Inducible nitric oxide synthase inhibition improves intestinal microcirculatory oxygenation and CO2 balance during endotoxemia in pigs

SOFA Score, Hemodynamics and Body Temperature Allow Early Discrimination between Porcine Peritonitis-Induced Sepsis and Peritonitis-Induced Septic Shock

Porcine model of peritonitis-induced sepsis is a well-established clinically relevant model of human disease. Interindividual variability of the response often complicates the interpretation of findings. To better understand the biological basis of the disease variability, the progression of the disease was compared between animals with sepsis and septic shock. Peritonitis was induced by inoculation of autologous feces in fifteen anesthetized, mechanically ventilated and surgically instrumented pigs and continued for 24 h. Cardiovascular and biochemical parameters were collected at baseline (just before peritonitis induction), 12 h, 18 h and 24 h (end of the experiment) after induction of peritonitis. Analysis of multiple parameters revealed the earliest significant differences between sepsis and septic shock groups in the sequential organ failure assessment (SOFA) score, systemic vascular resistance, partial pressure of oxygen in mixed venous blood and body temperature. Other significant functional differences developed later in the course of the disease. The data indicate that SOFA score, hemodynamical parameters and body temperature discriminate early between sepsis and septic shock in a clinically relevant porcine model. Early pronounced alterations of these parameters may herald a progression of the disease toward irreversible septic shock.

Nitric oxide production contributes to Bacillus anthracis edema toxin-associated arterial hypotension and lethality: ex vivo and in vivo studies in the rat

We showed previously that Bacillus anthracis edema toxin (ET), comprised of protective antigen (PA) and edema factor (EF), inhibits phenylephrine (PE)-induced contraction in rat aortic rings and these effects are diminished in endothelial-denuded rings. Therefore, employing rat aortic ring and in vivo models, we tested the hypothesis that nitric oxide (NO) contributes to ET's arterial effects. Compared with rings challenged with PA alone, ET (PA + EF) reduced PE-stimulated maximal contractile force (MCF) and increased the PE concentration producing 50% MCF (EC50) (P < 0.0001). Compared with placebo, l-nitro-arginine methyl-ester (l-NAME), an NO synthase (NOS) inhibitor, reduced ET's effects on MCF and EC50 in patterns that approached or were significant (P = 0.06 and 0.03, respectively). In animals challenged with 24-h ET infusions, l-NAME (0.5 or 1.0 mg·kg(-1)·h(-1)) coadministration increased survival to 17 of 28 animals (60.7%) compared with 4 of 27 (14.8%) given placebo (P = 0.01). Animals receiving l-NAME but no ET all survived. Compared with PBS challenge, ET increased NO levels at 24 h and l-NAME decreased these increases (P < 0.0001). ET infusion decreased mean arterial blood pressure (MAP) in placebo and l-NAME-treated animals (P < 0.0001) but l-NAME reduced decreases in MAP with ET from 9 to 24 h (P = 0.03 for the time interaction). S-methyl-l-thiocitrulline, a selective neuronal NOS inhibitor, had effects in rings and, at a high dose in vivo models, comparable to l-NAME, whereas N'-[3-(aminomethyl)benzyl]-acetimidamide, a selective inducible NOS inhibitor, did not. NO production contributes to ET's arterial relaxant, hypotensive, and lethal effects in the rat.

Microcirculatory and mitochondrial hypoxia in sepsis, shock, and resuscitation

After shock, persistent oxygen extraction deficit despite the apparent adequate recovery of systemic hemodynamic and oxygen-derived variables has been a source of uncertainty and controversy. Dysfunction of oxygen transport pathways during intensive care underlies the sequelae that lead to organ failure, and the limitations of techniques used to measure tissue oxygenation in vivo have contributed to the lack of progress in this area. Novel techniques have provided detailed quantitative insight into the determinants of microcirculatory and mitochondrial oxygenation. These techniques, which are based on the oxygen-dependent quenching of phosphorescence or delayed luminescence are briefly reviewed. The application of these techniques to animal models of shock and resuscitation revealed the heterogeneous nature of oxygen distributions and the alterations in oxygen distribution in the microcirculation and in mitochondria. These studies identified functional shunting in the microcirculation as an underlying cause of oxygen extraction deficit observed in states of shock and resuscitation. The translation of these concepts to the bedside has been enabled by our development and clinical introduction of hand-held microscopy. This tool facilitates the direct observation of the microcirculation and its alterations at the bedside under the conditions of shock and resuscitation. Studies identified loss of coherence between the macrocirculation and the microcirculation, in which resuscitation successfully restored systemic circulation but did not alleviate microcirculatory perfusion alterations. Various mechanisms responsible for these alterations underlie the loss of hemodynamic coherence during unsuccessful resuscitation procedures. Therapeutic resolution of persistent heterogeneous microcirculatory alterations is expected to improve outcomes in critically ill patients.

Arginine and citrulline and the immune response in sepsis

Arginine, a semi-essential amino acid is an important initiator of the immune response. Arginine serves as a precursor in several metabolic pathways in different organs. In the immune response, arginine metabolism and availability is determined by the nitric oxide synthases and the arginase enzymes, which convert arginine into nitric oxide (NO) and ornithine, respectively. Limitations in arginine availability during inflammatory conditions regulate macrophages and T-lymfocyte activation. Furthermore, over the past years more evidence has been gathered which showed that arginine and citrulline deficiencies may underlie the detrimental outcome of inflammatory conditions, such as sepsis and endotoxemia. Not only does the immune response contribute to the arginine deficiency, also the impaired arginine de novo synthesis in the kidney has a key role in the eventual observed arginine deficiency. The complex interplay between the immune response and the arginine-NO metabolism is further underscored by recent data of our group. In this review we give an overview of physiological arginine and citrulline metabolism and we address the experimental and clinical studies in which the arginine-citrulline NO pathway plays an essential role in the immune response, as initiator and therapeutic target.

Fluid resuscitation therapy in endotoxemic hamsters improves survival and attenuates capillary perfusion deficits and inflammatory responses by a mechanism related to nitric oxide

Background

Relative hypovolemia is frequently found in early stages of severe sepsis and septic shock and prompt and aggressive fluid therapy has become standard of care improving tissue perfusion and patient outcome. This paper investigates the role of the nitric oxide pathway on beneficial microcirculatory effects of fluid resuscitation.

Methods

After skinfold chamber implantation procedures and endotoxemia induction by intravenous Escherichia coli lipopolysaccharide administration (2 mg.kg⁻¹), male golden Syrian hamsters were fluid resuscitated and then sequentially treated with L-N^ω-Nitroarginine and L-Arginine hydrochloride (LPS/FR/LNNA group). Intravital microscopy of skinfold chamber preparations allowed quantitative analysis of microvascular variables including venular leukocyte rolling and adhesion. Macro-hemodynamic, biochemical and hematological parameters as well as survival rate were also evaluated. Endotoxemic hamsters treated with fluid therapy alone (LPS/FR group) and non-treated animals (LPS group) served as controls.

Results

Fluid resuscitation was effective in reducing lipopolysaccharide-induced microcirculatory changes. After 3 hours of lipopolysaccharide administration, non-fluid resuscitated animals (LPS group) had the lowest functional capillary density (1% from baseline for LPS group vs. 19% for LPS/FR one; p <0.05). At the same time point, arteriolar mean internal diameter was significantly wider in LPS/FR group than in LPS one (100% vs. 50% from baseline). Fluid resuscitation also reduced leukocyte-endothelium interactions and sequestration (p <0.05 for LPS vs. LPS/FR group) and increased survival (median survival time: 2 and 5.5 days for LPS and LPS/FR groups, respectively; p <0.05). Nitric oxide synthase inhibition prevented these protective effects, while L-Arginine administration markedly restored many of them.

Conclusion

Our results suggest that the underlying mechanism of fluid therapy is the restoration of nitric oxide bioavailability, because inhibition of NOS prevented many of its beneficial effects. Nevertheless, further investigations are required in experimental models closer to conditions of human sepsis to confirm these results.

Differentiated control of deranged nitric oxide metabolism: a therapeutic option in sepsis?

Derangement of nitric oxide (NO) metabolism represents one of the key mechanisms contributing to macro- and microcirculatory failure in sepsis. Sepsis-related therapy combining fluid resuscitation with administration of vasopressor and inotropic agents, however, does not guarantee correction of maldistributed nutritive perfusion between and within organs. Therefore, the differentiated and selective pharmacologic modulation of NO-mediated vascular function could play a useful role in hemodynamic management of patients with sepsis. This viewpoint carefully evaluates the potential role of intentionally using partially opposing effects of NO donors and NO synthase inhibitors to complement current therapy of hemodynamic stabilization in patients with sepsis.

From system to organ to cell: oxygenation and perfusion measurement in anesthesia and critical care

Maintenance or restoration of adequate tissue oxygenation is a main goal of anesthesiologic and intensive care patient management. Pathophysiological disturbances which interfere with aerobic metabolism may occur at any stage in the oxygen cascade from atmospheric gas to the mitochondria, and there is no single monitoring modality that allows comprehensive determination of "the oxygenation". To facilitate early detection of tissue hypoxia (or hyperoxia) and to allow a goal directed therapy targeted at the underlying problem, the anesthesiologist and intensive care physician require a thorough understanding of the numerous determinants that influence cellular oxygenation. This article reviews the basic physiology of oxygen uptake and delivery to tissues as well as the options to monitor determinants of oxygenation at different stages from the alveolus to the cell.

Microcirculation follows macrocirculation in heart and gut in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation in pigs

BACKGROUND

Disparity between the macro- and microcirculation is thought to occur as a result of (micro)vascular dysfunction in some types of shock. Whether this occurs during hemorrhagic shock, however, is unknown. We therefore investigated both macro- and microcirculatory variables in the heart as a vital organ and the gut as a nonvital organ. We hypothesized that the microcirculation in the gut would follow the macrocirculation in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation, but that the microcirculation in the heart would be preserved even under conditions of macrocirculatory depression.

STUDY DESIGN AND METHODS

Eleven pigs (23 ± 4 kg) were anesthetized and subjected to a controlled hemorrhagic shock (30 and 45% reduction of total blood volume) and isovolemic resuscitation with autologous blood. Quantitative measurement of microvascular oxygen pressures (µpO(2)) was performed by phosphorimetry on the gut and heart simultaneously. Measurements of systemic hemodynamic and regional oxygen-derived variables as well as µpO(2) were performed at baseline, after the first and second phases of hemorrhage, and after resuscitation.

RESULTS

Five pigs responded to resuscitation, while six pigs died spontaneously within 20 to 30 minutes after reinfusion of the withdrawn blood, without significant differences in macro- or microcirculatory variables at baseline and after hemorrhage. Correlation analysis showed that microvascular pO(2) in the heart and the gut were closely related to macrocirculatory variables (cardiac index, mean arterial pressure, and oxygen delivery) during hemorrhage and resuscitation.

CONCLUSIONS

This study demonstrated that the microcirculation in the gut (being a nonvital organ) and heart (being a vital organ) follow the macrocirculation in the acute phase of hemorrhagic shock and isovolemic autologous whole blood resuscitation.

Effects of a selective iNOS inhibitor versus norepinephrine in the treatment of septic shock

Inhibition of NOS is not beneficial in septic shock; selective inhibition of the inducible form (iNOS) may represent a better option. We compared the effects of the selective iNOS inhibitor BYK191023 with those of norepinephrine (NE) in a sheep model of septic shock. Twenty-four anesthetized, mechanically ventilated ewes received 1.5 g/kg body weight of feces into the abdominal cavity to induce sepsis. Animals were randomized into three groups (each n = 8): NE-only, BYK-only, and NE + BYK. The sublingual microcirculation was evaluated with sidestream dark-field videomicroscopy. MAP was higher in the NE + BYK group than in the other groups, but there were no significant differences in cardiac index or systemic vascular resistance. Mean pulmonary arterial pressure was lower in BYK-treated animals than in the NE-only group. PaO2/FiO2 was higher and lactate concentration lower in the BYK groups than in the NE-only group. Mesenteric blood flow was higher in BYK groups than in the NE-only group. Renal blood flow was higher in the NE + BYK group than in the other groups. Functional capillary density and proportion of perfused vessels were higher in the BYK groups than in the NE-only group 18 h after induction of peritonitis. Survival times were similar in the three groups. In this model of peritonitis, selective iNOS inhibition had more beneficial effects than NE on pulmonary artery pressures, gas exchange, mesenteric blood flow, microcirculation, and lactate concentration. Combination of this selective iNOS inhibitor with NE allowed a higher arterial pressure and renal blood flow to be maintained.

Aortic cross-clamping and reperfusion in pigs reduces microvascular oxygenation by altered systemic and regional blood flow distribution

BACKGROUND

In this study, we tested the hypothesis that aortic cross-clamping (ACC) and reperfusion cause distributive alterations of oxygenation and perfusion in the microcirculation of the gut and kidneys despite normal systemic hemodynamics and oxygenation.

METHODS

Fifteen anesthetized pigs were randomized between an ACC group (n = 10), undergoing 45 minutes of aortic clamping above the superior mesenteric artery, and a time-matched sham surgery control group (n = 5). Systemic, intestinal, and renal hemodynamics and oxygenation variables were monitored during 4 hours of reperfusion. Microvascular oxygen partial pressure (microPo(2)) was measured in the intestinal serosa and mucosa and the renal cortex, using the Pd-porphyrin phosphorescence technique. Intestinal luminal Pco(2) was determined by air tonometry and the serosal microvascular flow by orthogonal polarization spectral imaging.

RESULTS

Organ blood flow and renal and intestinal microPo(2) decreased significantly during ACC, whereas the intestinal oxygen extraction and Pco(2) gap increased. The intestinal response to reperfusion after ACC was a sustained reactive hyperemia but no such effect was seen in the kidney. Despite a sustained high intestinal O(2) delivery, serosal microPo(2) (median [range], 49 mm Hg [41-67 mm Hg] versus 37 mm Hg [27-41 mm Hg]; P < 0.05 baseline versus 4 hours reperfusion) and the absolute number of perfused microvessels decreased along with an increased intestinal Pco(2) gap (17 mm Hg [10-19 mm Hg] versus 23 mm Hg [19-30 mm Hg]; P < 0.05). In contrast, the kidney showed a progressive O(2) delivery decrease accompanied by a decrease in renal cortex oxygenation (70 mm Hg [52-93 mm Hg] versus 57 mm Hg [33-64 mm Hg]; P < 0.05).

CONCLUSION

Increased systemic and regional blood flow and oxygen supply after ACC does not ensure adequate regional blood flow and microcirculatory oxygenation in all organs.

Augmentation of platelet and endothelial cell eNOS activity decreases sepsis-related neutrophil-endothelial cell interactions

NO is an important mediator of microvascular patency and blood flow. The purpose of this study was to examine the role of enhanced eNOS activity in attenuating sepsis-induced neutrophil-endothelial cell interactions. Microslides coated with human umbilical vein endothelial cells were stimulated with plasma from patients with septic shock. Neutrophil and platelets from control subjects were also stimulated with plasma from patients in septic shock and perfused over stimulated endothelial cells. l-Arginine (LA) with and without NG-monomethyl l-arginine (LNMMA), a nonselective NOS inhibitor, and N-(3-(aminomethyl) benzyl acetamide) ethanimidamide dihydrochloride (1400W), a highly selective iNOS inhibitor, were added to the septic plasma. The number of neutrophils adherent to endothelial cells, neutrophil rolling velocity, and the number of neutrophil aggregates were determined. Cell activation and the formation of platelet-neutrophil aggregates were assessed by flow cytometry. Separate experiments were done with isolated platelets using platelet aggregometry. l-Arginine significantly decreased sepsis-related neutrophil adhesion and aggregation and increased rolling velocity. The addition of LNMMA to LA and cell suspensions reversed the effects of LA on these parameters, whereas the addition of 1400W had no effect on LA-related changes. Platelet-neutrophil aggregation, platelet aggregation, platelet activation, and neutrophil activation induced by septic plasma were also significantly decreased by LA. Again, the addition of LNMMA reversed the effects of LA on these parameters, whereas 1400W had no effect on LA-related changes. These data suggest that enhancement of platelet and endothelial cell eNOS activity decreases sepsis-induced neutrophil-endothelial cell interactions and may play a role in maintaining microvascular patency in septic shock.

Effects of levosimendan and dobutamine on experimental acute lung injury in rats

The effects of levosimendan on acute lung injury induced by peritonitis and abdominal hypertension in the early stages of sepsis in rats were investigated. Twenty-four adult male Wistar rats were randomized into: (1) sham, (2) subjected to abdominal hypertension and peritonitis induced lung injury using cecal ligation and puncture, then treated by dobutamine, (3) subjected to abdominal hypertension and peritonitis induced lung injury using cecal ligation and puncture, then treated by levosimendan, and (4) controls subjected to abdominal hypertension and peritonitis induced lung injury using cecal ligation and puncture with no treatment. In the control and levosimendan groups, cecal ligation and puncture resulted in moderate IL-1beta immunolabelling in lung tissue; marked IL-1beta immunolabelling was demonstrated in the dobutamine group. TNF-alpha immunolabelling was negative in both the sham and levosimendan groups, but moderate and weak immunoreactivities were observed in the dobutamine and control groups, respectively. There were almost no TUNEL positive cells in the sham, but they were prominent in the control. TUNEL positive cells were significantly less in the levosimendan treated lungs when compared to control and dobutamine groups. Immunoreactivity of eNOS was stronger in the dobutamine group when compared with the levosimendan group. In addition, iNOS immunoreactivity was strongly detected in the control group; this immunoreactivity was less in the levosimendan group than the dobutamine group. In this experimental sepsis model, treatment with levosimendan had a marked effect on attenuating or decreasing apoptosis and inflammation in the lung.

The heterogeneity of the microcirculation in critical illness

Microcirculation, a complex and specialized facet of organ architecture, has characteristics that vary according to the function of the tissue it supplies. Bedside technology that can directly observe microcirculation in patients, such as orthogonal polarization spectral imaging and sidestream dark field imaging, has opened the way to investigating this network and its components, especially in critical illness and surgery. These investigations have underscored the central role of microcirculation in perioperative disease states. They have also highlighted variations in the nature of microcirculation, both among organ systems and within specific organs. Supported by experimental studies, current investigations are better defining the nature of microcirculatory alterations in critical illness and how these alterations respond to therapy. This review focuses on studies conducted to date on the microcirculatory beds of critically ill patients. The functional anatomy of microcirculation networks and the role of these networks in the pathogenesis of critical illness are discussed. The morphology of microvascular beds that have been visualized during surgery and intensive care at the bedside are also described, including those of the brain, sublingual region, skin, intestine, and eyes.

Distribution of NOS isoforms in a porcine endotoxin shock model

Sepsis is a major cause of morbidity and mortality. NO, an endogenous vasodilator, has been associated with the hypotension, catecholamine hyporesponsiveness, and myocardial depression of septic shock. Although iNOS is thought to be responsible for the hypotension and loss of vascular tone occurring several hours after endotoxin administration, little is known on the effects of constitutive eNOS on LPS-induced organ dysfunction. This study assessed the distribution of eNOS and iNOS in various vascular beds in conscious pigs challenged with LPS. Cardiac and regional hemodynamic parameters were recorded over 8 h in the presence and absence of aminoguanidine, a rather selective inhibitor of iNOS activity, and N-methyl-L-arginine, a nonspecific NOS inhibitor. Our data show that LPS-induced cardiac depression was associated with coronary, renal, and mesenteric vasoconstrictions and a hepatic vasodilatation. LPS also induced increases in eNOS in the heart and lungs, whereas iNOS was mostly detected in the liver. Nitrotyrosine formation was mainly detected in the lungs, with traces in the kidney, liver, and gut. Accordingly, our results suggest that the early decrease in blood pressure and cardiac depression are likely due to activated eNOS, whereas both isoforms are involved in the hepatic vasodilation. In contrast, carotid, coronary, mesenteric, and renal vasoconstrictions were significant at 5 and/ or 6 h after LPS infusion, suggesting that NO is not the primary mediator, facilitating and/or unmasking the release of vasoconstrictor mediators. Consequently, developing newer tissue- or isoform-specific NOS inhibitors can lead to novel therapeutic agents in septic shock.

Systematic evaluation of nitric oxide, tetrahydrobiopterin, and anandamide levels in a porcine model of endotoxemia

PURPOSE

Using a lipopolysaccharide (LPS)-treated porcine model, we examined: (1) whether nitric oxide (NO), anandamide, and tetrahydrobiopterin (BH4) increased or not in early endotoxic shock; and (2) the location of the major site of production of these molecules, by comparing their concentrations in arteries and the portal and hepatic veins.

METHODS

Ten pigs received an infusion of LPS at 1.7 microg x kg(-1)x h(-1) via the portal vein for 240 min. Consecutive changes in systemic hemodynamics, hepatosplanchnic circulation, and oxygen delivery were measured. Furthermore, the variable changes in the concentrations of nitrite and nitrate (NOx), anandamide, and BH4 were measured. To access the effects of surgery, anesthesia, and fluid management on BH4, an experiment without LPS infusion was performed in two other animals.

RESULTS

Mean arterial pressure and cardiac index started to decrease at 60 min after LPS infusion. However, systemic vascular resistance remained unchanged. Total hepatic blood flow and hepatic oxygen delivery also decreased significantly. NOx and anandamide did not change during LPS infusion. BH4 values did not change without LPS infusion. However, BH4 values increased significantly in the arterial, portal, and hepatic circulation during LPS infusion, especially in the hepatic vein (from 136.8 +/- 27.5 to 281.3 +/- 123.2 mol/ml; P < 0.01).

CONCLUSION

Our data suggest that the BH4 values were significantly increased in several organs, especially in the liver during endotoxic shock. Impaired cardiac output and decreased blood pressure appeared in the early phase of porcine endotoxemia. Longer-term observation of these parameters after LPS treatment should be performed as the next step in future studies.

Persistent villi hypoperfusion explains intramucosal acidosis in sheep endotoxemia

OBJECTIVE

To test the hypothesis that persistent villi hypoperfusion explains intramucosal acidosis after endotoxemic shock resuscitation.

DESIGN

Controlled experimental study.

SETTING

University-based research laboratory.

SUBJECTS

A total of 14 anesthetized, mechanically ventilated sheep.

INTERVENTIONS

Sheep were randomly assigned to endotoxin (n = 7) or control groups (n = 7). The endotoxin group received 5 microg/kg endotoxin, followed by 4 microg x kg(-1) x hr(-1) for 150 mins. After 60 mins of shock, hydroxyethylstarch resuscitation was given to normalize oxygen transport for an additional 90 mins.

MEASUREMENTS AND MAIN RESULTS

Endotoxin infusion decreased mean arterial blood pressure, cardiac output, and superior mesenteric artery blood flow (96 +/- 10 vs. 51 +/- 20 mm Hg, 145 +/- 30 vs. 90 +/- 30 mL x min(-1) x kg(-1), and 643 +/- 203 vs. 317 +/- 93 mL x min(-1) x kg(-1), respectively; p < .05 vs. basal), whereas it increased intramucosal-arterial PCO2 (deltaPCO2) and arterial lactate (3 +/- 3 vs. 14 +/- 8 mm Hg, and 1.5 +/- 0.5 vs. 3.7 +/- 1.3 mmol/L; p < .05). Sublingual, and serosal and mucosal intestinal microvascular flow indexes, and the percentage of perfused ileal villi were reduced (3.0 +/- 0.1 vs. 2.3 +/- 0.4, 3.2 +/- 0.2 vs. 2.4 +/- 0.6, 3.0 +/- 0.0 vs. 2.0 +/- 0.2, and 98% +/- 3% vs. 76% +/- 10%; p < .05). Resuscitation normalized mean arterial blood pressure (92 +/- 13 mm Hg), cardiac output (165 +/- 32 mL x min(-1) x kg(-1)), superior mesenteric artery blood flow (683 +/- 192 mL x min(-1) x kg(-1)), and sublingual and serosal intestinal microvascular flow indexes (2.8 +/- 0.5 and 3.5 +/- 0.7). Nevertheless, deltaPCO2, lactate, mucosal intestinal microvascular flow indexes, and percentage of perfused ileal villi remained altered (10 +/- 6 mm Hg, 3.7 +/- 0.9 mmol/L, 2.3 +/- 0.4, and 78% +/- 11%; p < .05).

CONCLUSIONS

In this model of endotoxemia, fluid resuscitation corrected both serosal intestinal and sublingual microcirculation but was unable to restore intestinal mucosal perfusion. Intramucosal acidosis might be due to persistent villi hypoperfusion.

Neuronal nitric oxide synthase deficiency decreases survival in bacterial peritonitis and sepsis

OBJECTIVE

To investigate the role of neuronal nitric oxide synthase (NOS1) in murine polymicrobial peritonitis and sepsis.

DESIGN

Randomized experimental trial.

SETTING

Animal research facility.

SUBJECTS

B6129S NOS1+/+ and B6;129S4 NOS-/- mice.

INTERVENTIONS

NOS1+/+ and NOS1-/- animals underwent cecal ligation and puncture (CLP) or sham surgery and received the NOS1 inhibitor 7-nitroindazole (7-NI) or vehicle.

MEASUREMENTS AND MAIN RESULTS

After CLP, genetic deficiency and pharmacologic inhibition of NOS1 significantly increased risk of mortality [8.69 (3.27, 23.1), p<0.0001 and 1.71 (1.00, 2.92) p=0.05, hazard ratio of death (95% confidence interval) for NOS1-/- and 7-NI-treated NOS1+/+ respectively] compared with NOS1+/+ animals. In 7-NI-treated NOS1+/+ animals, there were increases (6 h) and then decreases (24 h), whereas in NOS-/- animals persistent increases in blood bacteria counts (p=0.04 for differing effects of 7-NI and NOS1-/-) were seen compared with NOS1(+/+) animals. After CLP, NOS1(-/-) had upregulation of inducible NOS and proinflammatory cytokines and greater increases in serum tumor necrosis factor-alpha and interleukin-6 levels compared with NOS1+/+ mice (all p<0.05). Following CLP, there were similar significant decreases in circulating leukocytes and lung lavage cells (p

CONCLUSIONS

Deficiency and inhibition of NOS1 increases mortality, possibly by increasing proinflammatory cytokine response and impairing bacterial clearance after CLP. These data suggest that NOS1 is important for survival, bacterial clearance, and regulation of cytokine response during infection and sepsis.

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Key Words

• sepsis
• peritonitis
• nos1
• nnos
• no
• rodents

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MESH Headings

• Animals
• Female
• Gene Expression
• Mice
• Nitric Oxide Synthase Type I/adverse effects
• Nitric Oxide Synthase Type I/analysis
• Nitric Oxide Synthase Type I/deficiency
• Nitric Oxide Synthase Type I/genetics
• Nitric Oxide Synthase Type I/metabolism
• Nitric Oxide Synthase Type I/pharmacology
• Peritonitis/mortality
• Peritonitis/physiopathology
• Random Allocation
• Risk Assessment
• Sepsis/mortality
• Sepsis/physiopathology
• Survival Analysis
• United States

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Grants

• Z01 CL008047 Intramural NIH HHS
• Z01 CL008047-06 Intramural NIH HHS
• Z01 CL009009 Intramural NIH HHS
• Z01 CL009009-01 Intramural NIH HHS

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Affiliation(s)

Xizhong Cui Critical Care Medicine Department, National Institutes of Health Clinical Center, National Institutes of Health, Bethesda, MD, USA
Virginia Besch
Alfia Khaibullina
Adrienne Hergen
Martha Quezado
Peter Eichacker
Zenaide M N Quezado

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The NO donor SIN-1 improves intestinal-arterial P(CO(2)) gap in experimental endotoxemia: an animal study

BACKGROUND

Dysfunction of the microcirculation is a prominent feature of sepsis and endotoxemia. Recently, it has been shown that microcirculatory alterations are completely reversed by local or systemic application of vasodilators in severely septic patients. Therefore, we investigated the influence of vasodilator therapy on microcirculatory dysfunction of the ileum during endotoxic shock in a prospective, controlled animal study.

METHODS

After baseline measurements, shock was induced in 12 domestic pigs by lipopolysaccharide via the mesenteric vein until the mean arterial pressure fell below 60 mmHg. After 30 min in shock, six animals were resuscitated with either fluid alone (control) or fluid and 2 microg/kg/min of the vasodilator 3-morpholino-sydnonimine (SIN-1). The systemic and regional hemodynamics and oxygenation parameters, tonometric ileal P(CO(2)) and microvascular oxygen pressures (muP(O(2))) (by oxygen-dependent Pd-porphyrin phosphorescence) were measured simultaneously.

RESULTS

The ileal-arterial P(CO(2)) gap increased during shock and the ileal mucosal and serosal muP(O(2)) decreased concurrently. SIN-1 in addition to fluid resuscitation significantly improved the ileal-arterial P(CO(2)), whereas fluid alone failed to decrease the P(CO(2)) gap. The SIN-1-induced improvement in the P(CO(2)) gap was accompanied by an increase in serosal muP(O(2)) above shock levels. Mucosal muP(O(2)) was resuscitated to baseline levels in both groups.

CONCLUSION

The application of the vasodilator SIN-1 in addition to fluid resuscitation improves the ileal-arterial P(CO(2)) gap and mucosal muP(O(2)), together with a moderate increase in serosal muP(O(2)), after endotoxic shock. This finding is consistent with the concept that vasodilators may correct pathologic flow distribution within the intestinal wall.

The effect of iNOS deletion on hepatic gluconeogenesis in hyperdynamic murine septic shock

OBJECTIVE

To investigate the role of the inducible nitric oxide synthase activation-induced excess nitric oxide formation on the rate of hepatic glucose production during fully resuscitated murine septic shock.

DESIGN

Prospective, controlled, randomized animal study.

SETTING

University animal research laboratory.

SUBJECTS

Male C57Bl/6 and B6.129P2-Nos2(tm1Lau)/J (iNOS-/-) mice.

INTERVENTIONS

Fifteen hours after cecal ligation and puncture, anesthetized, mechanically ventilated and instrumented mice (wild-type controls, n = 13; iNOS-/-, n = 12; wild-type mice receiving 5 mg.kg(-1) i.p. of the selective iNOS inhibitor GW274150 immediately after cecal ligation and puncture, n =8) received continuous i.v. hydroxyethylstarch and norepinephrine to achieve normotensive and hyperdynamic hemodynamics.

MEASUREMENTS AND RESULTS

Measurements were recorded 18, 21 and 24 h after cecal ligation and puncture. Liver microcirculatory perfusion and capillary hemoglobin O2 saturation (laser Doppler flowmetry and remission spectrophotometry) were well maintained in all groups. Despite significantly lower norepinephrine doses required to achieve the hemodynamic targets, the rate of hepatic glucose production (gas chromatography--mass spectrometry measurements of tissue isotope enrichment during continuous i.v. 1,2,3,4,5,6-13C6-glucose infusion) at 24 h after cecal ligation and puncture was significantly higher in both iNOS-/- and GW274150-treated mice, which was concomitant with a significantly higher hepatic phosphoenolpyruvate carboxykinase activity (spectrophotometry) in these animals.

CONCLUSIONS

In normotensive, hyperdynamic septic shock, both pharmacologic and genetic deletion of the inducible nitric oxide synthase allowed maintenance of hepatic glucose production, most likely due to maintained activity of the key regulatory enzyme of gluconeogenesis, phosphoenolpyruvate carboxykinase.

Mechanisms of critical illness--classifying microcirculatory flow abnormalities in distributive shock

Over 30 years ago Weil and Shubin proposed a re-classification of shock states and identified hypovolemic, cardiogenic, obstructive and distributive shock. The first three categories have in common that they are associated with a fall in cardiac output. Distributive shock, such as occurs during sepsis and septic shock, however, is associated with an abnormal distribution of microvascular blood flow and metabolic distress in the presence of normal or even supranormal levels of cardiac output. This Bench-to-bedside review looks at the recent insights that have been gained into the nature of distributive shock. Its pathophysiology can best be described as a microcirculatory and mitochondrial distress syndrome, where time and therapy form an integral part of the definition. The clinical introduction of new microcirculatory imaging techniques, such as orthogonal polarization spectral and side-stream dark-field imaging, have allowed direct observation of the microcirculation at the bedside. Images of the sublingual microcirculation during septic shock and resuscitation have revealed that the distributive defect of blood flow occurs at the capillary level. In this paper, we classify the different types of heterogeneous flow patterns of microcirculatory abnormalities found during different types of distributive shock. Analysis of these patterns gave a five class classification system to define the types of microcirculatory abnormalities found in different types of distributive shock and indicated that distributive shock occurs in many other clinical conditions than just sepsis and septic shock. It is likely that different mechanisms defined by pathology and treatment underlie these abnormalities observed in the different classes. Functionally, however, they all cause a distributive defect resulting in microcirculatory shunting and regional dysoxia. It is hoped that this classification system will help in the identification of mechanisms underlying these abnormalities and indicate optimal therapies for resuscitating septic and other types of distributive shock.

Influence of fluid resuscitation on renal microvascular PO2 in a normotensive rat model of endotoxemia

Introduction

Septic renal failure is often seen in the intensive care unit but its pathogenesis is only partly understood. This study, performed in a normotensive rat model of endotoxemia, tests the hypotheses that endotoxemia impairs renal microvascular PO₂ (μPO₂) and oxygen consumption (VO_2,ren), that endotoxemia is associated with a diminished kidney function, that fluid resuscitation can restore μPO₂, VO_2,ren and kidney function, and that colloids are more effective than crystalloids.

Methods

Male Wistar rats received a one-hour intravenous infusion of lipopolysaccharide, followed by resuscitation with HES130/0.4 (Voluven^®), HES200/0.5 (HES-STERIL^{® ®} 6%) or Ringer's lactate. The renal μPO₂ in the cortex and medulla and the renal venous PO₂ were measured by a recently published phosphorescence lifetime technique.

Results

Endotoxemia induced a reduction in renal blood flow and anuria, while the renal μPO₂ and VO_2,ren remained relatively unchanged. Resuscitation restored renal blood flow, renal oxygen delivery and kidney function to baseline values, and was associated with oxygen redistribution showing different patterns for the different compounds used. HES200/0.5 and Ringer's lactate increased the VO_2,ren, in contrast to HES130/0.4.

Conclusion

The loss of kidney function during endotoxemia could not be explained by an oxygen deficiency. Renal oxygen redistribution could for the first time be demonstrated during fluid resuscitation. HES130/0.4 had no influence on the VO_2,ren and restored renal function with the least increase in the amount of renal work.

Dual-wavelength phosphorimetry for determination of cortical and subcortical microvascular oxygenation in rat kidney

This study presents a dual-wavelength phosphorimeter developed to measure microvascular PO2 (microPO2) in different depths in tissue and demonstrates its use in rat kidney. The used phosphorescent dye is Oxyphor G2 with excitation bands at 440 and 632 nm. The broad spectral gap between the excitation bands combined with a relatively low light absorption of 632 nm light by tissue results in a marked difference in penetration depths of both excitation wavelengths. In rat kidney, we determine the catchments depth of the 440-nm excitation to be 700 microm, whereas the catchments depth of 632 nm is as much as 4 mm. Therefore, the measurements differentiate between cortex and outer medulla, respectively. In vitro, no difference in PO2 readings between both channels was found. On the rat kidney in vivo, the measured cortical microPO2 was on average 20 Torr higher than the medullary microPO2 over a wide PO2 range induced by variations in inspired oxygen fraction. Examples provided from endotoxemia and resuscitation show differences in responses of mean cortical and medullary PO2 readings as well as in the shape of the PO2 histograms. It can be concluded that oxygen-dependent quenching of phosphorescence of Oxyphor G2 allows quantitative measurement of microPO2 noninvasively in two different depths in vivo. Oxygen levels measured by this technique in the rat renal cortex and outer medulla are consistent with previously published values detected by Clark-type oxygen electrodes. Dual-wavelength phosphorimetry is excellently suited for monitoring microPO2 changes in two different anatomical layers under pathophysiological conditions with the characteristics of providing oxygen histograms from two depths and having a penetration depth of several millimeters.