The effects of ischemia-reperfusion on endothelial cell function in postnatal intestine

The conducted vasomotor response and the principles of electrical communication in resistance arteries

Biological tissues are fed by arterial networks whose task is to set blood flow delivery in accordance with energetic demand. Coordinating vasomotor activity among hundreds of neighboring segments is an essential process, one dependent upon electrical information spreading among smooth muscle and endothelial cells. The "conducted vasomotor response" is a functional expression of electrical spread, and it is this process that lies at the heart of this critical review. Written in a narrative format, this review first highlights historical manuscripts and then characterizes the conducted response across a range of preparations. Trends are highlighted and used to guide subsequent sections, focused on cellular foundations, biophysical underpinnings, and regulation in health and disease. Key information has been tabulated; figures reinforce grounding concepts and reveal a framework within which theoretical and experimental work can be rationalized. This summative review highlights that despite 30 years of concerted experimentation, key aspects of the conducted response remain ill defined. Of note is the need to rationalize the regulation and deterioration of conduction in pathobiological settings. New quantitative tools, along with transgenic technology, are discussed as a means of propelling this investigative field forward.

A systematic review and meta-analysis of the role of Doppler ultrasonography of the superior mesenteric artery in detecting neonates at risk of necrotizing enterocolitis

The role of postnatal Doppler measurements of the superior mesenteric artery (SMA) in detecting neonates at risk of necrotizing enterocolitis (NEC) remains uncertain; therefore, we systematically reviewed and meta-analyzed the existing evidence regarding the usefulness of SMA Doppler measurements in detecting neonates at risk for NEC. We used the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines, and we included studies which reported the following Doppler ultrasonography indices: peak systolic velocity, end-diastolic velocity, time average mean velocity, differential velocity, pulsatility index (PI) and resistive index. Eight studies were eligible for inclusion in the meta-analysis. Evidence suggested that, during the first postnatal day, neonates who developed NEC had a significantly higher peak systolic velocity (mean difference of 2.65 cm/s (95% confidence interval [CI] 1.23, 4.06, overall effect Z=3.66, P<0.001)), higher PI (mean difference of 1.52 (95% CI 0.00, 3.04, Z=1.96, P=0.05)) and higher resistive index (mean difference of 1.09 (95% CI 0.59, 1.60, Z=4.24, P<0.001)), compared to neonates who did not develop NEC. However, our findings do not support a strong association between the Doppler ultrasound indices and development of NEC at the time of disease onset. This meta-analysis suggests that first postnatal day SMA Doppler parameters, namely peak systolic velocity, PI and resistive index, are higher in neonates who develop NEC. On the other hand, the aforementioned indices are of uncertain significance once the diagnosis of NEC has been established.

In vivo phenotyping of the microvasculature in necrotizing enterocolitis with multicontrast optical imaging

OBJECTIVE

Necrotizing enterocolitis (NEC) is the most prevalent gastrointestinal emergency in premature infants and is characterized by a dysfunctional gut microcirculation. Therefore, there is a dire need for in vivo methods to characterize NEC-induced changes in the structure and function of the gut microcirculation, that is, its vascular phenotype. Since in vivo gut imaging methods are often slow and employ a single-contrast mechanism, we developed a rapid multicontrast imaging technique and a novel analyses pipeline for phenotyping the gut microcirculation.

METHODS

Using an experimental NEC model, we acquired in vivo images of the gut microvasculature and blood flow over a 5000 × 7000 μm² field of view at 5 μm resolution via the following two endogenous contrast mechanisms: intrinsic optical signals and laser speckles. Next, we transformed intestinal images into rectilinear "flat maps," and delineated 1A/V gut microvessels and their perfusion territories as "intestinal vascular units" (IVUs). Employing IVUs, we quantified and visualized NEC-induced changes to the gut vascular phenotype.

RESULTS

In vivo imaging required 60-100 s per animal. Relative to the healthy gut, NEC intestines showed a significant overall decrease (i.e. 64-72%) in perfusion, accompanied by vasoconstriction (i.e. 9-12%) and a reduction in perfusion entropy (19%)within sections of the vascular bed.

CONCLUSIONS

Multicontrast imaging coupled with IVU-based in vivo vascular phenotyping is a powerful new tool for elucidating NEC pathogenesis.

The role of the intestinal microcirculation in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) continues to be a devastating inflammatory disease of the newborn intestine. Despite advances in management, morbidity and mortality remain high. While it is clear that intestinal ischemia plays a large role in disease pathogenesis, attempts to link NEC to intestinal macrovascular derangement have been largely unsuccessful. More recently, there has been a concerted effort to characterize the pathologic changes of the intestinal microcirculation in response to intestinal injury, including NEC. This microcirculatory regulation is controlled by a balance of vasoconstrictor and vasodilator forces. Vasoconstriction is mediated primarily by endothelin-1 (ET-1), while vasodilation is mediated primarily by nitric oxide (NO). These chemical mediators have been implicated in many aspects of intestinal ischemic injury and NEC, with the balance shifting toward increased vasoconstriction associated with intestinal injury. With a proper understanding of these antagonistic forces, potential therapeutic avenues may result from improving this pathologic microcirculatory dysregulation.

Novel treatments for NEC: keeping IBD in mind

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disease of premature newborns, thought to result in part from overactivity of the innate immune system. NEC has been well-studied from the perspective of prevention; however, after the disease onset, there are limited treatment options to control its progression. This review discusses four potential therapies that target the overactive immune response in NEC: pentoxifylline, platelet activating factor modulators, glucocorticoids, and vasoactive substances. In addition, given the similar pathogenesis of NEC and inflammatory bowel disease (IBD), we propose that IBD therapies could provide promising leads for novel strategies with which to treat NEC.

Cyclosporine treatment improves mesenteric perfusion and attenuates necrotizing enterocolitis (NEC)-like intestinal injury in asphyxiated newborn piglets during reoxygenation

PURPOSE

Asphyxia-related intestinal injury in neonates may present similar to necrotizing enterocolitis (NEC) and is partially associated with hypoxia-reoxygenation injury. Cyclosporine has been shown to reduce myocardial cell death following ischemia-reperfusion. We hypothesize that cyclosporine treatment may attenuate NEC-like intestinal injury in asphyxiated newborn piglets during reoxygenation.

METHODS

Twenty piglets (1-4 days old) were acutely anesthetized and instrumented for continuous monitoring of systemic hemodynamics and superior mesenteric arterial (SMA) flow. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2 h followed by reoxygenation with 100% oxygen for 0.5 h, then 21% for 3.5 h. The piglets were blindly block-randomized to receive cyclosporine (10 mg/kg) or placebo (normal saline) boluses at 5 min of reoxygenation (n = 8/group). A sham-operated group was included (n = 4) and received no hypoxia-reoxygenation. Intestinal samples were collected for tissue lactate and histological assessment (Park's criteria).

RESULTS

At 2 h of hypoxia, piglets had cardiogenic shock (cardiac output 45% of baseline), hypotension (mean arterial pressure 30 mmHg), acidosis (pH 7.04), and decreased superior mesenteric perfusion (all P < 0.05 vs. sham-operated group, ANOVA). Cyclosporine treatment increased SMA flow (114 ± 6 vs. 78 ± 19% of baseline of controls, respectively) with improved SMA oxygen delivery and intestinal tissue lactate (all P < 0.05). Some control piglets had NEC-like injuries including pneumatosis intestinalis, which were attenuated in cyclosporine-treated piglets (P < 0.05 vs. controls).

CONCLUSIONS

This is the first study to demonstrate that post-resuscitation administration of cyclosporine improves mesenteric perfusion and attenuates NEC-like intestinal injury in newborn piglets following asphyxia-reoxygenation.

Peculiaridades da circulação mesentérica em recém-nascidos e suas implicações em doenças gastrintestinais do período neonatal

OBJETIVO:Descrever peculiaridades da circulação mesentérica neonatal e caracterizar fatores de suscetibilidade ao desenvolvimento de doenças gastrintestinais e alterações do fluxo sanguíneo da artéria mesentérica superior por meio da dopplerfluxometria. FONTES DE DADOS: Livros-textos e publicações indexadas no Medline e SciELO nos últimos 20 anos, utilizando-se as palavras chaves: "mesenteric artery", "superior mesenteric artery", "newborn intestinal circulation", "necrotizing enterocolitis", "doppler flow velocimetry". SÍNTESE DOS DADOS: Alterações do fluxo sanguíneo mesentérico são um dos fatores predisponentes da enterocolite necrosante, doença neonatal de alta morbimortalidade que acomete principalmente prematuros. A circulação mesentérica é peculiar no período neonatal tanto em relação ao seu estado basal, quanto à sua resposta frente a estímulos fisiológicos. Variações da irrigação mesentérica podem ser inerentes à própria fase de desenvolvimento vascular intestinal do recém-nascido pré-termo, com possíveis agravos de fatores perinatais como: insuficiência placentária, asfixia, infecção, cateterismo umbilical, drogas (indometacina e cafeína), fototerapia, alimentação artificial e progressão rápida da dieta. A dopplerfluxometria permite o estudo da irrigação de órgãos-alvo e pode quantificar o fluxo sanguíneo, a resistência vascular e predizer situações de risco para doenças do trato gastrintestinal no período neonatal. CONCLUSÕES: O recém-nascido apresenta peculiaridades de irrigação sanguínea gastrintestinal. A dopplerfluxometria da artéria mesentérica superior é um método não invasivo que determina as condições circulatórias no território intestinal.

Heparin-binding EGF-like growth factor is a potent dilator of terminal mesenteric arterioles

OBJECTIVE

We have previously shown that heparin-binding EGF-like growth factor (HB-EGF) protects the intestines from multiple forms of injury via direct cytoprotective effects on the intestinal mucosa. In this study, we examined the effects of HB-EGF on the hemodynamics of intestinal arterioles, the major resistance vessels that regulate blood flow to the intestines, as an additional mechanism of HB-EGF-mediated intestinal protection.

METHODS

The hemodynamic effects of HB-EGF in rodent terminal mesenteric arterioles and human submucosal arterioles were examined ex vivo using a video dimension analyzer. Cultured human intestinal microvascular endothelial cells (HIMEC) were used to elucidate the mechanisms of HB-EGF-induced vasodilation.

RESULTS

HB-EGF significantly increased vessel diameter under conditions of increasing intraluminal pressure and increased flow rate. These HB-EGF-mediated vasodilatory effects were observed in terminal mesenteric arterioles from adult rats and 3 day old rat pups. These effects were confirmed in submucosal arterioles from human intestine. Furthermore, HB-EGF significantly reduced endothelin-1-induced mesenteric arteriolar vasoconstriction. The vasodilatory effects of HB-EGF were blocked by ET(B) receptor antagonism in adult rat arterioles, and also by nitric oxide synthase inhibition in rat pup and human infant arterioles. In HIMEC, HB-EGF significantly increased endothelin B (ET(B)) receptor protein expression and provoked intracellular calcium mobilization.

CONCLUSIONS

HB-EGF is a potent vasodilator of the intestinal microvasculature, further supporting its use in diseases manifested by decreased intestinal blood flow, including necrotizing enterocolitis.

The neonatal intestinal vasculature: contributing factors to necrotizing enterocolitis

Based on the demonstration of coagulation necrosis, it is clear that intestinal ischemia plays a role in the pathogenesis of necrotizing enterocolitis (NEC). Intestinal vascular resistance is determined by a dynamic balance between vasoconstrictive and vasodilatory inputs. In the newborn, this balance heavily favors vasodilation secondary to the copious production of endothelium-derived nitric oxide (NO), a circumstance which serves to ensure adequate blood flow and thus oxygen delivery to the rapidly growing intestine. Endothelial cell injury could shift this balance in favor of endothelin (ET)-1-mediated vasoconstriction, leading to intestinal ischemia and tissue injury. Evidence obtained from animal models and from human tissue collected from infants with NEC implicates NO and ET-1 dysregulation in the pathogenesis of NEC. Strategies focused on maintaining the delicate balance favoring vasodilation in the newborn intestinal circulation may prove to be useful in the prevention and treatment of NEC.

Necrotizing enterocolitis

In necrotizing enterocolitis (NEC) the small (most often distal) and/or large bowel becomes injured, develops intramural air, and may progress to frank necrosis with perforation. Even with early, aggressive treatment, the progression of necrosis, which is highly characteristic of NEC, can lead to sepsis and death. This article reviews the current scientific knowledge related to the etiology and pathogenesis of NEC and discusses some possible preventive measures.

Developmental expression of eNOS in postnatal swine mesenteric artery

Developmental changes in the expression of endothelial nitric oxide synthase (eNOS) within the mesenteric artery of swine were studied in fetal (110 days postconception/117 days total gestation) and on postnatal days 1, 3, 10, and 30. Subjects in the 1-day-old group were subdivided into fed and nonfed. Transcription of eNOS was determined by real-time PCR, protein expression was evaluated by Western blotting, and hemodynamic and oxygenation parameters were measured within in situ gut loops before and after the administration of N(G)-monomethyl-L-arginine (L-NMMA). The abundance of eNOS mRNA remained steady throughout all ages. In contrast, expression of eNOS protein was twofold greater in the 1-day-old fed subjects compared with fetal or 1-day-old nonfed subjects. eNOS protein expression remained elevated on day 3, increased on day 10, and then declined to a level similar to the day 1 nonfed group by postnatal day 30. Intestinal vascular resistance was 31% lower in the day 1 fed group when compared to the day 1 nonfed group; resistance continued to decline through day 10 but then significantly increased on day 30. We conclude that the expression of eNOS changes within the mesenteric artery during early postnatal development at a posttranscriptional level.

Induction of oxidative stress and disintegrin metalloproteinase in human heart end-stage failure

Collagen degradation is required for the creation of new integrin binding sites necessary for cell survival. However, a complete separation between the matrix and the cell leads to apoptosis, dilatation, and failure. Previous studies have demonstrated increased metalloproteinase activity in the failing myocardium. To test the hypothesis that disintegrin metalloproteinase (DMP) is induced in human heart end-stage failure, left ventricle tissue from ischemic cardiomyopathic (ICM, n = 10) and dilated cardiomyopathic (DCM, n = 10) human hearts were obtained at the time of orthotopic cardiac transplant. Normal (n = 5) tissue specimens were obtained from unused hearts. The levels of reduced oxygen species (ROS) were 12 +/- 2, 25 +/- 3, and 16 +/- 2 nmol (means +/- SE, P < 0.005) in normal, ICM, and DCM, respectively, by spectrofluorometry. The percent levels of endothelial cells were 100 +/- 15, 35 +/- 19, and 55 +/- 11 in normal, ICM, and DCM, respectively, by CD31 labeling. The levels of nitrotyrosine by Western analysis were significantly increased, and endothelial nitric oxide (NO) by the Griess method was decreased in ICM and DCM compared with normal tissue. The synthesis and degradation of beta(1)-integrin and connexin 43 were significantly increased in ICM and DCM compared with normal hearts by Western analysis. Levels of DMP were increased, and levels of cardiac inhibitor of metalloproteinase (CIMP) were decreased. Aggrecanase activity of DMP was significantly increased in ICM and DCM hearts compared with normal. These results suggest that the occurrence of cardiomyopathy is significantly confounded by the increase in ROS, nitrotyrosine, and DMP activity. This increase is associated with decreased NO, endothelial cell density, and CIMP. In vitro, treatment of CIMP abrogated the DMP activity. The treatment with CIMP may prevent degradation of integrin and connexin and ameliorate heart failure.

Newborn intestinal circulation. Physiology and pathophysiology

The physiologic characteristics of the newborn intestinal circulation are unique when compared with the adult condition. Most important, intestinal vascular resistance across newborn intestine is exceptionally low and this transient reduction is mediated by an increased constitutive and stimulated production of NO. The low vascular resistance characteristic of newborn intestine alters the capacity of this vasculature to respond to systemic circulatory perturbations, such as hypotension and arterial hypoxemia. The essential role of endothelial production of NO in maintaining newborn intestinal hemodynamics might be important in the pathogenesis of NEC, because endothelial dysfunction would limit, or possibly eliminate, NO production, leading to substantial intestinal ischemia.

Endothelin ET(A) and ET(B) receptors in postnatal intestine

We aimed to characterize endothelin (ET) receptors in the swine intestinal vasculature and to determine ischemia-reperfusion (I/R) effects on these receptors. Saturation and competitive binding assays were performed on mesenteric artery protein membranes from 1- and 40-day-old animals, both control and those subjected to 1 h of partial ischemia followed by 6 h of reperfusion in vivo. Scatchard analysis of saturation binding with (125)I-labeled ET-1 in membranes from endothelium-denuded (E(-)) vessels revealed that the maximum number of binding sites was greater in younger animals. Competitive (125)I-ET-1 binding was significant for a one-site model with ET-1, ET-3, and sarafotoxin S6c (S6c) in membranes from endothelium-intact (E(+)) and E(-) vessels in both age groups. The maximum number of ET-1 binding sites was significantly greater in younger animals. In the presence of the ET(A) receptor antagonist BQ-123, competitive (125)I-ET-1 binding was significant for a one-site model with ET-1 and S6c in membranes from E(+) vessels in both age groups. The maximum number of ET-1 binding sites was significantly greater in younger animals. After I/R, the maximum number of ET-1 binding sites was unchanged. In the presence of BQ-123, specific binding by ET-1 and S6c was eliminated in both age groups after I/R. These results suggest that both ET receptor populations are expressed to a greater degree in younger animals and I/R significantly affects the ET(B) receptor.

Endothelin-mediated vasoconstriction in postischemic newborn intestine

We previously suggested that the profound, sustained vasoconstriction noted in 3-day-old swine intestine after a moderate episode of ischemia-reperfusion (I/R) reflects the unmasking of underlying constrictor tone consequent to a loss of endothelium-derived nitric oxide (NO). In this study, we sought to determine whether endothelin-1 (ET-1) was the unmasked constrictor and whether selective loss of endothelial ET(B) receptors, which mediate NO-based vasodilation, participated in the hemodynamic consequences of I/R in newborn intestine. Studies were performed in innervated, autoperfused intestinal loops in 3- and 35-day-old swine. Selective blockade of ET(A) receptors with BQ-610 had no effect on hemodynamics under control conditions; however, when administered before and during I/R, BQ-610 significantly attenuated the post-I/R vasoconstriction and reduction in arteriovenous O(2) difference in the younger group. In 3-day-old intestine, reduction of intestinal O(2) uptake to a level similar to that noted after I/R by lowering tissue temperature had no effect on the response to BQ-610 or ET-1, indicating that the change in response to BQ-610 noted after I/R was not simply consequent to the reduction in tissue O(2) demand. In studies in mesenteric artery rings suspended in myographs, we observed a leftward shift in the dose-response curve for ET-1 after selective blockade of ET(B) receptors with BQ-788 in 3- but not 35-day-old swine. Rings exposed to I/R in vivo behaved in a manner similar to control rings treated with BQ-788 or endothelium-denuded non-I/R rings.

The effect of asphyxia on superior mesenteric artery blood flow in the premature sheep fetus

BACKGROUND/PURPOSE

The aim of this study was to determine superior mesenteric artery blood flow changes during and after an asphyxial insult in utero in chronically instrumented unanaesthetised premature fetal sheep.

METHODS

Fetal sheep at 0.7 gestation (103 to 104 days) underwent 25 minutes of complete umbilical cord occlusion (n = 6) or sham occlusion (n = 6). Fetal heart rate, blood pressure, superior mesenteric artery (SMA) blood flow and vascular resistance, electroencephalographic activity, and nuchal electromyographic activity were measured from 6 hours before occlusion until 3 days after occlusion. Fetal gastrointestinal tissue was taken for histological assessment.

RESULTS

During occlusion, cardiovascular response was characterised by 3 phases: initial redistribution of blood flow away from the gut to maintain vital organ function, subsequently partial failure of this redistribution, and finally near terminal cardiovascular collapse with profound hypotension and gastrointestinal hypoperfusion. Postasphyxia there was a secondary period of hypoperfusion that was mediated by increased vascular resistance, not hypotension. There was no evidence of injury on standard histological assessment after 3 days of recovery.

CONCLUSIONS

SMA blood flow is not only significantly reduced during asphyxia, but also for several hours after an asphyxial insult. The authors speculate that these perturbations of gastrointestinal blood flow could compromise gut wall integrity potentially leading to increased vulnerability to necrotising enterocolitis.

Major vasodilator role for nitric oxide in the gastrointestinal circulation of the mid-gestation fetal lamb

As nitric oxide (NO) may be a particularly important vasodilator in early life, we investigated its role in the regulation of the gastrointestinal (GI) circulation at mid-gestation. Cardiac output and GI blood flow were measured by the radioactive microsphere technique in eight chronically instrumented and unanesthetized mid-gestation fetal sheep. Mean arterial pressure (MAP), heart rate, blood flow, oxygen delivery, and vascular resistance were determined before and after infusion of the specific NO synthase inhibitor, Nomega-nitro-L-arginine (L-NNA) at doses of 10 and 25 mg/kg. In response to L-NNA infusion, MAP increased (p < 0.01) and combined ventricular output decreased (p < 0.001). GI blood flow and oxygen delivery decreased and vascular resistance increased in the stomach and all segments of the small and large intestine (all p < 0.001). The greatest reduction in blood flow was in the small intestine (p < 0.01) and the basal differential pattern of small intestinal blood flow exceeding large intestinal flow was completely abolished. These changes were much greater than those previously described in late-gestation fetuses. Our results suggest that, at mid-gestation, NO plays a major role in the regulation of blood flow and vascular tone across all segments of the fetal GI tract, with its effects being more pronounced than later in development.

Developmental differences in response of mesenteric artery to acute hypoxia in vitro

Studies were conducted to determine if the response of in vitro mesenteric artery from 3- and 35-day-old swine to acute hypoxia was age dependent. Isometric tension developed by mesenteric artery rings was measured using a standard myograph apparatus. When the buffer aeration gas was changed from 95% O2-5% CO2 to 95% N2-5% CO2, phenylephrine-precontracted rings from both age groups consistently demonstrated a triphasic response, consisting of, in order, an initial, brief dilation, a sharp contraction, and a sustained loss of tone. The only portion of the triphasic response that was age dependent was the constrictor response, hypoxic vasoconstriction (HVC), which was significantly greater in rings from younger animals. HVC appeared to be mediated by a hypoxia-induced loss of constitutive nitric oxide production. Thus HVC was eliminated by endothelial removal, significantly attenuated by pretreatment with NG-monomethyl-L-arginine (L-NMMA), but not with NG-monomethyl-D-arginine, restored by coadministration of L-arginine, and accentuated by pretreatment with superoxide dismutase. Blockade of endothelin A receptors with BQ-610 or inhibition of cyclooxygenase or lipoxygenase activities with indomethacin or phenidone had no effect on HVC in either group. HVC appeared to be dependent on reduction in PO2, not on reduced ATP secondary to hypoxia, as it did not occur in rings administered 2,4-dinitrophenol, an agent that uncouples oxidative phosphorylation. The magnitude of HVC, which appears to be mediated by hypoxia-induced supression of NO production, is greater in mesenteric artery from 3-day-old swine than from 35-day-old swine.

Ischemia-reperfusion injury in the intestines of newborn pigs

Although the pathogenesis of necrotizing enterocolitis remains uncertain, ischemia appears to be an important contributing factor to the development of this disorder. Reperfusion plays a major role in ischemia-related injury, and oxygen free radicals produced during reperfusion most likely contribute to the injury. These oxidants can be generated during prostanoid metabolism, which increases during reperfusion of ischemic gut in adult subjects. The present study was designed to: 1) examine the effects of superior mesenteric artery occlusion, e.g. ischemia and reperfusion in vivo on the development of histopathologic intestinal injury; 2) determine whether products of arachidonic acid metabolism, e.g. prostanoids are increased during reperfusion of ischemic gut; and 3) determine whether oxygen free radical scavengers attenuate the injury in newborn pigs. Chronically catheterized placebo-pretreated newborn pigs exposed to ischemia-reperfusion, placebo-pretreated nonischemic control pigs, and polyethylene glycol-superoxide dismutase (SOD) plus polyethylene glycol-catalase (CAT)-pretreated, ischemic pigs were studied by examining changes in intestinal circulation, oxygenation, prostanoids, and tissue injury. In the placebo-pretreated pigs, intestinal blood flow decreased to very low levels during superior mesenteric artery occlusion. During reperfusion, blood flow increased, but remained below baseline. After ischemia, oxygen uptake returned to values that were similar to baseline. Intestinal efflux of the vasodilator 6-keto-prostaglandin F1alpha was evident (p < 0.05 versus no or zero efflux) during early reperfusion. Histopathologic scoring of terminal ileal samples showed significant mucosal necrosis, surface epithelial disruption, lamina propria congestion and hemorrhage, submucosal hemorrhage, edema, and increases in cells compared with the placebo-pretreated nonischemic pigs. In the SOD plus CAT-pretreated ischemic pigs, changes in intestinal blood flow, oxygen uptake, 6-keto-prostaglandin F1alpha efflux, and the pattern of the ileal tissue injury did not differ significantly from the placebo-pretreated ischemic pigs. In summary, superior mesenteric artery occlusion for 1 h and reperfusion for 2 h resulted in severe intestinal ischemia, early postocclusive limited increases in intestinal perfusion and oxygen uptake, efflux of vasodilating prostanoids during early reperfusion, and signs of ischemic tissue injury in the placebo- and SOD plus CAT-pretreated pigs. This study demonstrates that, after superior mesenteric artery occlusion and reperfusion, severe intestinal tissue injury is detected in vivo, prostanoid efflux increases, and SOD plus CAT given just before occlusion does not attenuate the extent of injury in newborn pigs.