Arginine-supplemented diets improve survival in gut-derived sepsis and peritonitis by modulating bacterial clearance. The role of nitric oxide

Nitroglycerin attenuates the bowel damage of necrotizing enterocolitis in a rabbit model

Endogenous enteric nitric oxide has multiple functions. Enteric nitric oxide may be diminished in the premature infant and may therefore predispose the immature intestine to injury. The aim of this study was to determine if the infusion of a nitric oxide donor (nitroglycerin) would attenuate intestinal damage in a rabbit model of necrotizing enterocolitis. Transmural injection of rabbit intestinal loops with an acidified solution of casein and calcium gluconate simulates certain aspects of necrotizing enterocolitis. After injection of acidified casein solution into rabbit intestinal loops, twelve rabbits were randomly divided into two groups: six received maintenance fluids only and six received maintenance fluids and a nitroglycerin infusion adjusted to maintain mean arterial pressure 10 mm Hg below baseline (range, 2 to 12 micrograms/kg/min). After 3 hours, the rabbits were killed, and the intestinal tissue graded histologically. Intestinal damage in the nitroglycerin-treated rabbits was significantly less than that of untreated controls (mean histological grade of 0.39 v 1.48, P < .001). In this rabbit model of necrotizing enterocolitis, infusion of the nitric oxide donor nitroglycerin significantly attenuates intestinal damage. We speculate that enteric nitric oxide deficiency, as may exist in the preterm infant, predisposes the intestine to necrotizing enterocolitis.

Nitric oxide protects cultured rat hepatocytes from tumor necrosis factor-alpha-induced apoptosis by inducing heat shock protein 70 expression

Nitric oxide (NO) and tumor necrosis factor-alpha (TNFalpha) play important roles in the pathogenesis of liver disease during acute inflammation. The present study was designed to elucidate the effect of NO pre-exposure on TNFalpha-induced hepatotoxicity. Pretreatment of primary cultures of rat hepatocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced the expression of heat shock protein 70 (HSP70) mRNA and protein, which was associated with thermotolerance and cytoprotection from TNFalpha+actinomycin D-induced hepatotoxicity and apoptosis. SNAP transiently changed the intracellular redox state by inducing glutathione (GSH) oxidation associated with the formation of S-nitrosoglutathione (GSNO). HSP70 mRNA was also induced by the GSH-oxidizing agent diamide and the GSH-conjugating agent N-ethylmaleimide, suggesting that NO induces HSP70 expression through GSH oxidation. The protective effect of SNAP pretreatment on TNFalpha-induced apoptosis correlated with the level of HSP70 expression. SNAP pretreatment inhibited reactive oxygen intermediate generation and lipid peroxidation effects that were reversed by blocking HSP70 expression using an antisense oligonucleotide to HSP70. Finally, endogenous NO formation, induced in hepatocytes stimulated with interferon-gamma and interleukin-1beta, led to the formation of GSNO and GSSG, induced HSP70, and attenuated TNFalpha-mediated cytotoxicity. These findings demonstrated that NO can induce resistance to TNFalpha-induced hepatotoxicity, possibly through the stimulation of HSP70 expression.

Enteral or parenteral nutrition? Pro-enteral

There is a convincing evidence for the superiority of enteral nutrition as compared with parenteral In critically ill and injured patients. The general objectives of providing nutritional support in the critically ill is to persevere body functions that are functioning normally and to facilitate recovery of those that are failing. The specific objective for enteral nutrition is, however, preservation and restoration of the gastrointestinal structure and function. Today, early enteral nutrition is an integral part of the acute management of critically ill patients. It is no longer a therapy which can be started "if" necessary just to prevent malnutrition. Early enteral nutrition can be successfully carried out in virtually all critically ill patients also after major abdominal surgery and in acute pancreatitis. There are very few contraindications for using enteral nutrition and severe complications are rare. Parenteral nutrition, on the other hand, is associated with increased incidence of infectious complications and is rarely indicated in critically ill patients.

Prophylactic administration of L-arginine improves the intestinal barrier function after mesenteric ischaemia

BACKGROUND

Ischaemia/reperfusion (I/R) of the intestine causes mucosal injury associated with a high death rate in rats.

AIM

To investigate whether nitric oxide (NO) might be implicated in the recovery of the intestinal mucosa after ischaemic insult.

METHODS

Wistar rats were subjected to mesenteric artery occlusion for 90 minutes. The animals were given either L-arginine, the substrate of NO synthase, or molsidomine, a NO donor. The controls received casein hydrolysate. The compounds were administered by gavage 19, 16, and 1.5 hours before ischaemia. Mucosal barrier permeability and cGMP content were determined 24 hours after ischaemia.

RESULTS

Survival after I/R was 50% in the control group. Animals treated with L-arginine or molsidomine exhibited a higher survival rate (70% and 83% respectively). Mucosal barrier permeability was decreased in rats receiving L-arginine or molsidomine compared with controls (4.0 (0.9) and 2.6 (0.6) v 11.2 (1.6) 14C-PEG pmol/segment, p < 0.05). Increased cGMP content was seen in the mucosa of the L-arginine group.

CONCLUSION

The findings suggest that pretreatment with L-arginine or molsidomine ameliorates survival after intestinal I/R and improves mucosal barrier function.

Oral arginine supplementation in acute liver injury

Acute liver failure is accompanied by a high rate of bacterial and septic complications. Arginine has a potent effect on the immune system and modulates bacterial clearance in septic models. We studied the effect of oral arginine supplementation on the extent of liver injury and the associated bacterial translocation in an acute liver injury model in rats. Sprague-Dawley rats were divided into normal, liver injury, and arginine supplemented groups. In the arginine group, 2% arginine was supplemented daily through a nasogastric tube for 8 d. Acute liver injury was induced on the eighth day by intraperitoneal injection of D-galactosamine (1.1 g/kg body wt). Samples were collected 24 h after the liver injury. In the arginine-supplemented group, alkaline phosphatase, bilirubin, and aspartate aminotransferase were reduced significantly compared with the acute liver injury control group. The results of bacterial translocation in the arginine-supplemented group showed a significantly reduced number of translocated bacteria to the liver and mesenteric lymph nodes than occurred in the acute liver injury group. The histological study of the liver in arginine-supplemented group showed scattered areas of hepatocellular necrosis and inflammatory cell infiltration, and in the acute liver injury group there were more and widespread hepatocellular necrosis and inflammatory cell infiltration. Oral supplementation of arginine in an acute liver injury model improves significantly the state of the liver injury and reduces bacterial translocation to the liver and mesenteric lymph nodes.

Effect of arginine on gastrointestinal immunity during total parenteral nutrition

It has been well recognized that the prolonged use of total parenteral nutrition (TPN) leads to intestinal immunodeficiency and bacterial translocation (BT). Arginine (ARG) is known to have immunostimulatory effects. But its effects on gut immunity are unknown. This experiment was designed to evaluate the effects of arginine on gut immunity during TPN. Male Sprague Dowley rats were randomized to three groups: group I (chow) was fed rat chow and water ad libitum, group II (TPN) received a standard formula of TPN and group III (TPN-ARG) received the same formula of TPN as group II with the amino acid composition containing 0.5% arginine. With the duration of TPN, the rates of BT increased and interleukin 2 (IL-2) production decreased in TPN group. The results in TPN-ARG group were partly reversed. When TPN was administered for 2 weeks, the rate of BT decreased significantly (P < 0.05) and IL-2 production increased markedly (P < 0.01) in the TPN-ARG group compared with those in the TPN group. Our results suggest that arginine can decrease BT and increase IL-2 production in rats during prolonged TPN.

Inhibition of the biologic activity of tumor necrosis factor maintains vascular endothelial cell function during hyperdynamic sepsis

BACKGROUND AND OBJECTIVE

Although vascular endothelial cell function (i.e., the release of endothelium-derived nitric oxide) decreases and plasma tumor necrosis factor (TNF) increases during sepsis, it is not known whether the elevated TNF is responsible for the depression of endothelial cell function under such conditions. The aim of this study, therefore, was to determine if inhibition of TNF biologic activity by polyethylene glycol dimerized conjugate of the recombinant human form of the p55 soluble TNF receptor (PEG-(rsTNF-R1)2) maintains endothelial function during sepsis.

DESIGN, MATERIALS AND METHODS

Rats were subjected to sepsis by cecal ligation and puncture (CLP). Immediately before the onset of sepsis, 600 microgram/rat PEG-(rsTNF-R1)2 or an equal volume of saline was infused intravenously. At 10 hours after CLP (i.e., hyperdynamic sepsis), the thoracic aorta was isolated, cut into rings, and placed in organ chambers. Dose responses for an endothelium-dependent vasodilator, acetylcholine (ACh), and an endothelium-independent vasodilator, nitroglycerine (NTG), were determined. Endothelial cell structure was examined by transmission electron microscopy.

RESULTS

Endothelium-dependent vascular relaxation was depressed at 10 hours after the onset of sepsis. Administration of PEG-(rsTNF-R1)2 before CLP, however, maintained ACh-induced relaxation. In contrast, no significant difference in NTG-induced relaxation was seen, irrespective of administration of PEG-(rsTNF-R1)2 Furthermore, the deterioration in endothelial structure during sepsis was prevented by PEG-(rsTNF-R1)2 pretreatment.

CONCLUSION

Since administration of PEG-(rsTNF-R1)2 maintains vascular endothelial cell structure and function, it can be concluded that TNF plays a pivotal role in producing endothelial dysfunction during sepsis. Thus, pharmacologic agents that inhibit TNF biologic activity and/or its production may be useful for protecting endothelial cells during sepsis.

Experimental gut-derived endotoxaemia and bacteraemia are reduced by systemic administration of monoclonal anti-LPS antibodies

This study aimed to investigate the effects and mechanisms of action of systemic administration of monoclonal antibodies, anti-endotoxin (HA-1A), in an animal model of gut-origin sepsis. In the first experiment, Balb/c mice were transfused with allogeneic blood (C3H/HeJ mice). Five days post-transfusion the animals were gavaged with 1 x 10(9) Escherichia coli and randomized into three groups (n = 22 each) to receive a sham burn (SB group) or a 20 per cent TBSA thermal injury, immediately followed by the systemic administration of monoclonal antibodies (3 mg/kg) (HA-1A group) or aliquots of sterile saline (Control group). The animal survival rate was observed for 10 days postburn. In the second experiment transfusion and burn injury were reproduced but the mice (n = 8/group) were gavaged with 10(9) E.coli labelled with 111indium oxine. Four hours after the burn the mesenteric lymph nodes, liver, lungs and blood were harvested to determine plasma endotoxin levels and the magnitude of translocation of labelled bacteria measured by the residual radioactivity in the organs. Circulating endotoxin levels were determined by limulus assay. The mortality rate of the HA-1A group (9 per cent) was similar to the SB group (0 per cent) and significantly lower than the control group (59 per cent) (P < 0.05). Both plasma endotoxin levels and degree of bacterial translocation in all extraintestinal tissues were significantly lower (by approximately 50 per cent) in the HA-1A group than in the control group (P < 0.05). Systemic administration of HA-1A exerts a beneficial effect by reducing the circulating levels of endotoxin and by increasing the gut barrier function to translocating microorganisms.

Nitrergic innervation and relaxant response of rectal circular smooth muscle

PURPOSE

This study was designed to investigate whether nitric oxide mediates inhibitory innervation in human rectal circular smooth muscle.

METHODS

Tissue was obtained from the midrectum of patients undergoing anterior resection for carcinoma. Adjacent strips of circular muscle were dissected and mounted in superfusion organ baths for isometric tension recording and initially loaded with 1 g of weight. Strips were continuously bathed with standard Krebs solution (37 degrees C, bubbled with 97 percent O2/3 percent CO2) containing 3 X X 10(-6) M guanethidine and 3 X 10(-6) M atropine sulfate to block adrenergic and muscarinic cholinergic neurotransmission. After equilibration, strips had no intrinsic tone, and reproducible and stable tension was, therefore, induced by the addition of 3 X 10 M histamine for five-minute "test" periods, during which electrical field stimulation (EFS) and additional drugs were applied.

RESULTS

EFS elicited frequency-dependent, neurogenic (tetrodotoxin-sensitive) relaxations of precontracted strips. Addition of N-w-nitro-L-arginine, a powerful competitive inhibitor of nitric oxide synthase, reduced the relaxant response to EFS in a dose-dependent fashion, and effect reversed by addition of s X 10(-4) M L-arginine but not by D-arginine. Addition of exogenous nitric oxide (sodium nitroprusside) mimicked the relaxant response induced by EFT.

CONCLUSIONS

Human rectal circular smooth muscle receives an intrinsic inhibitory innervation mediated by nitric oxide. The presennce of a residual response following blockade of the enzyme nitric oxide synthase suggests the involvement of additional neurotransmitters.

The nutrition management of the patient with acute renal failure

The clinical status of patients with acute renal failure (ARF) varies greatly. Some individuals have only mild or moderate ARF or may have only mild perturbations of their metabolic status. Other patients exhibit a severe reduction in renal function with oliguria or anuria. Depending upon their comorbid conditions, ARF patients may be among the most hypercatabolic patients in the hospital. Clinical trials have not clearly shown a beneficial effect of nutrition support on morbidity or mortality in patients with ARF, although limitations in sample size and experimental design and inclusion of patients with widely disparate clinical conditions may have contributed to the difficulty in demonstrating benefits. Several recent therapeutic approaches that have been studied either in experimental animals with ARF or in small numbers of humans with ARF hold promise for improving clinical outcome. Continuous arteriovenous or venovenous hemofiltration with or without dialysis is such a therapy. In comparison to intermittent hemodialysis this former treatment more safely removes large quantities of water and solutes from critically ill patients with unstable hemodynamics and allows them to receive rather large quantities of nutrients, including amino acids. Also promising are studies in experimental animals with ARF which indicate that several growth factors may accelerate the recovery of renal function. In rats with ARF, insulin-like growth factor 1 both enhances recovery of renal function and suppresses their enhanced catabolism. For most patients with ARF requiring nutrition support, evidence suggests that both essential and nonessential amino acids should be employed. However, there appears to be a therapeutic role for small quantities of essential amino acids, without nonessential amino acids, in selected patients. Data support the importance of proactive measures to prevent fluid and electrolyte imbalances in patients with ARF.

Route of nutritional supply influences local, systemic, and remote organ responses to intraperitoneal bacterial challenge

OBJECTIVE

The authors' aim was to investigate whether antecedent nutritional routes influence immune responses after surgical insult.

SUMMARY BACKGROUND DATA

Total parenteral nutrition (TPN) may influence host responses to infection. To the best of the authors' knowledge, however, no study has focused on the mechanisms underlying the influence of nutritional route on local, systemic, and remote organ (lung) responses after surgical insult.

METHODS

Sixty-eight rats were divided into TPN and total enteral nutrition (TEN) groups. The two groups received identical nutrients for 7 days and were then challenged intraperitoneally with 3 x 10(8) Escherichia coli. In the first experiment, the rats were observed for survival. In the second experiment, the rats were killed before (0 hours) challenge or 2 or 6 hours after challenge. Peritoneal exudative cells (PEC) and bronchoalveolar cells (BALC) were harvested and cultured in vitro. Colony-forming units of bacteria in the peritoneal lavage fluid (PLF) were determined. Tumor necrosis factor (TNF), interleukin-1 alpha (IL-1 alpha), interferon-gamma (IFN-gamma) levels in serum, PLF, bronchoalveolar lavage fluid (BALF), and cell culture supernatants were measured.

RESULTS

The 48-hour survival rate was higher in TEN than in TPN rats. Local immunity was depressed in the TPN group. Bacterial colony counts in PLF were significantly higher in the TPN group than in the TEN group after challenge. The number of PECs was significantly lower, and at 2 hours, local cytokine (TNF and IL-1 alpha) responses were diminished in the TPN group compared with the TEN group at 2 hours. The number of PECs showed a significant positive correlation with levels of local cytokines in the TEN group but not in the TPN group. Elevation of local IFN-gamma was significant from 0 to 6 hours in the TEN group but not in the TPN group. In vitro production of TNF by PEC was impaired in the TPN rats before challenge. Remote organ (lung) responses were suppressed in the TPN group. The number of BALCs and the TNF levels in BALF declined significantly between 0 and 2 hours in the TEN group but not in the TPN group. Interferon-gamma levels in BALF were higher in the TEN group than in the TPN group at 2 hours. Systemic cytokine responses were disturbed in the TPN group. Production of systemic TNF was greater, but the IFN-gamma response was diminished in the TPN group compared with the TEN group after intraperitoneal bacterial challenge.

CONCLUSION

Local, systemic, and remote organ (lung) immune responses to intraperitoneal bacterial challenge are suppressed in TPN-treated animals, leading to poor survival after challenge. Enteral nutrition before surgical insult may enhance host immune responses after the insult as compared to parenteral nutrition.

Pattern of cytokines and pharmacomodulation in sepsis induced by cecal ligation and puncture compared with that induced by endotoxin

The production of tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and IL-6 and their pharmacomodulation were evaluated in a model of polymicrobial sepsis induced in mice by cecal ligation and puncture (CLP) and were compared with the effects of endotoxin (lipopolysaccharide [LPS]) treatment. LPS levels rose as early as 1 h after CLP and increased further after 2 and 21 h. TNF-alpha was detectable in serum, spleen, liver, and lungs during the first 4 h, with a peak 2 h after CLP. IL-1 beta was measurable in serum after 24 h, and levels increased significantly in spleen and liver 4 and 8 h after CLP. IL-6 levels increased significantly in serum throughout the first 16 h after CLP. These cytokines were detectable after LPS injection, with kinetics similar to those after CLP but at a significantly higher level. To cast more light on the differences between these two animal models of septic shock, we studied the effects of different reference drugs. Pretreatment with dexamethasone (DEX); ibuprofen (IBU), an inhibitor of cyclooxygenase; and NG-nitro-L-arginine, an inhibitor of nitric oxide synthase, significantly reduced survival, while chlorpromazine (CPZ) and TNF did not affect it. Only the antibiotics and pentoxifylline significantly increased survival in mice with CLP. However, CPZ and DEX protected the mice from LPS mortality. On inhibiting TNF-alpha with DEX, CPZ, or pentoxifylline, survival was reduced, unchanged, and increased, respectively, and on increasing TNF-alpha with IBU and TNF, survival was decreased or unchanged, respectively, suggesting that the modulation of this cytokine does not play a significant role in sepsis induced by CLP, unlike treatment with LPS. The negative effects of IBU and N(G)-nitro-L-arginine suggest a protective role by prostaglandins and nitric oxide in sepsis induced by CLP.

Nitrergic inhibitory innervation of porcine rectal circular smooth muscle

This study was performed to determine whether nitric oxide contributes to inhibitory non-adrenergic non-cholinergic (NANC) neurotransmission in the circular smooth muscle layer of pig rectum. Smooth muscle strips were mounted for isometric tension recording in superfusion organ baths. In the presence of atropine sulphate and guanethidine, transmural electrical field stimulation (EFS) produced frequency-dependent relaxation of precontracted muscle strips. N omega-nitro-L-arginine (L-NOArg), a powerful competitive antagonist of nitric oxide synthase, reduced the relaxant response in dose-dependent fashion; this response was maximally reduced by mean(s.e.m.) 86.5(2.6) per cent (P = 0.0003) at a concentration of 3 x 10(-5) mol/l L-NOArg. The response was restored by the addition of L-arginine. Sodium nitroprusside, an exogenous donor of nitric oxide, mimicked the relaxant response. Responses to EFS were abolished by tetrodotoxin. These results suggest that inhibitory NANC neurotransmission in this tissue is mediated, at least in part, by nitric oxide. The failure of L-NOArg to completely abolish the relaxant response suggests that additional neurotransmitters may be involved.

Effect of different combinations of dietary additives on bacterial translocation and survival in gut-derived sepsis

BACKGROUND

Dietary arginine, glutamine, and fish oil each have been shown to improve resistance to infection. The purpose of this study was to assess the potential benefit of different combinations and amounts of these components on bacterial translocation and related mortality during gut-derived sepsis.

METHODS

Balb/c mice were fed for 10 days with an AIN-76A diet supplemented with different combinations and percentages of arginine, glutamine, glycine, fish oil, and medium-chain triglycerides. Controls were fed a complete AIN-76A diet or chow. After 10 days of feeding, all animals were transfused. On day 15, the animals were gavaged with 10(10) 111In-radiolabeled or unlabeled Escherichia coli and given a 30% burn injury. Animals gavaged with unlabeled bacteria were observed for survival (n = 317). Groups that showed the best survival as well as control groups were gavaged with labeled bacteria and killed 4 hours postburn (n = 60) for harvest of mesenteric lymph nodes, liver and spleen.

RESULTS

Mice fed diets enriched with 5% fish oil + 2% arginine, 2% arginine + 2% glutamine, or 5% fish oil + 2% glutamine had higher survival than control groups. The animals fed fish oil+glutamine had significantly reduced translocation to the liver and spleen. Animals fed arginine+glutamine had an enhanced ability to kill translocated organisms in the liver compared with other groups. Fish oil+arginine improved both barrier function and microbial killing.

CONCLUSIONS

Feeding with arginine+glutamine, fish oil+arginine, or fish oil+glutamine supplemented diets positively affects the outcome in a gut-derived sepsis model.

Enhancement of macrophage microbicidal activity: supplemental arginine and citrulline augment nitric oxide production in murine peritoneal macrophages and promote intracellular killing of Trypanosoma cruzi

The generation of nitric oxide (NO) is largely responsible for the intracellular killing of Trypanosoma cruzi by activated macrophages. The present study was carried out to determine whether the production of NO by activated murine macrophages cultured in physiologic levels of arginine can be augmented by increasing the availability of arginine, the substrate for NO biosynthesis. Increased exogenous arginine or citrulline resulted in a significant increase in NO production and complete clearance of the parasites by activated macrophages. As citrulline fully substituted for arginine in supporting NO production and trypanocidal activity, these results demonstrate the expression of a highly active citrulline-NO cycle in activated macrophages and that levels of arginine in plasma are limiting with respect to both NO production and trypanocidal activity in these cells. The results indicate that increasing plasma substrate levels for both arginine and NO biosynthesis may represent a means of enhancing microbicidal activity in vivo.

Plasma arginine, citrulline, and ornithine kinetics in adults, with observations on nitric oxide synthesis

The plasma fluxes of ornithine (Orn), arginine (Arg), and citrulline (Cit) and rate of conversion of labeled ornithine-to-citrulline (QOrn-->Cit) were estimated in six healthy adult men receiving an arginine-rich or arginine-free L-amino acid-based diet, each for 6 days. On day 7 an 8-h (3-h fast, 5-h fed) primed continuous intravenous infusion of L-[guanido-15N,15N] arginine, L-[ureido-13C]citrulline, L-[5,5,2H2]ornithine, and L-[5,5,5-2H3]leucine was conducted. Mean citrulline fluxes (mumol.kg-1.h-1) were 10.4-13.6 for the various conditions and/or diets and remained unchanged (P > 0.05). Arginine flux was lowered (P < 0.01) by 38% for fed state during arginine-free period. Ornithine fluxes for arginine-rich were (P < 0.01) reduced with the arginine-free diet. Rates of QOrn-->Cit declined by 30% (P < .05) during the fed arginine-free period. Short-term restriction in the dietary supply of arginine did not alter the rate of whole body nitric oxide synthesis. One subject showed a very high output of nitrate on arginine-free diet (6 times average for remaining subjects).

Use of L-arginine in the treatment of experimental necrotizing enterocolitis

Although multifactorial in etiology, prematurity and feeding are two of the most common risk factors associated with necrotizing enterocolitis (NEC). To understand the pathogenesis of NEC, the complex interaction between intestinal contents and clearing mechanisms in the immature human gut must be elucidated. Nitric oxide (NO) is a proposed mediator of nonadrenergic noncholinergic neural inhibition, causing relaxation in the gut. In addition to its role as a neuroeffector substance, studies suggest that endogenous formation of NO maintains intestinal mucosal integrity, protecting the gut from blood-borne toxins and tissue-destructive mediators. Thus, NO has a dual role in both gut smooth muscle relaxation and mucosal protection. Because two of the primary risk factors in the development of NEC are prematurity (as it relates to gut dysmotility) and enteral feeding (as it relates to mucosal damage by intraluminal substrate), the authors chose to investigate the role of NO in the pathogenesis of NEC induced by intraluminal injection of acidified casein solution in neonatal piglets.

METHODS

Having confirmed the consistent induction of NEC both macroscopically and histologically with this model (n = 32), the following were undertaken. Neonatal piglets (< 3 days old) were laparotomized, and intestinal loops were created from the terminal ileum to the proximal colon. The loops were injected with acidified casein solution and separated by saline-injected control loops. When the abdomen was closed, a continuous peripheral intravenous infusion of L-arginine, an NO synthase substrate (600 mg/kg/h [n = 6]), or N-omega-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor (20 mg/kg/h [n = 6]), was begun. Gut segments were harvested 3 hours later and processed for evaluation of the extent of necrosis.

RESULTS

Macroscopically, the L-NAME-treated group showed areas of hemorrhagic necrosis in the NEC-induced loops. The L-arginine-treated group had greatly diminished or virtually absent lesions. H&E-stained sections were graded microscopically, using a scale from 0 to 4, ranging from intact villi (grade 0) to transmural necrosis (grade 4). In the untreated NEC group, intestinal damage in the acidified casein loops was exhibited by areas of necrosis (extending, in some cases, transmurally), submucosal edema, and inflammatory cell infiltrate (average grade, 3.5). In the L-NAME-treated group, the intestinal damage was similar to that of the NEC-induced group (average grade, 3.5), but also presented with marked hemorrhagic congestion. In the L-arginine group, NEC-induced tissue damage was greatly attenuated, with necrosis limited primarily to the villus tips (average grade, 1). Nevertheless, inflammatory cell infiltrate and mild submucosal edema were still present.

CONCLUSION

Continuous intravenous infusion with the NO synthase substrate L-arginine markedly attenuates intestinal injury in this neonatal piglet model of NEC. Intravenous administration of the NO synthase inhibitor L-NAME causes hemorrhagic congestion of the gut wall. Based on these findings, the authors propose that treatment with the amino acid L-arginine should be considered as a potential therapeutic modality for NEC.

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.

Arginine-derived nitric oxide reduces fecal oocyst shedding in nude mice infected with Cryptosporidium parvum

Dietary L-arginine (4%) significantly reduced fecal oocyst shedding in athymic nude mice chronically infected with Cryptosporidium parvum. This effect appeared to be due to an increase in host nitric oxide (NO) production as it was not observed in arginine-supplemented animals administered the NO synthase inhibitor, N-nitro-L-arginine methyl ester. N-Nitro-L-arginine methyl ester alone significantly increased fecal oocyst shedding in chronically infected animals. In in vitro assays, oocyst excystation and sporozoite viability were significantly reduced by the NO donors sodium nitroprusside and S-nitroso-L-acetyl penicillamine in a concentration-dependent manner. These data suggest that arginine-derived NO may reduce the parasite load in experimental cryptosporidiosis.