Role of nitric oxide in thermoregulation during septic shock: involvement of vasopressin

We tested the hypothesis that the nitric oxide (NO) pathway in the central nervous system (CNS) plays a role in hypothermia, as well as in the febrile response during experimental septic shock, by regulating vasopressin (AVP) release. Experiments were performed on male Wistar rats treated with N ^G-nitro-l-arginine methyl ester (l-NAME), a non-selective NO synthase (NOS) inhibitor, injected intracerebroventricularly (250 µg/1 l) 30 min before lipopolysaccharide (LPS) 1.5 mg/kg i.v. injection. One hour after LPS administration we observed a significant drop in body temperature (hypothermic response), followed by a temperature increase after the second hour (febrile response), which remained until the end of the experiment. Increased plasmatic AVP levels were concomitantly observed during hypothermia, nearly returning to basal levels during the febrile phase. When l-NAME was administered with LPS, plasmatic AVP concentrations remained high throughout the experiment, hypothermia was accentuated and the febrile response was abolished. Additionally, pre-treatment with -mercapto-,-cyclopentamethylenepropionyl¹, O-Et-Tyr², Val⁴, Arg⁸-vasopressin, an AVP V1 receptor blocker (10 µg/kg) administered i.v., reduced hypothermia and exacerbated the febrile response to endotoxin. In conclusion, our data indicate that the central NO pathway plays an inhibitory role in AVP release during experimental septic shock, which seems to be critical for the thermoregulation during this pathophysiological state.     

Enhanced production of nitric oxide in rat organs in heat shock

Heat shock is shown to lend a marked boost to the production of nitric oxide (NO), which attains the maximal level 1 hour after exposure and returns to the initial level after 24 hours. The generation of NO in all studied organs is completely blocked by Nω-nitro-L-arginine, an inhibitor of NO synthase, both in the control and after hyperthermia. Thus, heat shock markedly stimulates NO synthesis. This generalized effect may underlie the drop in the peripheral vascular tone that is characteristic of heat shock. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, No. 5, pp. 520–523, May, 1996     

Vasopressin analogues and V1a receptor agonists in septic shock

This article reviews the role of arginine-vasopressin and the vasopressin analogue terlipressin as potent alternative vasoconstrictors in the treatment of fluid and catecholamine-refractory septic shock. Terlipressin is the most selective, clinically available V1 receptor agonist, and may be more potent than arginine-vasopressin in restoring catecholamine refractory septic shock. Recent experimental and clinical studies on terlipressin, as well as the possible benefit of selective V1a receptor agonists, are discussed.     

Increased fMet-Leu-Phe receptor expression and altered superoxide production of neutrophil granulocytes in septic and posttraumatic patients

Summary Activation of neutrophils by various inflammatory stimuli has been shown to play a pivotal role in septic and posttraumatic tissue injury. To further elucidate the mechanisms modulating the oxidative metabolism, we assessed superoxide production induced by N-formylmethionyl-leucylphenylalanine (FMLP) and phorbol myristate acetate and the expression of FMLP receptors of human neutrophils on several days during sepsis and after trauma. Neutrophils of septic patients isolated on days 0–4 after the diagnosis of sepsis showed a significant, more than twofold increase in specific binding of [³H]FMLP at 1, 120, and 240 nM. Scatchard plot analyses revealed that this increase in specific binding was due to an increase in the number of low- and high-affinity FMLP receptors with no changes in receptor affinity. On days 5–10 after the onset of sepsis the up-regulation of FMLP receptors on circulating neutrophils was followed by receptor down-regulation. Likewise, neutrophils from patients with trauma that was not complicated by sepsis bound significantly more [³H]FMLP than neutrophils from volunteers. However, the increase in FMLP receptors was less than that in septic neutrophils and returned earlier to normal. In accordance with the up-regulation of FMLP receptors, neutrophils obtained from patients with sepsis or after trauma on days 1–4 and days 1–2, respectively, produced significantly more superoxide anion upon stimulation with FMLP. However, after stimulation with phorbol myristate acetate, a receptor-independent activator of protein kinase C, these cells released less superoxide anion than controls. Our findings suggest that during sepsis and trauma circulating neutrophils become transiently primed for an enhanced oxidative metabolism upon stimulation with FMLP but desensitized to protein kinase C dependent stimulation.Abbreviations PMN neutrophilic granulocytes - FMLP N-formylmethionyl-leucyl-phenylalanine - PMA phorbol myristate acetate - SO oxygen superoxide - PKC protein kinase C - TNF tumor necrosis factor - HBSS Hank's balanced salt solution     

The role of nitric oxide in the immune response of tuberculosis.

Nitric oxide (NO) formed by the action of inducible form of nitric oxide synthase (iNOS), reacts with oxygen radical forming reactive nitrogen intermediate (RNI). NO and related RNI have been reported to possess antimycobacterial activity. Macrophages can inhibit the proliferation of Mycobacterium tuberculosis by producing NO. In murine models, the ability of macrophages to produce NO can determine the susceptibility of the host to M. tuberculosis and the virulence of M. tuberculosis. However, it is still not clear whether NO is involved in the defense mechanism against M. tuberculosis in humans. We have demonstrated that human peripheral blood mononuclear cells (PBMC) and airway epithelial cells can express iNOS mRNA expression and produce NO production in response to tubercle bacilli stimulation. Furthermore, H37Ra, avirulent strain of M. tuberculosis, induces a larger amount of NO in cultured PBMC than H37Rv, virulent strain, does. There was no difference in NO production between healthy volunteers and patients with tuberculosis. NO production in airway epithelial cells is closely related with IFN gamma concentration. The balance of stimulatory cytokines and inhibitory cytokines for NO production may play a critical role in the defense mechanism against M. tuberculosis considering that NO production is upregulated by IFN gamma, TNF alpha, and IL-1 beta and downregulated by IL-10 and TGF beta. The study of immune response to M. tuberculosis including NO production may give us a better understanding of the pathogenesis of tuberculosis.     

Role of nitric oxide in anaphylactic shock

Nitric oxide, synthesized from the guanidino group ofl-arginine by nitric oxide synthase, has an important role in pathophysiological changes associated with anaphylaxis. Nitric oxide production due to activation of constitutive nitric oxide synthase is detected using a nitric oxide-selective electrode in anaphylactic rabbitsin vivo. A nitric oxide synthase inhibitor attenuates hypotension and hemoconcentration and decreases venous return but does not improve cardiac depression. Nitric oxide functionally antagonizes the effects of vasoconstrictors released by anaphylaxisin vitro. In animals pretreated with a nitric oxide synthase inhibitor, the cardiac output falls significantly, although venous return is increased. Pulmonary resistance is significantly increased with a nitric oxide synthase inhibitor, andl-arginine attenuates the bronchospasm. These findings suggest that production of nitric oxide may reduce the pathophysiologic changes, except for vasodilatation, associated with anaphylaxis.     

The role of nitric oxide in cellular response to hyperbaric conditions

Nitric oxide (NO) acts as a regulator in cell proliferation and expression of growth factors and forms peroxynitrite (ONOO⁻) in oxidative conditions. The aim of the study was to investigate the role of NO in cellular response to hyperbaric oxygen (HBO). NO and nitrotyrosine (NT), biochemical marker for ONOO⁻, cell proliferation and growth factors, were ex-vivo studied in cell cultures under HBO and normobaric (NOR) conditions. A549 (epithelial), L929 (fibroblast) and SVEC (endothelial) were exposed to 100% O₂, at P = 280 kPa for t = 60 min, once daily for five sessions. Cell proliferation was determined as the incorporation of bromodeoxyuridine (BrdU) into cells and NO as nitrates/nitrites (NO₃ ⁻/ NO₂ ⁻) Gries reaction product in cell culture supernatant (CCSP). NT, vascular endothelial growth factor (VEGF) and transforming growth factor-beta 1 (TGFb1) were measured with enzyme-inked immunosorbent assay (ELISA) in CCSP. The time course of total NO was opposite to that of cell proliferation in HBO conditions, peaking after the second HBO session, while cell proliferation showed a reverse trend, minimizing at the same time, suggesting a reverse and transient anti-proliferative effect. Released growth factors were significantly increased in late HBO sessions. NT peaked after second treatment, indicating the formation of ONOO⁻. In control cultures (NOR), proliferation rate was downward and no significant differences were found for the other parameters. In conclusion, the data suggested a key role for NO in the beneficial HBO action, depending on its concentration, which fluctuated with the time of HBO exposure and the activation of oxidant–antioxidant (REDOX) mechanisms, regardless of cell type.     

Decreased production of nitric oxide by human neutrophils during septic multiple organ dysfunction syndrome

The objective of this study was to determine nitric oxide (NO) and superoxide anion release (O ₂ ^– ) by neutrophils (PMNs) in the septic multiple organ dysfunction syndrome (MODS) and to compare them with the response of normal cells to lipopolysaccharide (LPS) and cytokines. NO production was measured by the release of nitrites in the medium, its maximal production rate by a modified oxyhemoglobin assay and O ₂ ^– by standard methods. Normal cells were incubated with LPS, gamma interferon (IFN-), or tumor necrosis factor (TNF-) alone or in combination. Results showed that PMN release of both NO and O ₂ ^– was reduced in septic samples; in contrast, an association of LPS, IFN-, and TNF- promoted maximal NO release by normal cells (40–50%). We conclude that while interaction of normal PMNs with cytokines increases NO and O ₂ ^– release, progression of sepsis to a multiple organ dysfunction impairs these responses in both functions.     

NO及NO合成酶与感染性休克

感染性休克病理生理学过程十分复杂。NO在其中的作用既具有有害的一面,同时也存在有利的一面。受内毒素、细胞因子等诱导,iNOS表达上调并产生大量NO,引起循环衰竭、组织细胞损伤以及通过调节炎症介质基因表达扩大全身炎症反应。另一方面,eNOS所产生的NO对机体具有保护作用。然而,感染性休克时,eNOS蛋白质合成及其功能受到损害,反而成为血管内皮功能失常、诱发多器官功能障碍的重要原因。     

Glucocorticoid inhibition of adjuvant arthritis synovial macrophage nitric oxide production: role of lipocortin 1

Nitric oxide (NO) is a mediator of inflammatory injury which is inhibited by glucocorticoids and is implicated in rheumatoid (RA) and adjuvant arthritis (AA). The glucocorticoid-induced anti-inflammatory molecule lipocortin 1 is expressed in RA synovium, but the effects of lipocortin 1 on synovial inflammation have been little studied. We investigated the effects of glucocorticoids and lipocortin 1 on inducible NO synthase (iNOS) and glucocorticoids on the induction of lipocortin 1 in AA synovial macrophages. NO production was measured by Griess assay in supernatants of day 14 AA rat synovial explants and of synovial macrophages purified from enzyme-digested synovium and treated with lipopolysaccharide (LPS) 1 μg/ml, dexamethasone (DEX) 10^?7 M , and anti-lipocortin 1 MoAb. iNOS and lipocortin 1 expression were detected by flow cytometry using specific MoAb. Cell surface lipocortin was determined by Western blot. NO was produced by all AA synovial explants and NO was released by cultured synovial macrophages (14.5 ± 2.1 μmol/24 h). iNOS was detected in synovial macrophages (ED-1⁺) by permeabilization flow cytometry. LPS increased synovial macrophage NO release (P < 0.0001) and iNOS expression (P = 0.04). DEX inhibited constitutive (P = 0.002) and LPS-induced (P < 0.001) NO release and iNOS expression (P = 0.03). DEX inhibition of synovial macrophage NO was associated with induction of cell surface and intracellular lipocortin 1. Anti-lipocortin 1 MoAb treatment reduced the inhibition of NO release by DEX (P = 0.002), but had no effect on iNOS expression. These findings demonstrate a role for lipocortin 1 in the inhibition by glucocorticoids of AA synovial macrophage iNOS activity.     

NADPH oxidase, Nramp1 and nitric oxide synthase 2 in the host antimicrobial response

Using highly conserved, complex enzyme systems, leukocytes utilize the toxic nature of free radical intermediates, derived from oxygen and nitrogen, to control microbial pathogens as part of the innate immune response. Upon activation, NADPH oxidase generates superoxide anion radicals, which in turn give rise to further reactive oxygen intermediates. Similarly, activated nitric oxide synthase 2 catalyses the production of nitric oxide radicals, which leads to the formation of reactive nitrogen intermediates. Nitrogen- and oxygen-centered reactive intermediates can interact to form further reactive species. In addition, presence of the cationic transporter, Nrampl, may exacerbate the effects of these toxic compounds on invading microbes. While each of these antimicrobial systems can operate independently, the combination of their activities is synergistic in the successful containment of almost all invading pathogens. These systems are activated and modulated by microbial products and a series of temporally expressed cytokines. They also feed directly into the initiation of the adaptive immune response, which culminates in lasting specific immunity. The effector molecules, generated in the early innate immune response, are not specific to the invading pathogen and may also cause damage to the host. It is the critical balance of these processes in the initial stages of infection that determines the outcome of infectious disease.     

f-Met-Leu-Phe stimulates nitric oxide production in chick embryo neurons: the role of NF-kB

N-formyl-methionyl-leucyl-phenylalanine (fMLP) is a major chemotactic factor produced by Escherichia coli and other Gram-negative bacteria. In avian models the fMLP effects and the possible expression of FPRs have been poorly investigated. This report demonstrates that fMLP stimulation in vitro is able to elicit significant cellular responses from 10-day chick embryo nerve cells. Cell treatment with 10(-7) M fMLP at 37 degrees C induces a dramatic increase of nitric oxide (NO) production, after 24, 48, and 72 h, respectively. After 72 h of treatment with 10(-7) M fMLP the maximum nuclear translocation of the NF-kB complex protein p65 is visible, corresponding to the greatest NO production. In this context, 72 h of fMLP stimulation lead to a marked expression of the antiapoptotic protein Bcl-2, involved in cell survival. This suggests that activation of the NF-kB complex plays a protective role in chick neuronal cells treated with fMLP, confirmed by the significant neuronal cells degeneration observed after NF-kB inhibition with the specific inhibitor, TPCK. Overall, these data suggest a possible protective mechanism displayed by neurons against toxic molecules, like NO, released after cell exposure to bacterial products.