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.     

Involvement of nitric oxide and cGMP in the protective effect of neurotensin on hepatocytes

STUDY OBJECTIVE: Tetanus antibody levels have been shown to be inadequate in 50% of patients older than 65 years. Although immunization recommendations have been made for this age group, the efficacy of this intervention has not been well documented. We sought to determine the difference in tetanus antibody levels after the administration of one tetanus toxoid immunization to geriatric patients without adequate titers. METHODS: Thirty-five patients older than 65 years at a large urban comprehensive care geriatric center who were documented to have inadequate tetanus antibody titers were each given one tetanus toxoid immunization. Repeat titers were obtained at least 2 months after the immunization with the use of enzyme-linked immunosorbent assay (Bindazyme kit; the Binding Site Corporation, Birmingham, England). We considered tetanus antibody levels greater than .17 IU/mL protective. RESULTS: The mean age was 79.4 years; 30 of 35 (86%) were female. Repeat tetanus antibody titers were obtained an average of 123 days (range, 63 to 204 days) after immunization with tetanus toxoid. The mean preimmunization antibody titer was .1 IU/mL (range, .04 to .16 IU/mL). After immunization, antibody titers increased a mean of .61 IU/mL (range, -.01 to 2.23 IU/mL; 95% confidence interval, .35 to .87 IU/mL). Thirty of the 35 patients who received a single injection of tetanus toxoid (86%) developed protective titers. We found no relationship between seroconversion and age, sex, or medical history; nor did we find a relationship between antibody level and time elapsed since immunization when repeat titers were obtained. CONCLUSION: Administration of one tetanus toxoid injection affords protective immunity in many geriatric patients.     

The role of nitric oxide in mechanisms of the nephrotoxic effect of verografin

A clinic based cross-sectional study was conducted at Immunoprophylaxis Clinic at Govt. Medical College, Nagpur. Mothers of 217 children were interviewed for infant feeding practices. In 62.67% of children, breast-feeding was initiated within 24 hrs. after birth. About 22% mother used prelacteal feed and 70% mothers preferred demand feeding. Prominent area of concern includes discarding of colostrum, low exclusive breast feeding rate, delayed weaning and early termination of breast feeding. Further improvement in present day infant feeding practices is possible by emphasising on the health education component of existing nutritional programmes.     

Evidence that different mechanisms underlie smooth muscle relaxation to nitric oxide and nitric oxide donors in the rabbit isolated carotid artery

1. The endothelium-dependent relaxants acetylcholine (ACh; 0.03-10 microM) and A23187 (0.03-10 microM), and nitric oxide (NO), applied either as authentic NO (0.01-10 microM) or as the NO donors 3-morpholino-sydnonimine (SIN-1; 0.1-10 microM) and S-nitroso-N-acetylpenicillamine (SNAP; 0.1-10 microM), each evoked concentration-dependent relaxation in phenylephrine stimulated (1-3 microM; mean contraction and depolarization, 45.8+/-5.3 mV and 31.5+/-3.3 mN; n=10) segments of rabbit isolated carotid artery. In each case, relaxation closely correlated with repolarization of the smooth muscle membrane potential and stimulated a maximal reversal of around 95% and 98% of the phenylephrine-induced depolarization and contraction, respectively. 2. In tissues stimulated with 30 mM KCl rather than phenylephrine, smooth muscle hyperpolarization and relaxation to ACh, A23187, authentic NO and the NO donors were dissociated. Whereas the hyperpolarization was reduced by 75-80% to around a total of 10 mV, relaxation was only inhibited by 35% (n=4-7 in each case; P<0.01). The responses which persisted to ACh and A23187 in the presence of 30 mM KCl were abolished by either the NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME; 100 microM) or the inhibitor of soluble guanylyl cyclase 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 microM; 10 min; n=4 in each case; P<0.01). 3. Exposure to ODQ significantly attenuated both repolarization and relaxation to ACh, A23187 and authentic NO, reducing the maximum changes in both membrane potential and tension to each relaxant to around 60% of control values (n=4 in each case; P<0.01). In contrast, ODQ almost completely inhibited repolarization and relaxation to SIN-1 and SNAP, reducing the maximum responses to around 8% in each case (n=3-5; P<0.01). 4. The potassium channel blockers glibenclamide (10 microM), iberiotoxin (100 nM) and apamin (50 nM), alone or in combination, had no significant effect on relaxation to ACh, A23187, authentic NO, or the NO donors SIN-1 and SNAP (n=4 in each case; P>0.05). Charybdotoxin (ChTX; 50 nM) almost abolished repolarization to ACh (n=4; P<0.01) and inhibited the maximum relaxation to ACh, A23187 and authentic NO each by 30% (n=4-8; P<0.01). Application of ODQ (10 microM; 10 min) abolished the ChTX-insensitive responses to ACh, A23187 and authentic NO (n=4 in each case; P<0.01 5. When the concentration of phenylephrine was reduced (to 0.3-0.5 microM) to ensure the level of smooth muscle contraction was the same as in the absence of potassium channel blocker, ChTX had no effect on the subsequent relaxation to SIN-1 (n=4; P>0.05). However, in the presence of tone induced by 1-3 microM phenylephrine (51.2+/-3.3 mN; n=4), ChTX significantly reduced relaxation to SIN-1 by nearly 50% (maximum relaxation 53.2+/-6.3%, n=4; P<0.01). 6. These data indicate that NO-evoked relaxation of the rabbit isolated carotid artery can be mediated by three distinct mechanisms: (a) a cyclic GMP-dependent, voltage-independent pathway, (b) cyclic GMP-mediated smooth muscle repolarization and (c) cyclic GMP-independent, ChTX-sensitive smooth muscle repolarization. Relaxation and repolarization to both authentic and endothelium-derived NO in this large conduit artery appear to be mediated by parallel cyclic GMP-dependent and -independent pathways. In contrast, relaxation to the NO-donors SIN-1 and SNAP appears to be mediated entirely via cyclic GMP-dependent mechanisms.     

Chemical biology of nitric oxide: Insights into regulatory, cytotoxic, and cytoprotective mechanisms of nitric oxide

There has been confusion as to what role(s) nitric oxide (NO) has in different physiological and pathophysiological mechanisms. Some studies imply that NO has cytotoxic properties and is the genesis of numerous diseases and degenerative states, whereas other reports suggest that NO prevents injurious conditions from developing and promotes events which return tissue to homeostasis. The primary determinant(s) of how NO affects biological systems centers on its chemistry. The chemistry of NO in biological systems is extensive and complex. To simplify this discussion, we have formulated the "chemical biology of NO" to describe the pertinent chemical reactions under specific biological conditions. The chemical biology of NO is divided into two major categories, direct and indirect. Direct effects are defined as those reactions fast enough to occur between NO and specific biological molecules. Indirect effects do not involve NO, but rather are mediated by reactive nitrogen oxide species (RNOS) formed from the reaction of NO either with oxygen or superoxide. RNOS formed from NO can mediate either nitrosative or oxidative stress. This report discusses various aspects of the chemical biology of NO relating to biological molecules such as guanylate cyclase, cytochrome P450, nitric oxide synthase, catalase, and DNA and explores the potential roles of NO in different biological events. Also, the implications of different chemical reactions of NO with cellular processes such as mitochondrial respiration, metal homeostasis, and lipid metabolism are discussed. Finally, a discussion of the chemical biology of NO in different cytotoxic mechanisms is presented.     

Nitric oxide is overproduced by peritoneal macrophages in rat taurocholate pancreatitis: the mechanism of inducible nitric oxide synthase expression

To investigate the pathobiology of severe acute pancreatitis, we studied the expression of inducible nitric oxide synthase (iNOS) in peritoneal macrophages of experimental pancreatitis. Taurocholate (TCA) pancreatitis and cerulein (CE) pancreatitis were used as models of lethal and self-limited pancreatitis, respectively, and the mechanism of iNOS expression in peritoneal macrophages was studied. Serum nitrate and nitrite (NOx) concentrations increased during the course of TCA pancreatitis, and iNOS-immunoreactivity was detected in the peritoneal macrophages 12 h after the induction of TCA pancreatitis, but these phenomena were not observed in CE pancreatitis. Despite the difference in the iNOS expression, the iNOS messenger RNA (mRNA) and the activation of nuclear factor-kappa B (NF-kappa B) were detected in the peritoneal macrophages of both pancreatitis models. The supernatant of TCA pancreatitis ascites could induce iNOS in the peritoneal macrophages of normal rats in vitro, but the peritoneal lavage fluid of CE pancreatitis rats could not. The results indicated that there may be qualitative or quantitative differences in the macrophage activation between the two types of experimental pancreatitis and suggested that the ascites of rats with lethal acute pancreatitis contains some soluble factors that activate the macrophage/monocyte system and cause an overproduction of NO by the iNOS expression.     

Leukocyte-endothelial adherence correlates with pancreatic nitric oxide production in early cerulein-induced pancreatitis in rats

The authors retrospectively investigated the long-term visual recovery in 32 macular reattached eyes that had been monitored for more than 5 years after surgery. The best corrected visual acuities were better at 5 years postoperatively than at 3 months by two lines or more in 17 eyes (53%). In these 17 eyes, visual acuities continued to improve for up to 10 years after surgery. In the other 15 eyes, the visual acuities remained within one line of the 3-month values. Improvement of the long-term postoperative visual acuity was found to be statistically correlated with younger age, no or mild myopia (>-5 diopters), and shorter duration of macular detachment (< or =30 days). Surgeons should be aware that the visual function of reattached retinas may continue to improve over the long term, especially when these beneficial factors are present.     

Role of inducible nitric oxide synthase in endotoxin-induced acute lung injury

The role of nitric oxide (NO) in lung injury remains unclear. Both beneficial and detrimental roles have been proposed. In this study, we used mutant mice lacking the inducible nitric oxide synthase (iNOS) to assess the role of this isoform in sepsis-associated lung injury. Wild-type and iNOS knockout mice were injected with either saline or Escherichia coli endotoxin (LPS) 25 mg/kg and killed 6, 12, and 24 h later. Lung injury was evaluated by measuring lactate dehydrogenase activity in the bronchoalveolar lavage, pulmonary wet/dry ratio, and immunostaining for nitrotyrosine formation. In the wild-type mice, LPS injection elicited more than a 3-fold rise in lactate dehydrogenase activity, a significant rise in lung wet/dry ratio and extensive nitrotyrosine staining in large airway and alveolar epithelium, macrophages, and pulmonary vascular cells. This was accompanied by induction of iNOS protein and increased lung nitric oxide synthase activity. By comparison, LPS injection in iNOS knockout mice elicited no iNOS induction and no significant changes in lung NOS activity, lactate dehydrogenase activity, lung wet/dry ratio, or pulmonary nitrotyrosine staining. These results indicate that mice deficient in iNOS gene are more resistant to LPS-induced acute lung injury than are wild-type mice.     

Localization of inducible nitric oxide synthase in acute renal allograft rejection in the rat

There is increasing evidence for a role for nitric oxide (NO) in the alloimmune response and induction of NO synthesis occurs during allograft rejection. The aim of this study was to investigate the source of NO synthesis in rejecting allografts. Localization of inducible nitric oxide synthase (iNOS) was studied by immunohistochemistry, in a rat model of acute renal allograft rejection, in unmodified Lewis recipients in which rejection is complete 7 days after transplantation of F1 hybrid Lewis-Brown Norway kidneys. High levels of iNOS expression were found in infiltrating mononuclear cells in glomeruli and interstitium of rejecting kidneys; there was no expression in parenchymal renal cells, or in control isografts of either rat strain. Expression of iNOS in the cortex was present from 4 to 6 days posttransplantation, and had declined by the 7th day, where expression was principally in the medulla. The pattern of iNOS staining was similar to ED1 staining, a marker for rat macrophages. These findings suggest that infiltrating macrophages in the graft reaction are a prominent source of NO; this iNOS expression supports a role for NO in the modulation of local allogeneic responses, and possibly as a mediator of cytotoxic graft damage.     

Regulation of cardiac myocyte contractile function by inducible nitric oxide synthase (iNOS): mechanisms of contractile depression by nitric oxide

Inflammatory cytokines have been implicated in the reversible depression of cardiac contractile function accompanying local or systemic immune stimulation. Incubation of cardiac myocytes with soluble components in the supernatant from cultured rat lung macrophages activated with endotoxin decreases their contractile response to beta-adrenergic stimulation through the induction of iNOS and the subsequent production of nitric oxide by these cells. In the present study, we characterize the mechanisms underlying NO's attenuation of adrenergic responsiveness in cardiac myocytes. iNOS was induced in cultured ventricular myocytes from adult rats by incubation for 20 h with conditioned medium from lipopolysaccharide (LPS)-activated macrophages. iNOS induction did not induce any alteration in beta-adrenergic receptor density or affinity, Galphai protein abundance, or adenylyl cyclase activity in cultured myocytes. Myocyte exposure to activated macrophage-conditioned medium markedly attenuated the elevation of cAMP in response to isoproterenol (Iso, 2 nM). Induction of iNOS with the macrophage-conditioned medium also potentiated the Iso-induced increase in myocyte cGMP. This cGMP increase was totally abolished by NOS inhibitors. NOS inhibition also returned the attenuated cAMP response to 2 nM Iso to levels observed in control cells. Pre-incubation of the cells in isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor, also partly reversed the attenuation of cAMP increase with 2 nM Iso in cells expressing iNOS. Brief (15 min) exposure of myocytes to the NO donor, S-nitrosoacetylcysteine (SNAC, 100 micro M) which produced a three-fold increase in intracellular cGMP, also decreased by half the contractile response of cardiac myocytes to Iso (2 nM). We conclude that NO endogenously produced by iNOS decreases the intracellular levels of cAMP in response to beta-adrenergic stimulation in isolated cardiac myocytes, in part through a cGMP-mediated mechanism. This effect may participate in the NO-dependent depression of cardiac function following cytokine exposure.     

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.     

Cytokine and nitric oxide production in the acute phase of bacterial cell wall-induced arthritis

We have investigated the temporal relationship among proinflammatory cytokine expression, nitric oxide (NO) production and joint inflammation in the acute phase of bacterial cell wall-derived peptidoglycan polysaccharide (PG/PS)-induced arthritis. Acute joint inflammation was induced in female LEW/N rats by a single intraperitoneal injection of PG/PS. Arthritis index and paw volume were quantified and joint histopathology was evaluated during acute joint inflammation (0-10 days). Tumor necrosis factor (TNF), interleukin-1 (IL-1) and interleukin-6 (IL-6) were determined by bioassay whereas nitric oxide (NO) was quantified by measuring serum nitrate/nitrite levels via the Griess procedure. We found that serum levels of TNF and serum IL-1 preceded the increase in IL-6 and NO production. Furthermore, the production of these proinflammatory cytokines and NO preceded bone erosion and osteoclast activity. Erosion of subchondral bone preceded pannus formation and cellular synovitis in the acute phase of PG/PS-induced arthritis. The temporal expression of TNF, IL-1, IL-6 and NO suggest a cascade of inflammatory mediators in which monocytes and macrophages respond to PG/PS with enhanced synthesis of TNF and IL-1, which may in turn promote the synthesis of IL-6 and NO. We postulate that one or more of these inflammatory events are responsible for initiating the subchondral bone erosion observed in acute joint inflammation.     

Influence of atmospheric nitric oxide concentration on the measurement of nitric oxide in exhaled air

BACKGROUND: Measurement of nitric oxide (NO) in exhaled air shows promise as a non-invasive method of detecting lung inflammation. However, variable concentrations of NO are measured in environmental air. The aim of this study was to verify a possible relationship between exhaled NO and atmospheric NO values during high atmospheric NO days. METHOD: Exhaled air from 78 healthy non-smokers of mean age 35.3 years was examined for the presence of NO using a chemiluminescence NO analyser and NO levels were expressed as part per billion (ppb). The exhaled air from all the subjects was collected into a single bag and into two sequential bags. Before each test atmospheric NO was measured. RESULTS: The mean (SE) concentration of exhaled NO collected into the single bag was 17.1 (0.6) ppb while the mean values of exhaled NO in bags 1 and 2 were 16.7 (1.3) ppb and 13.8 (1.2) ppb, respectively. The atmospheric NO concentrations registered before each test varied from 0.4 to 71 ppb. There was a significant correlation between exhaled NO in the single bag and atmospheric NO (r = 0.38, p = 0.001). The atmospheric NO concentration also correlated with exhaled NO both in bag 1 (r = 0.44, p = 0.0001) and in bag 2 (r = 0.42, p = 0.0001). These correlations disappeared with atmospheric NO concentrations lower than 35 ppb. CONCLUSIONS: These results indicate a relationship between atmospheric NO and NO levels measured in exhaled air, therefore exhaled NO should not be measured on very high atmospheric NO days.     

Inhibition of nitric oxide modulates the effect of oral arginine supplementation in acute liver injury

We investigated the efficacy of bone marrow (BM) processing by an automated large-volume apheresis procedure (6 x original BM volume) in 10 paediatric and adult patients undergoing BM harvesting before myeloablative therapy. Volume-dependent kinetics during apheresis were analyzed by sequential collection of processed cells into a six-fold collection bag system with consecutive analysis of the single bags. BM processing resulted in an 83.3% (+/- 21) recovery of mononuclear cells (MNC), a 97.9% (+/- 1.1) reduction of erythrocytes (RBC) and a 87.7% (+/- 2.9) volume reduction. To determine volume-dependent kinetics of haematopoietic progenitor cell (HPC) enrichment during apheresis, leukocytes (WBC), mononuclear cells (MNC), CD34 cells and colony-forming cells (CFU-GM) were serially quantitated in subsequent collection bags. Large-volume BM processing significantly enhanced absolute yields of CD34+ cells (mean: 4.01 (+/- 2.81) x 10(6)/kg bw) and CFU-GM (mean: 1.92 (+/- 1.47) x 10(4)/kg bw) compared with the standard procedure (3 x BM volume) by 26.9% (+/- 10.9) and 27.2% (+/- 11.6), respectively. We concluded that large-volume apheresis for BM processing is an efficient technique significantly improving the yields of haematopoietic progenitor cells (HPC) without any relevant changes in the purity of the final product. Moreover, sequential collection and analysis of HPC represents a good model to investigate the volume-dependent kinetics and efficacy of BM processing.     

Utility of a nitric oxide electrode for monitoring the administration of nitric oxide in biologic systems

Von Hippel-Lindau (VHL) disease is an inherited autosomal dominant neoplastic disorder causing central nervous system haemangioblastomas. The VHL gene (3p25-3p26) is known to be a tumour suppressor gene, with its inactivation being responsible for a predisposition to tumour development. As far as we know, the present report of VHL disease manifestation in identical twins is unique. Genetic inquiry into the family background did not reveal this disease among their progenitors. For presymptomatic diagnosis of 17 presently unaffected family members, constitutional DNA of the twins was screened for VHL germline mutations, using loss of heterozygosity studies and exon-specific DNA sequencing. To determine the influence of somatic mutations of the VHL gene in tumourigenesis, DNA of five surgically removed intracerebral haemangioblastomas of the identical twins was analyzed in comparison with their constitutional DNA by DNA sequencing of the complete VHL coding region. However, no allelic losses were found for the VHL gene or for various other tumour suppressor genes (p53, BRCA1, BRCA2, DCC, and MCC). Furthermore, no mutations were found in the constitutional DNA of either twin sister or in the DNA of all five tumour lesions. Based on our observations, we conclude that in certain VHL families, presymptomatic molecular diagnosis of the disease is not feasible and requires close clinical surveillance of all individuals at risk.     

Factors influencing the tracheal fluctuation of inhaled nitric oxide in patients with acute lung injury

BACKGROUND: Inhaled nitric oxide (NO) improves arterial oxygenation in patients with acute lung injury (ALI) by selectively dilating pulmonary vessels perfusing ventilated lung areas. It can be hypothesized that NO uptake from the lung decreases with increasing ventilation perfusion mismatch. This study was undertaken to determine the factors influencing the fluctuation of tracheal NO concentration over the respiratory cycle as an index of NO pulmonary uptake in patients with ALI. METHODS: By using a prototype system (Opti-NO) delivering a constant flow of NO only during the inspiratory phase, 3 and 6 ppm of NO were administered during controlled mechanical ventilation into a lung model and to 11 patients with ALI. All patients had a thoracic computed tomography (CT) scan. Based on an analysis of tomographic densities, lungs were divided into three zones: normally aerated (-1.000 to -500 Hounsfield units [HU]), poorly aerated (-500 to -100 HU), and nonaerated (-100 to +100 HU), and the volume of each zone was computed. Concentrations of NO in the inspiratory limb and trachea were continuously measured by a fast-response chemiluminescence apparatus. RESULTS: In the lung model, tracheal NO concentration was stable with minor fluctuation. In contrast, in patients, tracheal NO concentration fluctuated widely during the respiratory cycle (55 +/- 10%). Because uptake of NO from the lungs was absent in the lung model but present in the patients, this fluctuation was considered as an index of pulmonary uptake of NO. This was further substantiated by (1) the coincidence of the peak and minimum tracheal NO concentration with the end-inspiratory and end-expiratory phases, respectively, and (2) continued decrease of tracheal NO concentration during prolonged expiratory phase. In patients with ALI, the fluctuation of tracheal NO concentration expressed as the difference between inspiratory and expiratory NO concentrations divided by inspiratory NO concentration was greater at 6 ppm than at 3 ppm (P < 0.01), was linearly correlated with normally aerated lung volume, inversely correlated with alveolar dead space and with poorly aerated lung volume. CONCLUSION: In patients with ALI, fluctuation of tracheal NO concentration over the respiratory cycle can be considered as an index of NO uptake from the lungs that depends on aerated lung volume and perfusion of ventilated lung areas. At bedside, it may be used to follow the evolution of ventilation-perfusion mismatch.     

Impaired platelet production of nitric oxide predicts presence of acute coronary syndromes

BACKGROUND: Thrombus formation within a coronary vessel is the acute precipitating event in most acute coronary syndromes. Recently, constitutive nitric oxide synthase (cNOS) has been identified in human platelets, and platelet-derived nitric oxide has been shown to inhibit platelet recruitment after aggregation. However, its role in regulating platelet responses under normal or pathologic conditions has not yet been elucidated. METHODS and RESULTS: We examined nitric oxide (NO) production by platelets isolated from 87 patients undergoing coronary angiography, 37 with stable angina and 50 with unstable angina or a myocardial infarction within 2 weeks. After stimulation with 5 micromol/L ADP, platelet aggregation and NO production were simultaneously measured with an NO-selective microelectrode adapted for use in a standard platelet aggregometer. Mean (+/-SEM) platelet-derived NO production was 1.78+/-0.36 pmol/10(8) and 0.26+/-0.05 pmol/10(8) platelets in coronary patients with stable angina and acute coronary syndromes, respectively (P=0. 0001). By logistic regression analysis, heparin treatment (odds ratio 6.6, CI 1.9 to 22.8, P=0.003), lower platelet-NO production (odds ratio 4.0, CI 1.3 to 11.5, P=0.01), and extent of atherosclerosis (odds ratio 1.5, CI 1.1 to 2.0, P=0.02) were independent predictors of an acute coronary syndrome. In the subset of patients with angiographic evidence of atherosclerosis (n=83), logistic regression demonstrated that platelet NO production (odds ratio 3.9, CI 1.3 to 11.1, P=0.01) and heparin treatment (odds ratio 6.4, CI 1.9 to 22.0, P=0.004) were independent predictors of an acute coronary syndrome, whereas extent of atherosclerosis was not. CONCLUSIONS: In summary, aggregating platelets from patients with acute coronary syndromes produce less NO. Since platelet aggregation and thrombus formation are implicated in unstable angina and myocardial infarction, impaired platelet-derived NO production may contribute to the development of acute coronary syndromes.