Substance P acts via the neurokinin receptor 1 to elicit bronchoconstriction, oxidative stress, and upregulated ICAM-1 expression after oil smoke exposure

This study aimed to 1) assess whether substance P (SP) acts via neurokinin (NK)-1 and NK-2 receptors to stimulate neurogenic inflammation (indicated by formation of ICAM-1 expression and oxidative stress) following oil smoke exposure (OSE) in rats; and 2) determine if pretreatment with antioxidants ameliorates the deleterious effects of OSE. Rats were pretreated with NK-1 receptor antagonist CP-96345, NK-2 receptor antagonist SR-48968, vitamin C, or catechins. OSE was for 30-120 min. Rats were killed 0-8 h later. Total lung resistance (RL), airway smooth muscle activity (ASMA), lung ICAM-1 expression, neurogenic plasma extravasation (via India ink and Evans blue dye), bronchoalveolar lavage fluid SP concentrations, and reactive oxygen species formation [via lucigenin- and luminal-amplified chemiluminescence (CL)] were assessed. Lung histology was performed. SP concentrations increased significantly in nonpretreated rats following OSE in a dose-dependent manner. RL and total ASMA increased over time after OSE. Vitamin C and catechin pretreatments were associated with significantly reduced lucigenin CL 2 and 4 h after OSE. Pretreatment with catechins significantly reduced luminal CL counts 4 and 8 h after OSE. Evans blue levels were significantly reduced following 60 and 120 min of OSE in catechin- and CP-96345-pretreated rats. ICAM-1 protein expression was significantly decreased in all pretreatment groups after OSE. Thickening of the alveolar capillary membrane, focal hemorrhaging, interstitial pneumonitis, and peribronchiolar inflammation were apparent in OSE lungs. These findings suggest that SP acts via the NK-1 receptor to provoke neurogenic inflammation, oxidative stress, and ICAM-1 expression after OSE in rats.     

Delayed stress-induced colonic hypersensitivity in male Wistar rats: role of neurokinin-1 and corticotropin-releasing factor-1 receptors

The mechanism(s) underlying stress-induced colonic hypersensitivity (SICH) are incompletely understood. Our aims were to assess the acute and delayed (24 h) effect of water avoidance (WA) stress on visceral nociception in awake male Wistar rats and to evaluate the role of two stress-related modulation systems: the substance P/neurokinin-1 receptor (SP/NK(1)R) and the corticotropin-releasing factor (CRF)/CRF(1) receptor (CRF/CRF(1)R) systems, as well as the possible involvement of the sympathetic nervous system. Visceral pain responses were measured as the visceromotor response to colorectal distension (CRD) at baseline, immediately after WA and again 24 h later. The NK(1)R antagonists RP-67580 and SR-140333 and the CRF(1)R antagonist CP-154526 were injected 15 min before WA or 1 h before the CRD on day 2. Chemical sympathectomy was performed by repeated injection of 6-hydroxydopamine. WA stress resulted in a significant increase in the visceromotor response on day 2, but no change immediately after WA. Injection of CP-154526 abolished delayed SICH when applied either before WA stress or before the CRD on day 2. Both NK(1)R antagonists only decreased SICH when injected before the CRD on day 2. Chemical sympathectomy did not affect delayed SICH. Our results indicate that in male Wistar rats, both NK(1)R and CRF(1)R activation, but not sympathetic nervous system activation, play a role in the development of SICH.     

Potent NK1 antagonism by SR-140333 reduces rat colonic secretory response to immunocyte activation

The potentneurokinin receptor 1 (NK₁) antagonist SR-140333has previously been shown to reduce castor oil-induced secretion inanimal models. The importance of tachykinins in neuroimmune control ofsecretion and the effect of SR-140333 on key points in this pathwaywere elucidated in the present study to determine the type ofintestinal dysfunction best targeted by this antagonist. Rat colonicsecretion and substance P (SP) release were determined in vitro withthe use of Ussing chamber and enzyme immunoassay techniques.NK₁ receptors played a secretory role as receptor agonistsstimulated secretion and SR-140333 antagonized the response to SPresponse (pK_b = 9.2). Sensory fiber stimulationreleased SP and evoked a large secretion that was reduced by 69% inthe presence of SR-140333 (10 nM). Likewise, mastocytes also released SP. The subsequent secretory response was reduced by 43% in the presence of SR-140333 (50 nM). SP was also released from granulocytes; however, this did not cause secretion. Functional NK₃receptors were present in the colon as senktide stimulated secretion,an effect that was increased during stress. We conclude thatNK₃ receptors may play a role in stress-related disorders,whereas NK₁ receptors are more important in mastcell/afferent-mediated secretion.

     

Neurokinin-1 receptor antagonism by SR140333: enhanced in vivo ACh in the hippocampus and promnestic post-trial effects

Substance P (SP) has memory-promoting, reinforcing and anxiolytic-like effects when applied systemically or centrally. Such effects may be mediated by the neurokinin-1 (NK-1) receptor, since SP preferentially binds to this receptor. We measured the effects of a selective non-peptide NK-1 receptor antagonist, SR140333 (1, 3 and 9 mg/kg i.p.) on ACh levels in frontal cortex, amygdala and hippocampus by microdialysis and HPLC. Levels of ACh in the hippocampus increased dose-dependently immediately after treatment. The same doses of SR140333 given post-trial had minor facilitative effects on inhibitory avoidance learning and open-field habituation, but did not have reinforcing effects in a conditioned place preference (CPP) task. The selective action of NK-1 receptor antagonism on hippocampal ACh may be related to its positive influence on learning.     

SR142801 behaves as a tachykinin NK-3 receptor agonist on a spinal nociceptive reflex in the rat

Effects of two commonly used tachykinin NK-3 receptor antagonists (SR 142801 and R820) intrathecally (i.t.) administered were assessed in the rat tail-flick test. SR142801 and its (R)-enantiomer SR142806 (1.3, 6.5 and 65 nmol) were found as potent as senktide and [MePhe7]NKB (NK-3 selective agonists) to induce transient antinociceptive effects. Naloxone (10 microg) and R820 (6.5 nmol) blocked reversibly the responses to 6.5 nmol senktide, [MePhe7]NKB, SR142801 and SR142806 when administered i.t. 15 min earlier. However, the antinociceptive responses induced by SR142801 and SR142806 were not affected by i.t. pretreatments with NK-1 (6.5 nmol SR140333) and NK-2 (6.5 nmol SR48968) receptor antagonists. In control experiments, the NK-1 and NK-2 antagonists prevented the hyperalgesic effects to NK-1 ([Sar9,Met(O2)11]SP) and NK-2 ([beta-Ala8] NKA(4-10)) receptor agonists (6.5 nmol i.t.), respectively. R820 had no direct effect on nociceptive threshold and failed to alter angiotensin II-induced antinociception. The data suggest that the antinociceptive effect of SR142801 is due to an agonist effect at NK-3 receptor in the rat spinal cord that involves a local opioid mechanism. These results can be best explained by the existence of inter-species NK-3 receptor subtypes.     

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.     

Neuropeptide regulation of human dermal microvascular endothelial cell ICAM-1 expression and function

There isincreasing evidence that sensory nerves may participate in cutaneousinflammatory responses by the release of neuropeptides such assubstance P (SP). We examined the direct effect of SP on human dermalmicrovascular endothelial cell (HDMEC) intercellular adhesion molecule1 (ICAM-1) expression and function. Our results indicated that,although cultured HDMEC expressed mRNA for neurokinin receptors 1, 2, and 3 (NK-1R, NK-2R, and NK-3R), SP initiated a rapid increase in HDMECintracellular Ca²⁺ levels,primarily by the activation of NK-1R. Immunohistochemistry studieslikewise demonstrated that HDMEC predominantly expressed NK-1R. Theaddition of SP to HDMEC resulted in a rapid increase in cellular ICAM-1mRNA levels, followed by a fivefold increase in ICAM-1 cell surfaceexpression. This functionally resulted in a threefold increase in⁵¹Cr-labeled binding of J-Ylymphoblastoid cells to HDMEC. In vivo studies demonstrated a markedincrease in microvascular ICAM-1 immunostaining 24 and 48 h afterapplication of capsaicin to the skin. These results indicate thatneuropeptides such as SP are capable of directly activating HDMEC toexpress increased levels of functional ICAM-1 and further support therole of the cutaneous neurological system in modulating inflammatoryprocesses in the skin.

     

Local disruption of the celiac ganglion inhibits substance P release and ameliorates caerulein-induced pancreatitis in rats

Primary sensory neurons of the C and Adelta subtypes express the vanilloid capsaicin receptor TRPV1 and contain proinflammatory peptides such as substance P (SP) that mediate neurogenic inflammation. Pancreatic injury stimulates these neurons causing the release of SP in the pancreas resulting in pancreatic edema and neutrophil infiltration that contributes to pancreatitis. Axons of primary sensory neurons innervating the pancreas course through the celiac ganglion. We hypothesized that disruption of the celiac ganglion by surgical excision or inhibition of C and Adelta fibers through blockade of TRPV1 would reduce the severity of experimental pancreatitis by inhibiting neurogenic inflammation. Resiniferatoxin (RTX) is a specific TRPV1 agonist that, in high doses, selectively destroys C and Adelta fibers. Sprague-Dawley rats underwent surgical ganglionectomy or application of 10 microg RTX (vs. vehicle alone) to the celiac ganglion. One week later, pancreatitis was induced by six hourly intraperitoneal injections of caerulein (50 microg/kg). The severity of pancreatitis was assessed by serum amylase, pancreatic edema, and pancreatic myeloperoxidase (MPO) activity. SP receptor (neurokinin-1 receptor, NK-1R) internalization in acinar cells, used as an index of endogenous SP release, was assessed by immunocytochemical quantification of NK-1R endocytosis. Caerulein administration caused significant increases in pancreatic edema, serum amylase, MPO activity, and NK-1R internalization. RTX treatment and ganglionectomy significantly reduced pancreatic edema by 46% (P < 0.001) and NK-1R internalization by 80% and 51% (P < 0.001 and P < 0.05, respectively). RTX administration also significantly reduced MPO activity by 47% (P < 0.05). Neither treatment affected serum amylase, consistent with a direct effect of caerulein. These results demonstrate that disruption of or local application of RTX to the celiac ganglion inhibits SP release in the pancreas and reduces the severity of acute secretagogue-induced pancreatitis. It is possible that selectively disrupting TRPV1-bearing neurons could be used to reduce pancreatitis severity.     

T cell substance P receptor governs antigen-elicited IFN-gamma production

Substance P (SP) enhances antigen-dependent T cell IFN-gamma production. It was determined if a T cell neurokinin-1 receptor (NK-1R) was critical for IFN-gamma regulation. T cells from schistosome-infected mice were mixed with splenocytes from uninfected NK-1R knockout (KO) animals. Thus only the schistosome egg antigen-specific T cells expressed NK-1R. The cells were cultured 18 h with or without SP. SP enhanced antigen-induced IFN-gamma production fourfold without affecting IL-4 or IL-5 secretion. NK-1R inhibitor blocked this stimulation. Neither purified T cells nor naive KO splenocytes cultured alone responded to antigen. To further define the importance of T cell NK-1R, we developed a T cell-selective NK-1R KO mouse by reconstituting T cell-deficient Rag mice with NK-1R KO T cells. These mice challanged with schistosomiasis developed abnormal liver granulomas. Granuloma size was smaller in T cell-selective NK-1R KO mice compared with granulomas in Rag reconstituted with normal T cells. Splenocytes and granuloma cells from NK-1R KO mice made less IFN-gamma. The mice also made less IgG2a. Thus T cell NK-1R is important for IFN-gamma regulation.     

Metalloproteinases and transforming growth factor-alpha mediate substance P-induced mitogen-activated protein kinase activation and proliferation in human colonocytes

Substance P (SP) participates in acute intestinal inflammation via binding to the G-protein-coupled neurokinin-1 receptor (NK-1R) and release of proinflammatory cytokines from colonic epithelial cells. SP also stimulates cell proliferation, a critical event in tissue healing during chronic colitis, via transactivation of the epidermal growth factor (EGF) receptor (EGFR) and activation of mitogen-activated protein kinase (MAPK). Here we examined the mechanism by which SP induces EGFR and MAPK activation. We used non-transformed human NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells) as well as untransfected U373 MG cells expressing high levels of endogenous NK-1R. Exposure of both cell lines to SP (10(-7) m) stimulated EGFR activation (1 min) followed by extracellular signal-regulated protein kinase (ERK1/2) activation (2-5 min). SP-induced ERK1/2 activation was blocked by pretreatment with the metalloproteinase inhibitor Batimastat/GM6001, the EGFR phosphorylation inhibitor AG1478, and the tumor necrosis factor-alpha-converting enzyme (TACE) inhibitor TAPI-1. Pretreatment with antibodies against potential EGFR ligands suggested that transforming growth factor-alpha (TGFalpha), but not the other EGFR ligands EGF, heparin-binding EGF, or amphiregulin, mediates SP-induced EGFR transactivation. SP stimulated TGFalpha release into the extracellular space that was measurable within 2 min, and this release was inhibited by metalloproteinase inhibitors and the TACE inhibitor TAPI-1. SP also induced MAPK-mediated cell proliferation that was inhibited by TACE, matrix metalloproteinase (MMP), EGFR, and MEK1 inhibitors. Thus, in human colonocytes, NK-1R-induced EGFR and MAPK activation and cell proliferation involve matrix metalloproteinases (most likely TACE) and the release of TGFalpha. These signaling mechanisms may be involved in the protective effects of NK-1R in chronic colitis.     

NK-1 receptor desensitization and neutral endopeptidase terminate SP-induced pancreatic plasma extravasation

Substance P (SP) induces plasma extravasation and neutrophil infiltration by activating the neurokinin-1 receptor (NK1-R). We characterized the mechanisms regulating this response in the rat pancreas. Anesthetized rats were continuously infused with SP, and plasma extravasation was quantified using Evans blue (EB) dye. Continuous infusion of SP (8 nmol. kg(-1). h(-1)) resulted in a threshold increase in EB at 15 min, a peak effect at 30 min (150% increase), and a return to baseline by 60 min. The NK1-R antagonist CP-96,345 blocked SP-induced plasma extravasation. After 60 min, the NK1-R was desensitized to agonist challenge. Resensitization was first detected at 20 min and increased until full recovery was seen at 30 min. Inhibition of the cell-surface protease neutral endopeptidase (NEP) by phosphoramidon potentiated the effect of exogenous SP; therefore endogenous NEP attenuates SP-induced plasma extravasation. Thus the continuous infusion of SP stimulates plasma extravasation in the rat pancreas via activation of the NK1-R, and these effects are terminated by both desensitization of the NK1-R and the cell-surface protease NEP.     

Neurokinin-1 receptor (NK-1R) expression is induced in human colonic epithelial cells by proinflammatory cytokines and mediates proliferation in response to substance P

We have previously shown that the receptor for substance P (SP), neurokinin-1 receptor (NK-1R), is a marker of human mucosal but not peripheral mononuclear cells. In the present study, we investigate NK-1R expression in the human colonic mucosa in vivo, particularly in the epithelial cells. We investigate the influence of proinflammatory Th1 cytokines and SP on expression and function of NK-1R in colonic epithelial cells in vitro. Using in situ hybridization to detect NK-1R mRNA, and immunohistochemistry to detect NK-1R protein, colonic epithelial cells were found to express NK-1R in vivo. In contrast, colon epithelial cell lines (Caco-2, HT29, SW620, T84) were negative for NK-1R mRNA and protein. However, stimulation with a proinflammatory cytokine cocktail containing IFN-gamma, TNF-alpha, and IL-1beta, caused induction of NK-1R expression. Expression of NK-1R in human colonic epithelial cells in vivo may therefore reflect cytokine conditioning by the mucosal microenvironment. SP did not alter ion transport in monolayers of cytokine-treated T84 cells. While SP stimulated epithelial ion transport in colonic mucosae ex vivo, this was not a direct effect of SP on the epithelial cells, and appeared to be neurally mediated. However, SP (10(-10)-10(-8) M) elicited a dose-dependent proliferative effect on cytokine-stimulated, but not unstimulated, SW620 cells. Proliferation of the epithelial cells in response to SP was mediated specifically via cytokine-induced NK-1R, since an NK-1R-specific antagonist (Spantide 1) completely blocked SP-mediated proliferation in the cytokine-treated cells. Our results therefore demonstrate that proinflammatory cytokines induce expression of NK-1R in human colonic epithelial cell lines, and that SP induces proliferation of the epithelial cells via cytokine-induced NK-1R.     

The substance P/neurokinin-1 receptor system in lung cancer: Focus on the antitumor action of neurokinin-1 receptor antagonists

The last decades have seen no significant progress in extending the survival of lung cancer patients and there is an urgent need to improve current therapies. The substance P (SP)/neurokinin-1 receptor (NK-1R) system plays an important role in the development of cancer: SP and NK-1R antagonists respectively induce cell proliferation and inhibition in human cancer cell lines. No study of the involvement of this system in non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cells has been carried out in depth. Here, we demonstrate the involvement of the SP/NK-1R system in human H-69 (SCLC) and COR-L23 (NSCLC) cell lines: (1) they express isoforms of the NK-1R and mRNA for the NK-1R; (2) they overexpress the tachykinin 1 gene; (3) the NK-1R is involved in their viability; (4) SP induces their proliferation; (5) NK-1R antagonists (Aprepitant (Emend), L-733,060, L-732,138) inhibit the growth of both cell lines in a concentration-dependent manner; (6) the specific antitumor action of these antagonists against such cells occurs through the NK-1R; and (7) lung cancer cell death is due to apoptosis. We also demonstrate the presence of NK-1Rs and SP in all the human SCLC and NSCLC samples studied. Our findings indicate that the NK-1R may be a promising new target in the treatment of lung cancer and that NK-1R antagonists could be new candidate antitumor drugs in the treatment of SCLC and NSCLC.     

Substance P is a mechanoresponsive, autocrine regulator of human tenocyte proliferation

It has been hypothesised that substance P (SP) may be produced by primary fibroblastic tendon cells (tenocytes), and that this production, together with the widespread distribution of the neurokinin-1 receptor (NK-1 R) in tendon tissue, could play an important role in the development of tendinopathy, a condition of chronic tendon pain and thickening. The aim of this study was to examine the possibility of endogenous SP production and the expression of NK-1 R by human tenocytes. Because tendinopathy is related to overload, and because the predominant tissue pathology (tendinosis) underlying early tendinopathy is characterized by tenocyte hypercellularity, the production of SP in response to loading/strain and the effects of exogenously administered SP on tenocyte proliferation were also studied. A cell culture model of primary human tendon cells was used. The vast majority of tendon cells were immunopositive for the tenocyte/fibroblast markers tenomodulin and vimentin, and immunocytochemical counterstaining revealed that positive immunoreactions for SP and NK-1 R were seen in a majority of these cells. Gene expression analyses showed that mechanical loading (strain) of tendon cell cultures using the FlexCell© technique significantly increased the mRNA levels of SP, whereas the expression of NK-1 R mRNA decreased in loaded as compared to unloaded tendon cells. Reduced NK-1 R protein was also observed, using Western blot, after exogenously administered SP at a concentration of 10⁻⁷ M. SP exposure furthermore resulted in increased cell metabolism, increased cell viability, and increased cell proliferation, all of which were found to be specifically mediated via the NK-1 R; this in turn involving a common mitogenic cell signalling pathway, namely phosphorylation of ERK1/2. This study indicates that SP, produced by tenocytes in response to mechanical loading, may regulate proliferation through an autocrine loop involving the NK-1 R.     

Phosphorylation and Desensitization of the Neurokinin-1 Receptor Expressed in Epithelial Cells

A rat kidney epithelial cell line expressing the rat neurokinin-1 receptor (NK-1 R) was used to investigate the relationship between receptor phosphorylation and desensitization. Substance P (SP) maximally stimulated cellular inositol 1,4,5-trisphosphate (IP3) production 14-fold within 3 s, after which cellular IP3 levels rapidly diminished to near basal levels in the continuing presence of SP. SP also caused concentration-dependent phosphorylation of the NK-1R, and this effect was blocked by a receptor antagonist. Stimulation with 100 nM SP for as little as 2 s resulted in 90% desensitization of the receptor to restimulation by SP, and near-maximal receptor phosphorylation was observed at 5 s. Receptor desensitization was not affected by agents that affect protein kinase A. Phorbol 12-myristate 13-acetate (PMA) also caused phosphorylation and desensitization of the receptor but with slower kinetics and to a lesser extent than SP. PMA- but not SP-induced NK-1 R desensitization and phosphorylation were abolished by the protein kinase C inhibitor bisindolylmaleimide 1. The concentration-response curves for SP-stimulated IP3 signaling and desensitization were similar, but the curve for NK-1R phosphorylation was shifted to the right and was steeper, suggesting that the relationship between desensitization and phosphorylation is complex. These results show that both rapid homologous and rapid heterologous NK-1R desensitizations may be mediated by receptor phosphorylation but occur via distinct mechanisms with different kinetics and efficacies.     

Cutting edge: hemokinin has substance P-like function and expression in inflammation

Substance P (SP) belongs to the tachykinin family of molecules. SP, cleaved from preprotachykinin A, is a neuropeptide and a proinflammatory leukocyte product. SP engages neurokinin 1 receptor (NK-1R) to stimulate cells. Hemokinin (HK) is another tachykinin that binds NK-1R. HK comes from preprotachykinin C, which is distinct from preprotachykinin A. We determined whether HK functions like SP at inflammatory sites. Preprotachykinin C mRNA was in murine schistosome granulomas and intestinal lamina propria mononuclear cells. Granuloma T cells and macrophages expressed preprotachykinin C mRNA. HK bound granuloma T cell NK-1R with high affinity. SP and HK stimulated IFN-gamma production with equal potency. NK-1R antagonist blocked the effect of SP and HK on IFN-gamma secretion. Thus, both HK and SP are expressed at sites of chronic inflammation and share cell origin, receptor, and immunoregulatory function. Two distinct but functionally overlapping tachykinins govern inflammation through NK-1R at sites of chronic inflammation.     

Neurokinin-1 receptor in peripheral nerve terminals mediates thermal hyperalgesia

Neurokinin-1 receptor (NK-1) plays an important role in nociception. The present study was to explore whether activation of peripheral NK-1 receptor, especially expressed on primary sensory afferents, could induce hyperalgesia and sensitize C-type sensory afferents. (1) Intraplantar administration of NK-1 agonist [Sar9, Met(O2)11]SP (Sar-SP, 0.2, 1 nmol, 20 microl) produced significant thermal hyperalgesia and edema, which was blocked by co-injection of NK-1 antagonist WIN51,708 (10 nmol). But in the rats with compound 48/80 treatment for mast cell depletion, the Sar-SP-induced edema, but not hyperalgesia, was attenuated. (2) Close-arterial injection of Sar-SP (1 nmol, 0.1 ml) excited and sensitized sensory C afferents of the sural nerve to heat stimuli. The results suggest involvement of NK-1 receptors expressed on the peripheral afferent terminals in thermal hyperalgesia mediated by directly sensitizing C-type sensory afferents.     

Inhaled nitric oxide decreases infarction size and improves left ventricular function in a murine model of myocardial ischemia-reperfusion injury

To learn whether nitric oxide (NO) inhalation can decrease myocardial ischemia-reperfusion (I/R) injury, we studied a murine model of myocardial infarction (MI). Anesthetized mice underwent left anterior descending coronary artery ligation for 30, 60, or 120 min followed by reperfusion. Mice breathed NO beginning 20 min before reperfusion and continuing thereafter for 24 h. MI size and area at risk were measured, and left ventricular (LV) function was evaluated using echocardiography and invasive hemodynamic measurements. Inhalation of 40 or 80 ppm, but not 20 ppm, NO decreased the ratio of MI size to area at risk. NO inhalation improved LV systolic function, as assessed by echocardiography 24 h after reperfusion, and systolic and diastolic function, as evaluated by hemodynamic measurements 72 h after reperfusion. Myocardial neutrophil infiltration was reduced in mice breathing NO, and neutrophil depletion prevented inhaled NO from reducing myocardial I/R injury. NO inhalation increased arterial nitrite levels but did not change myocardial cGMP levels. Breathing 40 or 80 ppm NO markedly and significantly decreased MI size and improved LV function after ischemia and reperfusion in mice. NO inhalation may represent a novel method to salvage myocardium at risk of I/R injury.