Increasing nitric oxide production improves survival in experimental hemorrhagic shock

TRAUMA INDUCES INTRAVASCULAR HEMOLYSIS, EXACERBATED BY RED BLOOD CELL TRANSFUSION AND ASSOCIATED WITH DISRUPTED ARGININE-NITRIC OXIDE METABOLISM

ABSTRACT

Background: Severe injury can provoke systemic processes that lead to organ dysfunction, and hemolysis of both native and transfused red blood cells (RBCs) may contribute. Hemolysis can release erythrocyte proteins, such as hemoglobin and arginase-1, the latter with the potential to disrupt arginine metabolism and limit physiologic NO production. We aimed to quantify hemolysis and arginine metabolism in trauma patients and measure association with injury severity, transfusions, and outcomes. Methods: Blood was collected from injured patients at a level I trauma center enrolled in the COMBAT (Control of Major Bleeding After Trauma) trial. Proteomics and metabolomics were performed on plasma fractions through liquid chromatography coupled with mass spectrometry. Abundances of erythrocyte proteins comprising a hemolytic profile as well as haptoglobin, l -arginine, ornithine, and l -citrulline (NO surrogate marker) were analyzed at different timepoints and correlated with transfusions and adverse outcomes. Results: More critically injured patients, nonsurvivors, and those with longer ventilator requirement had higher levels of hemolysis markers with reduced l -arginine and l -citrulline. In logistic regression, elevated hemolysis markers, reduced l -arginine, and reduced l -citrulline were significantly associated with these adverse outcomes. An increased number of blood transfusions were significantly associated with elevated hemolysis markers and reduced l -arginine and l -citrulline independently of New Injury Severity Score and arterial base excess. Conclusions: Severe injury induces intravascular hemolysis, which may mediate postinjury organ dysfunction. In addition to native RBCs, transfused RBCs can lyse and may exacerbate trauma-induced hemolysis. Arginase-1 released from RBCs may contribute to the depletion of l -arginine and the subsequent reduction in the NO necessary to maintain organ perfusion.

Effect of aminoguanidine on cardiovascular responses and survival time during blood loss: A study in normotensive and deoxycorticosterone acetate-salt hypertensive rats

Introduction:

Hemorrhagic shock causes more circulatory disturbances and mortality in hypertensive than normotensive subjects. In the late phase of hemorrhagic shock, nitric oxide (NO) overproduction leads to vascular decompensation. In this study, we evaluated the effect of inducible NO synthase (iNOS) inhibitor, aminoguanidine (AG), on hemodynamic parameters and serum nitrite concentration in decompensated hemorrhagic shock model in normotensive and hypertensive male rats.

Materials and Methods:

Twenty-four male rats were divided into hypertensive and normotensive groups (n = 12 each). Hypertension was induced by subcutaneous injection of deoxycorticoesterone acetate (DOCA), 30 mg/kg in uninephrectomized rats. Decompensated hemorrhagic shock was induced by withdrawing blood until the mean arterial pressure (MAP) reached 40 mmHg. After 120 min, each group was assigned to aminguanidine (100 mg/kg) and control group. Hemodynamic parameters were monitored for next 60 min. Blood samples were taken before and after shock period and 60 min after treatment. Survival rate was monitored for 72 h.

Results:

Infusion of AG in normotensive animals caused a transient increase in MAP and increase of heart rate, whereas it did not affect those parameters in hypertensive animals. Hemorrhagic shock caused a significant rise in serum nitrite concentration in normotensive and hypertensive rats and infusion of AG did not significantly change it in both groups. No significant differences observed in survival rate between AG-treated and not treated groups.

Conclusion:

It seems that inhibition of iNOS with AG does not have beneficial effects on hemodynamatic parameters and survival rate during decompensated hemorrhagic shock in normotensive and hypertensive animals.

Mechanisms of acute brain injury after subarachnoid hemorrhage

Brain injury after subarachnoid hemorrhage (SAH) is a biphasic event with an acute ischemic insult at the time of the initial bleed and secondary events such as cerebral vasospasm 3 to 7 days later. Although much has been learned about the delayed effects of SAH, less is known about the mechanisms of acute SAH-induced injury. Distribution of blood in the subarachnoid space, elevation of intracranial pressure, reduced cerebral perfusion and cerebral blood flow (CBF) initiates the acute injury cascade. Together they lead to direct microvascular injury, plugging of vessels and release of vasoactive substances by platelet aggregates, alterations in the nitric oxide (NO)/nitric oxide synthase (NOS) pathways and lipid peroxidation. This review will summarize some of these mechanisms that contribute to acute cerebral injury after SAH.

L-arginine infusion during resuscitation for hemorrhagic shock: impact and mechanism

BACKGROUND

Our previous work showed a survival advantage with L-arginine (L-Arg) pretreatment in a swine model of severe hemorrhagic shock. This study was designed to evaluating whether the benefit is sustained when L-Arg is given during resuscitation and whether the mechanism is mediated by enzymatic activation of nitric oxide (NO) synthesis.

METHODS

Adult rats (n = 30) underwent 40% blood volume loss and were resuscitated with saline (3 shed blood volume). Animals were divided into five treatment groups of six animals each: (1) Sham, (2) Control (resuscitation alone), (3) L-Arg (300 mg/kg)with resuscitation, (4) L-Arg + L-nitroarginine methyl ester pretreatment, and (5) D-arginine (300 mg/kg) with resuscitation.Animals were observed for 240 minutes postresuscitation or until death. Hemodynamic, metabolic, histologic, and survival outcomes were measured.

RESULTS

Administration of L-Arg after hemorrhage and before resuscitation significantly improved outcomes, relative to the control group.The L-Arg infusion improved terminal arterial pressures, lowered lactate, improved small bowel histologic signs of reperfusion injury, and increased survival (p < 0.05). Endpoints of the L-Arg group were similar to the Sham group. The benefits of L-Arg infusion were abolished or attenuated when animals were pretreated with L-nitro arginine methyl ester and potentiated with D-arginine, suggesting a NO-specific mechanism of L-Arg. Finally, severe shock and resuscitation injury significantly elevated circulating asymmetric dimethylarginine levels, which are potent competitive inhibitors of NO synthetase.

CONCLUSION

L-Arg infusion during resuscitation offers a significant functional, metabolic, and survival benefit after severe hemorrhagic shock.The mechanism seems to be by activation of NO synthesis with its attendant benefits to local perfusion and inflammation after global reperfusion.

Nitric oxide inhalation, a proposed strategy for early treatment of hemorrhagic shock

Nitric oxide (NO), an endothelial-derived relaxing factor, plays important roles in a variety of pathophysiological conditions such as hemorrhagic shock (HS). So far, the impact of NO administration in HS treatment has been controversial. Through literature review, we summarize here the biphasic effects of NO in early and late phases of HS. Evidence suggests that NO administration is beneficial in the early stage while detrimental in the late stage of HS. We further propose inhalation of NO as a novel therapeutic strategy for the treatment of HS in the early stage.

Nitric oxide in early brain injury after subarachnoid hemorrhage

Nitric Oxide (NO) is the major regulator of cerebral blood flow. In addition, it inhibits platelet adherence and aggregation, reduces adherence of leukocytes to the endothelium, and suppresses vessel injury. NO is produced on demand by nitric oxide synthase and has a very short half life. Hence maintenance of its cerebral level is crucial for normal vascular physiology. Time dependent alterations in cerebral NO level and the enzymes responsible for its synthesis are found after subarachnoid hemorrhage (SAH). Cerebral NO level decreases, recovers and increases within the first 24 h after SAH. Each change in cerebral NO level elicits a different pathological response form already compromised brain. These response range from constriction, platelet aggregation and vascular injury that occurs during the early hours and delayed occurring vasospasm, neuronal and axonal damage. This review summarizes the underlying mechanism and the consequence of alteration in cerebral NO level on brain during the first 72 h after SAH.

Nitric oxide-supplemented resuscitation improves early gastrointestinal blood flow in rats subjected to hemorrhagic shock without late consequences

BACKGROUND

we have shown that hemorrhage/resuscitation altered gastrointestinal blood flow (GI-BF) and that gastric perfusion did not recover after resuscitation. This study aimed to determine the effect of nitric oxide (NO) supplemented resuscitation on the mean arterial blood pressure (MAP), GI-BF, and outcome after hemorrhagic shock.

METHODS

rats were subjected to hemorrhage and resuscitation with/without the NO-donor S-nitroso human serum albumin (S-NO-HSA). GI-BF was determined using colored microspheres.

RESULTS

NO supplementation significantly decreased MAP at the end of resuscitation. At the same time point, the GI-BF has significantly increased in the stomach, duodenum, and colon. Two hours after treatment discontinuation, there was no difference in either MAP or GI-BF between NO-supplemented and control groups. The survival times indicated that S-NO-HSA treatment was noninferior compared with control.

CONCLUSIONS

NO-supplemented resuscitation improves the GI-BF during the early stage of resuscitation without a negative impact on short-/long-term survival despite a transient MAP decrease.

Nitric oxide and redox regulation in the liver: part II. Redox biology in pathologic hepatocytes and implications for intervention

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are created in normal hepatocytes and are critical for normal physiologic processes, including oxidative respiration, growth, regeneration, apoptosis, and microsomal defense. When the levels of oxidation products exceed the capacity of normal antioxidant systems, oxidative stress occurs. This type of stress, in the form of ROS and RNS, can be damaging to all liver cells, including hepatocytes, Kupffer cells, stellate cells, and endothelial cells, through induction of inflammation, ischemia, fibrosis, necrosis, apoptosis, or through malignant transformation by damaging lipids, proteins, and/or DNA. In Part I of this review, we will discuss basic redox biology in the liver, including a review of ROS, RNS, and antioxidants, with a focus on nitric oxide as a common source of RNS. We will then review the evidence for oxidative stress as a mechanism of liver injury in hepatitis (alcoholic, viral, nonalcoholic). In Part II of this review, we will review oxidative stress in common pathophysiologic conditions, including ischemia/reperfusion injury, fibrosis, hepatocellular carcinoma, iron overload, Wilson's disease, sepsis, and acetaminophen overdose. Finally, biomarkers, proteomic, and antioxidant therapies will be discussed as areas for future therapeutic interventions.

Molecular mechanisms of pharmaconutrients

Nutritional supplementation has become the standard of care for management of critically ill patients. Traditionally, nutritional support in this patient population was intended to replete substrate deficiencies secondary to stress-induced catabolism. Recognition of the influence of certain nutrients on the immune and inflammatory response of the critically ill has led to the evolution of more sophisticated nutritional strategies and concepts. Administration of immune-enhancing formulas supplemented with a combination of glutamine, arginine, omega-3 fatty acids (omega-3 FA), and nucleotides have been shown in most studies to reduce infectious outcomes. More recently, the separation of nutritional support from the provision of key nutrients has led to a further appreciation of the immunomodulatory and anti-inflammatory benefits of isolated nutrients, such as glutamine and antioxidants. The purpose of this article is to review the molecular mechanisms that are unique to each class of frequently utilized nutrients. A better understanding of the specific molecular targets of immunonutrients will facilitate application of more refined nutritional therapies in critically ill patients.

The role of L-arginine following trauma and blood loss

PURPOSE OF REVIEW

Vascular endothelial cells control vascular smooth muscle tone via the release of nitric oxide. Following adverse circulatory conditions, namely trauma and hemorrhage, endothelial cell dysfunction occurs, leading to a decrease in the release of endothelium-derived nitric oxide, which contributes to further alterations in tissue perfusion and organ function.

RECENT FINDINGS

Early administration of L-arginine (the precursor of nitric oxide) and the substrate for nitric oxide synthase in vascular endothelial cells has been found to restore the depressed organ blood flow and to reduce tissue injury following shock. This improvement in cardiovascular function was associated with restoration of the depressed cell-mediated immune responses and attenuation of the massive inflammatory response encountered under such conditions. Furthermore, the excessive infiltration of the liver with neutrophils following trauma-hemorrhage was decreased by L-arginine administration, thereby reducing hepatic injury. In addition, L-arginine treatment decreased the inflammatory response at the site of trauma and the improved wound-healing process following blood loss.

SUMMARY

Despite those promising results in animal models at present, none of the published clinical trials has demonstrated efficacy of L-arginine at doses above standard dietary practices on the outcome in critically ill surgical patients, besides the reduction in infectious complications.

Effects of early enteral arginine supplementation on resuscitation of severe burn patients

OBJECTIVES

To investigate the effects of dietary supplementation of l-arginine (l-Arg) on shock in severely burned patients.

METHODS

This was a prospective, randomized, single blind, controlled study. Forty-seven severely burned patients due to various causes with a total burn surface area (TBSA) more than 50% each admitted in early postburn phase (within 10h postburn) were included in this study. All patients were treated by the traditional resuscitation program of our institute. After the nasogastric feeding tube was placed, they were randomly divided into three groups-(1) group A400 (n = 16): giving gastrointestinal feeding with 500 ml 5% GNS, containing l-Arg (400 mg/ kgday) at equal pace with fluid resuscitation; (2) group A200 (n = 16): giving gastrointestinal feeding with 500 ml 5% GNS containing l-Arg (200 mg/ kgday); (3) group C (n = 15): giving gastrointestinal feeding with 500 ml 5% GNS without any supplementation. The feeding started within 12h after burn and lasted for 72 h, the feeding rate was controlled by an enteral feeding pump. The following parameters were observed on days (PBD) 1-4: serum nitric oxide content (NO), mean arterial blood pressure (MAP), oxygenation index (PO2/FiO2), and arterial blood content of lactic acid (LA). Gastric mucosal blood flow was measured by laser Doppler flow-metry on PBD1 and PBD2.

RESULTS

(1) Enteral feeding of l-Arg did not change MAP of severely burned patients, with no difference in MAP between the l-Arg supplemented and control groups. (2) There were significant changes of the l-Arg supplemented groups (A400 and A200), with an increased gastric mucosa blood flow, oxygenation index, and a decreased LA content in arterial blood, compared with the control group. (3) The serous NO content was significantly decreased in the A400 group on PBD2-4 (P < 0.01), and in the A200 group on PBD4 (P < 0.05) compared with the control group.

CONCLUSIONS

Enteral feeding with l-arginine supplementation on early stage of burn decreases NO production to a relatively normal level and exerts beneficial effects on the resuscitation of burned shock.

Exogenous nitric oxide donor and related compounds protect against lung inflammatory response after hemorrhagic shock and resuscitation

BACKGROUND

Resuscitation from hemorrhagic shock triggers an inflammatory response characterized by upregulation of cytokine and adhesion molecule expression, increased leukocyte activity, and accumulation of polymorphonuclear neutrophils in a variety of tissues. This study investigated the capability of an exogenous nitric oxide (NO) donor, sodium nitroprusside (NP); a NO substrate, L-arginine; and an inducible NO synthase inhibitor, L-N6-(1-iminoethyl)lysine (L-NIL) to reduce lung injury in an animal model of mixed controlled and uncontrolled hemorrhagic shock.

METHODS

For this study, 72 Sprague-Dawley rats weighing 250 to 300 g were subjected to a model of uncontrolled hemorrhagic shock for 150 minutes. Six groups of animals were included in this study (12 per group): sham-saline, sham-NP, shock-saline, shock-NP, shock-L-arginine, and shock-L-N6-(1-iminoethyl)lysine. After the period of hemorrhagic shock, resuscitation of the groups was accomplished using normal saline (groups 1 and 3), NP (0.5 mg/kg) (groups 2 and 4), L-arginine (300 mg/kg) (group 5), or L-NIL (50 mg/kg) (group 6). The following indices were evaluated: fluid requirements for resuscitation, mean arterial pressure (MAP), arterial po2, pco2, and pH, lung wet-to-dry weight ratio, lung histology and cytokine (interleukin [IL]-1 alpha, IL-beta 1, tumor necrosis factor-beta [TNF beta], IL-3, IL-4, IL-5, IL-6, IL-10, TNF alpha, IL-2, interferon-gamma [IFN gamma]), and mRNA expression in the lung by a ribonuclease protection assay (RPA).

RESULTS

Sodium nitroprusside significantly increased MAP and reduced fluid requirements during resuscitation after hemorrhage. There also was a significant improvement in lung function, as expressed by improvements in po2, pco2, and pH, and reduction of the wet-to-dry weight ratio. In addition, a significant reduction in acute lung injury was observed in the histologic studies. Furthermore, the expression of cytokines was reduced by NP treatment. The use of L-arginine and L-NIL offered similar protective results for the injured lung.

CONCLUSIONS

These data suggest that limiting inducible NO synthase-generated NO availability with the exogenous NO donor, sodium nitroprusside, may reduce lung injury after severe hemorrhage, possibly, among other effects, by downregulating the expression of inflammatory cytokines. L-arginine and L-NIL also had a beneficial effect on lung function and structure.

The attenuation of hepatic microcirculatory alterations by exogenous substitution of nitric oxide by s-nitroso-human albumin after hemorrhagic shock in the rat

Hepatic microcirculatory disorders such as narrowing of sinusoids after hemorrhagic shock play a major role in the pathogenesis of organ failure. It is known that the balance of vasoactive mediators such as endothelin and nitric oxide (NO) regulate microvascular perfusion, including the diameter of hepatic sinusoids. The present study was designed to evaluate the role of exogenous substitution of NO by S-nitroso-albumin (S-NO-HSA) in the prevention of pathophysiological alterations of hepatic microcirculation. Anesthetized Sprague-Dawley rats were instrumented for invasive hemodynamic monitoring. Hemorrhagic shock was induced by bleeding to a mean arterial pressure (MAP) of 40 mmHg and was maintained for 60 min. Thereafter, the animals were resuscitated with shed blood and Ringer's solution. During the first hour of resuscitation, S-NO-HSA or pure HSA was infused continuously (10 micromol/kg/h) and hepatic microcirculation was detected by intravital epifluorescence microscopy either 5 or 24 h after the insult. Results were compared with a sham-treated group (n = 6-8 per group). Shock-induced microcirculatory narrowing of sinusoids was significantly reduced in the S-NO-HSA group compared with the HSA group both at 5 and 24 h (HSA: 9.3 +/- 0.2 microm; S-NO-HSA: 12.1 +/- 0.2 microm, P < 0.05). Sinusoidal perfusion was significantly higher in the S-NO-HSA group than in the HSA group (HSA: 50,934 +/- 1,382 microm3/s; S-NO-HSA: 78,120 +/- 2,348 microm3/s, P < 0.05). Reversible leukocyte adhesion to sinusoidal endothelium, an indicator of the inflammatory response, was significantly reduced in the S-NO-HAS-treated group. The findings of this study in a rat model of hemorrhagic shock suggest that NO substitution by S-NO-HSA during resuscitation attenuates both early and late hepatic microcirculatory disturbances as well as the increase in leukocyte adherence.

Dexamethasone suppresses iNOS yet induces GTPCH and CAT-2 mRNA expression in rat lungs

The in vivo mechanisms by which glucocorticoids inhibit nitric oxide expression await detailed investigation. In cell culture experiments, glucocorticoids have been shown to inhibit inducible nitric oxide synthase (iNOS) formation and activity. Glucocorticoids can inhibit iNOS activity in cultured cells by blocking arginine transport and inhibiting tetrahydrobiopterin biosynthesis. We recently reported that changes in intrapulmonary formation of nitric oxide in endotoxemic rats correspond with changes in transcription of the predominant arginine transporter cationic amino acid transporter (CAT)-2. Realizing that hemorrhagic shock induces nitric oxide overproduction in intact animals, we sought to explore whether glucocorticoids attenuate hemorrhagic shock-induced increases in intrapulmonary nitric oxide formation and whether they might do so by inhibiting the formation of tetrahydrobiopterin, iNOS protein, and CAT-2. We randomly assigned 10 male Sprague-Dawley rats to receive dexamethasone or normal saline. Bleeding the animals to a mean systemic blood pressure of between 40 and 45 mmHg created the hemorrhagic shock. Dexamethasone abrogated the increase in exhaled nitric oxide concentrations caused by hemorrhagic shock. At the end of the experiment, plasma nitrate/nitrite values were lower in the dexamethasone group than in the control group. The iNOS protein concentrations were also lower in the dexamethasone group than in the control group. Dexamethasone decreased the intrapulmonary iNOS mRNA concentrations yet increased both guanosine triphosphate cyclohydrolase I mRNA and CAT-2 mRNA. Our results support the idea that dexamethasone inhibits nitric oxide formation in a manner that is independent of tetrahydrobiopterin and arginine transport yet dependent on downregulation of iNOS mRNA expression.

Effects of inspiratory oxygen concentration and ventilation method on a model of hemorrhagic shock in rats

The effect of inspiratory oxygen concentration and the ventilation method on hemorrhagic shock was investigated. Twenty-eight rats were divided into four groups: mechanical ventilation with pure oxygen (M100); mechanical ventilation with air (M21); spontaneous respiration with pure oxygen (S100); and spontaneous respiration with air (S21). Under intravenous pentobarbital anesthesia, hemorrhagic shock (HS) was induced by withdrawal of blood from the femoral artery. Mean arterial blood pressure (MAP) was maintained at 40-50 mmHg for 2 h. After HS, the blood remaining in the reservoir was reinfused. Then survival rate and MAP were monitored for 2 h. Blood samples were withdrawn and vascular reactivity to norepinephrine (NE; 3.0 micrograms/kg) was tested before and after HS. Results were shown by changes in MAP in response to NE. During HS, the survival rate of the S21 group was lower than that of the M100 and S100 groups (p < .05). Before HS, MAPs of M100 and S100 groups were significantly higher than those of M21 and S21 groups (p < .05). In the M100 and M21 groups, MAPs at 2 h after reinfusion were significantly lower than the baseline value (p < .05). Before HS, reactivity to NE of the M21 group was significantly higher than that of the other groups (p < .05). In the M21 group, reactivity to NE after HS was significantly lower than it was before HS (p < .05). Inspiratory oxygen concentration and the ventilation method affect the survival rate and vascular reactivity of the rat hemorrhagic shock model. Selection of the inspiratory oxygen concentration and the ventilation method should be made according to the purpose of the individual experiment.

Sodium nitroprusside decreases leukocyte adhesion and emigration after hemorrhagic shock

The adhesion of polymorphonuclear leukocytes to the capillary endothelium is one of the key events in the pathophysiology of hemorrhagic shock. We studied sodium nitroprusside (SNP) for its ability to modulate leukocyte-endothelial cell interactions induced by hemorrhagic shock and reinfusion of blood by using intravital microscopy of the rat mesentery. Administration of SNP at a dose of 0.1 microg x kg(-1) x min(-1) infusion neither significantly decreased mean arterial blood pressure nor significantly altered bleedout volumes in hemorrhagic rats, indicating that SNP at this dose did not modify the severity of the shock protocol. Resuscitation from 1 h of hemorrhagic shock (mean arterial blood pressure approximately 45 mm Hg) significantly increased the number of adherent and emigrated leukocytes in the rat mesenteric microcirculation. However, infusion of SNP, started 15 min before hemorrhage, and continued over the entire experimental period, markedly reduced the leukocyte adhesion after reinfusion and emigration during hemorrhagic shock and after reinfusion. We concluded that the nitric oxide donor SNP is effective at reducing the leukocyte-endothelial interaction after blood reinfusion after hemorrhagic shock in rats.

IMPLICATIONS

The i.v. infusion of 0.1 microg x kg(-1) x min(-1) of sodium nitroprusside, a dose that does not exert a significant vasodilator effect, reduces leukocyte adhesion and emigration after hemorrhagic shock.

The influence of l-arginine on heart rate and tissue oxygen extraction in haemorrhaged rabbits

Several studies have already indicated some beneficial effects of L-arginine in haemorrhaged rats. The aim of our study was to assess whether intravenous bolus injection of L-arginine could improve some cardiovascular and metabolic parameters in anaesthetized haemorrhaged rabbits (intermittent bleeding; 40% of the estimated blood volume for 15 min). I.v. bolus injection of L-arginine ( 300 mg kg(-1)--L-Arg(300)) increased heart rate (app. 10%) and decreased venous haemoglobin saturation with oxygen (sO(2)) (app. 23%) 60 min after the cessation of bleeding, without changes in arterial pressure. D-arginine (300 mg kg(-1)i.v. bolus-D-Arg(300)) produced similar, but insignificant haemodynamic and metabolic changes. In addition, no difference was found between the effects of the L- and D-isomers. Accordingly, L-arginine produces beneficial effects on the heart rate and tissue oxygen extraction in haemorrhaged rabbits. However, such changes do not appear to be stereospecific.

Role of nitric oxide in hemorrhagic shock-induced bacterial translocation

BACKGROUND

Hemorrhagic shock-induced bacterial translocation is an etiologic factor in the pathogenesis of multiple system organ damage. Excessive production of nitric oxide (NO) during hemorrhagic shock may lead to cellular injury and gut barrier failure that promotes bacterial translocation. We investigated the effect of aminoguanidine (AG) and N(G)-nitro-l-arginine methyl ester (l-NAME), both inhibitors of NO synthase, on hemorrhagic shock- induced bacterial translocation in the rat.

MATERIALS AND METHODS

Anesthetized male Sprague-Dawley rats were subjected to a hemorrhagic shock protocol for 30 min followed by intravenous injection (1 mL/kg body wt) with normal saline, AG (100 mg/kg), or l-NAME (10 mg/kg). Tissues/organs were examined histologically for damage and bacterial translocation. Plasma nitrate/nitrite was measured using a procedure based on the Griess reaction, and nitric oxide synthase (NOS) expression was determined immunohistochemically.

RESULTS

The shocked animals treated with saline died within 90 min, and deaths were associated with 100% bacterial translocation, increased tissue/organ damage, and elevated nitrate/nitrite production. In contrast, both AG and l-NAME increased the survival time of shocked rats to >72 h, abrogated bacterial translocation, reduced tissue/organ damage, and prevented excessive nitrate/nitrite production and upregulation of expression of endothelial NOS and inducible NOS.

CONCLUSIONS

Prevention of bacterial translocation by pharmacologic agents such as aminoguanidine and l-NAME could be an important therapeutic approach to lessen mortality rates following hemorrhagic shock.

L-arginine attenuates trauma-hemorrhage-induced liver injury

OBJECTIVES

Liver injury is common after trauma-hemorrhage for which the underlying mechanism is not clear. Although administration of the essential amino acid L-arginine has been reported to restore the depressed cardiovascular functions and cell-mediated immune responses after trauma-hemorrhage, it remains unknown whether L-arginine protects against liver injury under those conditions.

DESIGN

A prospective, controlled animal study.

SETTING

A university research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats underwent sham operation or laparotomy and were bled to and maintained at a mean arterial blood pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of lactated Ringer's solution. Hemorrhaged rats were then resuscitated with lactated Ringer's solution, four times the maximum shed blood volume over 1 hr. During resuscitation, animals received either 300 mg/kg of L-arginine or saline (vehicle) intravenously. At 3 and 5 hrs after resuscitation, rats were killed, blood was obtained, and the liver was fixed for histology (hematoxylin & eosin staining). Plasma glutathione S-transferase (a marker of liver damage), L-arginine, citrulline, and ornithine concentrations were assessed.

MEASUREMENTS AND MAIN RESULTS

The increased concentrations of plasma glutathione S-transferase observed in vehicle-treated hemorrhage animals were normalized with L-arginine treatment at 5 hrs after resuscitation. Moreover, the histology indicated that L-arginine prevented liver edema and neutrophil infiltration after trauma-hemorrhage. Plasma L-arginine and citrulline were increased in L-arginine-treated rats.

CONCLUSIONS

Because citrulline is a by-product of nitric oxide generation by nitric oxide synthase from L-arginine, this amino acid may be a useful adjunct for preventing hepatic injury after trauma-hemorrhage via endothelial derived nitric oxide production.

S-Nitroso-N-acetylpenicillamine (SNAP) during hemorrhagic shock improves mortality as a result of recovery from vascular hyporeactivity

Nitric oxide donors are protective against hemorrhagic shock (HS). However, no detailed investigation has been performed. We investigated this mechanism using S-nitroso-N-acetylpenicillamine (SNAP). HS (mean arterial pressure: 40 mm Hg) was induced in 20 dogs. Sixty min after HS, the animals were treated with saline (Cont-Gr: n = 7) or SNAP; 5 microg. kg(-1). 10 min(-1) followed by 5 microg. kg(-1). h(-1) (SNAP-Gr: n = 7). After another 60 min, the shed blood was reinfused. Reactivities to noradrenalin (NA), changes in hemodynamics, the plasma catecholamines, and nitric oxide derivatives were determined. In Cont-Gr, 3 dogs died at 90, 98, and 102 min after HS. In Cont-Gr, % changes of systolic arterial blood pressure to 1 and 2.5 microg/kg of NA after the recovery from HS decreased from 23.7% +/- 4.1% (before HS) to 6.5% +/- 0.6% and from 50.1% +/- 7.7% (before HS) to 14.5% +/- 2.6%, respectively (P < 0. 01). In SNAP-Gr, reactivity to NA was maintained. At 120 min after HS, mean arterial pressure and cardiac output in SNAP-Gr increased but not in Cont-Gr. Plasma catecholamine levels in SNAP-Gr were suppressed compared with those of Cont-Gr. In conclusion, a small dose of SNAP during HS decreased the mortality of the dogs. This might have been caused in part by residual vascular hyporeactivity.

IMPLICATIONS

The administration of a small dose of S-nitroso-N-acetylpenicillamine (a nitric oxide donor), a dose which did not exert a significant vasodilator effect, was administered during hemorrhagic shock in dogs. S-nitroso-N-acetylpenicillamine improved the vascular hyporeactivity to noradrenaline and decreased the mortality rate.

L-arginine: a unique amino acid for restoring the depressed macrophage functions after trauma-hemorrhage

BACKGROUND

Immune responses are markedly depressed very early after the onset of hemorrhage. Furthermore, endothelial cell dysfunction occurs after trauma-hemorrhage and may contribute to alterations in immune function. Recent studies have shown that administration of L-arginine restores the depressed organ blood flow, probably because of the provision of substrate for constitutive nitric oxide synthase. It remains unknown, however, whether administration of L-arginine would have any salutary effect on the depressed macrophage function after trauma-hemorrhage.

METHODS

Male rats underwent midline laparotomy (i.e., trauma was induced). After this, the animals were bled to and maintained at a mean blood pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of lactated Ringer's solution. Sham-operated rats underwent both femoral artery cannulation and ligation, but these animals were neither bled nor resuscitated. Hemorrhaged rats were then resuscitated with lactated Ringer's solution, receiving four times the maximum shed blood volume over 1 hour. During resuscitation, one group received 300 mg/kg L-arginine and the other group received saline (vehicle) intravenously. At 4 hours after resuscitation, splenic and peritoneal macrophage interleukin (IL)-1beta and IL-6 release as well as plasma IL-6 were measured.

RESULTS

Splenic and peritoneal macrophage IL-1beta and IL-6 release was significantly decreased in trauma-hemorrhage vehicle-treated rats. Administration of L-arginine after trauma-hemorrhage, however, improved splenic and peritoneal macrophage IL-1beta and IL-6 release. Moreover, the up-regulated plasma levels of IL-6 were attenuated by L-arginine administration.

CONCLUSION

L-Arginine administration after trauma-hemorrhage significantly improves the depressed macrophage function, presumably by decreasing the increased plasma IL-6 levels and improving organ blood flow. Early enhancement of the depressed constitutive nitric oxide synthase activity by provision of L-arginine after trauma-hemorrhage, therefore, represents a novel and safe approach for improving the depressed immune function and decreasing plasma IL-6 levels under such conditions.

L-Arginine restores splenocyte functions after trauma and hemorrhage potentially by improving splenic blood flow

Several studies indicate that immune responses are markedly depressed early after onset of hemorrhage. Decreased organ blood flow has been implicated in the pathophysiology of altered immune responses after trauma-hemorrhage. In this regard, administration of L-arginine has been shown to restore depressed intestinal and hepatic blood flow after trauma-hemorrhage, probably due to provision of substrate for constitutive nitric oxide synthase (cNOS). It remains unknown, however, whether administration of L-arginine also ameliorates depressed splenic blood flow and whether this agent has any salutary effects on depressed splenocyte functions after trauma-hemorrhage. Male rats underwent sham operation or laparotomy and were bled to and maintained at a mean arterial blood pressure of 40 mmHg until 40% of maximum shed blood volume (MBV) was returned as Ringer lactate (RL). Hemorrhaged rats were then resuscitated with RL (4 times MBV over 1 h). During resuscitation, rats received 300 mg/kg L-arginine or saline (vehicle) intravenously; 4 h later, splenic blood flow, splenocyte proliferation, and splenocyte interleukin (IL)-2 and IL-3 were determined. Administration of L-arginine improved depressed splenic blood flow and restored depressed splenocyte functions after trauma-hemorrhage. Therefore, provision of L-arginine during resuscitation after trauma-hemorrhage should be considered a novel and safe approach for improving splenic organ blood flow and depressed splenocyte functions under such conditions.

Small intestinal production of nitric oxide is decreased following resuscitated hemorrhage

BACKGROUND

Small intestine microvascular vasoconstriction and hypoperfusion develop after resuscitation (RES) from hemorrhage (HEM), despite restoration of central hemodynamics. The responsible mechanisms are unclear. We hypothesized that the microvascular impairment following HEM/RES was due to decreased intestinal microvascular nitric oxide (NO) production.

METHODS

Male Sprague-Dawley rats (195-230 g) were utilized and three experimental groups were studied: (1) SHAM (cannulated but no HEM), (2) HEM only, and (3) HEM/RES. HEM was to 50% of baseline mean arterial pressure for 60 min, and RES was with shed blood and an equivalent volume of saline. Ex vivo isolated intestinal perfusion and a fluorometric modification of the Greiss reaction were used to quantify production of NO metabolites (NOx). Perfusate von Willebrand factor (vWF) was used as an indirect marker of endothelial cell activation or injury. To assess the degree of NO scavenging by oxygen-derived free radicals, immunohistochemistry was used to detect nitrotyrosine formation in the intestine.

RESULTS

Intestinal NOx decreased following HEM/RES (SHAM 1.35 +/- 0.2 mM vs HEM/RES 0.60 +/- 0.1 mM, P < 0.05), but not with HEM alone (1.09 +/- 0.3 mM). There were no differences in serum NOx levels between the three groups. Release of vWF was increased during the HEM period (SHAM 0.18 +/- 0.1 g/dl vs HEM 1.66 +/- 0.6 g/dl, P < 0.05). There was no detectable nitrotyrosine formation in any group.

CONCLUSIONS

Intestinal NO metabolites decrease following HEM/RES. Elevated vWF levels during HEM and the lack of detectable nitrotyrosine suggest that this is due to decreased endothelial cell production of NO. HEM/RES-induced endothelial cell dysfunction may contribute to persistent small intestine post-RES hypoperfusion and vasoconstriction.