Increased nitric oxide in exhaled air of asthmatic patients

Nitric oxide (NO) gas is produced by various cells within the lower respiratory tract, including inflammatory and epithelial cells, and is detectable in the exhaled air of normal human subjects. We have measured exhaled NO in patients with asthma, since several cell types that are activated in asthma can produce NO after induction. NO was measured reproducibly by a slow vital capacity manoeuvre and an adapted chemiluminescence analyser. NO was detectable in exhaled air of 67 control subjects (mean peak concentration 80.2 [SE 4.1] ppb) and was significantly reduced by inhalation of the specific NO synthase inhibitor NG-monomethyl-L-arginine. 61 non-steroid-treated asthmatic subjects had significantly higher peak expired NO concentrations than controls (283 [16] ppb, p < 0.001) but 52 asthmatic patients receiving inhaled corticosteroids had levels similar to controls (101 [7] ppb). High exhaled NO concentrations in asthmatic patients may reflect induction of NO synthase, which is known to be inhibited by steroids. Measurement of exhaled NO concentrations may be clinically useful in detection and management of cytokine-mediated inflammatory lung disorders.     

Inter-relation of immediate and late asthmatic reactions in childhood

Following bronchial provocation tests with inhalent allergens, late asthmatic reactions (LAR) frequently follow immediate asthma reactions (IAR). This study of atopic asthmatic children demonstrated that patients could show IARs to one allergen, ryegrass extract, but isolated LARs without any preceding immediate response when challenged with an unrelated allergen extract of D. pteronyssinus. The patients' degree of skin sensitivity to the concentration of extract inhaled appeared one factor which determined whether an isolated LAR or IAR followed allergen inhalation.     

Increased nitric oxide synthesis and action preclude choroidal vasoconstriction to hyperoxia in newborn pigs

We tested the hypothesis that hyperoxia does not cause adequate constriction of choroidal vessels of the newborn (1 to 5 days old) pig, resulting in increased O2 delivery to the retina, possibly due to excess production and/or effects of vasodilators such as nitric oxide (NO). Hyperoxia (100% O2, 45 minutes) led to a decrease in retinal blood flow (RBF) of both newborn and juvenile (5 to 6 weeks old) pigs and also reduced choroidal blood flow (ChBF) in juvenile but not in newborn pigs; the absence of hyperoxia-induced ChBF response in the newborn was associated with a rise in choroidal O2 delivery. Ibuprofen (prostaglandin G/H synthase inhibitor) and 1,3-dimethyl-2-thiourea (a free radical scavenger) did not modify the choroidal hemodynamic responses to hyperoxia in newborn pigs. However, in newborn animals treated with the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME), hyperoxia caused a decrease in blood flow and O2 delivery to the choroid. Consistent with these effects of L-NAME, hyperoxia induced an increase in choroidal cGMP in newborn pigs ventilated with 100% O2 and stimulated nitrite production in isolated choroids exposed to hyperoxia from newborn but not juvenile pigs; these effects were inhibited by NOS blockers. Also, both constitutive and inducible NOS activities were higher in choroidal tissues from newborn than from juvenile animals. In addition, the vasorelaxant effect of the NO donor sodium nitroprusside in vitro was also greater on choroids from newborn than from juvenile pigs. Finally, L-NAME prevented the hyperoxia-induced increase in peroxidation products in the choroid of newborns. It is concluded that hyperoxia does not lead to a decrease in blood flow and O2 delivery to the choroid of the newborn because of increased NO synthesis and effects; since the choroid is the main source of O2 supply to the retina, the present data contribute in providing an explanation for the increased susceptibility of the immature neonate to hyperoxia-induced retinopathy.     

Increased production of nitric oxide in coronary arteries during congestive heart failure

Experiments were designed to determine whether a heterogeneity of endothelium-dependent relaxations in arteries from different vascular beds exists in experimental congestive heart failure (CHF) and to determine the mediators of those responses. CHF was produced in dogs by rapid ventricular pacing for 15 d. Rings of coronary, femoral, and renal arteries with and without endothelium from control and CHF dogs were suspended in organ chambers for measurement of isometric force. In arteries contracted with prostaglandin F2 alpha, endothelium-dependent relaxations to BHT 920 (an alpha 2-adrenergic agonist) were increased in coronary arteries from dogs with CHF (maximal relaxation: control -15 +/- 9% vs CHF -92 +/- 5%; n = 5-6; P < 0.05), with a modest enhancement in renal arteries. Relaxations to adenosine diphosphate and the calcium ionophore were unchanged. Relaxations to BHT 920 in CHF were reduced by NG monomethyl-L-arginine (L-NMMA) and pertussis toxin but not by indomethacin. These data suggest that endothelium-dependent relaxations are affected heterogeneously in CHF. The enhanced response to alpha 2-adrenergic agonists in the coronary artery is mediated by nitric oxide through a mechanism sensitive to inhibition by pertussis toxin. This selective increase in endothelium-dependent relaxations in the coronary artery may contribute to preserving coronary blood flow during CHF.     

Role of nitric oxide in responses to renin-angiotensin system inhibition in sodium-depleted guinea pig and rat

Previous reports have suggested that NO is an important mediator of the antihypertensive effects of renin-angiotensin system (RAS) inhibition. We examined the effects of the NO synthase inhibitor L-NNA on the hypotensive effects of captopril, the Ang II antagonist EXP 3174, or the renin inhibitor terlakiren. In sodium-depleted guinea pigs (GPs), L-NNA (3 mg/kg) increased MAP by 15-21% for at least 5 hours. L-NNA partially blocked the hypotensive effects of captopril (1 mg/kg, iv), but not those of EXP 3174 (1 mg/kg, iv) or terlakiren (3 mg/kg). In sodium-depleted rats, 10 mg/kg L-NNA (iv) increased MAP by 16-22%, and partially or fully blocked the hypotensive effect of EXP 3174 (1 mg/kg, iv) or captopril (3 mg/kg, iv), respectively. Thus, in contrast to the rat, NO in GPs appears to participate only in the hypotensive action of ACE inhibition and does not appear to be strongly involved in the hypotensive action of AII antagonism or renin inhibition. The involvement of NO in the hypotensive effects of RAS antagonists other than ACE inhibitors may be species-dependent.     

Localization of nitric oxide synthases and nitric oxide production in the rat mammary gland

We investigated nitric oxide (NO) production and the presence of nitric oxide synthase (NOS) in the mammary gland by use of an organ culture system of rat mammary glands. Mammary glands were excised from the inguinal parts of female Wistar-MS rats primed by implantation with pellets of 17beta-estradiol and progesterone and were diced into approximately 3-mm cubes. Three of these cubes were cultured with 2 ml of 10% FCS/DMEM plus carboxy-PTIO (an NO scavenger, 100 microM) in the presence or absence of LPS (0.5 microgram/ml) for 2 days. The amount of NO produced spontaneously by the cultured mammary glands was relatively minute at the end of the 2-day culture period, and the NO production was significantly enhanced by the presence of LPS. This enhancement of NO production was completely eliminated by addition of hydrocortisone (3 microM), an inhibitor of inducible NOS (iNOS), to the incubation medium. Immunoblot analyses with specific antisera against NOS isoforms such as iNOS, endothelial NOS (eNOS), and brain NOS (bNOS) showed immunoreactive bands of iNOS (122 +/- 2 kD) and eNOS (152 +/- 3 kD) in extracts prepared from the mammary glands in the culture without LPS. The immunoreactive band of iNOS was highly intense after the treatment of mammary glands with LPS, whereas the corresponding eNOS immunoreactive band was faded. The immunohistochemical study of anti-iNOS antiserum on frozen sections of the cultured mammary glands showed that an immunoreactive substance with the antiserum was localized to the basal layer (composed of myoepithelial cells of alveoli and lactiferous ducts) of the mammary epithelia and to the endothelium of blood vessels that penetrated into the interstitium of the mammary glands. Histochemical staining for NADPH-diaphorase activity, which is identical to NOS, showed localization similar to that of iNOS in the mammary glands. Similar observations were noted in the immunohistochemistry of eNOS. In contrast, the immunoreactive signal with the bNOS antiserum was barely detected in the epithelial parts of alveoli and lactiferous ducts of the mammary glands. These observations demonstrate that three isoforms of NOS are present not only in the endothelium of blood vessels but also in the parenchymal cells (the glandular epithelium) of the rat mammary gland, such as epithelial cells and myoepithelial cells, and suggest that NO may have functional roles in the physiology of the mammary glands.     

Increased nitric oxide production in the liver in the perioperative period of partial hepatectomy with Pringle''s maneuver

Environmental or endogenous toxins may cause nigral cell death in Parkinson's disease (PD) as a result of genetic susceptibility conferred by altered expression of P450 enzymes. Attention over the last 10 years has focused on CYP2D6 polymorphisms and susceptibility to PD. This review summarizes reports arising from both phenotypic and genotypic studies involving CYP2D6 and PD. Phenotypic studies have failed to support a link between CYP2D6 and PD. The more powerful genetic studies initially indicated a link between CYP2D6B mutations and PD, but critical analysis of the literature and recent studies emerging from independent laboratories fail to confirm this. Mutations in CYP2D6B are also not implicated in familial PD. As yet, there is no conclusive evidence to suggest that CYP2D6 polymorphisms confer susceptibility to PD. Whether polymorphisms in other P450s (for example, CYP1A1 and CYP2E1) are implicated in PD remains to be established.     

Pneumococci stimulate the production of the inducible nitric oxide synthase and nitric oxide by murine macrophages

The role of nitric oxide (NO) in the pathophysiology of gram-positive sepsis is uncertain. In inflammatory conditions, high-output NO production is catalyzed by the enzyme inducible nitric oxide synthase (iNOS). The ability of 2 strains of pneumococci, pneumococcal cell wall preparations, and purified pneumococcal capsule (Pnu-Imune 23) to trigger the production of iNOS protein and NO in RAW 264.7 murine macrophages was tested. Live pneumococci, oxacillin-killed pneumococci, and pneumococcal cell wall preparations stimulated the production of iNOS and NO by RAW 264.7 cells in the presence, but not the absence, of low concentrations of recombinant murine interferon-gamma. In contrast, purified pneumococcal capsule induced little or no iNOS or NO production by these cells. Thus, pneumococci stimulate high-output NO production by murine macrophages. The potential role of NO in the pathogenesis of pneumococcal sepsis deserves further study.     

Improvement in inner ear blood flow by nitric oxide following experimentally induced cochlear thrombosis in anesthetized guinea pigs

The nitric oxide (NO) donor sodium nitropruside (SNP) applied to the round window membrane has recently been found to increase cochlear blood flow (CoBF) in normal guinea pigs and in normal and presbyacusic mice. This study examined the effect of topical applications of SNP on experimentally impaired CoBF in anesthetized guinea pigs. Small (3 microliters) portions of 3% SNP were applied to the round window niche of both normal and thrombosed cochleas. Local vascular impairment was produced by ferromagnetic thrombosis of cochlear blood vessels and the microcirculation measured using laser Doppler flowmetry. Ferromagnetic thrombosis resulted in a mean decrease of CoBF to 52% of baseline. There was a clear improvement in mean CoBF to 84% of baseline by the topical application of SNP that depended on the degree of ischemic damage produced. Under neuroleptanalgesia and ketamine-xylazine anesthesia, significant increases in CoBF were measured in normal ears as well as in the thrombosed ones. However, several SNP applications were needed to improve the impaired CoBF, while a single portion was sufficient in the normal cochlea to cause a drastic increase in mean CoBF to 234% of baseline. In urethane-anesthetized animals, no flow increase was found despite repeated drug administration. Careful evaluation of the laser Doppler signals was necessary to accurately determine the concentrations of the moving blood cells and their mean velocities.     

In vivo quantification of endotoxin-induced nitric oxide production in pigs from Na15NO3-infusion

1. In this investigation the NO production rate is quantified in the pig during normotensive endotoxin-induced shock with increased cardiac output and during subsequent treatment with the NO synthase inhibitor N omega-monomethy-L-arginine (L-NMMA). NO production rate was derived from the plasma isotope-enrichment of 15N-labelled nitrate (15NO3-). 2. Three groups of animals (control, n = 5; endotoxin, n = 6; endotoxin + L-NMMA, n = 6) were anaesthetized and instrumented for the measurement of systemic and pulmonary haemodynamics. Each animal received a primed-continuous infusion of stable, non-radioactively labelled Na15 NO3 (bolus 30 mg, infusion rate 2.1 mg h-1). Arterial blood samples were taken 5, 10, 15, 30, 60 and 90 min later and every 90 minutes until the end of the experiment. 3. Continuous i.v. infusion of endotoxin was incrementally adjusted until mean pulmonary artery pressure (PAP) reached 50 mmHg and subsequently titrated to keep mean PAP approximately 35 mmHg. Hydroxyethylstarch was administered as required to maintain mean arterial pressure (MAP) > 60 mmHg. Six hours after the start of the endotoxin continuous i.v. L-NMMA (1 mg kg-1 h-1) was administered to the endotoxin + L-NMMA group. Haemodynamic data were measured before as well as 9 h after the start of the endotoxin. 4. After conversion of NO3- to nitro-trimethoxybenzene and gas chromatography-mass spectrometry analysis the total NO3- pool, basal NO3- production rate and the increase per unit time in NO3- production rate were calculated from the time-course of the 15NO3- plasma isotope-enrichment. A two compartment model was assumed for the NO3- kinetics, one being an active pool in which newly generated NO3- appears and from which it is eliminated, the other being an inactive volume of distribution in which only passive exchange takes place with the active compartment. 5. Although MAP did not change during endotoxin infusion alone, cardiac output (CO) increased by 42 +/- 40% (P < 0.05 versus baseline) by the end of the experiment due to a significant (P < 0.05 versus baseline) fall in systemic vascular resistance (SVR) to 65 +/- 25% of the baseline value. L-NMMA given with endotoxin did not change MAP, and both CO and SVR were maintained close to the pre-shock levels. 6. Baseline plasma NO3- concentrations were 43 +/- 13 and 40 +/- 10 mumol l-1 in the control and endotoxin animals, respectively, and did not differ at the end of the experiment (39 +/- 8 and 44 +/- 15 mumol l-1, respectively). The mean NO3- pool and basal NO3- production rate were 1155 +/- 294 mumol and 140 +/- 32 mumol h-1, respectively, without any intergroup difference. Endotoxin significantly increased NO3- production rate (23 +/- 10 mumol h-2, P < 0.05 versus control (6 +/- 7 mumol h-2) and endotoxin + L-NMMA groups). L-NMMA given with endotoxin (-1 +/- 2 mumol h-2, P < 0.05 versus control and endotoxin groups) had no effect. 7. Analysis of the time course of the 15NO3- plasma isotope enrichment during primed-continuous infusion of Na15NO3 allowed us to quantify the endotoxin-induced increase in NO3- production rate independently of total NO3- plasma concentrations. Low-dose L-NMMA blunted the increase in NO3- production rate while maintaining basal NO3- formation.     

Angiotensin II stimulates production of nitric oxide in guinea pig airways via AT1 receptor activation

Angiotensin II (Ang II) and nitric oxide (NO) regulate a variety of physiological functions. In this study, we suggest that inhaled Ang II produces an initial bronchodilation apparently by stimulating NO production via AT1 receptors. Also, we demonstrate that following the initial bronchodilation, Ang II causes bronchoconstriction in the guinea pig, also via AT1 receptors. Both of the findings are important for our understanding of airway functions induced by Ang II.     

In vitro expression of inducible nitric oxide synthase in the nasal mucosa of guinea pigs after incubation with lipopolysaccharides or cytokines

In order to demonstrate the involvement of nitric oxide synthases (NOS)--in particular the inducible isoform (iNOS)--in inflammatory processes within the nasal airways, we used organ-bath incubation to study isolated inferior turbinates and mucosa of the maxillary sinus of guinea pigs. The pattern of the expression in various substructures of the nasal mucosa was of special interest. Mucosa was incubated for 6 h with lipopolysaccharides (LPS) produced by E. coli, interleukin II (IL-2) or tumor necrosis factor-alpha (TNF-alpha). Saline was used as the control solution. Following incubation the specimens were fixed in buffered 4% formaldehyde solution over a period of 4 h. Tissues were next exposed to nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reaction and immunostained with specific antibodies to iNOS. Results then showed a clearly increased or initiated expression of iNOS in epithelium, glands, leucocytes and blood vessels of treated tissues in comparison to the control specimens. The inflammatory mediator LPS and the cytokines Il-2 or TNF-alpha alone were found to be capable of increasing the expression of iNOS, although the effects of LPS clearly exceeded those of the cytokines. This finding implicates iNOS-generated nitric oxide as a key factor for causing nasal swelling, secretion and obstruction during nasal infections and allergic episodes.     

Increased airway osmolarity inhibits the action of nitric oxide in the rabbit

Retractile mesenteritis is a rare inflammatory mesenteric disorder that involves the intestine secondarily. The natural history of this process is diverse, but most patients require some empiric therapeutic measures. Up to now, pharmacological therapy has included corticosteroids, colchicine, and immunosuppressive drugs. Although these drugs are successful in most patients, some have been refractory to these therapies and, in others, the beneficial effects were counterbalanced by adverse reactions. Many patients require surgery, but most have poor results. This report describes a 42-year-old man with histologically proven retractile mesenteritis refractory to surgical intervention who had a good response to oral progesterone (10 mg/day for 6 months) with complete disappearance of tumor mass and clinical symptoms. No adverse effects were detected. Current knowledge about the mechanism by which progesterone affects fibrogenesis is scanty. It seems likely that progesterone down-regulates proliferation and metabolism of fibroblasts and fibrogenesis.     

Up-regulation of inducible nitric oxide synthase and production of nitric oxide by the Swarm rat and human chondrosarcoma

Phospholipids are the major constituents of cell membranes, and have numerous structural and functional roles in the nervous system. Although the metabolic pathways responsible for the syntheses of the phosphatides phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), and phosphatidylserine (PtdSer) are well understood, the mechanisms controlling these pathways in neural tissue have not been fully characterized. Recent studies have suggested that the main factors controlling PtdCho and PtdEtn synthesis by the Kennedy cycle tend to be the intracellular levels of key substrates for the biosynthetic enzymes, or changes in the activities of the rate-limiting enzymes. Moreover, different control mechanisms may operate, depending upon the functional state of the tissue.     

Cell-specific effects of pentoxifylline on nitric oxide production and inducible nitric oxide synthase mRNA expression

Cytokine-stimulated astrocytes and macrophages are potent producers of nitric oxide (NO), a free radical proposed to play an important role in organ-specific autoimmunity, including demyelinating diseases of the central nervous system. The aim of this study was to investigate effects of pentoxifylline (PTX), a phosphodiesterase inhibitor with immunomodulatory properties, on NO production and inducible NO synthase (iNOS) mRNA expression in rat astrocytes and macrophages. We have shown that PTX affects cytokine (interferon-gamma, IFN-gamma; interleukin-1, IL-1; tumour-necrosis factor-alpha, TNF-alpha)-induced NO production in both cell types, but in the opposite manner--enhancing in astrocytes and suppressive in macrophages. While PTX did not have any effect on enzymatic activity of iNOS in activated cells, expression of iNOS mRNA was elevated in astrocytes and decreased in macrophages treated with cytokines and PTX. Treatment with PTX alone affected neither NO production nor iNOS mRNA levels in astrocytes or macrophages. This study indicates involvement of different signalling pathways associated with iNOS induction in astrocytes and macrophages, thus emphasizing complexity of regulation of NO synthesis in different cell types.     

Ventilatory responses in awake guinea pigs exposed to acid aerosols

This study reports experiments designed to evaluate the dose and temporal effects of an atmospheric pollutant, sulfuric acid (H2SO4) aerosol, on the dynamic components of the respiratory cycle. Ventilation was measured in a whole-body barometric plethysmograph in unanesthetized, unrestrained animals following a 4-h exposure to H2SO4 aerosol at 14.1, 20.1, or 43.3 mg/m3. Lung injury was assessed by histopathology and bronchoalveolar lavage (BAL). Aerosol exposure with H2SO4 caused marked alterations in both the magnitude and composition of the ventilatory response, which were both dose and time dependent. At the highest concentration tested, there was a significant increase in tidal volume (deltaVt) and a decrease in breathing frequency (f) immediately after exposure. Analysis of BAL fluid at this time showed increased inflammatory cells and protein in the acid exposed animals, and histology showed hyaline membranes and acute inflammatory cells in the proximal acinar region. By 24 h postexposure, f significantly increased whereas deltaVt decreased. This pattern of breathing was interspersed with short periods of apnea. The onset of rapid, shallow breathing was associated with histological evidence of diffuse pulmonary edema. By contrast, the immediate postexposure period at the lowest concentration of H2SO4 aerosol was characterized by a significant increase in f and little or no effect on deltaVt. These effects diminished with time, and at 24 h postexposure ventilatory parameters were indistinguishable from baseline values. An apparent crossover between the effects associated with the high and low exposure concentrations was seen at the intermediate exposure concentration; however, closer inspection of these findings on an animal-by-animal basis revealed two populations of animals with respiratory characteristics of either the high-exposure or low-exposure groups. The data suggest that the guinea pig exhibits complex interactions between dose and time to response that are consistent with the activation of neural reflexes. The indirect plethysmographic method provides a simple means to assess these responses in a model system that avoids the use of anesthetics, surgery, and restraint.     

Altered cytokine production and impaired antimycobacterial immunity in protein-malnourished guinea pigs

Protein malnutrition leads to multiple detrimental alterations of host immune responses to mycobacterial infection. In this study, we demonstrated that splenocytes from low-protein (LP) guinea pigs vaccinated 6 weeks previously with attenuated Mycobacterium tuberculosis H37Ra failed to control the accumulation of virulent M. tuberculosis H37Rv in cocultured autologous peritoneal macrophages, despite the fact that they were able to control the accumulation of virulent tubercle bacilli in cocultured syngeneic peritoneal macrophages from normally nourished guinea pigs as successfully as did those from high-protein (HP) counterparts. Vaccine-induced growth control of virulent M. tuberculosis H37Rv in these cocultures appeared to be mediated by CD4 lymphocytes but not CD8 cells. Tuberculin (purified protein derivative [PPD])-induced lymphoproliferation was markedly impaired in vaccinated LP guinea pigs, and the depletion of CD4 lymphocytes significantly decreased lymphocyte proliferation whereas CD8 cell depletion did not. Protein malnutrition also impaired the abilities of cells from vaccinated LP guinea pigs to produce cytokines, including interferon, tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta), in response to PPD, despite the demonstration of higher serum levels of TNF-alpha and TGF-beta after an intravenous injection of PPD into LP guinea pigs. In contrast, peritoneal macrophages from protein-malnourished guinea pigs produced a higher level of TGF-beta 4 days after infection in vitro with M. tuberculosis H37Rv than did those from protein adequate controls. These results suggest that dietary protein malnutrition impairs vaccine-induced resistance to M. tuberculosis, in part, by altering the cytokine profile to favor macrophage deactivation.     

Cardiovascular and abdominal motor responses evoked by intravenous neurotensin in guinea pigs

Developing T cells in the thymus are subject to a screening process, through interactions with thymic stromal cells, from which T cells with appropriate T-cell receptors are selected. The recent generation of T-cell receptor transgenic mice and mice homozygous for disrupted T-cell receptor genes have now supplied tools that improve the prospect for a better understanding of the molecular mechanisms of this thymic selection process. In addition these model systems appear to indicate a role for a, not yet fully characterized, pre-T cell receptor complex in survival and further differentiation of pre-T cells.     

Increased nitric oxide activity in a rat model of acute pancreatitis

BACKGROUND: Overproduction of nitric oxide (NO) via induction of the inducible NO synthase (iNOS) is an important factor in the haemodynamic disturbances of several inflammatory states. AIMS: To identify the role of NO in a caerulein induced model of acute pancreatitis in the rat. METHODS: Arterial blood pressure and plasma NO metabolites were measured at zero and seven hours in adult male Wistar rats administered caerulein (n=10) or saline (n=10). Pancreatic activity of NOS (inducible and constitutive) was assayed biochemically. The pancreatic expression and cellular localisation of NOS and nitrotyrosine (a marker of peroxynitrite induced oxidative tissue damage) were characterised immunohistochemically. RESULTS: Compared with controls at seven hours, the pancreatitis group displayed raised plasma NO metabolites (mean (SEM) 70.2 (5.9) versus 22.7 (2.2) micromol/l, p<0.0001) and reduced mean arterial blood pressure (88.7 (4.6) versus 112.8 (4.1) mm Hg, p=0.008). There was notable iNOS activity in the pancreatitis group (3.1 (0.34) versus 0.1 (0.01) pmol/mg protein/min, p<0.0001) with reduced constitutive NOS activity (0.62 (0.12) versus 0.96 (0.08) pmol/mg protein/min, p=0.031). The increased expression of iNOS was mainly localised within vascular smooth muscle cells (p=0.003 versus controls), with positive perivascular staining for nitrotyrosine (p=0.0012 versus controls). CONCLUSIONS: In this experimental model of acute pancreatitis, iNOS induction and oxidative tissue damage in the pancreas is associated with raised systemic NO and arterial hypotension. Excess production of NO arising from the inducible NO synthase may be an important factor in the systemic and local haemodynamic disturbances associated with acute pancreatitis.