Differential inducible nitric oxide synthase expression in systemic and pulmonary vessels after endotoxin

Endothelial cells are intrinsically defective in xenophagy of Streptococcus pyogenes

Group A Streptococcus (GAS) is deleterious pathogenic bacteria whose interaction with blood vessels leads to life-threatening bacteremia. Although xenophagy, a special form of autophagy, eliminates invading GAS in epithelial cells, we found that GAS could survive and multiply in endothelial cells. Endothelial cells were competent in starvation-induced autophagy, but failed to form double-membrane structures surrounding GAS, an essential step in xenophagy. This deficiency stemmed from reduced recruitment of ubiquitin and several core autophagy proteins in endothelial cells, as demonstrated by the fact that it could be rescued by exogenous coating of GAS with ubiquitin. The defect was associated with reduced NO-mediated ubiquitin signaling. Therefore, we propose that the lack of efficient clearance of GAS in endothelial cells is caused by their intrinsic inability to target GAS with ubiquitin to promote autophagosome biogenesis for xenophagy.

Milrinone relaxes pulmonary veins in guinea pigs and humans

Introduction

The phosphodiesterase-III inhibitor milrinone improves ventricular contractility, relaxes pulmonary arteries and reduces right ventricular afterload. Thus, it is used to treat heart failure and pulmonary hypertension (PH). However, its action on pulmonary veins (PVs) is not defined, although particularly PH due to left heart disease primarily affects the pulmonary venous bed. We examined milrinone-induced relaxation in PVs from guinea pigs (GPs) and humans.

Material and Methods

Precision-cut lung slices (PCLS) were prepared from GPs or from patients undergoing lobectomy. Milrinone-induced relaxation was studied by videomicroscopy in naïve PVs and in PVs pre-constricted with the ET_A-receptor agonist BP0104. Baseline luminal area was defined as 100%. Intracellular cAMP was measured by ELISA and milrinone-induced changes of segmental vascular resistances were studied in the GP isolated perfused lung (IPL).

Results

In the IPL (GP), milrinone (10 µM) lowered the postcapillary resistance of pre-constricted vessels. In PCLS (GP), milrinone relaxed naïve and pre-constricted PVs (120%) and this relaxation was attenuated by inhibition of protein kinase G (KT 5823), adenyl cyclase (SQ 22536) and protein kinase A (KT 5720), but not by inhibition of NO-synthesis (L-NAME). In addition, milrinone-induced relaxation was dependent on the activation of K_ATP-, BK_Ca²⁺- and K_v-channels. Human PVs also relaxed to milrinone (121%), however only if pre-constricted.

Discussion

Milrinone relaxes PVs from GPs and humans. In GPs, milrinone-induced relaxation is based on K_ATP-, BK_Ca²⁺- and K_v-channel-activation and on cAMP/PKA/PKG. The relaxant properties of milrinone on PVs lead to reduced postcapillary resistance and hydrostatic pressures. Hence they alleviate pulmonary edema and suggest beneficial effects of milrinone in PH due to left heart disease.

Advances in mesenchymal stem cell research in sepsis

BACKGROUND

Sepsis remains a source of morbidity and mortality in the postoperative patient despite appropriate resuscitative and antimicrobial approaches. Recent research has focused upon additional interventions such as exogenous cell-based therapy. Mesenchymal stem cells (MSCs) exhibit multiple beneficial properties through their capacity for homing, attenuating the inflammatory response, modulating immune cells, and promoting tissue healing. Recent animal trials have provided evidence that MSCs may be useful therapeutic adjuncts.

MATERIALS AND METHODS

A directed search of recent medical literature was performed utilizing PubMed to examine the pathophysiology of sepsis, mechanisms of mesenchymal stem cell interaction with host cells, sepsis animal models, and recent trials utilizing stem cells in sepsis.

RESULTS

MSCs continue to show promise in the treatment of sepsis by their intrinsic ability to home to injured tissue, secrete paracrine signals to limit systemic and local inflammation, decrease apoptosis in threatened tissues, stimulate neoangiogenesis, activate resident stem cells, beneficially modulate immune cells, and exhibit direct antimicrobial activity. These effects are associated with reduced organ dysfunction and improved survival in animal models.

CONCLUSION

Research utilizing animal models of sepsis has provided a greater understanding of the beneficial properties of MSCs. Their capacity to home to sites of injury and use paracrine mechanisms to change the local environment to ultimately improve organ function and survival make MSCs attractive in the treatment of sepsis. Future studies are needed to further evaluate the complex interactions between MSCs and host tissues.

Altered monocyte and macrophage numbers in blood and organs of chickens injected i.v. with lipopolysaccharide

Lipopolysaccharide (LPS) is a Gram-negative bacteria cell wall component that activates monocytes and macrophages to produce nitric oxide (NO) from inducible nitric oxide synthase. Nitric oxide production in the plasma of chickens peaks 5-6-h post-i.v. LPS injection reflecting iNOS activation. To determine monocyte responsiveness after an i.v. LPS injection, a time course study was conducted examining the concentrations among peripheral blood leukocytes post-i.v. LPS injection in male and female chickens, the proportions among peripheral mononuclear leukocyte (PBMC; containing lymphocytes, thrombocytes, and monocytes) populations isolated from the blood samples collected at various times post-i.v. LPS treatment, and the ability of monocytes to produce NO with and without further LPS stimulation in vitro using the PBMC NO production assay. Additionally, monocyte extravasation activity was determined by analyzing macrophage proportions after the i.v. LPS injection in spleen, lung, and liver tissues. Blood was collected from male and female chickens at 0 h (pre-LPS injection control) and at 1, 3, 6, 24, and 48 h post-LPS injection, and additionally, at 72 h from female chickens. Tissues were collected 0, 1, 6, and 48 h post-i.v. LPS injection from male chickens. Monocyte concentrations dropped substantially by 1h in both males and females. In males, monocyte concentrations returned to control concentrations by 6h and increased at 24- and 48-h post-LPS injection, whereas in females, monocyte concentrations recovered more slowly, returning to near control concentrations by 24-48-h and increasing above control levels by 72 h. Lipopolysaccharide stimulated NO production by PBMC cultures established from blood samples obtained at various times post-LPS injection in vivo followed the same pattern as monocyte concentrations in the blood. Hence, NO concentrations within PBMC cultures were dependent upon the number of monocytes that were in the PBMC cultures isolated at different times post-i.v. LPS injection. Furthermore, macrophage proportions in spleen tissues responded similarly to monocyte concentrations in the blood, decreased in lung tissue, and varied widely in liver tissue throughout 48 h after an LPS injection. Monocytes and other leukocytes may attach to the endothelium post-i.v. LPS injection preventing the monocytes from entering the needle during blood collection resulting in what seems to be leukopenia in blood and in PBMC cultures attenuating NO production in PBMC cultures. Furthermore, monocyte differentiation and recruitment from the bone marrow is a likely contributor to the reconstitution and rise of monocyte concentrations in blood samples post-i.v. LPS injection.

Effects of San-Huang-Xie-Xin-Tang on U46619-induced increase in pulmonary arterial blood pressure

ETHNOPHARMACOLOGICAL RELEVANCE

San-Huang-Xie-Xin-Tang (SHXT), composed of Coptidis rhizoma, Scutellariae radix and Rhei rhizoma, is traditionally used to treat hypertension.

AIM OF THE STUDY

Our aim was to investigate the pharmacology effect of SHXT on a thromboxane A(2) analogue U46619-induced increase in pulmonary hypertension and protein expression in primary pulmonary smooth muscle cells (PASMCs).

MATERIALS AND METHODS

Arterial blood pressure and isometric tension in the aorta and pulmonary artery of rats were measured by pressure and force transducers, respectively. Protein expressions on PASMCs were detected by Western blotting.

RESULTS

SHXT significantly attenuated U46619-induced increase in arterial blood pressure. The inhibitory effect of SHXT on pulmonary arterial pressure was greater than systemic arterial pressure in U46619 treated rats. Similarly, the inhibitory effect of SHXT on U46619-induced vasoconstriction in rat pulmonary arterial rings was greater than that in aortic rings. In U46619 treated PASMCs, SHXT down-regulated expression of phosphodiesterase type 5 (PDE5), Rho-kinase (ROCK) II, cyclooxygenase-2 (COX-2) and up-regulated expression of soluble guanylyl cyclase (sGC) alpha(1) and sGCbeta(1).

CONCLUSIONS

SHXT attenuated U46619-induced increase in systemic and pulmonary arterial blood pressure. Inhibition of PDE5, ROCK-II, COX-2 and stimulation of sGC may play important roles in the cardiovascular effects of SHXT.

Discrepant effects of inducible nitric oxide synthase modulation on systemic and splanchnic endothelial nitric oxide synthase activity and expression in cirrhotic rats

BACKGROUND

Arterial vasodilatation, which is a major factor in the pathogenesis of the hyperkinetic circulatory state and portal hypertension in cirrhosis, is due to arterial nitric oxide (NO) overproduction secondary to endothelial NO synthase (eNOS) and inducible NOS (iNOS) upregulation. However, in cirrhosis, the respective roles of eNOS and iNOS isoforms in NO overproduction are still unknown and the effect of iNOS modulation on eNOS activity and expression has not been evaluated in the systemic or splanchnic vessels. The aim of this study was to evaluate the effects of modulating aortic and superior mesenteric arteries (SMA) iNOS on arterial eNOS activity and expression in rats with cirrhosis.

METHODS

eNOS and iNOS protein expression and eNOS activity (assessed by its phosphorylation at serine 1177) were measured in the aortas and SMA in untreated and treated cirrhotic rats with lipopolysaccharide (LPS), N-iminoethyl-L-lysine (L-NIL), a selective iNOS inhibitor, and LPS plus L-NIL.

RESULTS

LPS administration significantly increased eNOS and iNOS protein expression and eNOS activity in the aortas of both sham-operated and cirrhotic rats. However, in SMA, LPS administration induced a decrease in eNOS protein expression and activity and an increase in iNOS protein expression.

CONCLUSION

The results of this study may explain the worsening of the hyperdynamic state in cirrhosis during septic shock by direct LPS-induced eNOS activation in large systemic vessels, and its inhibition in concomitant small splanchnic vasculature by iNOS synthesized NO.

Comparison of the systemic and pulmonary inflammatory response to endotoxin of neutropenic and non-neutropenic rats

Background

Neutrophil infiltration commonly occurs in acute lung injury and may be partly responsible for the inflammatory response. However, acute lung injury still occurs in the neutropenic host. The objectives of this study are to determine if inflammation and acute lung injury are worse in neutropenic versus the normal host after endotoxemia.

Methods

Rats were divided into four groups: 1) control, 2) neutropenic, 3) endotoxemic and 4) endotoxemic and neutropenic. Tumor necrosis factor (TNF)-α and macrophage inflammatory protein (MIP-2) were measured in the blood, lung lavage and for mRNA in the lung. Arterial blood gases were measured to determine the alveolar-arterial oxygen gradient which reflects on lung injury.

Results

In endotoxemia, the neutropenic rats had lower plasma TNF-α (116 ± 73 vs. 202 ± 31 pg/ml) and higher plasma MIP-2 (26.8 + 11.9 vs. 15.6 + 6.9 ng/ml) when compared to non-neutropenic rats. The endotoxemic, neutropenic rats had worse lung injury than the endotoxemic, non-neutropenic rats as shown by increase in the alveolar-arterial oxygen gradient (24 ± 5 vs. 12 ± 9 torr). However, lavage concentrations of TNF-α and MIP-2 were similar in both groups.

Conclusion

Neutrophils may regulate TNF-α and MIP-2 production in endotoxemia. The elevation in plasma MIP-2 in the endotoxemic, neutropenic rat may be secondary to the lack of a neutrophil response to inhibit production or release of MIP-2. In endotoxemia, the severe lung injury observed in neutropenic rats does not depend on TNF-α or MIP-2 produced in the lung.

Variation in the Pulmonary Hypertensive Responsiveness of Broilers to Lipopolysaccharide and Innate Variation in Nitric Oxide Production by Mononuclear Cells

Variability among broilers in their pulmonary hypertensive (PH) responsiveness to lipopolysaccharide (LPS) appears to reflect innate variation in the types or proportions of vasodilators and vasoconstrictors released by leukocytes and endothelial cells. Two experiments were designed to evaluate possible correlations between the PH responsiveness to LPS in vivo and the quantities of nitric oxide (NO; a potent pulmonary vasodilator) produced by mononuclear cells in vitro. In Experiment 1, blood samples were collected from male broilers from a base population (control group) and from survivors of a 60% lethal dose i.v. injection of cellulose microparticles (MP survivor group). In Experiment 2, blood samples were collected from male broilers from a relaxed line and from lines known to be susceptible or resistant to pulmonary hypertension syndrome. Peripheral mononuclear cells (PMNC) from each blood sample were cultured at 2 million cells per well, remained unstimulated, or were stimulated with LPS to elicit the expression of inducible NO synthase, and the 24-h production of NO was measured. In both experiments, unstimulated PMNC cultures did not produce consistently detectable levels of NO, whereas LPS-stimulated cultures produced quantities of NO that varied widely among individuals. Nitric oxide production by cultured PMNC also was evaluated by flow cytometry, demonstrating that LPS-stimulated PMNC produced substantially more NO than did unstimulated cells in all of the groups evaluated. Moreover, NO-producing PMNC were identified to be monocytes. The same broilers from which PMNC had been isolated were catheterized subsequently to record pulmonary arterial pressure, LPS was injected i.v. to assess the amplitudes of peak and postpeak PH responses, then N(omega)-nitro-L-arginine methyl ester was injected to inhibit ongoing NO production. In Experiment 1, the amplitude of the peak and postpeak PH responses to LPS were correlated with the quantity of NO produced by LPS-stimulated cultured PMNC from broilers in the control group but not for MP survivors. In Experiment 2, the postpeak PH response to LPS was correlated with the quantity of NO produced by LPS-stimulated PMNC from broilers in the relaxed line, but not in the susceptible or resistant lines. In all groups, N(omega)-nitro-L-arginine methyl ester injections triggered substantial increases in pulmonary arterial pressure (> or = 8 mm Hg), thereby revealing a significant ongoing modulation by NO of the PH response to LPS. We concluded that most of the modulatory NO generated in vivo during the acute PH response to LPS (within 60 min postinjection) likely is produced by constitutive NO synthase in the vascular endothelium. In addition, the NO produced by inducible NO synthase in PMNC appeared to have modulated the LPS-stimulated PH responses of unselected broilers having the broadest range of pulmonary vascular capacities (control broilers and relaxed line), but not in broilers whose pulmonary vascular capacities had been selected to represent the higher (MP survivors, resistant line) or lower (susceptible line) extremes of the population.

p38 mitogen-activated protein kinase mediates the sustained phase of hypoxic pulmonary vasoconstriction and plays a role in phase I vasodilation

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present common and formidable clinical problems for thoracic, transplant, and trauma surgeons. We hypothesized that acute hypoxia causes pulmonary artery (PA) contraction and that p38 mitogen-activated protein (MAP) kinase is a key mediator in that process. To test this hypothesis, we measured isometric force displacement in isolated rat pulmonary artery rings during hypoxia in the presence and absence of the selective p38 MAP kinase inhibitor SB-20358, and stimulator anisomycin. In separate experiments, we measured the functional effects in isolated rat pulmonary artery rings of inhibiting p38 MAP kinase during normoxic conditions. p38 MAP kinase inhibition significantly attenuated the delayed, but not early, contractile phase of HPV. Additionally, stimulation of p38 MAP kinase significantly decreased the phase I vasodilation of HPV. Under normoxia conditions, there was no statistically significant difference in isometric force displacement between control and p38 MAPK inhibitor-treated pulmonary artery rings. We conclude that p38 MAP kinase may be a key mediator in the pathogenesis of HPV and that further understanding may lead to new therapies for HPV associated with acute lung injury.

Influence of aminoguanidine, an inhibitor of inducible nitric oxide synthase, on the pulmonary hypertensive response to microparticle injections in broilers

The pulmonary hypertensive response to pulmonary vascular obstruction caused by intravenously injected microparticles is amplified by pretreatment with N(omega)nitro-L-arginine methyl ester (L-NAME). The L-NAME prevents the synthesis of the potent vasodilator nitric oxide (NO) by inhibiting both the constitutive [endothelial NO synthase (eNOS or NOS-3)] and inducible [inducible NO synthase (iNOS or NOS-2)] forms of NO synthase. In the present study we used the selective iNOS inhibitor aminoguanidine (AG) to evaluate the role of iNOS in modulating the pulmonary hypertension (PH) triggered by microparticle injections. Experiment 1 was conducted to confirm the ability of AG to inhibit NO synthesis by iNOS in broiler peripheral blood mononuclear cells exposed to bacterial lipopolysaccharide (LPS, endotoxin). Mononuclear leukocytes treated with LPS produced 10-fold more NO than untreated (control) cells. The LPS-stimulated production of NO was partially inhibited by L-NAME and was fully inhibited by AG, thereby confirming that AG inhibits LPS-mediated iNOS activation in broilers. In Experiment 2 we evaluated the responses of male progeny from a base population (MP Base) and from a derivative line selected for one generation from the survivors of an LD50 microparticle injection (MP Select). The pulmonary arterial pressure (PAP) was lower in MP Select than in MP Base broilers. Both lines exhibited similar percentage increases in PAP after microparticles were injected, and AG modestly amplified the PH triggered by microparticles in both lines. In Experiment 3 we evaluated the responses of male progeny from a second base population (PAC Base) and from a derivative line selected for 3 generations using the unilateral pulmonary artery clamp technique (PAC Select). The PAP was lower in PAC Select than in PAC Base broilers, and both lines exhibited similar percentage increases in PAP in response to the microparticles. The PH triggered by microparticles was not amplified by AG but was doubled by L-NAME. These experiments demonstrate that during the 30 min following pulmonary vascular entrapment of microparticles, iNOS modulated the PH elicited in broilers derived from the MP pedigree line, but not in broilers from the PAC pedigree line. Different NOS-mediated responses among broiler populations may affect pulmonary hemodynamic characteristics of broiler lines selected using i.v. microparticle injections.

Pulmonary hypertension triggered by lipopolysaccharide in ascites-susceptible and -resistant broilers is not amplified by aminoguanidine, a specific inhibitor of inducible nitric oxide synthase

Nitric oxide (NO) is a potent pulmonary vasodilator that modulates the pulmonary vasoconstriction and pulmonary hypertension (PH) triggered by bacterial lipopolysaccharide (LPS) in broilers. The amplitude and duration of the LPS-induced PH are markedly enhanced following pretreatment with N(omega)-nitro-L-arginine methyl ester (L-NAME), which inhibits NO synthesis by both the constitutive (endothelial) and inducible (inflammatory) forms of nitric oxide synthase (eNOS and iNOS, respectively). In the present study L-NAME and the selective iNOS inhibitor aminoguanidine (AG) were administered to differentiate between iNOS and eNOS as the primary source of NO that attenuates the pulmonary vascular response to LPS. Clinically healthy male progeny from ascites-susceptible and ascites-resistant lines were anesthetized, and their pulmonary artery was cannulated. The initial pulmonary arterial pressure (PAP) was recorded, then the broilers either remained untreated (control group) or were injected i.v. with AG. Ten minutes later all birds received an i.v. injection of LPS, followed 40 min later by an i.v. injection of L-NAME. When compared with untreated controls, AG neither increased the baseline PAP nor did it increase or prolong the PH response to LPS. The ascites-susceptible broilers maintained a higher PAP than the ascites-resistant broilers throughout the experiment, and the ascites-resistant broilers exhibited greater relative increases in PAP in response to LPS than did the ascites-susceptible broilers. Within 40 min after the LPS injection, PAP subsided to a level that did not differ from the respective preinjection value for each line. Injecting L-NAME reversed the decline in PAP, and within 5 min PAP returned to hypertensive levels approaching the maximum peak PH response to LPS. The absence of any impact of AG coupled with the profound response to L-NAME indicates that NO synthesized by eNOS rather than iNOS likely modulated the acute (within 1 h) PH elicited by LPS. Evidently eNOS is activated by the increased shear stress exerted on the endothelium during the PH response to LPS, whereas LPS-mediated up-regulation of iNOS expression may take longer than 1 h before biologically effective quantities of NO are produced.

Plasma levels of nitrites, PGF1α and nitrotyrosine in LPS-treated rats: functional and histochemical implications in aorta

We investigated the effects of lipopolysaccharide (LPS) administration on plasma nitrite, nitrotyrosine and 6-keto prostaglandin F1alpha, (PGF1alpha) levels and the related resultant changes in function and histochemistry of aorta in rats. Plasma nitrite and PGF1alpha nitrotyrosine levels were analysed after 5 mg/kg intravenous LPS was administered to rats compared with those in non-treated rats. The distribution of nitrotyrosine in the aorta was studied immunohistochemically. The contractile responses of aortic rings to phenylephrine (PE) from both the LPS-treated and control rats were studied in the organ baths. There were increases in plasma nitrite, PGF1alpha, and nitrotyrosine concentrations of LPS-treated rats compared to non-treated rats. Immunoreactivity of nitrotyrosine residues were detected in the endothelial and smooth muscle cells in LPS-treated but not in control rat aorta. The contractile responses to PE of the LPS-treated rat aortic rings were significantly reduced as compared with those of control rat's. Incubation of the aortic rings from LPS-treated rats with cyclooxygenase inhibitor indomethacine or with a combination of indomethacine and nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) increased the contractile responses to the levels observed in control rats suggesting that both prostanoids and particularly nitric oxide (NO) are involved in the reduced contractile responses in LPS-treated rats. These results supported the view that LPS might cause an increment in both NO and PGI2 levels. This increase in the NO and PGI2 levels may be responsible from the reduction in responses of aorta to contractile agents in LPS-treated rats. Increased peroxynitrite formation in LPS-treated rats may lead to nitration of the tyrosil residues of the proteins in the aorta.

Evaluation of Total Plasma Nitric Oxide Concentrations in Broilers Infused Intravenously with Sodium Nitrite, Lipopolysaccharide, Aminoguanidine, and Sodium Nitroprusside

Nitric oxide (NO) is a potent vasodilator that is synthesized by constitutive and inducible isoforms of the enzyme NO synthase (eNOS and iNOS, respectively). The half-life of NO averages only 3 to 4 s in biological fluids, where it is rapidly converted to the stable oxidation products nitrite (NO2-) and nitrate (NO3-). Our objectives were to use 2 commercial kits to measure total plasma NO, as NO2- + NO3-, and to assess plasma NO values during experimental protocols designed to influence NO accumulation in the plasma. One kit employed copper-coated cadmium as a catalyst for reducing NO3- to NO2-; the second kit employed the enzyme NO3- reductase for the same purpose. Both then employed Griess reagent for the colorimetric determination of NO2- as a measure of total plasma NO. Broilers in Experiment 1 were infused i.v. with solutions containing increasing concentrations of sodium NO2-. Broilers in Experiment 2 were injected with 1 mg of lipopolysaccharide (LPS), which is known to stimulate iNOS activity. Both commercial kits successfully detected increases in total plasma NO attributable to ongoing i.v. NO2- infusion or to increased iNOS expression at 5 h after the LPS injection. In Experiment 3, we compared the total plasma NO responses to LPS in the presence and absence of aminoguanidine (AG), a selective inhibitor of iNOS. The AG significantly attenuated the LPS-mediated increase in total plasma NO at 5 h post-injection. In Experiment 4, broilers were infused with sodium nitroprusside (SNP), an exogenous NO donor molecule that previously had been shown to lower the pulmonary arterial pressure in broilers. The SNP infusion did substantially reduce the pulmonary arterial pressure, but an increase in total plasma NO was not detected during the SNP infusion. Overall, NO accumulation in the plasma was successfully detected after sustained infusion of NaNO2 and administration of LPS for 5 h, but biologically effective levels of NO released from SNP were not detected. Therefore, total plasma NO concentrations (assayed as NO2- + NO3-) qualitatively reflect whole-body NO synthesis, but biologically relevant quantities of NO may be produced at levels that cannot be detected by colorimetric assays.

Disparate IL-1β and iNOS Gene Expression in the Aorta and Pulmonary Artery after Endotoxemia

BACKGROUND

Endotoxemia causes paradoxical effects on the systemic and pulmonary vasculature, resulting in systemic hypotension and increased pulmonary artery pressure. The local production of inflammatory mediators may have important effects on vascular tissue function. The purpose of this study was to delineate differences in function and the expression of tissue cytokine genes in the aorta and pulmonary artery after endotoxemia.

METHODS

Thoracic aorta and pulmonary artery branches were isolated from adult Sprague- Dawley rats (n = 4-6/group) 6 h after intraperitoneal injection of lipopolysaccharide (Salmonella typhimurium, 20 mg/kg) or vehicle (1.0 mL of saline). Arteries were suspended in perfused organ baths for measurement of isometric force transduction, and dose-response curves to phenylephrine (0.01-10 micromol/L), acetylcholine (0.01-10 micromol/L), and sodium nitroprusside (0.001-10 micromol/L) were generated. The vascular segments were also assessed for expression of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, and inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) by semiquantitative reverse transcriptase- polymerase chain reaction.

RESULTS

Endotoxemia resulted in decreased contractility of the aorta (508.63 +/- 81.89 mg vs. 2544.16 +/- 142.05 mg in the vehicle group) and pulmonary artery (352.50 +/- 38.11 mg vs. 535.83 +/- 45.51 mg in the vehicle group) and decreased endothelium-dependent pulmonary artery relaxation (52.86 +/- 5.63% vs. 80.58 +/- 6.39% in the vehicle group). Expression of IL-1beta and iNOS mRNA by the pulmonary artery, but not the aorta, increased significantly in the endotoxintreated animals. Interleukin-6 was increased in both the pulmonary artery and the aorta during endotoxemia, whereas TNF concentrations were unchanged.

CONCLUSIONS

Endotoxemia may cause aortic hypocontractility and impaired endothelium-dependent pulmonary artery vasorelaxation. Expression of inflammatory genes in vascular tissue may be site-specific and may contribute to the functional derangements associated with sepsis.

S-nitrosoglutathione inhibits alpha1-adrenergic receptor-mediated vasoconstriction and ligand binding in pulmonary artery

Endogenous nitric oxide donor compounds (S-nitrosothiols) contribute to low vascular tone by both cGMP-dependent and -independent pathways. We have reported that S-nitrosoglutathione (GSNO) inhibits 5-hydroxytryptamine (5-HT)-mediated pulmonary vasoconstriction via a cGMP-independent mechanism likely involving S-nitrosylation of its G protein-coupled receptor (GPCR) system. Because catecholamines, like 5-HT, constrict lung vessels via a GPCR coupled to G(q), we hypothesized that S-nitrosothiols modify the alpha1-adrenergic GPCR system to inhibit pulmonary vasoconstriction by receptor agonists, e.g., phenylephrine (PE). Rat pulmonary artery rings were pretreated for 30 min with and without an S-nitrosothiol, either GSNO or S-nitrosocysteine (CSNO), and constricted with sequential concentrations of PE (10(-8)-10(-6) M). Effective cGMP-dependence was tested in rings pretreated with soluble guanylate cyclase inhibitors {either 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or LY-83583} or G kinase inhibitor (KT-5823), and a thiol reductant [dithiothreitol (DTT)] was used to test reversibility of S-nitrosylation. Both S-nitrosothiols attenuated the PE dose response. The GSNO effect was not prevented by LY-83583, ODQ, or KT-5823, indicating cGMP independence. GSNO inhibition was reversed by DTT, consistent with S-nitrosylation or other GSNO-mediated cysteine modifications. In CSNO-treated lung protein, the alpha1-adrenergic receptor was shown to undergo S-nitrosylation in vitro using a biotin switch assay. Studies of alpha1-adrenergic receptor subtype expression and receptor density by saturation binding with 125I-HEAT showed that GSNO decreased alpha1-adrenergic receptor density but did not alter affinity for antagonist or agonist. These data demonstrate a novel cGMP-independent mechanism of reversible alpha1-adrenergic receptor inhibition by S-nitrosothiols.

Up-regulation of endothelial nitric oxide synthase inhibits pulmonary leukocyte migration following lung ischemia-reperfusion in mice

Endogenous nitric oxide (NO) is known to modulate post-ischemic inflammatory response in various organs. However, the role of nitric oxide synthase isoforms (NOS) in mediating pulmonary post-ischemic inflammatory response is poorly understood. We therefore studied post-ischemic endothelial adhesion molecule expression and leukocyte migration in endothelial NOS knockout (eNOS-KO) mice subjected to pulmonary ischemia and reperfusion in vivo. Under anesthesia and mechanical ventilation, the left pulmonary hilum in wild-type (WT) and eNOS-KO mice was clamped for 1 hour, followed by reperfusion for up to 24 hours. In WT mice, we observed a selective up-regulation of both eNOS mRNA and protein in lung tissue, while inducible NOS (iNOS) and neuronal NOS (nNOS) remained unchanged. Survival in eNOS-KO mice was reduced due to severe pulmonary edema, underlining an increased susceptibility to ischemia-reperfusion (I/R) injury. Interstitial tissue infiltration by CD18- and CD11a-positive white blood cells as well as lung tissue water content peaked at 5 hours of reperfusion and were found significantly higher than in WT mice. Enhanced leukocyte-endothelial interaction was associated with pronounced up-regulation of vascular cell adhesion molecule (VCAM) in eNOS-KO mice during post-ischemic reperfusion. We conclude that eNOS attenuates post-ischemic inflammatory injury to the lung most probably via inhibition of endothelial adhesion molecule expression.

Vascular pharmacology of acute lung injury and acute respiratory distress syndrome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) following sepsis, major trauma and surgery are leading causes of respiratory insufficiency, warranting artificial ventilation in the intensive care unit. It is caused by an inflammatory reaction in the lung upon exogenous or endogenous etiologies eliciting proinflammatory factors, and results in increased alveolocapillary permeability and protein-rich alveolar edema. The interstitial and alveolar inflammation and edema alter ventilation perfusion matching, gas exchange and mechanical properties of the lung. The current therapy of the condition is supportive, paying careful attention to fluid balance, relieving the increased work of breathing and improving gas exchange by mechanical ventilation, but in vitro, animal and some clinical research is done to evaluate the value of anti-inflammatory therapies on morbidity and outcome, including inflammatory cell-stabilizing corticosteroids, xanthine derivates, prostanoids and inhibitors, O(2) radical scavenging factors such as N-acetylcysteine, surfactant replacement, vasodilators including inhaled nitric oxide, vasoconstrictors such as almitrine, and others. None of these compounds has been proven to benefit survival in patients, however, even though carrying a physiologic benefit, except perhaps for steroids that may improve outcome in the later stage of ARDS. This partly relates to the difficulty to assess the lung injury at the bedside, to the multifactorial pathogenesis and the severity of comorbidity, adversely affecting survival.