Inhibition of endothelium-dependent vasodilation by Escherichia coli endotoxemia

Assessment of cerebral circulation in a porcine model of intravenously given E. coli induced fulminant sepsis

BACKGROUND

The aim of the present work was to assess cerebral hemodynamic changes in a porcine model of E.coli induced fulminant sepsis.

METHODS

Nineteen healthy female Hungahib pigs, 10-12 weeks old, randomly assigned into two groups: Control (n = 9) or Septic Group (n = 10). In the Sepsis group Escherichia coli culture suspended in physiological saline was intravenously administrated in a continuously increasing manner according to the following protocol: 2 ml of bacterial culture suspended in physiological saline was injected in the first 30 min, then 4 ml of bacterial culture was administered within 30 min, followed by infusion of 32 ml bacterial culture for 2 h. Control animals received identical amount of saline infusion. Systemic hemodynamic parameters were assessed by PiCCo monitoring, and cerebral hemodynamics by transcranial Doppler sonography (transorbital approach) in both groups.

RESULTS

In control animals, systemic hemodynamic variables and cerebral blood flow velocities and pulsatility indices were relatively stable during the entire procedure. In septic animals shock developed in 165 (IQR: 60-255) minutes after starting the injection of E.coli solution. Blood pressure values gradully decreased, whereas pulse rate increased. A decrease in cardiac index, an increased systemic vascular resistance, and an increased stroke volume variation were observed. Mean cerebral blood flow velocity in the middle cerebral artery did not change during the procedure, but pulsatility index significantly increased.

CONCLUSIONS

There is vasoconstriction at the level of the cerebral arterioles in the early phase of experimental sepsis that overwhelmes autoregulatory response. These results may serve as additional pathophysiological information on the cerebral hemodynamic changes occurring during the septic process and may contribute to a better understanding of the pathomechanism of septic encephalopathy.

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.

Genetic interleukin-10 deficiency causes vascular remodeling via the upregulation of Nox1

BACKGROUND AND HYPOTHESIS

Interleukin (IL)-10 is an anti-inflammatory cytokine. Nox1 is a mitogenic oxidase (p65-mox). The objective of this study was to test a hypothesis that IL-10 deficiency would cause vascular remodeling via the upregulation of Nox1.

METHODS AND RESULTS

Recombinant adeno-associated virus (AAV) carrying short hairpin small interference RNA for Nox1 (AAV.Nox1shRNA) was constructed for in-vivo-specific inhibition of Nox1. Three groups of IL-10 gene knockout (IL-10KO) mice and three groups of wild-type mice were used. Three groups of each strain received intravenous delivery of AAV.Nox1shRNA, AAV with scrambled shRNA, and PBS, respectively. Animals were euthanized at 3 weeks after gene delivery. IL-10KO increased Nox1 protein expression, NADPH oxidase activity, and superoxide production in aortas. IL-10KO also resulted in a significant decrease in aortic medial thickness, a loss of smooth muscle cells (SMCs), and an increase in vascular collagen deposition, indicating vascular remodeling. The IL-10KO induced increases in NADPH oxidase activity and superoxide production, and vascular remodeling were abolished by silencing of Nox1 (p65-mox), suggesting that these effects may be mediated by the upregulation of Nox1. In addition, IL-10KO increased endothelin-1 levels in plasma and aortas, and this effect was partially blocked by silencing of Nox1. RNA interference silencing of Nox1 obliterated the IL-10KO-induced increases in IL-6 expression in aortas, superoxide production, and matrix metalloproteinase-9 activity in aortic SMCs, and SMC migration.

CONCLUSION

IL-10 is essential for the maintenance of normal vasculature, as IL-10 deficiency resulted in vascular damage and remodeling. The IL-10KO-induced vascular structure damage may be mediated by the upregulation of Nox1.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Effects of pharmaconutrients on cellular dysfunction and the microcirculation in critical illness

PURPOSE OF REVIEW

A growing body of data has revealed that specific nutrient deficiencies contribute to microvascular and cellular dysfunction following critical illness. Further, targeted administration of these 'pharmaconutrients' may reverse or improve this dysfunction and improve clinical outcome.

RECENT FINDINGS

Specific nutrient therapy with glutamine protects cellular metabolism and vascular function via induction of heat shock proteins, which are key proteins found to be deficient following acute illness. Arginine becomes rapidly deficient following trauma and surgery. This leads to significant immunosuppression, which when treated by arginine administration significantly reduces postoperative infection. Omega-3 fatty acids attenuate the inflammatory response and provide for resolution of ongoing inflammatory injury via production of resolvins/protectins. Antioxidants (vitamin C and selenium) and trace elements (zinc) become rapidly depleted in critical illness and replacement appears vital to ensure optimal cellular and microvascular function. Data on targeted metabolic (mitochondrial) therapies (i.e. co-enzyme Q10) show promise to improve myocardial function following cardiac surgery.

SUMMARY

These specific nutrients have newly discovered vital mechanistic roles in the optimization of cellular and microcirculatory function in critical illness and injury. A growing body of literature is demonstrating that correction of key nutrient deficiencies via therapeutic administration of these pharmaconutrients can improve clinical outcome in critically ill patients.

Early effects of lipopolysaccharide on cytokine release, hemodynamic and renal function in newborn piglets

BACKGROUND

Gram-negative sepsis in newborns is associated with high mortality and morbidity. Lipopolysaccharide (LPS) and cytokines released upon exposure to gram-negative sepsis are well known to be involved in the pathophysiology.

OBJECTIVE

In this report we investigate cytokine release, hemodynamic, and renal function induced by LPS in a newborn animal model with the intention to further examine early changes in gram-negative sepsis.

METHODS

Five 7- to 10-day-old domestic piglets were anesthetized and catheters placed in the jugular veins, left ventricle, and femoral artery. Urine output was monitored via suprapubic cystostomy. Mean arterial pressure, heart rate, and arterial blood gases were continuously monitored. Thirty minutes after line placement and obtaining baseline values, 0.06 mug/kg LPS were administered intravenously. One, 2, and 3 h later samples were taken to monitor tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, endothelin, and nitric oxide (NO)/nitrate via ELISA. In addition, blood flow was assessed by the microsphere method.

RESULTS

Our data show an initial surge of TNF-alpha and IL-1beta at 1 h after exposure to LPS. NO/nitrate, endothelin, and hemodynamic as well as metabolic changes became apparent mostly 3 h after exposure, by which time TNF-alpha and IL-1beta fell back to baseline.

CONCLUSIONS

Our sepsis model suggests a brief initial TNF-alpha and IL-1beta surge following LPS challenge; however, their effects become apparent by the time the levels are already subsiding. The emergence of vasoactive substances, NO and endothelin, precedes the first substantial clinical symptoms.

Exogenous arginine in sepsis

Sepsis is a severe condition in critically ill patients and is considered an arginine deficiency state. The rationale for arginine deficiency in sepsis is mainly based on the reduced arginine levels in sepsis that are associated with the specific changes in arginine metabolism related to endothelial dysfunction, severe catabolism, and worse outcome. Exogenous arginine supplementation in sepsis shows controversial results with only limited data in humans and variable results in animal models of sepsis. Since in these studies the severity of sepsis varies but also the route, timing, and dose of arginine, it is difficult to draw a definitive conclusion for sepsis in general without considering the influence of these factors. Enhanced nitric oxide production in sepsis is related to suggested detrimental effects on hemodynamic instability and enhanced oxidative stress. Potential mechanisms for beneficial effects of exogenous arginine in sepsis include enhanced (protein) metabolism, improved microcirculation and organ function, effects on immune function and antibacterial effects, improved gut function, and an antioxidant role of arginine. We recently performed a study indicating that arginine can be given to septic patients without major effects on hemodynamics, suggesting that more studies can be conducted on the effects of arginine supplementation in septic patients.

IN SILICO MODELS OF ACUTE INFLAMMATION IN ANIMALS

Trauma and hemorrhagic shock elicit an acute inflammatory response, predisposing patients to sepsis, organ dysfunction, and death. Few approved therapies exist for these acute inflammatory states, mainly due to the complex interplay of interacting inflammatory and physiological elements working at multiple levels. Various animal models have been used to simulate these phenomena, but these models often do not replicate the clinical setting of multiple overlapping insults. Mathematical modeling of complex systems is an approach for understanding the interplay among biological interactions. We constructed a mathematical model using ordinary differential equations that encompass the dynamics of cells and cytokines of the acute inflammatory response, as well as global tissue dysfunction. The model was calibrated in C57Bl/6 mice subjected to (1) various doses of lipopolysaccharide (LPS) alone, (2) surgical trauma, and (3) surgery + hemorrhagic shock. We tested the model's predictive ability in scenarios on which it had not been trained, namely, (1) surgery +/- hemorrhagic shock + LPS given at times after the beginning of surgical instrumentation, and (2) surgery + hemorrhagic shock + bilateral femoral fracture. Software was created that facilitated fitting of the mathematical model to experimental data, as well as for simulation of experiments with various inflammatory challenges and associated variations (gene knockouts, inhibition of specific cytokines, etc.). Using this software, the C57Bl/6-specific model was recalibrated for inflammatory analyte data in CD14-/- mice and was used to elucidate altered features of inflammation in these animals. In other experiments, rats were subjected to surgical trauma +/- LPS or to bacterial infection via fibrin clots impregnated with various inocula of Escherichia coli. Mathematical modeling may provide insights into the complex dynamics of acute inflammation in a manner that can be tested in vivo using many fewer animals than has been possible previously.

THE ACUTE INFLAMMATORY RESPONSE IN DIVERSE SHOCK STATES

A poorly controlled acute inflammatory response can lead to organ dysfunction and death. Severe systemic inflammation can be induced and perpetuated by diverse insults such as the administration of toxic bacterial products (e.g., endotoxin), traumatic injury, and hemorrhage. Here, we probe whether these varied shock states can be explained by a universal inflammatory system that is initiated through different means and, once initiated, follows a course specified by the cellular and molecular mechanisms of the immune and endocrine systems. To examine this question, we developed a mathematical model incorporating major elements of the acute inflammatory response in C57Bl/6 mice, using input from experimental data. We found that a single model with different initiators including the autonomic system could describe the response to various insults. This model was able to predict a dose range of endotoxin at which mice would die despite having been calibrated only in nonlethal inflammatory paradigms. These results show that the complex biology of inflammation can be modeled and supports the hypothesis that shock states induced by a range of physiologic challenges could arise from a universal response that is differently initiated and modulated.

Evaluation of beta3-adrenoceptor-mediated relaxation in intact and endotoxin-treated equine digital veins

OBJECTIVE

To investigate the functional expression of beta3-adrenoceptors (beta3-ARs) in equine digital veins (EDVs) and to examine whether beta3-AR relaxation was altered in EDVs incubated with endotoxin.

SAMPLE POPULATION

Forelimbs obtained from 30 horses.

PROCEDURE

Forelimbs were obtained from horses in an abattoir. Equine digital veins were carefully removed from distal portions of the forelimbs. Rings of dissected EDVs were mounted in 5-mL organ baths to record isometric tension in the presence of various beta3-AR agonists (SR 58611A, ZD 2079, and ZM 215001).

RESULTS

In intact EDVs, isoprenaline, SR 58611A, ZD 2079, and ZM 215001 induced concentration-dependent relaxation. Isoprenaline and SR 58611A-induced relaxations were reduced or unaffected by nadolol, respectively. In intact EDVs, SR 58611A-induced relaxation was significantly reduced in the presence of 2 microM ZM 215001 (used as a beta3-AR antagonist). In endothelium-denuded EDVs or intact EDVs in the presence of a nitric oxide synthase inhibitor, isoprenaline and SR 58611A-induced relaxations were significantly decreased. The endothelium-independent relaxation to SR 58611A was significantly inhibited in the presence of ZM 215001. In endotoxin-treated EDV, isoprenaline- and SR 58611A-induced relaxations were significantly reduced. In these conditions, cycloheximide (a protein synthesis inhibitor) and ibuprofen (a cyclooxygenase inhibitor) restored the relaxant response to SR 58611A.

CONCLUSIONS AND CLINICAL RELEVANCE

Beta3-adrenoceptors are functionally expressed in EDVs. Incubation in the presence of endotoxin, used as an in vitro model of laminitis, induced an alteration of beta-AR-mediated relaxations in EDVs, which could be the consequence of cyclooxygenase induction and subsequent prostanoid production.

NO-dependent vasorelaxation is impaired after gene transfer of inducible NO-synthase

Proinflammatory stimuli produce expression of inducible NO-synthase (iNOS) within blood vessels and are associated with impaired endothelium-dependent relaxation. Gene transfer of iNOS was used to test the hypothesis that expression of iNOS in blood vessels produces impairment of NO-dependent relaxation as well as contraction. An adenoviral vector containing cDNA for murine iNOS, AdCMViNOS, and a control virus, AdCMVBglII, were used for gene transfer to rabbit carotid arteries in vitro and in vivo. After gene transfer of iNOS in vitro, contractile responses to KCl, phenylephrine, and U46619 were impaired. Relaxation in response to acetylcholine, ADP, A23187, and nitroprusside was also impaired. For example, maximum relaxation of vessels to acetylcholine (10 micromol/L) was 78+/-4% (mean+/-SE) after AdBglII (10(10.5) plaque-forming units) and 34+/-5% after AdiNOS (10(10.5) plaque-forming units, P<0.05). NO-independent relaxation in response to 8-bromo-cGMP and papaverine was not impaired after AdiNOS. Contraction and relaxation were improved in carotid arteries expressing iNOS by aminoguanidine and L-N-iminoethyl lysine, inhibitors of iNOS. After intraluminal gene transfer of iNOS in vivo, contraction of vessels in vitro was normal, but responses to acetylcholine were impaired. In summary, the major finding is that NO-dependent relaxation is impaired in arteries after gene transfer of iNOS in vitro and in vivo. Thus, expression of iNOS per se impairs NO-dependent relaxation.

Tumor necrosis factor-alpha impairs contraction but not relaxation in carotid arteries from iNOS-deficient mice

We used mice deficient in expression of inducible NO synthase (iNOS -/-) to directly examine the role of iNOS in impaired vasoconstrictor responses following tumor necrosis factor-alpha (TNF-alpha). In iNOS +/+ mice, contraction of carotid arteries in response to prostaglandin F(2alpha) (PGF(2alpha)) was impaired following TNF-alpha (100 microg/kg ip)(n = 10, P < 0.01). In contrast to responses in wild-type mice, contraction to low concentrations of PGF(2alpha) were normal, but maximum contraction to PGF(2alpha) was impaired in arteries from iNOS -/- mice treated with TNF-alpha [0.35 +/-.0.02 g (n = 8) following vehicle and 0.25 +/- 0.02 g (n = 7) following TNF-alpha (P < 0.05)]. Aminoguanidine, a relatively selective inhibitor of iNOS, partially restored contraction to PGF(2alpha) in vessels from iNOS +/+ mice but had no effect in iNOS -/- mice injected with TNF-alpha, suggesting that a mechanism(s) other than iNOS contributes to impaired responses. In contrast to contractile responses, relaxation of the carotid artery in response to acetylcholine and nitroprusside was not altered following TNF-alpha in iNOS +/+ or iNOS -/-mice. Responses of carotid arteries from iNOS -/- mice and effects of aminoguanidine suggest that both iNOS-dependent and iNOS-independent mechanisms contribute to impaired contractile responses following TNF-alpha.

IL-10 deficiency increases superoxide and endothelial dysfunction during inflammation

Little is known about the role of interleukin-10 (IL-10), an anti-inflammatory cytokine, in blood vessels. We used IL-10-deficient mice (IL-10 -/-) to examine the hypothesis that IL-10 protects endothelial function after lipopolysaccharide (LPS) treatment. The responses of carotid arteries were studied in vitro 6 h after injection of a relatively low dose of LPS (10 microgram ip). In IL-10 -/- mice, the maximum relaxation to ACh (3 microM) was 56 +/- 6% (means +/- SE) after LPS injection and 84 +/- 4% after vehicle injection (P < 0.05). Thus endothelium-dependent relaxation was impaired in carotid arteries from IL-10 -/- mice after LPS injection. In contrast, this dose of LPS did not alter relaxation to ACh in vessels from wild-type (IL-10 +/+) mice. Relaxation to nitroprusside and papaverine was similar in arteries from both IL-10 -/- and IL-10 +/+ mice after vehicle or LPS injection. Because inflammation is associated with increased levels of reactive oxygen species, we also tested the hypothesis that superoxide contributes to the impairment of endothelial function by LPS in the absence of IL-10. Results using confocal microscopy and hydroethidine indicated that levels of superoxide are elevated in carotid arteries from IL-10 -/- mice compared with IL-10 +/+ mice after LPS injection. The impaired relaxation of arteries from IL-10 -/- mice after LPS injection was restored to normal by polyethylene glycol-suspended superoxide dismutase (50 U/ml) or allopurinol (1 mM), an inhibitor of xanthine oxidase. These data provide direct evidence that IL-10 protects endothelial function after an acute inflammatory stimulus by limiting local increases in superoxide. The source of superoxide in this model may be xanthine oxidase.

Aminoethyl-isothiourea, a nitric oxide synthase inhibitor and oxygen radical scavenger, improves survival and counteracts hemodynamic deterioration in a porcine model of streptococcal shock

OBJECTIVE

To test the effect of a continuous infusion of the nitric oxide (NO) synthase (S) inhibitor aminoethyl-isothiourea (AE-ITU) on survival time, hemodynamics, and oxygen transport in a porcine model of live group A streptococcal (GAS) sepsis. Furthermore, to examine the role of endothelin-1, histamine, and reactive oxygen species (ROS) in streptococcal shock.

DESIGN

Prospective, randomized trial.

SETTING

Laboratory at a university hospital.

SUBJECTS

Twenty-eight pigs with an average weight of 25 kg.

INTERVENTIONS

Sixteen animals received a continuous infusion of live Streptococcus pyogenes 1.3 x 10(10) colony forming units/hr: eight received fluids only, and the other eight received an intravenous infusion of AE-ITU 10 mg/kg/hr starting 30 mins before the GAS challenge. Six control pigs received AE-ITU 10 mg/kg/hr iv for 5 hrs. Another six animals received half the dose of GAS over 5 hrs.

MEASUREMENTS AND MAIN RESULTS

GAS infusion caused a rapid increase in pulmonary, hepatic, and systemic vascular resistance, followed by hypotension with a 90% lethality at 4 hrs. Treatment with AE-ITU increased 4-hr survival in septic animals from 1/8 to 8/8 and 5-hr survival from 0/8 to 5/8, prevented hypotension, and increased urine output. AE-ITU attenuated the decrease in cardiac output, liver blood flow, and oxygen delivery, and hepatic arterial blood flow as a fraction of cardiac output increased (all p < .05). Plasma nitrate/nitrite levels decreased in all animals. Inducible NOS and endothelial constitutive NOS activities in liver, gut, and lung were not increased during sepsis, nor were they decreased after AE-ITU. Plasma levels of endothelin-1 and methylhistamine increased in all septic animals and were not modified by AE-ITU. AE-ITU prevented the increase in monocyte ROS production caused by GAS. In control animals, AE-ITU caused an increase in mean arterial pressure, liver blood flow, and oxygen delivery.

CONCLUSIONS

In this model of porcine GAS-induced septic shock, which was not associated with enhanced NO production, infusion of the NOS inhibitor AE-ITU prolonged survival, prevented hypotension, and improved cardiac contractility, organ perfusion, and tissue oxygenation. These beneficial effects of AE-ITU might be a result of the combined effect of ROS scavenging and modulation of local NO production, thus improving the balance of vasodilator and vasoconstrictor forces and reducing oxidative stress.

Hypoxic contraction of small pulmonary arteries from normal and endotoxemic rats: fundamental role of NO

The present study was aimed at examining the role of nitric oxide (NO) in the hypoxic contraction of isolated small pulmonary arteries (SPA) in the rat. Animals were treated with either saline (sham experiments) or Escherichia coli lipolysaccharide [LPS, to obtain expression of the inducible NO synthase (iNOS) in the lung] and killed 4 h later. SPA (300- to 600-micrometer outer diameter) were mounted as rings in organ chambers for the recording of isometric tension, precontracted with PGF2alpha, and exposed to either severe (bath PO2 8 +/- 3 mmHg) or milder (21 +/- 3 mmHg) hypoxia. In SPA from sham-treated rats, contractions elicited by severe hypoxia were completely suppressed by either endothelium removal or preincubation with an NOS inhibitor [NG-nitro-L-arginine methyl ester (L-NAME), 10(-3) M]. In SPA from LPS-treated rats, contractions elicited by severe hypoxia occurred irrespective of the presence or absence of endothelium and were largely suppressed by L-NAME. The milder hypoxia elicited no increase in vascular tone. These results indicate an essential role of NO in the hypoxic contractions of precontracted rat SPA. The endothelium independence of HPV in arteries from LPS-treated animals appears related to the extraendothelial expression of iNOS. The severe degree of hypoxia required to elicit any contraction is consistent with a mechanism of reduced NO production caused by a limited availability of O2 as a substrate for NOS.

Hepatic oxygen metabolism in porcine endotoxemia: the effect of nitric oxide synthase inhibition

The role of endotoxin (lipopolysaccharide, LPS) and nitric oxide in hepatic oxygen metabolism was investigated in 36 pigs receiving 1) LPS (1.7 microgram. kg-1. h-1) for 7 h and NG-nitro-L-arginine methyl ester (L-NAME; 25 mg/kg) after 3 h, 2) LPS, 3) NaCl and L-NAME, and 4) NaCl. Infusion of LPS reduced hepatic oxygen delivery (DO2H) from 60 +/- 4 to 30 +/- 5 ml/min (P < 0.05) and increased the oxygen extraction ratio from 0.29 +/- 0.07 to 0.68 +/- 0.04 after 3 h (P < 0.05). Hepatic oxygen consumption (VO2H) was maintained (18 +/- 4 and 21 +/- 4 ml/min, change not significant), but acidosis developed. Administration of L-NAME during endotoxemia caused further reduction of DO2H from 30 +/- 3 to 13 +/- 2 ml/min (P < 0.05) and increased hepatic oxygen extraction ratio from 0.46 +/- 0.04 to 0.80 +/- 0.03 (P < 0.05). There was a decrease in VO2H from 13 +/- 2 to 9 +/- 2 ml/min that did not reach statistical significance, probably representing a type II error. Acidosis was aggravated. Administration of L-NAME in the absence of endotoxin also increased the hepatic oxygen extraction ratio, but no acidosis developed. In a different experiment, liver blood flow was mechanically reduced in the presence and absence of endotoxin, comparable to the flow reductions caused by L-NAME. The increase in hepatic oxygen extraction ratio (0.34) and maximum hepatic oxygen extraction ratio (approximately 0.90) was similar whether DO2H was reduced by occlusion or by L-NAME. We concluded that L-NAME has detrimental circulatory effects in this model. However, neither endotoxin nor L-NAME seemed to prevent the ability of the still circulated parts of the liver to increase hepatic oxygen extraction ratio to almost maximum when oxygen delivery was reduced. The effect of L-NAME on oxygen transport thus seems to be caused by a reduction in DO2H rather than by alterations in oxygen extraction capabilities.

Human and rat neutrophils constitutively express neural nitric oxide synthase mRNA

Freshly isolated rat circulating neutrophils (PMN) constitutively expressed neural nitric oxide synthase (nNOS) mRNA and nNOS protein and exhibited spontaneous basal release of low concentrations of nitrate and nitrite anion (RNI). In contrast, rat peripheral monocytes and macrophages were devoid of nNOS mRNA and protein and did not exhibit basal or spontaneous release of RNI. Constitutive neural NOS mRNA was also found in human PMN. However, nNOS protein was not expressed and spontaneous generation of RNI was absent in the human PMN. Spontaneous release of RNI from rat PMN was inhibited by 7-nitroindazole but not by L-N-iminoethyllysine, which further supported the nNOS origin of the spontaneously produced RNI. Intravenous administration of Escherichia coli endotoxin (0.6 mg/kg) did not acutely affect the content of nNOS mRNA or protein but inhibited nNOS-derived production of RNI in PMN and up-regulated iNOS mRNA and iNOS protein in PMN, macrophages, and monocytes. This communication demonstrates the existence of nNOS mRNA in rat and human PMN and nNOS protein in rat PMN. Moreover, the data also show that the nNOS system in rat PMN is functional and is inhibitable by the nNOS inhibitor 7-nitroindazole. These findings offer an explanation for the spontaneous formation of the PMN-derived relaxing factor resembling nitric oxide (NO). Moreover, since basal production of NO can affect expression of adhesion molecules and cell-cell binding, the nNOS system within the rat may play an important role in PMN function in normal and disease states. Finally and speculatively, if constitutively expressed nNOS mRNA is subject to activation and translation into nNOS protein, nNOS may also play a role in the function of human PMN.

Effects of the nitric oxide synthase inhibitors N(G)-nitro-L-arginine methyl ester and aminoethyl-isothiourea on the liver microcirculation in rat endotoxemia

BACKGROUND/METHODS

The question whether nitric oxide protects or impairs organ perfusion during early endotoxemia has not been completely answered. To evaluate the regulative function of nitric oxide on organ microvascular perfusion and leukocyte accumulation during endotoxemia, we studied the influence of a non-selective nitric oxide inhibitor and a preferential inducible nitric oxide synthase inhibitor (respectively, N(G)-nitro-L-arginine methyl ester and aminoethyl-isothiourea) on liver microcirculation (intravital fluorescence microscopy) in a rat model.

RESULTS

Two hours after intraportal injection of lipopolysaccharide (5 mg/kg in 10 min) the rats were randomly treated and received a bolus dose of N(G)-nitro-L-arginine methyl ester (10 mg/kg, n = 7), aminoethyl-isothiourea (10 mg/kg, n = 6) or normal saline, (n = 7). After 1 h, N(G)-nitro-L-arginine methyl ester blockade yielded a higher rate of non-perfused sinusoids than normal saline (27 +/- 2% vs 19 +/- 5%, p < 0.05). LPS-induced leukocyte stagnation in sinusoids was further increased (p < 0.05) in all groups after 1 h treatment, but N(G)-nitro-L-arginine methyl ester clearly accentuated leukocyte accumulation in sinusoids as compared to normal saline (69 +/- 19% vs 16 +/- 4%, p < 0.05). Both modalities of nitric oxide blockade elicited a significant enhancement in the number of leukocytes adherent to the postsinusoidal venules in contrast to normal saline (N(G)-nitro-L-arginine methyl ester 48 +/- 17%, aminoethyl-isothiourea 33 +/- 9% vs normal saline 1 +/- 5%, p < 0.05).

CONCLUSIONS

We conclude that complete nitric oxide blockade aggravates lipopolysaccharide-induced hepatic microvascular perfusion failure and enhances leukocyte accumulation, in both sinusoids and post-sinusoidal venules. The preferential inducible nitric oxide synthase inhibitor aminoethyl-isothiourea has a moderate negative effect, favoring leukocyte adhesion in postsinusoidal venules, and its usefulness demands further research, especially concerning its late effects.

Effects of activating and deactivating cytokines on the functionally linked tetrahydrobiopterin. No pathways in vascular smooth muscle cells

The functional relationship of nitric oxide (NO) production and synthesis of tetrahydrobiopterin (BH4), the requisite cofactor for NO synthase, was investigated in rat aortic smooth muscles cells (SMC). Inflammatory cytokines induced BH4 and NO synthesis in different ratios, IL-1 beta induced mainly NO synthesis with concomitant but limiting amounts of BH4 for maximal NO production. TNF alpha did not induce NO synthesis but induced BH4 synthesis. IFN gamma was ineffective on both the induction of NO and BH4 synthesis. TGF beta downregulated NO production but did not affect BH4 biosynthesis. IL-4 and IL-10 had no effect on both BH4 and NO synthesis. Activating cytokines strongly synergized in induction of NO production, whereas endogenous BH4 production became insufficient for maximal NO synthesis. Exogenous cofactor in the form of sepiapterin or authentic BH4, but not the natural isomer 7-BH4, enhanced NO production twofold. Inhibition of BH4 synthesis with dicumarol abolished NO production that could be restored in the presence of BH4.