Roles of nitric oxide synthases in platelet-activating factor-induced intestinal necrosis in rats

Antioxidants and/or fish oil reduce intermittent hypoxia-induced inflammation in the neonatal rat terminal ileum

Intermittent hypoxia (IH) is associated with the pathogenesis of necrotizing enterocolitis (NEC). We tested the hypothesis that early supplementation with antioxidants and/or fish oil protects the terminal ileum from oxidative injury induced by neonatal IH. Newborn rats were exposed to neonatal IH from birth (P0) until P14 during which they received daily fish oil, coenzyme Q10 (CoQ10), glutathione nanoparticles (nGSH), fish oil + CoQ10, or olive oil. Pups were then placed in room air from P14 to P21 with no further supplementation. Terminal ileum was assessed for IH-induced injury and inflammatory biomarkers. Neonatal IH induced severe damage consistent with NEC, and was associated with oxidative stress and elevations in PGE₂, PGF_2α, TxB₂, NOS-2 and TLR-4, effects that were ameliorated with nGSH and combination CoQ10+fish oil. Early postnatal supplementation with antioxidants and/or fish oil during neonatal IH may be favorable for preserving gut integrity and reducing oxidative injury.

Roles of neuronal nitric oxide synthase and inducible nitric oxide synthase in intestinal transplantation of rats

OBJECTIVE

The study was designed to evaluate the role of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in ischemia-reperfusion injury (IRI) and acute rejection (AR) in rat intestinal transplantation, by administration of nitric oxide inhibitor N(G)-nitro-L-arginine methyl ester (LNAME).

MATERIALS AND METHODS

Rats that underwent orthotopic intestinal transplantation were assigned to 2 sets of groups: (1) iso-geneic group (Lewis-Lewis), L-NAME 0 mg/kg/d group (1-1), 4 mg/kg/d (group 1-2), or 8 mg/kg/d (group 1-3) injected intraperitoneally or (2) allogeneic group (Dark Agouti-Lewis), L-NAME 0 mg/kg/d (group 2-1) or 8 mg/kg/d (group 2-2) injected intraperitoneally. We examined survival times, light microscopy as well as maltose absorption tests. The nNOS and iNOS activities were measured by immunohistochemical methods.

RESULTS

Histologic examination showed inhibited iNOS activity compared with group l-l, and Park scores decreased significantly in group 1-2 at 30 minutes after reperfusion (1.42 ± 0.38 vs 2.58 ± 0.49, P < .01). Both iNOS and nNOS activities were inhibited and Park scores increased significantly in group 1-3 from 30 minutes to day 3 after reperfusion (P < .0l). nNOS activity decreased and iNOS activity increased among group 2-1 during AR. Compared with group 2-1, iNOS activity was inhibited, progression of AR delayed, and survival significantly prolonged in group 2-2 (10.17 ± 0.98 vs 6.83 ± 0.75, P < .01).

CONCLUSION

This study suggested that decreased nNOS and increased iNOS activity both contributed to IRI and AR. More importantly, nNOS more importantly than iNOS activity was closely related to graft structure and function.

Direct peritoneal resuscitation augments ileal blood flow in necrotizing enterocolitis via a novel mechanism

PURPOSE

Endothelin-1, prostaglandins (PGs), and nitric oxide (NO) have been implicated in the intestinal microvascular dysfunction of necrotizing enterocolitis (NEC). We hypothesized that direct peritoneal resuscitation (DPR) dilates the intestinal microvasculature and improves blood flow independent of these mechanisms.

METHODS

Rat pups were assigned by litter to experimental NEC or CONTROL groups. Laser Doppler flowmetry evaluation of intestinal microvascular blood flow was studied at baseline, with mediator blockade (endothelin-A receptor, endothelin-B receptor, PG synthesis, or NO synthase) and with DPR. Repeated-measures analysis of variance test was applied with Tukey-Kramer honestly significant difference test (P < .05).

RESULTS

At baseline, NEC animals demonstrated significantly decreased ileal blood flow as compared with CONTROLs (P < .05). Endothelin-A receptor and PG inhibition increased flow in the intestinal microvasculature, but this was significantly augmented by the addition of DPR (P < .05). Blockade of NO synthase decreased intestinal blood flow, which was overcome with addition of DPR (P < .05).

CONCLUSION

Ileal blood flow was significantly reduced in NEC animals as compared with CONTROLs. The addition of DPR to the peritoneum increased ileal blood flow significantly in all groups in spite of blockade of these known vasoactive mechanisms. Direct peritoneal resuscitation may be a novel strategy to improve intestinal blood flow in NEC.

Effect of polyethylene glycol in pig intestinal allotransplantation without immunosuppression

OBJECTIVES

We evaluated whether IGL-1, a graft preservation solution containing polyethylene glycol, improves the outcome of small bowel grafts in comparison to the University of Wisconsin (UW) solution in a pig allotransplantation model.

MATERIALS AND METHODS

Seventeen pigs were randomly allocated to group 1 (n = 10; intestinal allotransplantation with IGL-1) and group 2 (n = 7; allotransplantation with UW). Pigs received no immunosuppression and were sacrificed on postoperative d (POD) 8. Intestinal specimens were obtained from the animal immediately before cold flushing (T0), 2 h after graft reperfusion (T1), and at sacrifice (T2).

RESULTS

Survival rate to POD 8 was 50% in group 1 compared with 16% in group 2 (P < 0.05); 62% of pigs in group 1 did not present any acute cellular rejection (ACR) compared to 16% in group 2 (P < 0.05). Severe ACR rate was 25% in group 1 and 66% in group 2 (P < 0.05). iNOS activity and intestinal caspase 3 levels increased significantly between T0 and T1 in group 1 compared to group 2 (P < 0.05). Cell necrosis increased significantly between TO and T1 in group 2 compared with group 1 (P < 0.05) whereas cell apoptosis was significantly higher at T1 compared with T0 in group 1 in comparison to group 2.

CONCLUSIONS

Our results show that IGL-1 improves intestinal graft viability as compared to UW solution, possibly by reducing graft immunogenicity and by favoring intestinal epithelial repair.

The effect of NG-nitro L-arginine methyl ester on colonic anastomosis after increased intra-abdominal pressure

BACKGROUND

Intestinal ischemia-reperfusion (I/R) is associated with augmented nitric oxide (NO) production. Increased intra-abdominal pressure (IAP) during surgical pneumoperitoneum (P) facilitates I/R injury. We previously demonstrated decreased strength and healing of colocolic anastomoses after high IAPs. The effect of an NO synthase inhibitor, N (G)-nitro-arginine methyl ester (L: -NAME), on anastomoses realized in colonic tissue exposed to high IAPs was investigated in this study, a randomized, controlled, and experimental study with blind outcome assessment.

METHOD

Fifty Wistar-albino rats were randomized to five groups; all underwent colocolic anastomosis. P was maintained for 60 min at IAPs of 14, 20, 25, and 30 mmHg in study groups 1, 2, 3, and 4, respectively; P was preceded by intraperitoneal L: -NAME (2.5 mg/kg) and followed by anastomosis. The control group was not subjected to IAP or L: -NAME.

RESULTS

Anastomosis bursting pressure (ABP) values and histopathological findings were determined on the 7th-14th postoperative days. The ABPs of groups 3-4 were significantly lower than the others. Groups 1-2 had results similar to controls. Histopathological findings of the groups were consistent with their ABPs.

CONCLUSION

Administration of a 2.5-mg/kg intraperitoneal L: -NAME dose was found to provide a beneficial role, implying a role in impaired anastomotic healing after IAPs of 14 and 20 mmHg.

Role of neuronal nitric oxide synthase and inducible nitric oxide synthase in intestinal injury in neonatal rats

AIM: To investigate the dynamic change and role of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in neonatal rat with intestinal injury and to define whether necrotizing enterocolitis (NEC) is associated with the levels of nitric oxide synthase (NOS) in the mucosa of the affected intestine tissue.

METHODS: Wistar rats less than 24 h in age received an intraperitoneal injection with 5 mg/kg lipopolysaccharide (LPS). Ileum tissues were collected at 1, 3, 6, 12 and 24 h following LPS challenge for histological evaluation of NEC and for measurements of nNOS and iNOS. The correlation between the degree of intestinal injury and levels of NOS was determined.

RESULTS: The LPS-injected pups showed a significant increase in injury scores versus the control. The expression of nNOS protein and mRNA was diminished after LPS injection. There was a negative significant correlation between the nNOS protein and the grade of median intestinal injury within 24 h. The expression of iNOS protein and mRNA was significantly increased in the peak of intestinal injury.

CONCLUSION: nNOS and iNOS play different roles in LPS-induced intestinal injury. Caution should be exerted concerning potential therapeutic uses of NOS inhibitors in NEC.

Tetrahydrobiopterin prevents platelet-activating factor-induced intestinal hypoperfusion and necrosis: Role of neuronal nitric oxide synthase

OBJECTIVE

We reported previously that neuronal nitric oxide synthase (nNOS) is the predominant NOS in rat small intestine and is down-regulated by platelet-activating factor (PAF). The severity of the bowel injury induced by PAF is inversely related to its suppressing effect on nNOS. Here, we investigated whether intestinal perfusion is regulated by nNOS and whether tetrahydrobiopterin, a co-factor and stabilizer of nNOS, reverses PAF-induced intestinal hypoperfusion and injury.

SETTING

Animal laboratory.

DESIGN

We first examined nNOS regulation of splanchnic blood flow by measuring the perfusion of the heart, lung, ileum, and kidney in rats after a nNOS inhibitor. We then examined the protective effect of tetrahydrobiopterin on PAF-induced bowel injury, mesenteric hypoperfusion, and systemic inflammation.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTION

In part 1 of the experiment, rats were given 7-nitroindazole (a specific nNOS inhibitor, 50 mg.kg.day). In part 2 of the experiment, rats were treated with tetrahydrobiopterin (20 mg/kg) 5 mins before and 30 mins after PAF challenge (2.2 microg/kg, intravenously)

MEASUREMENTS

Perfusion of the heart, lung, ileum, and kidney was measured at 1 and 4 days after 7-nitroindazole, using fluorescent microspheres. Intestinal injury and inflammation (myeloperoxidase content), blood perfusion, calcium dependent-NOS activity, and systemic inflammation (hypotension and hematocrit increase) were assessed 1 hr after PAF with and without tetrahydrobiopterin treatment.

RESULTS

In part 1 of the experiment, 7-nitroindazole induced a long-lasting reduction of blood perfusion and inducible NOS expression selectively in the ileum but not in nonsplanchnic organs such as heart, lungs, and kidneys. In part 2, tetrahydrobiopterin protected against PAF-induced intestinal necrosis, hypoperfusion, neutrophil influx, and NOS suppression. It also reversed hypotension and hemoconcentration. Sepiapterin (2 mg/kg, stable tetrahydrobiopterin precursor) also attenuated PAF-induced intestinal injury.

CONCLUSIONS

We conclude that nNOS selectively regulates intestinal perfusion. Tetrahydrobiopterin prevents PAF-induced intestinal injury, probably by stabilizing nNOS and maintaining intestinal perfusion.

Elevated expression of iNOS mRNA and protein in coeliac disease

BACKGROUND

The role of nitric oxide synthase (NOS) in the pathophysiology of coeliac disease (CD) was investigated.

METHODS

We examined mRNA (reverse transcription multiplex polymerase chain reaction) and protein expression (Western blotting) of i,e and nNOS in enterocytes isolated from the duodenum of patients with untreated CD (n=22) and iron deficiency anaemia (IDA, n=22). Expression of IL1beta and TNFalpha, two pivotal "NOS-controlling" cytokines, was also studied.

RESULTS

Enterocytes from both patient groups were negative for eNOS and TNF(alpha) message but positive for n and iNOS. nNOS gene expression was not statistically different between groups (158.38+/-29.11% vs. 114.95+/-24.17%, IDA vs. CD, p=0.07, Mann-Whitney U). iNOS expression was higher in patients with CD when compared to patients with IDA (96.95+/-17.82% vs. 48.76+/-8.07%, p<0.006). Low levels of IL1beta mRNA (15.66+/-3.70%) were detected in nine samples-all of these samples were isolated from patients with CD representing a positive result in 40% of coeliac patients. In support of these observations, patients with CD expressed more iNOS protein than those with IDA (159.7+/-14.9% vs. 69.8+/-20%, p<0.05).

CONCLUSION

These results suggest that iNOS could be an important mediator in coeliac disease. Expression of this regulatory protein may be under the control of IL1beta.

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Lipopolysaccharide induces nitric oxide synthase expression and platelet-activating factor increases nitric oxide production in human fetal membranes in culture

BACKGROUND

Platelet-activating factor and nitric oxide may be involved in the initiation of human labour as inflammatory mediators. The aim of this study was to test whether platelet-activating factor and lipopolysaccharide were able to induce nitric oxide synthase expression and stimulate the production of nitric oxide in human fetal membrane explants in culture.

METHODS

Fetal membranes were collected from Caesarean sections at term. RNA was extracted from membranes and subjected to a qualitative RT-PCR to assess the baseline expression of iNOS. Discs of fetal membranes were cultured for 24 hours in the presence of platelet-activating factor at a dose range of 0.1 nanomolar--1 micomolar or 1 microgram/ml lipopolysaccharide. Nitric oxide production was measured via nitrite ions in the culture medium and mRNA for iNOS was detected by RT-PCR.

RESULTS

Culturing the membrane discs in medium containing serum induced nitric oxide synthase expression and platelet-activating factor significantly stimulated the production of nitric oxide under these conditions. When cultured without serum inducible nitric oxide synthase expression was induced by lipopolysaccharide, but not by platelet-activating factor.

CONCLUSION

Platelet-activating factor may have a role in the initiation of labour, at term or preterm, via the increased local production of nitric oxide as an inflammatory mediator. In this model of intrauterine infection, lipopolysaccharide was found to induce iNOS expression by fetal membranes, and this mechanism could be involved in preterm labour.

Current issues in the management of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common surgical emergency in the neonatal intensive care unit and remains a major cause of death in neonates. Although the pathophysiology of NEC has not been completely elucidated, progress has been made in the characterization of the molecular events which may take place during an episode of ischemia. This possible initiating event is followed by a complex cascade of inflammatory mediators active in NEC: epidermal growth factor, platelet-activating factor, and, nitric oxide. Additionally, unique characteristics of the premature gut are thought to be crucial to the development of NEC. The diagnosis of NEC continues to be based on clinical and radiographic features. Several new laboratory tests are under investigation for the purposes of earlier diagnosis, but none have prevailed at this time. Both exploratory laparotomy, with intestinal resection and peritoneal drainage are widely practiced. Mortality rates remain high and have improved little over the last couple of decades. Therefore, prevention remains crucial in order to decrease the incidence of NEC. Cautious feeding regimens, the use of maternal breast milk, passive immunization, and the use of probiotics have all been suggested but not proven as possible preventive methods. Although many advances have been made, significant opportunity remains to improve our understanding of the disease process and to develop better strategies for prevention and treatment.

Macrophages in the small intestinal muscularis externa of embryos, newborn and adult germ-free mice

Previously, we demonstrated the presence of a constant and regularly distributed macrophage population of ramified cells in the intestinal muscle layers of smaller rodents. The function of these resident macrophages under normal conditions remains unknown. Histochemistry, immunohistochemistry and electron microscopy were applied to the muscularis externa of 15- and 17-day-old embryos, 2-day-old mice, adult germ-free and conventional mice. Since lipopolysaccharides (LPS) activates macrophages and inflammation affects gut motility, LPS-treated mice were also included in the study. Two macrophage antibodies, F4/80 and 2F8 were used to demonstrate the presence of macrophages in the muscle layers. The localization was confirmed by electron microscopy. In contrast to conventional adult mice, the muscle layers in embryos, newborn and germ-free adult mice were devoid of class II MHC antigen reactive cells. The acid phosphatase reaction and antibodies directed towards a lysosomal protein (Lamp-2) were used in order to verify other activation markers. None of these showed specific staining of the muscularis macrophages. Only LPS-treated adult mice showed iNOS-positive cells in whole mounts. We conclude that the characteristic organization and distribution of muscularis macrophages in adult mice are also present in embryos, newborn and germ-free mice and thus develop independently of foreign antigens. Further, these macrophages are truly resident and appear to have differential responses to exogene stimuli.

Candidate???s Thesis: Platelet-Activating Factor???Induced Hearing Loss: Mediated by Nitric Oxide?

OBJECTIVES/HYPOTHESIS

Platelet-activating factor (PAF)in middle ear effusion is thought to induce hearing loss. The purpose of this study is to investigate the role of nitric oxide (NO) in the mechanism of PAF-induced hearing loss by studying the effects of PAF application on the round window membrane (RWM) with and without PAF-antagonist NO-blocker.

STUDY DESIGN

Longitudinal study on randomized guinea pigs using PAF to induce hearing loss. METHODS Guinea pigs were divided into four groups: PBS, PAF, PAF-antagonist, and L-NAME. The PBS group received phosphate buffered saline (PBS) and the PAF groups received 10, 20, and 40 microg of PAF soaked into gelfoam and placed on the RWM. PAF-antagonist (WEB 2170) and NOS inhibitor NG-nitro-l-arginine-methylester (L-NAME) were injected intraperitoneally prior to PAF 20 microg application on the RWM. The following three tests were performed on each animal group: Hearing was tested with an auditory brainstem response (ABR) test over 24 hours. At the end of 24 hours, cochlear hair cells were examined by scanning electron microscopy (SEM) and immunohistochemistry was carried out on the cochlea to test the expression of inducible nitric oxide synthase (iNOS).

RESULTS

The PAF group developed significant elevation of ABR threshold and cochlear hair cell damage in the SEM group as compared with the PBS control group. The PAF-antagonist (WEB 2170) and the L-NAME groups did not show significant elevation of ABR threshold and cochlear hair cell damage compared with the group administered PAF 20 microg, but in the PAF-antagonist group, the elevation of ABR threshold was significant compared with that of the PBS control group, whereas it was not significant compared with the PBS group in the L-NAME group. Strong expression of iNOS on cochlea was observed in the PAF group and lighter expression was seen in PBS, WEB 2170, and L-NAME groups.

CONCLUSIONS

This study demonstrated that PAF placed on the RWM induced hearing loss and cochlear hair cell damage. The PAF-antagonists and L-NAME prevented the PAF-induced hearing loss and inhibited iNOS expression in the cochlea. These findings suggest that the PAF-induced hearing loss caused by cochlear hair cell damage may have been mediated by NO. PAF-antagonists and L-NAME may have future therapeutic implications in preventing sensorineural hearing loss associated with chronic otitis media. The results of this study have significant potential clinical application.

Mild hypothermia during hemorrhagic shock in rats improves survival without significant effects on inflammatory responses

OBJECTIVE

To explore the hypothesis that the survival benefit of mild, therapeutic hypothermia during hemorrhagic shock is associated with inhibition of lipid peroxidation and the acute inflammatory response.

DESIGN

Prospective and randomized.

SETTING

Animal research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats underwent pressure-controlled (mean arterial pressure 40 mm Hg) hemorrhagic shock for 90 mins. They were randomized to normothermia (38.0 +/- 0.5 degrees C) or mild hypothermia (33-34 degrees C from hemorrhagic shock 20 mins to resuscitation time 12 hrs). Rats were killed at resuscitation time 3 or 24 hrs.

MEASUREMENTS AND MAIN RESULTS

All seven rats in the hypothermia group and seven of 15 rats in the normothermia group survived to 24 hrs (p <.05). Hypothermic rats had lower serum potassium and higher blood glucose concentrations at 90 mins of hemorrhagic shock (p <.05). At resuscitation time 24 hrs, the hypothermia group had less liver injury (based on serum concentrations of ornithine carbamolytransferase and liver histology) and higher blood glucose than the normothermia group (p <.05). There were no differences in serum free 8-isoprostane (a marker of lipid peroxidation by free radicals) between the two groups at either baseline or resuscitation time 1 hr. Serum concentrations of interleukin- 1 beta, interleukin-6, and tumor necrosis factor-alpha peaked at resuscitation time 1 hr. Tumor necrosis factor-alpha concentrations were higher (p <.05) at resuscitation time 1 hr in the hypothermia group compared with the normothermic group. Serum cytokine concentrations were not different between survivors and nonsurvivors in the normothermia group. Serum cytokine concentrations returned to baseline values in both groups by 24 hrs. There were no differences in the number of neutrophils in the lungs or the small intestine between the groups. More neutrophils were found in the lungs at resuscitation time 3 hrs than at resuscitation time 24 hrs in both groups (p <.01).

CONCLUSIONS

These data suggest that lipid peroxidation and systemic inflammatory responses to hemorrhagic shock are minimally influenced by mild hypothermia, although liver injury is mitigated and survival improved. Other mechanisms of benefit from mild hypothermia need to be explored.

Neonatal necrotizing enterocolitis: clinical considerations and pathogenetic concepts

Necrotizing enterocolitis (NEC), a disease affecting predominantly premature infants, is a leading cause of morbidity and mortality in neonatal intensive care units. Although several predisposing factors have been identified, such as prematurity, enteral feeding, and infection, its pathogenesis remains elusive. In the past 20 years, we have established several animal models of NEC in rats and found several endogenous mediators, especially platelet-activating factor (PAF), which may play a pivotal role in NEC. Injection of PAF induces intestinal necrosis, and PAF antagonists prevent the bowel injury induced by bacterial endotoxin, hypoxia, or challenge with tumor necrosis factor-a (TNF) plus endotoxin in adult rats. The same is true for lesions induced by hypoxia and enteral feeding in neonatal animals. Human patients with NEC show high levels of PAF and decreased plasma PAF-acetylhydrolase, the enzyme degrading PAF. The initial event in our experimental models of NEC is probably polymorphonuclear leukocyte (PMN) activation and adhesion to venules in the intestine, which initiates a local inflammatory reaction involving proinflammatory mediators including TNF, complement, prostaglandins, and leukotriene C4. Subsequent norepinephrine release and mesenteric vasoconstriction result in splanchnic ischemia and reperfusion. Bacterial products (e.g., endotoxin) enter the intestinal tissue during local mucosal barrier breakdown, and endotoxin synergizes with PAF to amplify the inflammation. Reactive oxygen species produced by the activated leukocytes and by intestinal epithelial xanthine oxidase may be the final pathway for tissue injury. Protective mechanisms include nitric oxide produced by the constitutive (mainly neuronal) nitric oxide synthase, and indigenous probiotics such as Bifidobacteria infantis. The former maintains intestinal perfusion and the integrity of the mucosal barrier, and the latter keep virulent bacteria in check. The development of tissue injury depends on the balance between injurious and protective mechanisms.

Systemic hypothermia, but not regional gut hypothermia, improves survival from prolonged hemorrhagic shock in rats

BACKGROUND

Extracorporeal blood perfusion of the gut or enterectomy can improve survival during hemorrhagic shock (HS), suggesting that the gut may be of primary importance in resuscitation. We hypothesized that cooling the gut alone could improve survival in a rat HS model and avoid potential deleterious effects of systemic hypothermia.

METHODS

Thirty-two Sprague-Dawley rats were anesthetized with halothane. The gut (small intestine, cecum, and colon) was exteriorized. The right atrial (T ), rectal, and gut (T ) intraluminal temperatures were monitored. HS was induced by withdrawal of 2 mL of blood per 100 g body weight over 10 minutes. Mean arterial pressure was then maintained at 35 to 40 mm Hg to HS 90 min. From HS 20 min to resuscitation time 1 h, rats were randomized into four groups (n = 8 each): normothermia (T and T approximately 38.0 degrees C), gut-25 degrees C (T approximately 38 degrees C, T approximately 25 degrees C, induced by rinsing the gut with cooled saline), gut-33 degrees C (T approximately 38 degrees C, T approximately 33 degrees C), and systemic hypothermia (T approximately 33 degrees C, T approximately 25 degrees C). At HS 90 min, shed blood and Ringer's solution were infused to restore normotension. Survival, metabolism, and tissue damage were observed to 72 hours.

RESULTS

Blood pressure was not different between groups. Compared with the normothermia group, the systemic hypothermia group had lower base deficit and lactate, and needed less fluid during resuscitation for normotension (p < 0.05), but these values were not different in the gut hypothermia groups. In addition, there were no significant improvements in tissue protection induced by regional gut hypothermia, whereas the systemic hypothermia group had lower plasma potassium, lower ornithine carbamoyltransferase (marker of liver injury), and higher glucose levels after HS (all p < 0.05). All rats in the systemic hypothermia group survived to 72 hours, whereas there was only one survivor in the normothermia group, two in the gut-33 degrees C group, and none in the gut-25 degrees C group (all p < 0.05 vs. systemic hypothermia).

CONCLUSION

Cooling the gut alone does not improve acute survival from HS, suggesting that early deaths are not secondary to gut ischemia. Mild systemic hypothermia allowed 100% survival from prolonged HS.

Intraperitoneal, but not enteric, adenosine administration improves survival after volume-controlled hemorrhagic shock in rats

OBJECTIVE

To circumvent the potential adverse systemic side effects of adenosine, this study explored the potential benefit of intraperitoneal or enteric adenosine on survival and inflammatory responses after volume-controlled hemorrhagic shock.

DESIGN

Prospective, randomized, and blinded. A three-phase, volume-controlled hemorrhagic shock model was used: hemorrhagic shock phase (120 mins), resuscitation phase (60 mins), and observation phase (72 hrs). Three groups were compared: controls, intraperitoneal adenosine, and enteric adenosine.

SETTING

Animal research facility.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Starting at 20 mins of hemorrhagic shock and continuing through the resuscitation phase, all three groups received both intraperitoneal lavage and repeated bolus injections into the ileum of vehicle (normal saline) or adenosine. In the intraperitoneal adenosine group (n = 10), adenosine solution (0.1 mM) was used for intraperitoneal lavage. In the enteric adenosine group (n = 10), adenosine (1.0 mM) was injected into the ileum. Blood cytokine concentrations and leukocyte infiltration in lungs and liver were studied in 12 separate rats (control and intraperitoneal adenosine, n = 6 each) with the same hemorrhagic shock model at resuscitation time 1 hr or 4 hrs.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure and heart rate were similar between the three groups during hemorrhagic shock and resuscitation. Potassium, lactate, and blood urea nitrogen concentrations were lower and arterial pH was higher in the intraperitoneal and enteric adenosine groups compared with the control group (both p <.05). Survival time to 72 hrs was longer in the intraperitoneal adenosine group than in the control group(p <.05). Neither plasma interleukin-1beta, interleukin-6, interleukin-10, and tumor necrosis factor-alpha concentrations nor leukocyte infiltration in the lungs and liver was different between the control and intraperitoneal adenosine groups.

CONCLUSIONS

The administration of adenosine via the intraperitoneal route improves survival time after severe volume-controlled hemorrhagic shock in rats without worsening hypotension or bradycardia. This beneficial effect may not be attributable to effects of adenosine on the inflammatory response.

Platelet-activating factor and endotoxin activate CCAAT/enhancer binding protein in rat small intestine

The transcription factor family CCAAT/enhancer binding proteins (C/EBP) is involved in inflammation via the regulation of the gene expression of various pro-inflammatory cytokines and proteins. PAF and endotoxin (lipopolysaccharide, LPS) are known agents causing intestinal inflammation and injury. In this study, we examined the binding activity of C/EBP isoforms in rat small intestine in response to PAF (1.5 microg kg(-1), i.v.) or LPS (5 mg kg(-1), i.v.). We found that C/EBP is constitutively active in normal small intestine, mainly as C/EBP-alpha and beta (C/EBP-beta>alpha). Both C/EBP-alpha and beta are localized in the intestinal epithelial cells: C/EBP-alpha mainly in the crypts, and C/EBP-beta in both villi and crypts, as well as in some lamina propria cells. Only minute amounts of C/EBP-delta were found. PAF rapidly upregulates the binding activity of C/EBP-alpha and beta within 30 min. The increase in C/EBP-alpha is prominent in the crypt cells, whereas the change of C/EBP-beta is more widespread. LPS also increases the binding activity of C/EBP-alpha and beta, and the response is slower than PAF. PAF synergizes with LPS to markedly activate all three subunits. The increase in C/EBP-alpha is transient, whereas the other two have a sustained elevation until 120 min. After challenge with PAF (but not LPS), small amounts of nuclear factor -kappaB (NF-kappaB) p50 and p65 subunits are found in the C/EBP-DNA binding complex, indicating cross-dimerization of the two transcription families. Pretreatment of rats with pyrrolidine dithiocarbamate (PDTC) suppresses LPS-, but not PAF-, induced NF-kappaB and C/EBP binding activity, and significantly increases the C/EBP-delta subunit in LPS- or PAF-induced C/EBP complex. These results suggest that PAF and LPS activate intestinal C/EBP in vivo, probably via different pathways.

Neuronal nitric oxide synthase (NOS) regulates the expression of inducible NOS in rat small intestine via modulation of nuclear factor kappa B

We previously reported that neuronal nitric oxide synthase (nNOS) is the predominant NOS in the intestine. Inducible NOS (iNOS), an enzyme involved in the inflammatory response, is regulated by cytokines via the transcriptional factor NF-kappaB. We examined a new mechanism of intestinal iNOS regulation with respect to the role of nNOS and its effect on NF-kappaB. Young Sprague-Dawley rats were treated for 4 days with 1) saline, 2) 7-nitroindazole (7-NI, specific nNOS inhibitor), 3) 7-NI + pyrrolidine dithiocarbamate (PDTC, NF-kappaB inhibitor), or 4) PDTC. Intestinal iNOS mRNA, NF-kappaB activity, and the tissue content of the regulatory IkappaBalpha were examined. We found that 7-NI-treated animals had higher intestinal NF-kappaB (p50-p65) activity, lower IkappaBalpha content, and increased intestinal iNOS mRNA, iNOS protein, and iNOS activity compared with controls. All of these changes were abolished when PDTC was given together with 7-NI. PDTC alone had no effect. 7-NI induces a delayed increase in intestinal myeloperoxidase activity (after elevation in NF-kappaB and iNOS), which could be abrogated by PDTC. We conclude that in normal rat small intestine, nNOS suppresses the gene expression of iNOS through NF-kappaB down-regulation and that nNOS suppression leads to IkappaBalpha degradation, NF-kappaB activation, and iNOS expression.

Type I nitric oxide synthase (NOS) is the predominant NOS in rat small intestine. Regulation by platelet-activating factor

Constitutive nitric oxide synthase (cNOS) may play an important protective role in the intestine, since our previous study has shown that the degree of bowel injury induced by platelet-activating factor (PAF), a potent inflammatory mediator, is inversely related to the cNOS content of the intestine. This study aims to examine the composition of the cNOS system in rat small intestine, and its regulation by PAF. We found that an approximately 120 kDa NOS I (neuronal NOS) is the predominant NOS in rat intestine, as evidenced by the following: (a) immunoblotting with specific antibodies detected a NOS I of approximately 120 kDa, but little NOS III; (b) the Ca(2+)-dependent, constitutive NOS (cNOS) activity of the rat intestine was removed by immunoprecipitation with the anti-NOS I, but not anti-NOS II or anti-NOS III antibodies; (c) RT-PCR revealed constitutive expression of NOS I in the intestinal tissue, but only a minute amount of NOS III. Immunofluorescent staining with anti-NOS I located NOS in the Auerbach plexus and nerve fibers in the muscle layer. We also found that this 120 kDa NOS I is rapidly (within 1 h) down-regulated in response to PAF administration. The protein level, enzyme activity as well as mRNA of nNOS were all decreased in the intestine.