Ischemia-reperfusion injury in the intestines of newborn pigs

Variability in splanchnic tissue oxygenation during preterm red blood cell transfusion given for symptomatic anaemia may reveal a potential mechanism of transfusion-related acute gut injury

BACKGROUND

There is increasing evidence indicating an association between red blood cell (RBC) transfusions and necrotising enterocolitis (NEC) in preterm infants, especially late-onset NEC. This phenomenon is referred to as transfusion-related acute gut injury (TRAGI). One theory as to a pathophysiological mechanism is that transfusion may result in an ischemia-reperfusion injury to intestinal tissue. We tested the hypothesis that there is significantly greater variability during transfusion in splanchnic tissue oxygen saturation (SrSO2) than in cerebral tissue oxygen saturation (CrSO2).

MATERIALS AND METHODS

This was a prospective, observational study using near-infrared spectroscopy to monitor SrSO2 and CrSO2 in preterm neonates undergoing RBC transfusion for symptomatic anaemia. Mean, standard deviation, highest and lowest SrSO2 and CrSO2 values during each transfusion were determined. The greatest difference in SrSO2 and CrSO2 during each transfusion was calculated, along with the coefficient of variation.

RESULTS

We studied 37 subjects. Throughout all transfusions, the mean SrSO2 was 45.6% ±13.8 and the mean CrSO2 was 65.4% ±6.9 (p<0.001). The variability of SrSO2 was significantly greater than that of CrSO2. Averaging data from all subjects, the greatest difference in SrSO2 was 43.8% ±13.4 compared with 23.3% ±7.6 for CrSO2 (p<0.001). The mean coefficient of variation in all transfusions was 20.5% for SrSO2 and 6.0% for CrSO2 (p<0.001). Increasing post-conceptional age did not affect SrSO2 variability (R(2) =0.022; p=0.379), whereas CrSO2 variability during transfusion decreased with increasing post-conceptional age (R(2)=0.209; p=0.004).

DISCUSSION

In preterm infants, there is a large degree of tissue oxygenation variability in splanchnic tissue during RBC transfusion and this does not change with increasing maturity. We speculate that these findings, combined with lower average tissue oxygenation, may demonstrate susceptibility of the preterm gut to TRAGI.

Red blood cell transfusion-related necrotizing enterocolitis in very-low-birthweight infants: a near-infrared spectroscopy investigation

BACKGROUND

Recent evidence suggests that antecedent red blood cell (RBC) transfusions increase the risk for necrotizing enterocolitis (NEC), the most common gastrointestinal emergency encountered by very-low-birthweight (VLBW) infants. The underlying mechanism for this association is unknown. Altered oxygenation of the mesenteric vasculature during RBC transfusion has been hypothesized to contribute to NEC development and was investigated in this study.

STUDY DESIGN AND METHODS

Oxygenation patterns among four VLBW infants who developed transfusion-related NEC (TR-NEC) were compared to four VLBW infants with similar gestational age who were transfused but did not develop NEC (non-NEC). Cerebral and mesenteric patterns were recorded before, during, and 48 hours after RBC transfusion using near-infrared spectroscopy (NIRS) technology. Percentage change from mean baseline regional oxygen saturation values and cerebrosplanchnic oxygenation ratios were analyzed.

RESULTS

All TR-NEC infants (24-29 weeks' gestation; 705-1080 g) demonstrated greater variation in mesenteric oxygenation patterns surrounding transfusions than non-NEC infants (27.6-30 weeks' gestation; 980-1210 g). TR-NEC infants received larger mean volumes of total blood (27.75 ± 8.77 mL/kg) than non-NEC infants (15.25 ± 0.5 mL/kg).

CONCLUSION

Wide fluctuation and decreases in mesenteric oxygenation patterns are more pronounced in TR-NEC infants, especially before TR-NEC onset, compared to non-NEC infants. Greater total volume of infused blood was associated with TR-NEC in preterm infants. Using NIRS, larger prospective studies are needed to further evaluate potential risk factors for NEC in this high-risk population.

Necrotizing enterocolitis in very low birth weight infants: a systemic review

Necrotizing enterocolitis (NEC) is the most common serious gastrointestinal disorder affecting very preterm or very low birth weight infants. The risk is inversely proportional to gestational age and weight at birth. Fetal growth restriction and compromise may be additional specific risk factors. Despite extensive research and animal studies etiopathogenesis, preventive strategies and management options remain controversial. The present paper reviews the literature for recent advances and newer insights for changing epidemiological trends, pathogenesis, role of inflammatory cytokines, and various preventive and management strategies.

Intestinal hemodynamics and oxygenation in the perinatal period

The neonatal gastrointestinal tract is a site of intense anabolic and metabolic activity, as it is responsible for the assimilation of nutritional intake and exhibits accelerated growth shortly after birth. The hypermetabolic state of the gastrointestinal tract requires sufficient blood flow and oxygen delivery to sustain adequate oxygen consumption to meet these metabolic needs. Therefore, an understanding of the mechanisms regulating intestinal vascular perfusion in the normal state and during pathophysiological conditions in the perinatal period is important to elucidate potential contributions to the development of intestinal pathologies in the neonate. The goal of this review is to summarize the available literature on the regulation of intestinal blood flow and oxygenation in the fetus and newborn in normal states and during pathological stress.

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.

Intestinal gene expression in pigs: effects of reduced feed intake during weaning and potential impact of dietary components

The weaning transition is characterised by morphological, histological and microbial changes, often leading to weaning-associated disorders. These intestinal changes can partly be ascribed to the lack of luminal nutrition arising from the reduced feed intake common in pigs after weaning. It is increasingly becoming clear that changes in the supply with enteral nutrients may have major impacts on intestinal gene expression. Furthermore, the major dietary constituents, i.e. carbohydrates, fatty acids and amino acids, participate in the regulation of intestinal gene expression. However, nutrients may also escape digestion by mammalian enzymes in the upper gastrointestinal tract. These nutrients can be used by the microflora, resulting in the production of bacterial metabolites, for example, SCFA, which may affect intestinal gene expression indirectly. The present review provides an insight on possible effects of reduced feed intake on intestinal gene expression, as it may occur post-weaning. Detailed knowledge on effects of reduced feed intake on intestinal gene expression may help to understand weaning-associated intestinal dysfunctions and diseases. Examples are given of intestinal genes which may be altered in their expression due to supply with specific nutrients. In that way, gene expression could be modulated by dietary means, thereby acting as a potential therapeutic tool. This could be achieved, for example, by influencing genes coding for digestive or absorptive proteins, thus optimising digestive function and metabolism, but also with regard to immune response, or by influencing proliferative processes, thereby enhancing mucosal repair. This would be of special interest when designing a diet to overcome weaning-associated problems.

Protective effects of Ginkgo biloba extract in rats with hypoxia/reoxygenation-induced intestinal injury

BACKGROUND

The purpose of this study is to investigate the protective effects of Ginkgo biloba extract (EGb 761) in rat pups with hypoxia/reoxygenation (H/R)-induced bowel injury.

METHODS

One-day-old Wistar albino rat pups (n = 21) were randomly divided into 3 groups: group 1 (control, untreated and not exposed to H/R, n = 7), group 2 (untreated but exposed to H/R, n = 7), and group 3 (EGb 761 + H/R, n = 7). Ginkgo biloba extract was administered (100 mg/kg per day, subcutaneously) to group 3 for 3 days. On the fourth day, all animals except controls were exposed to H/R and were killed 6 hours after H/R. Histopathologic injury scores (HIS), malondialdehyde, glutathione (GSH), GSH-peroxidase (Px) activities, and nitric oxide (NO) levels were measured on intestinal samples.

RESULTS

Although the control group had normal HIS, group 2 had grade 3 HIS. In contrast, group 3 had minimal HIS, and these results were significantly better than those of group 2 (P < .001). Malondialdehyde and NO levels of group 3 were significantly lower than those of group 2 (P < .01). Glutathione and GSH-Px activities of group 1 were higher than those of groups 2 and 3 (P < .05). However, there were no significant differences for GSH and GSH-Px activities between groups 2 and 3.

CONCLUSIONS

This study showed that hypoxia and NO contributed to the pathogenesis of H/R-induced intestinal injury and that prophylactically administered EGb 761 had a protective effect on bowel injury.

Protective effects of clarithromycin in rats with hypoxia/reoxygenation-induced intestinal injury

BACKGROUND

This study was designed to determine the role of oxidative stress, nitric oxide (NO), and glutathione-related antioxidant enzymes in rat pups with hypoxia/reoxygenation (H/R)-induced bowel injury and to evaluate the potential benefits of prophylactic clarithromycin.

METHODS

One-day-old Wistar albino rat pups (N = 21) were randomly divided into 3 groups: group I (control), group II (exposed to H/R), and group III (clarithromycin + H/R). Clarithromycin was administered (40 mg/kg) subcutaneously to group III for 3 days. On the fourth day, all rats except controls were exposed to H/R and were killed at 6 hours after H/R. Histopathologic injury scores (HIS), malonyldialdehyde, glutathione (GSH), glutathione-peroxidase (GSH-Px) activities, and NO levels were measured on intestinal samples.

RESULTS

Whereas there was no difference for malonyldialdehyde levels among groups, HIS and NO levels were higher in group II than groups I and III (P < .05). However, GSH and GSH-Px activities were lower in group II than groups I and III (P < .05). Clarithromycin significantly increased GSH and GSH-Px activities and reduced HIS and NO levels in group III.

CONCLUSION

This study showed that oxidative stress and NO contributed to the pathogenesis of H/R-induced bowel injury and that clarithromycin had a protective effect on bowel injury owing to anti-inflammatory and antioxidant effects.

Mathematical modeling in necrotizing enterocolitis--a new look at an ongoing problem

Necrotizing enterocolitis (NEC) is the most common and lethal disease that affects the gastrointestinal (GI) tract of the premature infant. The etiology of NEC remains undefined. The only consistent epidemiological precursors for NEC are prematurity and enteral alimentation. Various inflammatory mediators, including tumor necrosis factor (TNF)-a, interleukin (IL)-1, IL-6, IL-8, IL-10, IL-18, platelet-activating factor (PAF), and nitric oxide (NO) have been implicated in the pathogenesis of NEC, but the kinetics and role of these agents are ill-defined. Currently, there are no biomarker predictors of NEC risk and severity. Sera or tissue from early time points in the development of the disease may help delineate early inflammatory events that predispose an individual to NEC, thus providing an interventional opportunity. We suggest that the lack of diagnostic and therapeutic modalities for NEC are due to the absence of a systems view of the disease, which in turn is hindered by a lack of sensitive physiological measurements that predict perturbations in the intestinal tissue compartment and an inability to reliably test serial samples for the presence of inflammatory mediators in small volumes and in a high-throughput manner. Computational modeling is a useful tool in the study of complex systems such as the inflammatory process. Computation models provide an "existence proof" for a given mechanism, uncover subtle inconsistencies between the underlying hypotheses and quantitative data, and force one to ask how much is known. We suggest that a properly validated and calibrated mathematical model of inflammation and its pathologic consequences in NEC will be useful for predicting the physiologic and biologic response in infants suffering from the disease.

Intestinal microcirculatory dysfunction during the development of experimental necrotizing enterocolitis

The aim of this study was to evaluate changes in intestinal microcirculation during necrotizing enterocolitis (NEC) and to examine the effect of endothelin (ET)-1 on the intestinal microcirculation. Prematurely born rats were either hand-fed formula (NEC) or dam fed (DF) and were exposed to asphyxia and cold stress twice daily to induce disease. At 0, 2, 3, and 4 d after the birth, the microcirculation in the ileum was examined using in vivo microscopic methods. The nutritive microvascular perfusion in the NEC group was progressively compromised from d 3 to d 4 (35% and 50% decrease, respectively) when compared with DF rats. Concomitantly, intestinal blood flow assessed by laser Doppler flowmetry was significantly reduced at d 2, 3, and 4 (by 31%, 36%, and 73%, respectively). Levels of ET-1 mRNA in the ileum were increased 3.7-fold. Microvascular responses to topically applied ET-1 were significantly increased in the NEC group, which was associated with decreased expression of ETB receptor. These results suggest that microcirculatory dysfunction in the distal ileum of neonatal rats with NEC contributes to disease progression and that enhanced microvascular responsiveness to ET-1 may participate in these microcirculatory disturbances.

Effects of L-arginine and L-carnitine in hypoxia/reoxygenation-induced intestinal injury

BACKGROUND

This study was designed to show the role of oxidative stress, nitric oxide and glutathione-related antioxidant enzymes in hypoxia/reoxygenation (H/R)-induced intestinal injury model in mice and to evaluate the potential benefits of arginine and carnitine supplementation.

METHODS

A total of 28 young Balb/c mice were divided into four groups: Group 1 (untreated) was given physiological saline before the experiment; group 2 H/R mice were supplemented with L-arginine; group 3 H/R mice were given L-carnitine for 7 days; and group 4 mice served as controls. At the end of day 7, H/R injury was induced and intestinal tissue malondialdehyde (MDA), nitrate levels and glutathione peroxidase (GSH-Px), glutathione reductase (GR) and glutathione-S-transferase (GST) activities were measured.

RESULTS

MDA levels were higher in the untreated animals than in the other three groups. MDA levels were higher in the L-arginine-treated animals than in the L-carnitine-treated animals. Nitrate levels were found to be increased in the L-arginine-treated group when compared to the controls. GSH-Px and GR activities were increased in the untreated, the L-arginine and the L-carnitine-treated H/R groups when compared to the control group. GST activities were indifferent between the groups.

CONCLUSIONS

Oxidative stress contributes to the pathogenesis of H/R-induced intestinal injury. The glutathione redox cycle may have a crucial role in the H/R-induced intestinal injury. L-arginine and L-carnitine supplementations ameliorate the histological evidence of H/R-induced intestinal injury and decrease lipid peroxidation but do not alter the glutathione-related antioxidant enzyme activities.

Hypoxemic reperfusion after 120 mins of intestinal ischemia attenuates the histopathologic and inflammatory response *

OBJECTIVE

It has been suggested that reactive oxygen species play a pivotal role in the initial organ-tissue injury during reperfusion, eliciting inflammatory reaction and multiple organ failure. It was investigated if hypoxemic reperfusion attenuates tissue injury and inflammatory response.

DESIGN

Randomized animal study.

SETTING

Medical school laboratory.

SUBJECTS

Twenty-five male pigs weighing 25-28 kg.

INTERVENTIONS

Pigs were subjected to 120 mins of intestinal ischemia by clamping the superior mesenteric artery. Upon declamping, the animals were randomly assigned to receive either hypoxemic reperfusion (HR group, n = 9) reperfused with a Pao2 = 30-35 or normoxemic reperfusion (control group, n = 16) reperfused with a Pao2 = 100 mm Hg for 120 mins. Fluids without inotropes were given to combat circulatory shock during reperfusion.

MEASUREMENTS AND MAIN RESULTS

Portal blood and intestinal and lung biopsies were collected at baseline, end of ischemia, and end of reperfusion. Histopathologic changes were scored, and interleukin-1beta, qualitative Limulus amebocyte, lysate test, and Pao2/Fio2 were measured. Eight of 16 animals of the control group and seven of nine of the HR group survived (p = .22). At the end of reperfusion, the intestinal (p = .004) and lung (p = .028) pathologic scores were lower in the HR group compared with controls. The only significant difference in concentration of interleukin-1beta in the portal blood between the two animal groups occurred 120 mins after reperfusion (p = .006). The number of HR animals with a positive Limulus test was significantly smaller compared with controls at 60 (p = .041) and 120 (p = .07) mins of reperfusion. During the period of ischemia, the Pao2/Fio2 decreased similarly in the control and HR group, whereas after 120 mins of reperfusion the rate was significantly higher in the HR group.

CONCLUSIONS

Hypoxemic reperfusion represents an intervention that may attenuate the triggering of multifactorial cascade and organ tissue injury.

Resuscitation with 100% oxygen causes intestinal glutathione oxidation and reoxygenation injury in asphyxiated newborn piglets

OBJECTIVE

To compare mesenteric blood flow, oxidative stress, and mucosal injury in piglet small intestine during hypoxemia and reoxygenation with 21%, 50%, or 100% oxygen.

SUMMARY BACKGROUND DATA

Necrotizing enterocolitis is a disease whose pathogenesis likely involves hypoxia-reoxygenation and the generation of oxygen-free radicals, which are known to cause intestinal injury. Resuscitation of asphyxiated newborns with 100% oxygen has been shown to increase oxidative stress, as measured by the glutathione redox ratio, and thus may predispose to free radical-mediated tissue injury.

METHODS

Newborn piglets subjected to severe hypoxemia for 2 hours were resuscitated with 21%, 50%, or 100% oxygen while superior mesenteric artery (SMA) flow and hemodynamic parameters were continuously measured. Small intestinal tissue samples were analyzed for histologic injury and levels of oxidized and reduced glutathione.

RESULTS

SMA blood flow decreased to 34% and mesenteric oxygen delivery decreased to 9% in hypoxemic piglets compared with sham-operated controls. With reoxygenation, SMA blood flow increased to 177%, 157%, and 145% of baseline values in piglets resuscitated with 21%, 50%, and 100% oxygen, respectively. Mesenteric oxygen delivery increased to more than 150% of baseline values in piglets resuscitated with 50% or 100% oxygen, and this correlated significantly with the degree of oxidative stress, as measured by the oxidized-to-reduced glutathione ratio. Two of eight piglets resuscitated with 100% oxygen developed gross and microscopic evidence of pneumatosis intestinalis and severe mucosal injury, while all other piglets were grossly normal.

CONCLUSIONS

Resuscitation of hypoxemic newborn piglets with 100% oxygen is associated with an increase in oxygen delivery and oxidative stress, and may be associated with the development of small intestinal hypoxia-reoxygenation injury. Resuscitation of asphyxiated newborns with lower oxygen concentrations may help to decrease the risk of necrotizing enterocolitis.

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.

Surfactant and inhaled nitric oxide in rats alleviate acute lung injury induced by intestinal ischemia and reperfusion

BACKGROUND

Respiratory distress and acute lung injury (ALI) are severe complications of intestinal ischemia and reperfusion injury (I/R). The authors hypothesize that a combined surfactant and inhaled nitric oxide (iNO) may alleviate I/R-induced ALI.

METHODS

Adult rats (body weight 285 to 315 g, n = 45) were allocated randomly to either a negative control group (N-Control, n = 9) with only sham laparotomy, or groups (n = 9 each) for induction of I/R by occlusion of superior mesenteric artery, followed by treatment with (1) surfactant at 100 mg/kg (Surf), (2) iNO at 20 ppm (NO), (3) both surfactant and iNO (SNO), or (4) no surfactant no iNO (a positive control, P-Control). Mechanical ventilation was provided for 120 minutes with variable peak insufflation pressure and FIO2 to achieve adequate arterial pH, PaO2, and PaCO2. Blood gas values, dynamic lung compliance (Cdyn), and airway resistance (Raw) were measured during the 2-hour treatment. Lung wet-to-dry weight ratio (W/D), histopathology, and morphometric analysis of alveolar expansion (V(V)) were determined at the end of the experiment.

RESULTS

After 120 minutes of treatment, the SNO group had the highest PaO2 and Cdyn values, close to that of the N-Control group. The Surf, NO, and SNO groups had higher V(V) and lower CV (V(V)) values than the P-Control, but modest decrease of W/D values. The NO group had moderately improved PaO2 but Cdyn and V(V) were as low as that of the P-Control. The lungs of the SNO group had significantly alleviated edema and neutrophil infiltration compared with the P-Control.

CONCLUSIONS

The combined surfactant and iNO treatment alleviated rat ALI induced by I/R, and exerted effects better than the use of surfactant or iNO alone.

Extent of intestinal damage in the developing chick embryo after repetitive hypoxia under normoxic or hyperoxic conditions

BACKGROUND

Episodes of hypoxia and reperfusion play an important role in the development of intestinal damage during perinatal development. The aim of this study was to investigate the histopathology of the intestine in the developing chick embryo after exposure to repetitive hypoxia and recovery under two different conditions: normoxic and hyperoxic (60% O2).

METHODS

Chick embryos were exposed to 5 minutes of hypoxia. This was repeated six times with a recovery period of 15 minutes under normoxic conditions (21% O2) for chick embryos in test group 1 (TG1) and under hyperoxic conditions (100% O2) for chick embryos in test group 2 (TG2), from day 11 until day 20. Chick embryos that recovered under hyperoxic conditions (100% O2) were previously incubated under hyperoxic conditions (60% O2 for 24 hours). Histologic evaluation of the ileum was performed at different times after the interventions (2, 4, 8, 16, and 24 hours).

RESULTS

In both test groups, only chick embryos older than 19 days showed intestinal damage. Intestinal histology on day 19 showed vasodilation of villus capillaries (10% in TG1 and 15% in TG2), necrosis in the top of the villi (29% in TG1 and 30% in TG2), and necrosis with preservation of base of the crypts (2% in TG1) and transmucosal necrosis (2% in TG2).

CONCLUSIONS

Significant histologic changes, compared with the control group, were only found in chick embryos that were studied 2 hours after the interventions. Furthermore, recovery under hyperoxic conditions did not cause more intestinal damage compared with recovery under normoxic conditions.

Moderate hypothermia ameliorates liver energy failure after intestinal ischaemia-reperfusion in anaesthetised rats

BACKGROUND/PURPOSE

Intestinal ischaemia-reperfusion (IR) can cause liver failure. The aims of this work were to study the effects of intestinal IR on liver energy metabolism and to evaluate the effects of moderate hypothermia.

METHODS

Intestinal IR (90-minute intestinal ischaemia plus 60-minute or 240-minute reperfusion) was achieved by clamping and unclamping the superior mesenteric artery in rats. Normothermia or moderate hypothermia (30 degrees to 33 degrees C) was maintained by adjusting the environmental temperature. The ratio of hepatic inorganic phosphate to adenosine triphosphate (ATP) was monitored continuously during intestinal IR using in vivo phosphorus ((31)P) magnetic resonance spectroscopy. Phosphorus metabolites also were measured in extracts prepared from freeze-clamped liver and intestine.

RESULTS

Mortality occurred exclusively during normothermic intestinal IR. A progressive increase in the hepatic inorganic phosphate to ATP ratio after normothermic intestinal IR was observed. Moderate hypothermia delayed this effect. Analysis of liver extracts confirmed above findings. However, there was no difference in intestinal phosphocreatine or ATP between normothermic and hypothermic rats undergoing intestinal IR.

CONCLUSIONS

Intestinal IR at normothermia was associated with liver energy failure and high mortality rate. Moderate hypothermia ameliorated liver energy failure but did not attenuate intestinal energy failure after intestinal IR. Hypothermia may prove to be useful in the management of patients with intestinal IR injuries in the future.

Intestinal metabolism after ischemia-reperfusion

PURPOSE

This study explores the effects of ischemia-reperfusion on various metabolic aspects of the small intestine.

METHODS

Intestinal ischemia-reperfusion was obtained by clamping and unclamping the superior mesenteric artery in adult rats. Four groups of animals were studied: (A) sham operation for 150 minutes, (B) 90-minute intestinal ischemia, (C) 150-minute intestinal ischemia, and (D) 90-minute intestinal ischemia followed by 60-minute reperfusion. Body temperature was maintained at normothermia (36.5 to 37.5 degrees C). Concentrations of intestinal glucose, succinate, lactate, amino acids, phosphocholine (PC), glycerophosphocholine (GPC), choline, and phosphoenergetics were measured using magnetic resonance spectroscopy of freeze-clamped small intestine extracts.

RESULTS

Intestinal ischemia (groups B and C) alone caused a significant drop in glucose and phosphoenergetics but caused an increase in amino acids, succinate, and lactate. Ischemia and ischemia-reperfusion decreased PC and GPC but increased choline. After intestinal reperfusion (group D), no recovery of phosphoenergetics was observed, but there was partial recovery of glucose, succinate, lactate, and amino acids.

CONCLUSIONS

There is no recovery of phosphoenergetics after 90 minutes of intestinal ischemia followed by 60 minutes of reperfusion. Partial recovery of glucose, succinate, lactate, and amino acids may reflect equilibration of these metabolites between damaged cells and extracellular fluid.

Essential fatty acid metabolism in the micropremie

Lipids are structural components of all tissues and are indispensable for cell membrane synthesis. The brain, retina, and other neural tissues are particularly rich in LCPUFAs, affecting neural structural development and function. LCPUFAs serve also as specific precursors for eicosanoid production (prostaglandins, prostacyclins, thromboxanes, and leukotrienes). These autocrine and paracrine mediators are powerful regulators of numerous cell and tissue functions (e.g., thrombocyte aggregation, inflammatory reactions, and leukocyte functions, vasoconstriction and vasodilatation, blood pressure, bronchial constriction, uterine contraction). Dietary lipid intake affects cholesterol metabolism at an early age and is associated with cardiovascular morbidity and mortality in later life. Over recent years, the role of fatty acids in modulating signal transduction and regulating gene expression have been described, emphasizing the complex of fatty acid effects. Dietary fatty acids, especially LCPUFA, can have significant effects in the modulation of developmental processes affecting the clinical outcomes of extremely premature infants.