including nutrients and growth factors, may be directed at maximizing absorptive function beyond that which occurs with intestinal adaptation. Continued research aimed at further elucidating the process of intestinal adaptation may allow us to use the various peptides and hormones that act as growth factors for the bowel mucosa. Knowledge gained from these studies combined with gene therapy techniques will result in the permanent enhancement of intestinal function beyond the normal adaptation process, eliminate the dependence on total parenteral nutrition, and avoid the need for intestine transplantation.

Intestinal adaptation: structure, function, and regulation

After massive small bowel resection (SBR), the remnant intestine undergoes an adaptive process characterized by increases in wet weight, protein and DNA content, villus height and crypt depth, and absorptive surface area. These changes are the result of a proliferative stimulus that increases crypt cell mitosis and augments cellular progression along the villus axis. Functionally, there is upregulation of the Na(+)/glucose cotransporter, Na(+)/H(+) exchanger, and other enzymes involved in intestinal digestion and absorption. These physiologic events are a compensatory response to the sudden loss of digestive and absorptive capacity by the remnant intestine. A major consequence of inadequate intestinal adaptation is lifelong dependence on parenteral nutrition, which results ultimately in cholestatic liver dysfunction. Furthermore, adaptation may be associated with changes in intestinal permeability and an increased risk of bacterial translocation and sepsis. Several mediators thought to be integral to the postresection adaptive response have been proposed, including luminal nutrients, gastrointestinal secretions, and humoral factors. A thorough understanding of intestinal adaptation will be essential in the rational development of new and innovative therapies that amplify this complex but important process.

Effect of bowel rehabilitative therapy on structural adaptation of remnant small intestine: animal experiment

AIM: To investigate the individual and the combined effects of glutamine, dietary fiber, and growth hormone on the structural adaptation of the remnant small bowel.

METHODS: Forty-two adult male Sprague-Dawley rats underwent 85% mid-small bowel resection and received total parenteral nutrition (TPN) support during the first three postoperational days. From the 4th postoperational day, animals were randomly assigned to receive 7 different treatments for 8 d: TPNcon group, receiving TPN and enteral 20 g·L^-1 glycine perfusion; TPN + Gln group, receiving TPN and enteral 20 g·L^-1 glutamine perfusion; ENcon group, receiving enteral nutrition (EN) fortified with 20 g·L^-1 glycine; EN + Gln group, enteral nutrition fortified with 20 g·L^-1 glutamine; EN + Fib group, enteral nutrition and 2 g·L^-1 oral soybean fiber; EN + GH group, enteral nutrition and subcutaneous growth hormone (GH) (0.3IU) injection twice daily; and ENint group, glutamine-enriched EN, oral soybean fiber, and subcutaneous GH injection.

RESULTS: Enteral glutamine perfusion during TPN increased the small intestinal villus height (jejunal villus height 250 µm ± 29 µm in TPNcon vs 330 µm ± 54 µm in TPN + Gln, ileal villus height 260 µm ± 28 µm in TPNcon vs 330 µm ± 22 µm in TPN + Gln, P < 0.05) and mucosa thickness (jejunal mucosa thickness 360 µm ± 32 µm in TPNcon vs 460 µm ± 65 µm in TPN +Gln, ileal mucosa thickness 400 µm ± 25 µm in TPNcon vs 490 µm ± 11 µm in TPN + Gln, P < 0.05) in comparison with the TPNcon group. Either fiber supplementation or GH administration improved body mass gain (end body weight 270 g ± 3.6 g in EN + Fib, 265.7 g ± 3.3 g in EN + GH, vs 257 g ± 3.3 g in ENcon, P < 0.05), elevated plasma insulin-like growth factor (IGF-I) level (880 µg·L^-1± 52 µg·L^-1 in EN + Fib, 1200 µg·L^-1± 96 µg·L^-1 in EN ± GH, vs 620 µg·L^-1± 43 µg·L^-1 in ENcon, P < 0.05), and increased the villus height (jejunum 560 µm ± 44 µm in EN ± Fib, 530 µm ± 30 µm in EN ± GH, vs 450 µm ± 44 µm in ENcon, ileum 400 µm ± 30 µm in EN + Fib, 380 µm ± 49 µm in EN ± GH, vs 320 µm ± 16 µm in ENcon, P < 0.05) and the mucosa thickness (jejunum 740 µm ± 66 µm in EN ± Fib, 705 µm ± 27 µm in ENGH, vs 608 µm ± 58 µm in ENcon, ileum 570 µm ± 27 µm in EN ± Fib, 560 µm ± 56 µm in EN ± GH, vs 480 µm ± 40 µm in ENcon, P < 0.05) in remnant jejunum and ileum. Glutamine-enriched EN produced little effect in body mass, plasma IGF-I level, and remnant small bowel mucosal structure. The ENint group had greater body mass (280 g ± 2.2 g), plasma IGF-I level (1450 µg·L^-1± 137 µg·L^-1), and villus height (jejunum 620 µm ± 56 µm, ileum 450 µm ± 31 µm) and mucosal thickness (jejunum 800 µm ± 52 µm, ileum 633 µm ± 33 µm) than those in ENcon, EN + Gln (jejunum villus height and mucosa thickness 450 µm ± 47 µm and 610 µm ± 63 µm, ileum villus height and mucosa thickness 330 µm ± 39 µm and 500 µm ± 52 µm), EN + GH groups (P < 0.05), and than those in EN + Fib group although no statistical significance was attained.

CONCLUSION: Both dietary fiber and GH when used separately can enhance the postresectional small bowel structural adaptation. Simultaneous use of these two gut-trophic factors can produce synergistic effects on small bowel structural adaptation. Enteral glutamine perfusion is beneficial in preserving small bowel mucosal structure during TPN, but has little beneficial effect during EN.

Glutamine ameliorates mechanical obstruction-induced intestinal injury

BACKGROUND

Glutamine has been shown to be an important dietary component for the maintenance of gut integrity. Although considered a nonessential amino acid in normal circumstances, glutamine may become conditionally essential for the bowel during episodes of severe illness and malnutrition. In this study, we employed an animal model simulating mechanical intestinal obstruction to explore the beneficial effects of glutamine on the intestine in response to obstruction-induced injury.

MATERIALS AND METHODS

Rats were on three feeding regimens-standard diet and water (control group), diet and water containing 2% glutamine (glutamine group), or diet and water containing 2% arginine (arginine group)-for 3 days prior to surgical preparation of intestinal obstruction. The bowel distension, fluid accumulation, and histological alterations in the intestinal mucosa were measured 40 h after ileal ligation.

RESULTS

After 3 days of drinking water intervention, the plasma glutamine levels in the glutamine group (677 +/- 12 microM) were higher than those in the control (451 +/- 27 microM) and arginine (379 +/- 25 microM) groups. The distension ratio measured 40 h after ileal ligation was significantly lower in the glutamine group (30.9 +/- 4.2%) than in the control and arginine groups (45.9 +/- 1.7 and 46.1 +/- 3.4%, respectively). Also, glutamine markedly decreased the fluid accumulation in the obstructed bowel segment (control group, 178.41 +/- 18.60 mg/cm; glutamine group, 104.97 +/- 13.17 mg/cm; arginine group, 141.4 +/- 12.85 mg/cm). Furthermore, the obstruction-induced mucosal injury was substantially improved in glutamine-fed rats.

CONCLUSIONS

Our findings indicate that glutamine can significantly reduce the degree of those physiological derangements induced by mechanical intestinal obstruction.

Glutamine-enriched parenteral nutrition regulates the activity and expression of intestinal glutaminase

The aim of this study was to examine the effect of glutamine-enriched parenteral nutrition on the activity, expression and distribution of glutaminase mRNA within the small intestine of rats. Central venous lines were inserted into 30 male Wistar rats before they were fed for 6 days with either: (a) conventional parenteral nutrition, (b) 2.5% glutamine-enriched parenteral nutrition, or (c) rat food ad libitum. Jejunal glutaminase activity per milligram of dry matter was greatest in the animals fed rat food (0.94+/-0.29), intermediate in the glutamine supplemented rats (0.69+/-0.19) and least in the rats nourished with conventional parenteral nutrition (0.55+/-0.24) (P<0.05). The data for glutaminase expression exhibited a similar trend (P<0.05). In situ hybridisation analysis confirmed that glutaminase is expressed in the mucosa along the whole length of the small intestine. It was concluded that provision of glutamine alters the activity and expression of glutaminase in intestinal enterocytes. The results suggest that glutamine increases glutaminase activity by promoting the accumulation of intestinal glutaminase mRNA.

Effects of enteral glutamine on gut mucosal protein synthesis in healthy humans receiving glucocorticoids

In hypercatabolic patients, the beneficial effects of glutamine on gut mucosa could be partly due to a stimulation of protein synthesis. The fractional synthesis rate (FSR) of gut mucosal protein was measured in four groups of healthy volunteers treated with glucocorticoids for 2 days. Two groups were studied in the postabsorptive state while receiving glutamine or a nitrogen equivalent (control) and two groups in the fed state with or without glutamine, using a 5-h intravenous infusion of [(13)C]leucine, [(2)H(5)]phenylalanine, and cortisone. After nutrient and tracer infusion, duodenal biopsies were taken. In the postabsorptive state, FSR of gut mucosal protein were 87 and 76%/day in the control group and 130% (P = 0.058 vs. control) and 104% (P = 0.17 vs. control)/day in the glutamine group, with leucine and phenylalanine as tracers, respectively. During feeding, FSR did not increase and no significant difference was observed between glutamine and control groups. Overall, FSR of the four groups were two- to threefold higher than those obtained previously in healthy humans, suggesting that glucocorticoids may increase gut mucosal protein synthesis. However, in this situation, a moderate enteral glutamine supply failed to demonstrate a significant effect on gut mucosal protein synthesis in the postabsorptive state and during feeding.

Double-blind randomized controlled trial of glutamine-enriched polymeric diet in the treatment of active Crohn's disease

BACKGROUND

Glutamine is traditionally considered a nonessential amino acid but may be conditionally essential in patients with catabolic conditions. Glutamine-supplemented foods in these patients have been shown to prevent deterioration of gut permeability, protect against the development of intestinal mucosal atrophy, and improve nitrogen balance. Animal models of inflammatory bowel disease suggest that glutamine-enriched enteral diets may lead to less severe intestinal damage, less weight loss, improved nitrogen balance, and reduced disease activity. The purpose of the current study was to compare the efficacy of a glutamine-enriched polymeric diet with a standard low-glutamine polymeric diet in the treatment of active Crohn's disease.

METHODS

Eighteen children with active Crohn's disease were randomly assigned to receive a 4-week course of either a standard polymeric diet with a low glutamine content (4% of amino acid composition; group S) or a glutamine-enriched polymeric diet (42% of amino acid composition; Group G). The two diets were isocaloric and isonitrogenous with an identical essential amino acid profile. Remission rates were analysed on an intent-to-treat basis. Changes in clinical and laboratory parameters of disease activity were also compared after 4 weeks of nutritional treatment.

RESULTS

Two of the children, both in group G, were withdrawn from the trial because of nontolerance of the diet. There was no difference between the two groups in proportion of patients achieving remission (intent-to-treat basis): 5 (55.5%) of 9 in group S versus 4 (44.4%) of 9 in group G (p = 0.5). Improvement in mean paediatric Crohn's disease activity index (PCDAI) was significantly more in group S (p = 0.002) but changes in orosomucoid level, platelet count, and weight were not different between the groups.

CONCLUSIONS

The findings suggest that a glutamine-enriched polymeric diet offers no advantage over a standard low-glutamine polymeric diet in the treatment of active Crohn's disease. Rather, it appears to be less effective in improving PCDAI. The reported beneficial effects of glutamine seen in many catabolic states must be viewed with caution when extrapolating to the management of Crohn's disease.

Luminal amino acids acutely decrease intestinal mucosal protein synthesis and protease mRNA in piglets

Because parenteral feeding is associated with negative N balance and reduced rates of protein synthesis in intestinal mucosa, we hypothesized that luminal exposure to specific amino acids or energy fuels would stimulate intestinal protein synthesis. We studied the acute effects of luminal nutrients on mucosal protein synthesis in the absence of systemic influences. Multiple jejunal segments constructed in piglets deprived of food overnight (n = 6) were randomly assigned to luminal perfusion with saline, 30 mmol/L amino acid mixture with or without 50 mmol/L glucose, or 30 mmol/L glutamine for 90 min. Protein synthesis was then measured by luminal perfusion with L-[2,6-(3)H]-phenylalanine. Energy substrates (glucose, short-chain fatty acids or beta-hydroxybutyrate) had no effect on mucosal protein synthesis. Relative to saline, a 30 mmol/L amino acid mixture or 30 mmol/L glutamine suppressed mucosal protein synthesis by 20-25% (P < 0.05). On the basis of these surprising results, we speculated that a coordinate reduction of proteolytic processes would be required to maintain positive intestinal N balance. Although intestinal protein catabolism cannot be assessed directly, the 30 mmol/L amino acid mixture acutely suppressed mucosal levels of mRNA encoding ubiquitin, 14-kDa ubiquitin conjugating enzyme and the C9 subunit of the proteasome by 20-30% (P < 0.05), demonstrating the sensitivity of components of the ATP-ubiquitin proteolytic pathway to acute regulation by nutrients. The suppression of protein synthesis by luminal amino acids in the absorptive state might lower intestinal utilization of amino acids to ensure efficient allocation of absorbed nutrients to nonintestinal tissues.

Glutamine for the gut: mystical properties or an ordinary amino acid?

Glutamine is a nonessential amino acid that can be synthesized from glutamate and glutamic acid by glutamine synthetase. It is the preferred fuel for the small intestine in the rat. Results from animal studies suggest that both glutamine-supplemented parenteral nutrition and enteral diets may prevent bacterial translocation. This effect may be modulated through the preservation and augmentation of small bowel villus morphology, intestinal permeability, and intestinal immune function. The existing data from studies with humans are less compelling. What, if any, intestinal deficits actually occur during provision of exclusive parenteral nutrition remains unclear. Furthermore, the clinical significance of these changes is largely undefined. Nevertheless, glutamine and glutamine supplementation appear to be important for the normal maintenance of intestinal morphology and function, intestinal adaptation following resection, and prevention of clinical infection related to bacterial translocation. The existing data on the use of parenteral and enteral glutamine for preservation of intestinal morphology and function and prevention of bacterial translocation in humans are reviewed in this article. Pertinent animal data are also described.

Glutamine supplementation in low-birth-weight infants: mechanisms of action

Very low-birth-weight infants have minimal endogenous nutritional reserves and are at high risk for stresses that induce further breakdown of these diminished reserves. They frequently receive very little glutamine because enteral feedings are often delayed and glutamine is not included in parenteral nutrition. Here we describe studies of glutamine supplementation in very low-birth-weight infants and discuss potential mechanisms for the beneficial effects.

Effect of intravenous glutamine on duodenal mucosa protein synthesis in healthy growing dogs

To determine whether glutamine acutely stimulates protein synthesis in the duodenal mucosa, five healthy growing dogs underwent endoscopic biopsies of duodenal mucosa at the end of three 4-h primed, continuous intravenous infusions of L-[1-13C]leucine on three separate days, while receiving intravenous infusion of 1) saline, 2) L-glutamine (800 micromol. kg-1. h-1), and 3) isonitrogenous amounts of glycine. The three infusions were performed after 24 h of fasting, a week apart from each other and in a randomized order. Glutamine infusion induced a doubling in plasma glutamine level, and glycine caused a >10-fold rise in plasma glycine level. During intravenous infusions of [13C]leucine, the plasma leucine labeling attained a plateau value between 3.22 and 3.68 mole % excess (MPE) and [13C]ketoisocaproate ([13C]KIC) of 2.91-2. 84 MPE; there were no significant differences between glutamine, glycine, and saline infusion days. Plasma leucine appearance rate was 354 +/- 33 (SE), 414 +/- 28, and 351 +/- 35 micromol. kg-1. h-1 (not significant) during glycine, saline, and glutamine infusion, respectively. The fractional synthetic rate (FSR) of duodenal mucosa protein was calculated from the rise in protein-bound [13C]leucine enrichment in the biopsy sample, divided by time and with either plasma [13C]KIC or tissue free [13C]leucine as precursor pool enrichment. Regardless of the precursor pool used in calculations, duodenal protein FSR failed to rise significantly during glutamine infusion (65 +/- 11%/day) compared either with saline (84 +/- 18%/day) or glycine infusion days (80 +/- 15%/day). We conclude that 1) plasma [13C]KIC and tissue free [13C]leucine can be used interchangeably as precursor pools to calculate gut protein FSR; and 2) short intravenous infusion of glutamine does not acutely stimulate duodenal protein synthesis in well-nourished, growing dogs.

The role of glutaminase in the small intestine

Glutaminase is the enzyme which hydrolyses glutamine, the main respiratory fuel of the intestine, to yield glutamate and ammonia. Glutaminase has a central role in intestinal metabolism: the products of the reaction catalyzed by glutaminase can be transaminated, catabolized to yield energy or used for the biosynthesis of pyrimidine nucleotides. Experimental treatments which deprive the intestine of glutamine induce intestinal atrophy. In this review, attention is paid to the role of glutaminase in intestinal metabolism. Background information on the structure, kinetics and distribution of glutaminase precede a discussion of the metabolism of glutamine within the intestine. In closing, we review the factors known to regulate glutaminase activity and emphasise that the regulation of glutaminase within the intestine is poorly understood.

A comparison of parenteral and enteral feeding in neonatal piglets, including an assessment of the utilization of a glutamine-rich, pediatric elemental diet

BACKGROUND

The amino acid requirement profile for infants is different than that for adults and needs to be established; this profile also is different for infants receiving total parenteral nutrition. We used the neonatal piglet as a model for the infant to address (1) the metabolic and physiologic changes due to route of feeding and (2) the adequacy of the amino acid pattern in a pediatric elemental diet.

METHODS

Diets differed only in their amino acid pattern (modified human milk [MHM] and a commercial pediatric elemental diet [PED]) and were fed continuously for 8 days. Control piglets were fed MHM diet via gastric catheters (IG) and were compared with pigs fed MHM diet via venous catheters (IV) or to pigs IG-fed PED.

RESULTS

MHM-IV piglets experienced enlarged livers and gut atrophy, and lower nitrogen retention and body protein content. Higher glutamine (and lower glutamate) in PED-IG, compared with MHM-IG, produced no apparent advantage with respect to gut growth or histology. Proline, histidine, and lysine may have been limiting, and isoleucine and valine excessive, in the PED-IG diet as indicated by plasma concentrations, compared with sow-fed piglets; however, imbalances in the amino acid profile were not excessive because nitrogen retention was not different between MHM-IG or PED-IG pigs.

CONCLUSIONS

Therefore, the amino acid profile of MHM needs to be modified to improve nitrogen retention during parenteral feeding and the profile of oral PED could be improved to normalize plasma amino acid concentrations.

The role of enterocytes in gut dysfunction

Stem cells in the intestinal epithelium give rise to enterocytes, goblet cells, enteroendocrine cells, and Paneth cells. Each of these cell lines plays a role in cytoprotection of the intestinal mucosa. In particular, it has been demonstrated that mature enterocytes can act as antigen presenting cells. Parenteral and enteral nutrition are used to nourish critically ill patients. However, these regimens are unfortunately associated with gut atrophy. Glutamine, the preferred intestinal nutrient, reverses this gut atrophy and plays a key role in maintaining the barrier function of the gut. Specific nutrients (putrescine, spermidine, spermine) have been used to modulate intestinal adaption. In addition, ornithine has been shown to act as a regulator of intestinal adaption. In this review, we discuss the relationship between the biology of enterocytes and failure of the gut barrier.

Short bowel syndrome

Short bowel syndrome has significant morbidity and is potentially lethal especially when intestinal loss is extensive. The pathophysiology of short bowel syndrome, its aetiology, prognosis and our understanding of the mechanisms of adaptation are reviewed. Management by a multi-disciplinary nutritional care team is advocated and should be directed to the maintenance of growth and development, the promotion of intestinal adaptation, the prevention of complications and the establishment of enteral nutrition. The choice of enteral feed, the role of drugs and the use of pro-adaptive nutrients and agents are discussed. Complications including cholestasis and catheter related sepsis are outlined with strategies to reduce them. Finally the roles of secondary surgical interventions including transplantation are discussed.

The effect of minimum luminal nutrition on mucosal cellularity and immunity of the gut

Many catabolic patients can only consume small volumes of enteral nutrients. The aim of this study was to evaluate markers of cellularity and immunity in the small intestine of rats randomized to receive 6 days of parenteral nutrition, 25% enteral and 75% parenteral nutrition (i.e. minimum luminal nutrition) or enteral nutrition. The same glutamine-enriched solution was used for both parenteral and enteral nutrition. Enteral nutrition was associated with the least amount of jejunal atrophy (P<0.01), with the results from the minimum luminal nutrition group approximating those of the parenteral nutrition group. Parenteral nutrition was associated with the greatest number of CD2+ cells (P< 0.05) and the lowest CD4/CD8 cell ratio (P< 0.01) in the jejunal mucosa. In essence, we failed to demonstrate that there are any appreciable benefits associated with the enteral consumption of 25% of a nutrient load.

Randomised trial of glutamine-enriched enteral nutrition on infectious morbidity in patients with multiple trauma

BACKGROUND

Infections are an important cause of morbidity and mortality in patients with multiple trauma. Studies in both animals and human beings have suggested that glutamine-enriched nutrition decreases the number of infections.

METHODS

Patients with multiple trauma with an expected survival of more than 48 h, and who had an Injury Severity Score of 20 or more, were randomly allocated glutamine supplemented enteral nutrition or a balanced, isonitrogenous, isocaloric enteral-feeding regimen along with usual care. Each patient was assessed every 8 h for infection, the primary endpoint. Data were analysed both per protocol, which included enteral feeding for at least 5 days, and by intention to treat.

FINDINGS

72 patients were enrolled and 60 received enteral feeding (29 glutamine-supplemented) for at least 5 days. Five (17%) of 29 patients in the glutamine-supplemented group had pneumonia compared with 14 (45%) of 31 patients in the control group (p<0.02). Bacteraemia occurred in two (7%) patients in glutamine group and 13 (42%) in the control group (p<0.005). One patient in the glutamine group had sepsis compared with eight (26%) patients in the control group (p<0.02).

INTERPRETATION

There was a low frequency of pneumonia, sepsis, and bacteraemia in patients with multiple trauma who received glutamine-supplemented enteral nutrition. Larger studies are needed to investigate whether glutamine-supplemented enteral nutrition reduces mortality.

Parenteral glutamine infusion alters insulin-mediated glucose metabolism

BACKGROUND

Glutamine is a conditionally essential amino acid that is critical for many basic cellular processes. Its supplementation has been found to be beneficial during several critical illnesses. This study examines the effects of increased glutamine availability on insulin-mediated glucose homeostasis in vivo in multicatheterized conscious canines (n = 5).

METHODS

Two weeks before the study, catheters were placed in the femoral artery and the portal, hepatic, femoral, and renal veins for blood sampling and in the splenic vein for intraportal infusion of insulin and glucagon. Doppler probes were placed to measure blood flow. The metabolic study consisted of equilibration, basal, and experimental periods during which [3-3H]glucose was infused to measure glucose kinetics. During the 5-hour experimental period, a hyperinsulinemic-euglycemic clamp was performed by infusing somatostatin, basal glucagon, fivefold basal insulin, and glucose to maintain euglycemia. The experimental period was divided evenly into two subperiods performed in random order: (1) i.v. glutamine infusion (0.72 mmol kg(-1) h(-1)) and (2) i.v. saline infusion.

RESULTS

With glutamine, the glucose required to maintain euglycemia was increased 46% over saline (6.8 +/- 1.0 to 9.9 +/- 1.7 mg kg(-1) min(-1). In addition, whole-body glucose production and utilization were increased by 1.4 and 4.6 mg kg(-1) min(-1), respectively. Finally, the increase in whole-body glucose utilization was manifested by increased hepatic and hindlimb glucose utilization.

CONCLUSIONS

Increased glutamine availability blunted insulin's action on glucose production and enhanced insulin-mediated glucose utilization with the changes in utilization being threefold greater than the changes in production. Thus parenteral glutamine has potential benefit as a nutrient adjuvant during clinical situations associated with insulin resistance.

Glutamine reduces heat shock-induced cell death in rat intestinal epithelial cells

Glutamine supplementation is beneficial for preventing intestinal atrophy and maintaining mucosal functions in metabolically stressed patients. The mechanisms by which glutamine prevents mucosal atrophy remain unclear. In particular, the role of glutamine in the survival of cells under stress is unknown. Intestinal epithelial cells (IEC-6) were cultured in media with or without supplementation of L-glutamine. A low concentration of L-glutamine (1.0 mmol/L) was sufficient to minimize the percentage of floating cells under basal conditions. Heat shock at 43 degrees C for 90 min decreased (P < 0. 001) the number of attached cells, while increasing (P < 0.001) the number of floating cells, which is a measurement of the extent of cell death in these cultures. Glutamine enhanced attached cell count and diminished heat shock-induced cell death in a dose-dependent manner. Of note, 2 mmol/L was suboptimal in both respects, thus indicating that heat-shocked cells require higher concentrations of glutamine for optimal cell survival. Maximal effect was achieved with 8 mmol/L glutamine, which increased (P < 0.001) cell growth (indicated by the number of attached cells) and diminished (P < 0. 001) cell death (indicated by the number of floating cells). Further increase of L-glutamine concentration to 12 or 20 mmol/L did not provide additional benefit in minimizing cell death. Heat shock protein 70 (hsp 70) mRNA was induced by heat shock only in cultures supplemented with L-glutamine, and the induction was more consistent and greater in cultures containing higher concentrations of glutamine. Thus, glutamine supplementation reduced heat shock-induced cell death. This effect, together with the maintenance of cell growth, may play a key role in the prevention of intestinal mucosal atrophy.

Glutamine metabolism in the gastrointestinal tract of the rat assess by the relative activities of glutaminase (EC 3.5.1.2) and glutamine synthetase (EC 6.3.1.2)

The activities of the two key enzyme involved in glutamine metabolism, glutaminase (EC 3.5.1.2) and glutamine synthetase (EC 6.3.1.2), have been measured in the various tissues of the gastrointestinal (GI) tract of the rat, from the mouth to the rectum. Glutaminase activity was particularly high in the mucosa of the small intestine, where its activity accounted for more than 80% of the total activity of the GI tract. In contrast, the mouth and oesophagus had very low activities, accounting for less than 2% of the total. Glutamine synthetase was mainly confined to the lower part of the stomach, which accounted for almost 90% of the total activity of the GI tract. Activity in the small intestine was very low, accounting for less than 2% of the total, and similarly low levels were found in the mouth and oesophagus. The data provide the most complete information on the distribution of these enzymes in the GI tract of the rat and suggest: (a) that the mucosa of the small intestine has the highest capacity for glutamine breakdown but the lowest capacity for its synthesis, and so requires an external source of this amino acid; (b) that there is little potential for glutamine synthesis or breakdown in the mouth and oesophagus: and (c) that the lower stomach has a substantial capacity to synthesize glutamine, in contrast to the rest of the GI tract. The results of the investigation are relevant to sites of glutamine metabolism in therapeutic studies involving glutamine administration discussed with reference to reports of the effects of glutamine administration on GI tract injury.