The early response of the jejunal brush border glutamine transporter to endotoxemia.

The early effects of endotoxin (4 hr after a single dose of Escherichia coli LPS, 7.5 mg/kg) on L-glutamine (GLN) transport across the jejunal brush border of rats were studied. Jejunal brush border membrane vesicles (BBMVs) were prepared by a Mg2+ aggregation/differential centrifugation technique. Vesicle purity and integrity were confirmed by a 15-fold enrichment of brush border marker enzymes, osmotic activity, transport overshoots in the presence of sodium, and similar 1- and 2-hr equilibrium values. L-[3H]GLN transport in jejunal BBMVs was measured by a millipore filtration technique. Na(+)-dependent glutamine transport, which accounted for greater than 80% of total transport, was increased twofold in BBMVs from endotoxin-treated rats (67 +/- 5 pmole/mg protein/15 sec vs 38 +/- 3, P less than 0.01). Endotoxin treatment did not alter the activity of the Na(+)-independent carrier. Simultaneously, intestinal extraction of glutamine from the bloodstream fell by 56% (15.1 +/- 2.3% in controls vs 6.6 +/- 1.3% in endotoxin-treated rats, P less than 0.01). This reduction in the uptake of circulating glutamine could not be accounted for by a fall in the arterial concentration. Thus, soon after endotoxemia brush border glutamine uptake is increased while consumption of glutamine across the basolateral membrane is decreased. This increased uptake may support protein synthesis and may provide a biochemical rationale for the use of early enteral nutrition after the onset of critical illness.     

Endotoxin and renal glutamine metabolism.

The effect of endotoxin on renal glutamine metabolism and ammoniagenesis was investigated in vivo in the rat to gain further insight into the altered glutamine flow that characterizes critical illness. Studies were done 15 hours following a single dose of Escherichia coli lipopolysaccharide (10 mg/kg). Renal blood flow and arterial glutamine concentration were similar in control and study rats, but the kidney switched from an organ of slight glutamine uptake in controls (129 +/- 52 nmol/100 g of body weight per minute) to net release in the endotoxin-treated animals (-273 +/- 170 nmol/100 g of body weight per minute). Simultaneously, the specific activity of renal glutamine synthetase increased by almost 50% (374 +/- 40 nmol/mg of protein per hour in rats given endotoxin vs 253 +/- 12 nmol/mg of protein per hour in controls), while glutaminase was unchanged. Urinary ammonia excretion was reduced by 35% in the endotoxin-treated animals (47 +/- 6 mumol/12 h in endotoxin-treated animals vs 70 +/- 8 mumol/12 h in controls) despite a 10% fall in the arterial bicarbonate value. Endotoxin alters the net flux of glutamine across the kidney which appears to be partially regulated enzymatically. This may impair the kidneys' ability to maintain acid/base homeostasis.     

Effects of tumor necrosis factor on system ASC-mediated glutamine transport by human fibroblasts.

The effects of tumor necrosis factor-alpha (TNF) on glutamine GLN transport by cultured human fibroblasts were studied. Uptake of 3H-GLN was assayed in both the presence and absence of sodium in order to differentiate Na(+)-dependent and Na(+)-independent transport systems. GLN transport was linear (r = 0.99) for at least 15 min and occurred predominantly via a single Na(+)-dependent pathway, consistent with System ASC. Incubation of fibroblasts with TNF (1000 units/ml) for 12 hr resulted in a significant decrease in system ASC-mediated glutamine transport activity. TNF did not alter cell morphology or protein content. Kinetic studies indicated that the decrease in carrier-mediated Na(+)-dependent GLN transport was not due to a change in transporter affinity (Km = 117 +/- 23 microM in controls vs 86 +/- 23 microM in TNF, P = NS), but instead to a 45% decrease in maximal transport rate (Vmax = 4088 +/- 354 pmole/mg protein/30 sec in controls vs 2230 +/- 510 in TNF, P less than 0.05). TNF also decreased Na(+)-independent transport by 50% (mean uptake of 50 microM GLN = 94 +/- 13 pmole/mg protein/30 sec in controls vs 46 +/- 6 in TNF, P less than 0.02). In human fibroblasts, the activity of System ASC, which has generally been viewed as a hormonally unresponsive carrier, is decreased by TNF. This impairment in glutamine transport may result in inadequate amounts of intracellular glutamine to support fibroblast metabolism and possibly function.     

The effects of sepsis and endotoxemia on gut glutamine metabolism.

The effects of sepsis on gut glutamine (GLN) metabolism were studied to gain further insight into the regulation of the altered glutamine metabolism that characterizes critical illnesses. Studies were done in laboratory rats and in hospitalized patients. The human studies were done in seven healthy surgical patients (controls) and six septic patients who underwent laparotomy. Radial artery and portal vein samples were obtained during operation and were analyzed for GLN and oxygen content. Despite no reduction in arterial glutamine concentration in the septic patients, gut glutamine extraction was diminished by 75% (12.0% +/- 1.6% in controls vs. 2.8% +/- 0.8% in septic patients, p less than 0.01). Similarly gut oxygen extraction was diminished by nearly 50% in the septic patients (p less than 0.05). To further investigate these abnormalities, endotoxin (10 mg/kg intraperitoneally) or saline (controls) was administered to adult rats 12 hours before cannulation of the carotid artery and portal vein. The arterial GLN concentration was increased by 13% in the endotoxin-treated animals (p less than 0.05) but gut glutamine uptake was diminished by 46% (526 +/- 82 nmol/100 g BW/minute in controls vs. 282 +/- 45 in endotoxin, p less than 0.01). Simultaneously gut glutaminase activity was diminished by 30% (p less than 0.01) and intestinal glutamate release fell by two thirds. Blood cultures were negative in control animals (0 of 20), but were positive in 25% of endotoxemic animals (6 of 24) for gram-negative rods (p = 0.019). Sepsis and endotoxemia impair gut glutamine metabolism. This impairment may be etiologic in the breakdown of the gut mucosal barrier and in the development of bacterial translocation.     

Brush border transport of glutamine and other substrates during sepsis and endotoxemia

The effects of severe infection on luminal transport of amino acids and glucose by the small intestine were investigated. Studies were done in endotoxin-treated rats and in septic patients who underwent resection of otherwise normal small bowel. In rats the kinetics of the brush border glutamine transporter and the glutaminase enzyme were examined. In patients the effects of severe infection on the transport of glutamine, alanine, leucine, and glucose were studied. Transport was measured using small intestinal brush border membrane vesicles that were prepared by Mg++ aggregation/differential centrifugation. Uptake of radiolabeled substrate was measured using a rapid mixing/filtration technique. Vesicles demonstrated 15-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 2-hour equilibrium values. The sodium-dependent pathway accounted for nearly 90% of total carrier-mediated transport. Kinetic studies on rat jejunal glutaminase indicated a decrease in activity as early as 2 hours after endotoxin secondary to a decrease in enzyme affinity for glutamine (Km = 2.23 +/- 0.20 mmol/L [millimolar] in controls versus 4.55 +/- 0.67 in endotoxin, p less than 0.03), rather than a change in Vmax. By 12 hours the decrease in glutaminase activity was due to a decrease in Vmax (222 +/- 36 nmol/mg protein/min in controls versus 96 +/- 16 in endotoxin, p less than 0.03) rather than a significant change in Km. Transport data indicated a decrease in sodium-dependent jejunal glutamine uptake 12 hours after endotoxin secondary to a 35% reduction in maximal transport velocity (Vmax = 325 +/- 12 pmol/mg protein/10 sec in controls versus 214 +/- 8 in endotoxin, p less than 0.0001) with no change in Km (carrier affinity). Sodium-dependent glutamine transport was also decreased in septic patients, both in the jejunum (Vmax for control jejunum = 786 +/- 96 pmol/mg protein/10 sec versus 417 +/- 43 for septic jejunum, p less than 0.01) and in the ileum (Vmax of control ileum = 1126 +/- 66 pmol/mg protein/10 sec versus 415 +/- 24 in septic ileum, p less than 0.001) The rate of jejunal transport of alanine, leucine, and glucose was also decreased in septic patients by 30% to 50% (p less than 0.01). These data suggest that there is a generalized down-regulation of sodium-dependent carrier-mediated substrate transport across the brush border during severe infection, which probably occurs secondary to a decrease in transporter synthesis or an increase in the rate of carrier degradation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cytokine modulation of Na(+)-dependent glutamine transport across the brush border membrane of monolayers of human intestinal Caco-2 cells.

Previous studies have demonstrated that Na(+)-dependent brush border glutamine transport is diminished in septic patients. To examine the potential regulation of this decreased transport by endotoxin, cytokines, or glucocorticoids, the human intestinal Caco-2 cell line was studied in vitro. Na(+)-dependent glutamine transport across the apical brush border membrane was assayed in confluent monolayers of differentiated cells that were 10 days old. Uptake of 50 microM glutamine was determined after a 12-hour incubation with varying doses (10 to 1000 U/mL) of tumor necrosis factor-alpha, interleukin-1, interleukin-6, interferon-gamma, and various combinations of these cytokines. Studies were also done in cells incubated with E. coli endotoxin (1 micrograms/mL) or dexamethasone (1 and 10 microM). Endotoxin, tumor necrosis factor, interleukin-1, and interleukin-6 alone and in combination did not significantly reduce Na(+)-dependent glutamine transport across the brush border of Caco-2 cells. Dexamethasone decreased glutamine transport by 20%, but this decrease was not apparent for 48 hours. Interferon consistently decreased glutamine transport by 30%; this was due to a reduction in carrier maximal transport velocity (3427 +/- 783 pmol/mg protein/minute in controls versus 2279 +/- 411 in interferon, p less than 0.05) rather than a change in Km (276 +/- 29 microM in controls versus 333 +/- 74 in interferon, p = not interferon + dexamethasone + tumor necrosis factor + interleukin-1 resulted in a 38% decrease in transport activity. Cytokines and glucocorticoids may work independently and synergistically in regulating Na(+)-dependent brush border glutamine transport in human intestinal cells. Whether these signal molecules play a central role in the cause of the diminished brush border glutamine transport that occurs in septic patients requires further study.     

Burn injury alters intestinal glutamine transport

Several studies have established that intestinal glutamine (GLN) metabolism is altered during catabolic states. It remains unclear whether these alterations are due to a defect in metabolism or in transport of the amino acid. The present study examines the kinetics of GLN transport across basolateral membrane vesicles (BLMV) of enterocytes obtained from control rats and rats subjected to 20% full-thickness scald burn, 48 hr previously. BLMV were prepared from freshly isolated enterocytes using differential centrifugation with separation on a Percoll density gradient. BLMV were enriched (10- to 12-fold) with Na+-K+-ATPase while markers for brush border membranes were impoverished. Previous studies from our laboratory indicated that, in this preparation, GLN transport is into an osmotically sensitive space, dependent on GLN concentration, linear up to 30 sec, and both temperature and Na+ dependent. Our results indicate that in thermal injury, initial rates of GLN uptake were depressed (y = 3.67 + 0.435X for burned rats vs y = 18.7 + 0.907X for controls, P less than 0.01). Kinetic analysis of GLN uptake showed a marked decrease in transport Vmax (81.8 +/- 15 nmole/mg protein/15 sec for burned rats vs 185 +/- 17 nmole/mg protein/15 sec for controls, P less than 0.001). Transport Km also decreased from 0.25 +/- 0.004 mM for controls to 0.08 +/- 0.03 mM glutamine for burned rats (P less than 0.001). Kinetic studies performed at GLN levels greater than 0.6 mM showed that GLN uptake proceeded by a nonsaturable process in both the control and burned rats. No significant alteration in this nonsaturable component was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective stimulation of brush border glutamine transport in the tumor-bearing rat

Intestinal extraction of circulating glutamine across the basolateral membrane is diminished in the tumor-bearing rat (TBR). This study was designed to investigate the effects of progressive malignant growth on brush border glutamine transport in order to gain further insight into the adaptive/regulatory changes in intestinal glutamine metabolism that occur in the tumor-bearing rat. Fischer 344 rats (225 +/- 5 g) were implanted with fibrosarcoma cells and were studied at various time points after implantation when the tumors comprised 7%, 20%, and 29% of total body weight. Control and tumor-bearing rats were pair-fed throughout the study. Jejunal brush border membrane vesicles (BBMVs) were prepared by magnesium aggregation/differential centrifugation and transport of radioactively labeled L-glutamine, L-leucine, L-alanine, and D-glucose by BBMVs was measured using a Millipore filtration technique. BBMVs were enriched 15-fold in alkaline phosphatase, indicating brush border vesicle purity. Uptake of all substrates occurred into an osmotically active space, exhibited overshoots, and had similar 1-hr equilibrium values. The rate of glutamine uptake by BBMVs from all tumor-bearing rats was significantly greater than controls, regardless of tumor size. The increase in transport activity was not due to a change in carrier affinity but rather to an increase in maximal transport velocity. In rats with small tumors (7% of body weight), the Vmax was 431 +/- 40 pmole/mg protein/10 sec compared to 259 +/- 30 in control animals (P less than 0.01). In marked contrast, the mean transport of alanine was diminished in BBMVs from TBR (31 +/- 3 pmole/mg protein/10 sec in TBR vs 23 +/- 2 in controls, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cytokine modulation of glutamine transport by pulmonary artery endothelial cells.

The effects of tumor necrosis factor and interleukin-1 on sodium-dependent glutamine transport by cultured pulmonary artery endothelial cells (PAECs) were studied. Incubation of PAECs with cytokines (10 to 1000 units/ml) resulted in a significant increase in System ASC-mediated glutamine transport that was dose-dependent, first observable after 8 hours, and maximal after 12 hours of exposure. Kinetic studies indicated that the increase in carrier-mediated activity was not due to a change in Km (transporter affinity) but instead to a 45% to 75% increase in maximal transport rate (Vmax). The cytokine-stimulated increase in glutamine uptake by PAECs was completely blocked by actinomycin D and cycloheximide, indicating that the accelerated glutamine transport was dependent on de novo RNA and protein synthesis, perhaps of the transporter itself. The data indicate that these cytokines accelerate glutamine uptake by PAECs, either directly or indirectly, a response which may be required to support endothelial metabolism, structure, and function during infection and inflammation. The results of this study represent, to our knowledge, the first reports of cytokine-mediated modulation of System ASC activity, a carrier that has historically been unresponsive to hormonal regulation in other tissues.     

Adaptive regulation of alanine transport in hepatic plasma membrane vesicles from the endotoxin-treated rat

The mechanisms by which hepatic alanine consumption is increased during endotoxemia were investigated to gain further insight into the altered amino acid metabolism which characterizes critical illness. Rats were studied 12 hr after receiving endotoxin (ENDO) or saline. Hepatic alanine delivery was determined in vivo and hepatic alanine content was measured. Hepatocyte transport activity was studied by evaluation of [3H]-alanine accumulation in hepatocyte plasma membrane vesicles (HPMVs). Vesicle integrity was demonstrated by electron microscopy and a 14-fold enrichment in 5'-nucleotidase. Endotoxin treatment resulted in a state of hyperalaninemia and a threefold increase in hepatic alanine delivery (2.79 +/- 0.17 mu mole/100 g body weight/min in controls vs 8.13 +/- 0.98 in ENDO animals; P less than 0.001). Data from HPMVs revealed the presence of a high- and low-affinity component of alanine transport. Endotoxin treatment resulted in a 30% decrease in the Vmax of the high-affinity transport component (3355 +/- 177 pmole/mg protein/10 sec in controls vs 2338 +/- 270 in the ENDO group; P less than 0.05). Concomitant with the observed changes in alanine delivery and transport activity, endotoxin treatment resulted in a 56% rise in hepatic alanine content (2.53 +/- 0.29 mu mole/g liver in controls vs 3.95 +/- 0.23 in ENDO; P less than 0.005). These data indicate that the accelerated hepatic alanine consumption which occurs during endotoxemia is primarily the result of increased hepatic substrate delivery. Despite the resultant repression of transport activity, delivery begins to outdistance the metabolic capacity of the hepatocyte to utilize alanine and intracellular alanine levels rise.     

Glutamine metabolism by the endotoxin-injured lung.

The alterations in lung glutamine (GLN) metabolism that occurs in the endotoxin-injured lung were studied in rats and subsequently correlated with flux changes that occur in patients with the adult respiratory distress syndrome (ARDS). Measurements in animals were made at various time-points following the administration of endotoxin, while studies in surgical patients were done in a group of healthy controls, in patients with "early" sepsis who had normal chest x-ray films, and in patients with radiographic and physiologic evidence of ARDS. In healthy control rats, net amounts of GLN are released by the lungs into the systemic circulation. This release rate doubled 30 minutes after intravenous endotoxin (1,580 +/- 320 nmol GLN/100 g BW/min vs. 736 +/- 179 in controls, p less than 0.01) but glutamine synthetase activity was unchanged, suggesting an outpouring of cellular glutamine stores. Two hours after endotoxin treatment, this accelerated fractional release of glutamine by the lungs was no longer detected. By the 12-hour time-point, the lungs reversed to an organ of net glutamine balance (234 +/- 248 nmol/100 g BW/min, p less than 0.05 vs. controls and ENDO30 min) despite a more than two-fold increase in glutamine synthetase activity (p less than 0.01). Simultaneously, lung weights were increased by 21% (p less than 0.01) and histologic examination showed an interstitial infiltrate and pulmonary edema. Similar observations were made in humans; patients with "early" sepsis exhibited a marked increase in lung glutamine release, while patients with ARDS demonstrated glutamine balance across the lungs (4,030 +/- 910 nmol GLN/kg BW/min vs. 637 +/- 496 in ARDS, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

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

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

Effects of enteral supplementation with glutamine granules on intestinal mucosal barrier function in severe burned patients

Glutamine is an important energy source in intestinal mucosa, the small intestine is the major organ of glutamine uptake and metabolism and plays an important role in the maintenance of whole body glutamine homeostasis. The purpose of this clinical study is to observe the protection effects of enteral supplement with glutamine granules on intestinal mucosal barrier function in severe burned patients. Forty-eight severe burn patients (total burn surface area 30-75%, full thickness burn area 20-85%) were randomly divided into two groups: burn control group (B group, 23 patients) and glutamine treated group (Gln group, 25 patients). Glutamine granules 0.5 g/kg were supplied orally for 14 days in Gln group, and the same dosage of placebo were given for 14 days in B group. The plasma level of glutamine, endotoxin and the activity of diamine oxidase (DAO), as well as intestinal mucosal permeability were determined. The results showed that the levels of plasma endotoxin, activity and urinary lactulose and mannitol (L/M) ratio in all patients were significant higher than that of normal control. After taking glutamine granules for 14 days, plasma glutamine concentration was significantly higher in Gln group than that in B group (607.86+/-147.25 microM/l versus 447.63 +/- 132.28 microM/l, P < 0.01). On the other hand, the levels of plasma DAO activity and urinary L/M ratio in Gln group were lower than those in B group. In addition, the wound healing was better and hospital stay days were reduced in the Gln group (46.59 +/- 12.98 days versus 55.68 +/- 17.36 days, P < 0.05). These results indicated that glutamine granules taken orally could abate the degree of intestine injury, lessen intestinal mucosal permeability, ameliorate wound healing and reduce hospital stay.     

Mechanisms of increased hepatic glutamine uptake in the endotoxin-treated rat.

The mechanisms underlying the accelerated hepatic consumption of glutamine that occurs during endotoxemia were investigated in rats 12 hr after treatment with Escherichia coli lipopolysaccharide. Hepatic glutamine delivery and consumption were calculated from measurements of hepatic blood flow and blood glutamine levels. Hepatic glutaminase activity and glutamine and glutamate content were determined. Hepatocyte plasma membrane transport activity was evaluated employing isolated hepatic plasma membrane vesicles (HPMVs). Endotoxin treatment resulted in an 11-fold increase in hepatic glutamine consumption and a 2-fold increase in the delivered load of glutamine to the liver. Hepatic glutamate content doubled while glutamine content was unaffected, not withstanding a decrease in the specific activity of glutaminase. Studies employing HPMVs demonstrated that hepatic plasma membrane transport activity was unaffected by endotoxin treatment. The enhanced hepatic consumption of glutamine secondary to endotoxemia appears to be the result of both a mass-action effect and the concurrent activation of intracellular metabolism. Responses at the level of plasma membrane transport do not appear to play an active role in mediating this enhanced hepatic uptake.     

Disposition of total and unbound prednisolone in renal transplant patients receiving anticonvulsants

Kidney transplant patients receiving phenytoin or phenobarbital may have decreased graft survival. These drugs have been shown to enhance the metabolism of glucocorticoids. We determined the disposition of total and unbound prednisolone in six stable kidney transplant patients receiving prednisone for immunosuppression and phenytoin or phenobarbital for a seizure disorder. Six similar patients not on anticonvulsants served as controls. A single intravenous dose of prednisolone was administered, and plasma samples were analyzed for prednisolone using a high-performance liquid chromatographic assay. Equilibrium dialysis was used to determine unbound prednisolone concentrations. Pharmacokinetic analysis showed that the half-life of prednisolone was shorter in the anticonvulsant group compared to the controls, based on both total (2.3 +/- 0.4 vs. 3.4 +/- 0.2 hr (SD), P less than 0.01) and unbound (1.7 +/- 0.3 vs. 2.4 +/- 0.2 hr, P less than 0.01) concentrations. Total drug clearance was 10.4 +/- 2.8 liters/hr (0.171 +/- 0.087 liters/hr X kg) in the anticonvulsant group versus 7.2 +/- 1.2 liters/hr (0.100 +/- 0.014 liters/hr X kg) in the controls (P less than 0.05). Unbound prednisolone clearance was 57.2 +/- 12.1 versus 46.4 +/- 8.7 liters/hr (P greater than 0.05) and for weight-corrected estimates 0.886 +/- 0.224 liters/hr X kg versus 0.644 +/- 0.115 liters/hr X kg (P less than 0.05) in the two groups, respectively. Thus, the disposition of prednisolone is altered by anticonvulsants in kidney transplant patients and may require dose alteration.     

Postoperative alterations in interorgan glutamine exchange in enterectomized dogs

The effect of enterectomy on postoperative visceral organ glutamine exchange was studied in order to gain further understanding of the role of the intestinal tract in the altered glutamine metabolism that occurs following catabolic illness. In addition to studying glutamine, which transports 1/3 of whole blood amino acid nitrogen, we determined the fluxes of glutamate and alanine across the gastrointestinal tract, liver, and kidneys in 18 postoperative dogs. Arterial glutamine and glutamate were significantly higher in enterectomized animals than in controls. With enterectomy the gut became an organ of glutamine balance while in control dogs the GI tract consumed glutamine (0.11 +/- 0.04 vs 1.67 +/- 0.14 mumole/kg X min, P less than 0.001). The gut switched from an organ of glutamate release to one of net glutamate uptake following enterectomy and intestinal alanine release simultaneously fell by 50%. Simultaneously, the liver reduced its uptake of alanine and became an organ of glutamine release. Renal glutamine consumption was also diminished in enterectomy animals. The interorgan exchange of glutamine and other amino acids is altered by enterectomy. The increase in circulating glutamine levels in enterectomized animals suggests that the accelerated intestinal glutamine consumption that characterizes catabolic illnesses contributes to the low glutamine levels in these stress states. In addition, it becomes apparent that the gut is an important supplier of alanine to the liver, which supports gluconeogenesis. Metabolic adaptation and cooperation between organs is essential during organ absence or dysfunction if the organism is to survive critical illness.