Nitric oxide synthase inhibition during experimental sepsis improves renal excretory function in the presence of chronically increased atrial natriuretic peptide

Septic acute kidney injury: a review of basic research

Sepsis is a major cause of acute kidney injury (AKI) among patients in the intensive care unit. However, the numbers of basic science papers for septic AKI account for only 1% of all publications on AKI. This may be partially attributable to the specific pathophysiology of septic AKI as compared to that of the other types of AKI because it shows only modest histological changes despite functional decline and often requires real-time functional analysis. To increase the scope of research in this field, this article reviews the basic research information that has been reported thus far on the subject of septic AKI, mainly from the viewpoint of functional dysregulation, including some knowledge acquired with multiphoton intravital imaging. Moreover, the efficacy and limitation of the potential novel therapies are discussed. Finally, the author proposes several points that should be considered when designing the study, such as monitoring the long-term effects of the intervention and reflecting the clinical settings for identifying the molecular mechanisms and for challenging the intervention effects.

Selective iNOS inhibition for the treatment of sepsis-induced acute kidney injury

The incidence and mortality of sepsis and the associated development of acute kidney injury (AKI) remain high, despite intense research into potential treatments. Targeting the inflammatory response and/or sepsis-induced alterations in the (micro)circulation are two therapeutic strategies. Another approach could involve modulating the downstream mechanisms that are responsible for organ system dysfunction. Activation of inducible nitric oxide (NO) synthase (iNOS) during sepsis leads to elevated NO levels that influence renal hemodynamics and cause peroxynitrite-related tubular injury through the local generation of reactive nitrogen species. In many organs iNOS is not constitutively expressed; however, it is constitutively expressed in the kidney and, in humans, a relationship between the upregulation of renal iNOS and proximal tubular injury during systemic inflammation has been demonstrated. For these reasons, the selective inhibition of renal iNOS might have important implications for the treatment of sepsis-induced AKI. Various animal studies have demonstrated that selective iNOS inhibition-in contrast to nonselective NOS inhibition-attenuates sepsis-induced renal dysfunction and improves survival, a finding that warrants investigation in clinical trials. In this Review, the selective inhibition of iNOS as a potential novel treatment for sepsis-induced AKI is discussed.

Effect of ablated bronchial blood flow on survival rate and pulmonary function after burn and smoke inhalation in sheep

The bronchial circulation plays a significant role in the pathophysiological changes of burn and smoke-inhalation injury. Bronchial blood flow markedly increases immediately after inhalational injury. This study examines whether the ablation of the bronchial artery attenuates pathophysiological changes and improves survival after burn and smoke-inhalational injury in an ovine model. Acute lung injury was induced by 40% total body surface-area third-degree cutaneous burn and cotton smoke inhalation (48 breaths of cotton smoke, <40 degrees C) under deep anaesthesia. Twelve adult female sheep were divided into two groups: (1) sham (injured, non-ablated bronchial artery, n=6); (2) ablation (injured, ablated bronchial artery, n=6). Ablation of the bronchial artery was performed 72 h before the injury. The experiment was continued for 96 h. Burn and smoke-inhalation injury significantly increased regional blood flow in the bronchi. Ablation of the bronchial artery significantly reduced acute regional blood flow increases in the proximal and distal bronchi. All animals in the ablation group survived to 96 h. Four of these were successfully weaned off the ventilator. Three animals of the sham group met standardised euthanasia criteria at 60 h, while another met the criteria at 78 h. The lung wet-to-dry weight ratio, histology score and myeloperoxidase (MPO) activity were significantly increased by the insult, but ablation of the bronchial artery attenuated these changes. Burn and smoke-inhalation injury induced a significant increase in bronchial blood flow and accelerated airway obstruction, pulmonary vascular changes, pulmonary oedema and pulmonary dysfunction. Ablated bronchial circulation attenuated these pathophysiological changes.

Sepsis produced by Pseudomonas bacteremia does not alter plasma volume expansion after 0.9% saline infusion in sheep

Clinicians generally consider sepsis to be a state in which fluid is poorly retained within the vasculature and accumulates within the interstitium. We hypothesized that infusion of 0.9% saline in conscious, chronically instrumented sheep with hyperdynamic bacteremic sepsis would be associated with less plasma volume expansion (PVE) and greater interstitial fluid volume expansion than in conscious, nonseptic sheep. Six conscious adult sheep received an IV infusion of 25 mL/kg of 0.9% saline over 20 min (1.25 mL.kg(-1).min(-1)) in a control nonseptic state and during early and late sepsis (4 and 24 h, respectively, after initiation of a standard infusion of live Pseudomonas aeruginosa). The distribution and elimination of infused fluid were studied by mass balance (after measurement of plasma volume using Evans blue dye) and volume kinetic analysis. Mass balance demonstrated no significant differences in the time-course of PVE between control, early sepsis, and late sepsis. At the end of the infusions, which averaged 1050 +/- 125 mL in sheep weighing an average of 42 +/- 5 kg, calculated PVE was 312 +/- 50 mL, 386 +/- 34 mL, and 400 +/- 51, respectively. Volume kinetic analysis was similar in all three protocols. In both nonseptic and septic sheep, infusion of 0.9% saline resulted in similar peak PVE and resolution of PVE over a 3-h interval and similar kinetic parameters. Contrary to clinical impressions and to our hypothesis, the distribution of 0.9% saline in this animal model was not changed by bacteremia produced by infusion of Pseudomonas aeruginosa.

Role of atrial natriuretic peptide in pulmonary permeability and vasoregulation in ovine sepsis

OBJECTIVE

Atrial natriuretic peptide is regarded as an important regulator of pulmonary vasomotor tone and permeability. This study investigated the role of atrial natriuretic peptide in sepsis-associated pulmonary pathophysiology.

DESIGN

Prospective experimental investigation.

SETTING

Laboratory at a university hospital.

SUBJECTS

Twelve awake, chronically instrumented sheep.

INTERVENTIONS

The sheep were instrumented with lung lymph fistulas and received a continuous infusion with live Pseudomonas aeruginosa for 48 hrs. After 40 hrs, the atrial natriuretic peptide-receptor antagonist HS-142-1 was continuously infused in the HS-124-1 group (3 mg/kg/hr, n = 6) for 8 hrs, whereas the control group received the carrier (n = 6).

MEASUREMENTS AND MAIN RESULTS

Lung lymph flow was markedly elevated in response to sepsis after 40 hrs in both groups. Atrial natriuretic peptide-receptor blockade further increased lymph flows by 41 +/- 17% (41 hrs) up to 64 +/- 20% (44 hrs, p < .05) in the presence of normal permeability to protein. Although mean pulmonary artery pressure increased (p < .05 vs. 40 hrs), capillary pressure remained unaffected. Despite identical fluid balances in both groups, cardiovascular filling variables significantly increased in the HS-142-1 group. This was associated with increasing cardiac index and mean arterial pressure (p < .05 vs. 40 hrs). In the control group, all variables remained constant between 41 and 48 hrs.

CONCLUSION

Blockade of atrial natriuretic peptide receptors increases pulmonary transvascular fluid flux independent of changes in permeability to protein in chronic ovine sepsis. Atrial natriuretic peptide may therefore play a protective role for the alveolar-capillary barrier during sepsis.

Early multiple organ failure after recurrent endotoxemia in the presence of vasoconstrictor-masked hypovolemia

OBJECTIVE

Critically ill patients who develop multiple organ failure during systemic inflammatory states are often predisposed to hypovolemia and vasoconstrictor therapy. Although numerous investigations have evaluated the sequelae of systemic inflammation, no data are available on the contribution of chronic vasoconstrictor-masked hypovolemia to organ dysfunction and morphology.

DESIGN

Prospective, randomized laboratory investigation.

SETTING

University research laboratory.

SUBJECTS

Eighteen adult chronically instrumented sheep.

INTERVENTIONS

The animals were randomly assigned to one of three groups. In the norfenefrine-masked hypovolemia plus endotoxemia (NMH+ENDO) group, mean arterial pressures of 80 mm Hg were maintained by using the alpha1-adrenergic catecholamine norfenefrine for 52 hrs during hypovolemia. Hypovolemia was induced by hemorrhage (about 23 mL x kg(-1)) until mean arterial pressures reached 40 mm Hg. Endotoxin (0.5 microg x k(-1)) was then injected after 4, 16, 28, and 40 hrs. The NMH group received norfenefrine-masked hypovolemia but no endotoxin. In the ENDO group, recurrent endotoxemia was induced during normovolemia.

MEASUREMENTS AND MAIN RESULTS

Despite profound differences in fluid management, cardiovascular filling pressures were not statistically different between groups. Endotoxemia induced norfenefrine-refractory shock (p < .05 vs. the other groups) and contributed to renal dysfunction only during vasoconstrictor-masked hypovolemia. Norfenefrine-masked hypovolemia caused disseminated cardiac cell necrosis independent of endotoxemia (p < .05 vs. ENDO).

CONCLUSIONS

Hypovolemia can be masked when volume status is monitored by filling pressures. In this new model of endotoxemia-associated multiple organ failure, chronic vasoconstrictor-masked hypovolemia turned systemic inflammation into a life-threatening condition with renal and cardiovascular failure. Cardiomyocyte necroses were caused by vasoconstrictor-masked hypovolemia but were unrelated to cardiovascular failure.

GW274150, a potent and highly selective inhibitor of iNOS, reduces experimental renal ischemia/reperfusion injury

BACKGROUND

Generation of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) may contribute to renal ischemia/reperfusion (I/R) injury. The aim of this study was to investigate the effects of GW274150, a novel, highly selective, potent and long-acting inhibitor of iNOS activity in rat and mouse models of renal I/R.

METHODS

Rats were administered GW274150 (5 mg/kg intravenous bolus administered 30 minutes prior to I/R) and subjected to bilateral renal ischemia (45 minutes) followed by reperfusion (6 hours). Serum and urinary indicators of renal dysfunction, tubular and reperfusion injury were measured, specifically, serum urea, creatinine, aspartate aminotransferase (AST) and N-acetyl-beta-d-glucosaminidase (NAG) enzymuria. In addition, renal sections were used for histologic scoring of renal injury and for immunologic evidence of nitrotyrosine formation and poly [adenosine diphosphate (ADP)-ribose] (PAR). Nitrate levels were measured in rat plasma using the Griess assay. Mice (wild-type, administered 5 mg/kg GW274150, and iNOS-/-) were subjected to bilateral renal ischemia (30 minutes) followed by reperfusion (24 hours) after which renal dysfunction (serum urea, creatinine), renal myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels were measured.

RESULTS

GW274150, administered prior to I/R, significantly reduced serum urea, serum creatinine, AST, and NAG indicating reduction of renal dysfunction and injury caused by I/R. GW274150 reduced histologic evidence of tubular injury and markedly reduced immunohistochemical evidence of nitrotyrosine and PAR formation, indicating reduced peroxynitrite formation and poly (ADP-ribose) polymerase (PARP) activation, respectively. GW274150 abolished the rise in the plasma levels of nitrate (indicating reduced NO production). GW274150 also reduced the renal dysfunction in wild-type mice to levels similar to that observed in iNOS-/- mice subjected to I/R. Renal MPO activity and MDA levels were significantly reduced in wild-type mice administered GW274150 and iNOS-/- mice subjected to renal I/R, indicating reduced polymorphonuclear leukocyte (PMN) infiltration and lipid peroxidation.

CONCLUSIONS

These results suggest that (1). an enhanced formation of NO by iNOS contributes to the pathophysiology of renal I/R injury and (2). GW274150 reduces I/R injury of the kidney. We propose that selective inhibitors of iNOS activity may be useful against renal dysfunction and injury associated with I/R of the kidney.

The hemodynamic effects of diaspirin cross-linked hemoglobin in dopamine-resistant endotoxic shock in swine

As the blood substitute Diaspirin Cross-linked Hemoglobin (DCLHb) has potent vasopressor activity, we assessed its hemodynamic effects in a clinically relevant dopamine-resistant endotoxic shock model in swine. In a randomized and controlled study, E. coli LPS was administered to anesthetized and invasively monitored swine. Group I (n = 3) control pigs were not resuscitated. Groups II (n = 5) and III (n = 6) pigs received dopamine (DA) after MAP decreased 30%, and hetastarch and DCLHb, respectively, after dopamine-resistance occurred. Progressive hemodynamic decline occurred in Group I pigs. DA failed to restore MAP to baseline. However, 0% and 67% of pigs also treated with heta-starch and DCLHb, respectively, achieved temporary restoration of baseline MAP (p = 0.03), prompting a reduction in the dose of DA in 0% of hetastarch vs. 50% of DCLHb treated pigs. Except for increased MPAP and decreased heart in DCLHb treated pigs (p<0.001), hemodynamics and survival were not different (p>0.05). In conclusion, although DCLHb exacerbated pulmonary hypertension and did not improve O2 utilization or survival, because DCLHb restored MAP to baseline and had a dopamine sparing effect, further investigation of DCLHb's hemodynamic effects in adrenergic agent-resistant endotoxemia is warranted.

Renal effects of nitric oxide in endotoxemia

Nitric oxide (NO) is postulated to play a key role in the pathophysiology of renal failure in sepsis. Whether the renal effects of increased NO are beneficial or harmful remains unclear. In a porcine model of lipopolysaccharide (LPS)-induced shock, we evaluated the effect of LPS on glomerular filtration rate (GFR) and renal blood flow (RBF). We then administered the nonselective nitric oxide synthase (NOS) inhibitor N(G)-L-arginine methyl ester (L-NAME), and compared its effects on GFR and RBF with those of S-methylisothiourea (SMT), a selective NOS inhibitor, and those of saline. We postulated that SMT, by maintaining constitutive NO, would be more beneficial than either L-NAME or saline. LPS infusion decreased mean arterial pressure (MAP), and increased cardiac output, RBF, and medullary NO content. The increased RBF was diverted to the medulla. There was no evidence of renal dysfunction in the saline-resuscitated group. Both NOS inhibitors increased MAP but decreased RBF, but only L-NAME reduced GFR and increased sodium excretion and renal oxygen extraction. We conclude that NO in endotoxemia is beneficial because it maintains RBF and GFR. Additionally, selective NOS inhibition did not offer any advantages over saline resuscitation.

Effects of nitric oxide in septic shock

Nitric oxide (NO) is believed to play a key role in the pathogenesis of septic shock, although many aspects of NO's involvement remain poorly defined. Recent years have seen advances in our understanding of the production and effects of NO, but much of the work has been done in animal models and may not be directly relevant to the clinical situation. Differences between species and models can account for many of the apparently conflicting results obtained. Nevertheless, NO-directed strategies have been developed and tested clinically. However, NO can have both beneficial and detrimental effects on many organ systems in sepsis and attempts to nonselectively block all its actions may therefore not yield positive results on outcome. Further exploration and precision of the role of NO and development of techniques to assess the NO balance in individual patients is necessary before further progress can be made in this field.

Nitric oxide in septic shock

Septic shock is a major cause of death following trauma and is a persistent problem in surgical patients throughout the world. It is characterised by hypotension and vascular collapse, with a failure of the major organs within the body. The role of excessive nitric oxide (NO) production, following the cytokine-dependent induction of the inducible nitric oxide synthase (iNOS), in the development of septic shock is discussed. Emphasis is placed upon the signal-transduction process by which iNOS is induced and the role of NO in cellular energy dysfunction and the abnormal function of the cardiovascular system and liver during septic shock.

Role of nitric oxide in sepsis-associated pulmonary edema

Transient pulmonary hypertension after inhibition of nitric oxide synthase (NOS) does not alter pulmonary reflection coefficients or lymph flows in endotoxemic sheep. To test the effects of persistent pulmonary hypertension induced by N omega-nitro-L-arginine methylester (L-NAME) and of inhaled NO on pulmonary edema, 18 sheep (three groups) were chronically instrumented with pulmonary artery catheters, femoral arterial fiberoptic thermistor catheters, and tracheostomy. The awake, spontaneously breathing animals received Salmonella typhi endotoxin (lipopolysaccharide; LPS) (10 ng/kg/ min) for 28 h. After 24 h, an airflow of 6 L/min was delivered through the tracheostomy. One group of animals (L-NAME/air) received L-NAME intravenously (25 mg/kg + 5 mg/kg/h) and breathed air. The second group (L-NAME/NO) was given L-NAME and NO (40 ppm) was added to the airflow. The third group was given NaCl 0.9% and breathed air (NaCl/air). Extravascular lung water was measured through the double-indicator dilution technique. Endotoxemia caused pulmonary edema, which was aggravated by L-NAME. Breathing of NO normalized pulmonary artery pressure (Ppa) and ameliorated pulmonary edema. Inhalation of NO may therefore be a therapeutic option for pulmonary edema associated with pulmonary hypertension.

Selective inhibition of inducible nitric oxide synthase: effects on hemodynamics and regional blood flow in healthy and septic sheep

OBJECTIVES

To investigate the effects of S-ethylisothiourea (S-EITU) on hemodynamics, oxygen transport, and regional blood flow in healthy and septic sheep.

DESIGN

Prospective, randomized, controlled experimental study with repeated measures.

SETTING

Investigational intensive care unit at a university medical center.

SUBJECTS

Eleven healthy, female adult sheep of the Merino breed, divided into a control group (n = 5) and into a group treated with S-EITU (n = 6).

INTERVENTIONS

All sheep were chronically instrumented. After a 5-day recovery period, they were randomly assigned to either control or S-EITU groups. While control sheep received only saline, S-EITU was administered in increasing doses of 1, 3, and 9 mg/kg/hr over 1 hr each (nonseptic phase). After 2 days of recovery, a continuous infusion of live Pseudomonas aeruginosa (2.5 x 106 colony-forming units/min) was started in all sheep and maintained for the remainder of the experiment. After 24 hrs of sepsis, the sheep again received their assigned treatment (septic phase). In both the nonseptic and septic phases, the sheep received colored microspheres through a left atrial catheter to allow analysis of regional blood flows. All animals were autopsied at the end of the experiments, and organ probes were removed for blood flow analyses.

MEASUREMENTS AND MAIN RESULTS

The administration of S-EITU caused a dose-dependent vasoconstriction in the nonseptic phase. After 24 hrs of Pseudomonas infusion, all sheep developed a hyperdynamic circulatory state, with increased cardiac indices and reduced arterial pressures and systemic vascular resistances. Oxygen extraction decreased significantly, preventing an increase in oxygen consumption, despite an increased oxygen delivery. The hyperdynamic circulation was dose dependently reversed by S-EITU, causing an increase in arterial pressure by peripheral vasoconstriction. Sheep in the control group showed a continuation of the hyperdynamic circulation. The effects of S-EITU on hemodynamics and regional blood flows were comparable under septic and nonseptic conditions.

CONCLUSIONS

With the inducible form of nitric oxide synthase expressed under septic, but not under nonseptic conditions, S-EITU was expected to have vasoconstrictive properties only in the septic phase. It produced a comparable vasoconstriction during the nonseptic phase of the experiment. Thus, either S-EITU does not selectively block the inducible nitric oxide synthase in sheep, or other vasodilators besides nitric oxide play an important role in septic vasodilation.

Differential expression of inducible nitric oxide synthase messenger RNA along the longitudinal and crypt-villus axes of the intestine in endotoxemic rats

OBJECTIVES

To characterize the mechanisms leading to excessive production of nitric oxide within the gut as a consequence of endotoxemia. We sought to: a) determine the time course of inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) expression in the intestine after challenging rats with lipopolysaccharide (LPS); and b) investigate whether there is differential expression of iNOS in enterocytes along the longitudinal or crypt-villus axes of the intestine in rats after LPS administration.

DESIGN

Prospective, randomized, unblinded study.

SETTING

Research laboratories at a large university-affiliated medical center.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

At T = 0 hr, rats were injected with O111:B4 Escherichia coli LPS (5 mg/kg) or a similar volume of the saline vehicle. At various time points thereafter, samples of duodenum, jejunum, ileum, colon, and liver were harvested for subsequent extraction of RNA. In some cases, populations of enterocytes enriched in either crypt or villus cells were harvested from the ileum. In some studies, rats were injected with cycloheximide (25 mg i.p.) 15 mins before being challenged with LPS or dexamethasone (2 mg i.p.) 30 mins before being injected with LPS.

MEASUREMENTS AND MAIN RESULTS

iNOS mRNA was undetectable in ileal tissue from rats under basal conditions, but was evident by T = 1 hr and was maximal at T = 2 hrs after injection of LPS. Thereafter, ileal iNOS mRNA concentrations decreased and were undetectable again at T = 24 hrs. At T = 2 hrs after LPS injection, there was marked expression of iNOS mRNA in the ileum, whereas much lower concentrations of iNOS mRNA were detected in the jejunum and colon, and no iNOS mRNA was detected in the duodenum. At T = 3 hrs after LPS injection, expression of iNOS mRNA was up-regulated in both villus and crypt cells, although LPS-induced iNOS mRNA was more prominent in the former than the latter cell type. Pretreatment of rats with dexamethasone virtually abrogated the expression of iNOS mRNA in ileal samples obtained 3 hrs after the injection of LPS. Prior treatment of rats with the protein synthesis inhibitor, cycloheximide, also blunted LPS-induced iNOS mRNA expression.

CONCLUSIONS

LPS-induced iNOS expression is differentially regulated along both the longitudinal and crypt villus axes of the intestinal mucosa, being most prominent in the villus cells of the ileum. LPS-induced iNOS expression is blunted by pretreating rats with dexamethasone or cycloheximide. The latter finding suggests that LPS-induced expression of iNOS mRNA in the gut requires new protein synthesis. Differential regulation of nitric oxide production along the longitudinal and crypt-villus axes of the gut may be a determinant of the pattern of sepsis-induced intestinal damage.

Pyridoxalated hemoglobin polyoxyethylene conjugate reverses hyperdynamic circulation in septic sheep

We investigated the effects of modified hemoglobin on regional blood flow and function of different organs during hyperdynamic sepsis. Fourteen sheep were surgically prepared for the study. After a 5-day recovery period, a continuous infusion of live Pseudomonas aeruginosa bacteria was begun and maintained for 48 h. At 24 h, after a hyperdynamic circulation had developed, the animals were randomly assigned to two groups: 1) a treatment group (n = 7) that received an infusion with 100 mg/kg pyridoxalated hemoglobin polyoxyethylene conjugate (PHP) over 30 min and 2) a control group (n = 7) that received only the vehicle. PHP infusion increased mean arterial pressure from 86 +/- 2.8 to 101.8 +/- 3.5 mmHg (P < 0.05) and systemic vascular resistance index from 769 +/- 42.1 to 1,087 +/- 56.8 dyn . s . m2 . cm-5 (P < 0.05). PHP infusion did not decrease regional blood flow, measured with fluorescent microspheres, below the baseline values in any of the analyzed tissues. None of the investigated blood chemistry variables showed any changes indicative of impaired organ function after PHP infusion. In our model of ovine sepsis we found no side effects after PHP infusion that would limit the use of PHP as a nitric oxide scavenger in sepsis.

Endogenous nitric oxide and the pulmonary microvasculature in healthy sheep and during systemic inflammation

Nitric oxide (NO) influences microvascular integrity. NO synthase inhibitors are regarded as therapeutic options, but their impact on the pulmonary microvasculature is not well defined. We studied the microvascular effects of the nonselective NO synthase inhibitor N(omega)-nitro L-arginine methylester (L-NAME) in healthy sheep and during systemic inflammation. Permeability analysis was performed in 30 adult ewes with chronic lung lymph fistulas and pulmonary venous occluders. Experiment 1: 20 sheep received Escherichia coli endotoxin (lipopolysaccharide, 10 ng/kg/min) for 32 h. After 24 h of endotoxemia, 10 sheep were given L-NAME (25 mg/kg), and 10 sheep received NaCl 0.9%. Experiment 2: six sheep were treated with L-NAME (25 mg/kg), and four animals received NaCl 0.9%. Endotoxin induced a phasic pulmonary microvascular response with early transiently increased endothelial permeability at 4 h and late normalization of microvascular integrity to large molecules after 24 h. At that time systemic vasodilation had occurred. L-NAME raised pulmonary artery pressure and pulmonary vascular resistance index without signs of increased permeability in either experiment. NO is involved in vascular tone in healthy sheep and during systemic inflammation, but it does not seem to play a role in the integrity of the pulmonary microvascular barrier function to large molecules.

Effects of nitric oxide on blood flow distribution and O2 extraction capabilities during endotoxic shock

The effects of the nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) and the NO donor 3-morpholinosydnonimine (SIN-1) were tested in 18 endotoxic dogs. L-NMMA infusion (10 mg . kg-1 . h-1) increased arterial and pulmonary artery pressures and systemic and pulmonary vascular resistances but decreased cardiac index, left ventricular stroke work index, and blood flow to the hepatic, portal, mesenteric, and renal beds. SIN-1 infusion (2 microg . kg-1 . min-1) increased cardiac index; left ventricular stroke work index; and hepatic, portal, and mesenteric blood flow. It did not significantly influence arterial and pulmonary artery pressures but decreased renal blood flow. The critical O2 delivery was similar in the L-NMMA group and in the control group (13.3 +/- 1.6 vs. 12.8 +/- 3.3 ml . kg-1 . min-1) but lower in the SIN-1 group (9.1 +/- 1.8 ml . kg-1 . min-1, both P < 0.05). The critical O2 extraction ratio was also higher in the SIN-1 group than in the other groups (58.7 +/- 10.6 vs. 42.2 +/- 7.6% in controls, P < 0.05; 43.0 +/- 15.5% in L-NMMA group, P = not significant). We conclude that NO is not implicated in the alterations in O2 extraction capabilities observed early after endotoxin administration.

Nitric oxide synthase inhibition restores hypoxic pulmonary vasoconstriction in sepsis

Hypoxic pulmonary vasoconstriction (HPV) is inhibited by inhaled nitric oxide (NO) in healthy animals and is blunted in endotoxemia. We investigated whether the loss of HPV during sepsis could be reversed by NO synthase (NOS) inhibition. Hypoxic challenges were induced in intubated, awake sheep breathing 100% nitrogen to the left lung and 100% oxygen to the right lung. HPV was assessed as the decrease in left pulmonary blood flow during hypoxia, measured with an ultrasonic flow probe around the left pulmonary artery. Group I (n = 5) received carrier solutions and Groups II (n = 6) and III (n = 8) received an infusion containing Pseudomonas aeruginosa. After 24 h, Group III also received an infusion of 6.6 mg.kg.h-1 N omega-monomethyl-L-arginine (L-NMMA). After 24 h of sepsis, HPV decreased from 60 +/- 9% in Group II and 56 +/- 4% in Group III to 27 +/- 2% and 26 +/- 4%, respectively. Group I showed no change in HPV. During infusion of L-NMMA, HPV increased to 38 +/- 4%. Pulmonary shunt during hypoxia increased in Group III to 161 +/- 10% of its baseline value, and decreased to 121 +/- 11% during infusion of L-NMMA. We conclude that L-NMMA improves but does not restore HPV, indicating that other vasodilatory mediators besides NO also influence HPV in sepsis.

Nitric oxide is required for effective innate immunity against Klebsiella pneumoniae

Nitric oxide (NO) has been associated with protection against various parasitic and viral infections and may play a similar role in bacterial infections. We studied the role of NO in host defense against Klebsiella pneumoniae infection in the lung. Initial studies demonstrated a time-dependent increase in NO production of the lungs of CBA/J mice following the intratracheal administration of K. pneumoniae (7 x 10(2) CFU). To assess the role of NO in Klebsiella pneumonia, mice were treated intraperitoneally with either L-NAME (N-omega-nitro-L-arginine methylester), a competitive inhibitor of NO synthesis, or D-NAME, an inert enantiomer. The treatment of Klebsiella-infected mice with L-NAME resulted in a 10- and 46-fold increase in K. pneumoniae CFU in lungs and blood, respectively, at 48 h post-K. pneumoniae inoculation compared to treatment of mice with D-NAME. In addition, a greater-than-twofold increase in mortality was evident in L-NAME-treated mice compared to the mortality in control animals. No significant difference in bronchoalveolar lavage inflammatory cell profiles was noted between L-NAME- and D-NAME-treated mice with Klebsiella pneumonia. Interestingly, increased levels of tumor necrosis factor, gamma interferon, macrophage inflammatory protein 1alpha (MIP-1alpha), and MIP-2 mRNA and protein were noted in infected mice treated with L-NAME compared to the levels in mice treated with D-NAME. Importantly, the in vitro incubation of murine alveolar macrophages with L-NAME, but not with D-NAME, resulted in a significant impairment in both the phagocytosis and killing of K. pneumoniae. In total, these results suggest that NO plays a critical role in antibacterial host defense against K. pneumoniae, in part by regulating macrophage phagocytic and microbicidal activity.

The atrial natriuretic peptide receptor antagonist HS 142-1 improves cardiovascular filling and mean arterial pressure in a hyperdynamic ovine model of sepsis

OBJECTIVE

To test whether systemic vascular resistance and mean arterial pressure increase during the administration of the atrial natriuretic peptide antagonist, HS 142-1, in ovine experimental hyperdynamic sepsis.

DESIGN

Prospective trial.

SETTING

Research laboratory at a large university medical center.

SUBJECTS

Chronically instrumented Merino breed ewes (n = 14).

INTERVENTIONS

Continuous infusion of Pseudomonas aeruginosa (2.5 x 10(6) colony-forming units/min) for the experimental period of 48 hrs. One group (HS 142-1) received a continuous infusion of HS 142-1 (3 mg/kg/hr) from 40 to 48 hrs; the remaining sheep ("control") were given the vehicle sodium chloride 0.9%.

MEASUREMENTS AND MAIN RESULTS

All sheep developed a hyperdynamic cardiovascular response by 40 hrs that was characterized by low values of systemic vascular resistance index (p < .05) and mean arterial pressure (p < .05), and an increased cardiac index (p < .05). HS 142-1 increased cardiac filling pressures (p < .05) without apparent effects on fluid balance, and was associated with a significantly (p < .05) higher mean arterial pressure than was found in the control group at 44 and 48 hrs. HS 142-1 did not change systemic vascular resistance index. At 44 and 48 hrs, cardiac index values were found to have significantly (p < .05) increased in the animals receiving HS 142-1, when these data were compared with cardiac output values at 40 hrs.

CONCLUSION

HS 142-1 increases cardiac filling pressures and maintains mean arterial pressure in hyperdynamic sepsis without reversal of sepsis-induced vasodilation.

Nitric oxide and shock

Shock can be defined as the failure of the circulatory system to provide necessary cellular nutrients, including oxygen, and to remove metabolic wastes. Although it is now recognized that more than 100 different forms of shock exist, this recognition is more a reflection of the widespread use of the term to describe a variety of disease states. For the purpose of this monograph, we concentrate on various forms of cardiovascular shock, in particular, shock that may be linked to inappropriate vasodilation from overproduction of the endogenous vasodilator, nitric oxide. Some forms of shock have been extensively studied, and convincing evidence exists for the role of nitric oxide. Other disease states have been less well characterized in terms of their association with excess nitric oxide production. Available evidence of a role for nitric oxide is discussed in the hope of stimulating the interest of investigators to explore these areas more thoroughly.

Nitric oxide synthase inhibition versus norepinephrine for the treatment of hyperdynamic sepsis in sheep

OBJECTIVES

To investigate the effects of Nomega-mono-methyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthesis, on hemodynamics, oxygen transport, and regional blood flow in an ovine model of hyperdynamic sepsis and to compare these effects with the responses to norepinephrine.

DESIGN

Prospective, nonrandomized, controlled experimental study with repeated measures.

SETTING

Investigational intensive care unit at a university medical center.

SUBJECTS

Twenty-five female, healthy, adult sheep of the Merino breed, divided into three groups: nine control sheep; eight sheep treated with L-NMMA; and eight sheep treated with norepinephrine.

INTERVENTIONS

All sheep were chronically instrumented. After a 5-day recovery period, a continuous infusion of live Pseudomonas aeruginosa (2.5 x 10(6) colony-forming units/min) was started and maintained for the remainder of the experiment. After 24 hrs of sepsis, eight sheep received L-NMMA (7 mg/kg/hr), eight sheep received norepinephrine, and nine sheep received the vehicle alone (0.9% saline). The norepinephrine dosage was continuously and individually adjusted to achieve the same increase in blood pressure as was observed in a matched sheep of the L-NMMA group.

MEASUREMENTS AND MAIN RESULTS

After 24 hrs of sepsis, all sheep developed a hyperdynamic circulatory state with increased cardiac indices and reduced arterial pressures, and systemic vascular resistances. L-NMMA reversed the hyperdynamic circulation, causing an increase in arterial pressure by peripheral vasoconstriction. Norepinephrine led to an increase in blood pressure by augmenting cardiac indices, leaving the systemic vascular resistance unaffected. The norepinephrine dose needed to keep the blood pressure high had to be continuously increased, reflecting the reduced vascular responsiveness to catecholamines during sepsis. Renal blood flow remained unaffected by all treatment forms. Norepinephrine and L-NMMA led to a dramatic increase in urine production. Blocking the nitric oxide synthase with L-NMMA did not interfere with the host's pulmonary ability to clear bacteria, nor did treatment with norepinephrine.

CONCLUSIONS

Blocking nitric oxide synthase had a marked vasoconstrictive effect. Both norepinephrine and L-NMMA increased arterial pressure without reducing renal blood flow, leading to an improved renal function.