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1.
《Mutation Research Letters》1992,281(3):193-202
Nitric oxide (NO) is produced both by macrophages in vivo as a physiological response to infection and by a variety of cell types as an intercellular messenger. In addition, NO and nitrogen dioxide (NO2) are significant components of many combustion processes. The ubiquitous exposure of humans to nitrogen oxides (NOx), both endogenously and exogenously, may play a significant role in the carcinogenic process due to nitrosation of amines by NOx. We report here that exposure to low concentrations of NO, alone or in combination with NO2, results in significantly enhanced mutation in Salmonella typhimurium TA1535 using a modified Ames Salmonella reversion assay. The observed mutagenicity requires that the bacteria be actively dividing at the time of exposure to NO or NO2, suggesting that the nitrogen oxides, or their reaction products, function as direct-acting mutagens and that the induced lesion is easily repairable by non-dividing cells. Exposure to NO resulted in a time- and dose-dependent increase in the number of revertants approximately proportional to the square of the NO concentration from 0 to 20 ppm. NO was a more effective mutagen relative to NO2, however, the observed requirement for 02 suggests limited oxidation of NO (presumably to NO2) is necessary. Numerous lipid- and aqueous-phase inhibitors of nitrosation, as well as a number of other general antioxidants and free-radical trapping agents, were examined for their effectiveness in blocking the mutagenic effects of NO. The mutagenic activity of NO was most effectively inhibited by β-carotene and tocopherols. BHT, dimethyl sulfoxide and mannitol also blocked the mutagenic effects of NOx but appeared less effective than β-carotene or vitamin E, while ascorbate was ineffective as an inhibitor of mutation resulting from NO exposure.  相似文献   

2.
Nitrite and nitrate in body fluids and tissues result from dietary source, endogenous nitric oxide (NO) production and from NO and its higher oxides (NOx) present as pollutants in the atmosphere. Nitrite and nitrate in human blood serum and plasma or urine are commonly used as biomarkers and measures of endogenous NO synthesis. In addition to dietary intake of nitrite and nitrate, our study indicates that NOx naturally present in the laboratory air may be an abundant source for nitrite and nitrate in human serum, plasma, and urine ex vivo. These artifacts can be effectively reduced by closing sample-containing vials during sample treatment.  相似文献   

3.
Exogenous gaseous nitric oxide (gNO) is an FDA approved drug for treatment of a variety of human pathologies like Persistent Pulmonary Hypertension in neonates and premature babies, skin lesions and fungal dermatophyte infections. Substantial disadvantages of current gNO-based therapies are the high therapy costs, high storage costs of the gas cylinders, and the rapid contamination of compressed NO gases with various decomposition products. Here we describe a new, very simple, and inexpensive photolytic generator of uncontaminated NO-containing gas mixtures at therapeutic concentrations. The new method bases on UVA-induced and redox-assisted decomposition of nitrite ions in aqueous solutions. NO formation via UVA-induced photolysis of nitrite is accompanied by an OH radical-dependent production of NO2 that beside its toxic character additionally strongly reduces the NO yield by consuming NO in its reaction to N2O3. During the UVA-induced photodecomposition process both, inhibition of NO2 formation or NO2 depletion by antioxidants hinders the NO-consuming reaction with NO2 and ensured a maximal purity and maximal yield of NO-containing gas mixtures. Therefore, NO-containing gas mixtures generated by the described method are suitable for medical applications like inhalation or gassing of chronic non-healing wounds. Control of temperature, UVA intensity and composition of the reaction mixture allows facile control over the final NO level in the carrier gas over a wide concentration range. We demonstrate the sustained and stable release of NO over a wide dynamic range (10–5000 ppm NO) for many hours. The method avoids contamination-prone long time storage of NO gas. As such, it appears particularly relevant for applications involving the additional presence of oxygen (e.g. inhalation).  相似文献   

4.
Nitrogen dioxide is formed endogenously via the oxidation of NO by O2 or O2 and from NO2 via peroxidases, among other pathways. This radical has many potential biological targets and its concentration, like that of NO and other reactive nitrogen species, is thought to be elevated at sites of inflammation. To investigate the specific cytotoxic or mutagenic effects of NO2, it is desirable to be able to maintain its concentration at constant, predictable, and physiological levels in cell cultures, in the absence of NO. To do this, a delivery system was constructed in which NO2-containing gas mixtures contact a liquid within a small (110 ml) stirred reactor. In such gas mixtures NO2 is present in equilibrium with its dimer, N2O4. The uptake of NO2 and N2O4 was characterized by measuring the accumulation rates of NO2 and NO3, the stable products of N2O4 hydrolysis, in buffered aqueous solutions. In some experiments NO2-reactive 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulfonate) (ABTS) was included and formation of the stable ABTS radical was measured. A reaction–diffusion model was developed that predicts the accumulation rates of all three products to within 15% for gas-phase concentrations of NO2 spanning 3 orders of magnitude. The model also provides estimates for the NO2 concentration in the liquid. This system should be useful for exposing cells to NO2 concentrations similar to those in vivo.  相似文献   

5.
A new bacterial strain isolated from soil consumed nitric oxide (NO) under oxic conditions by oxidation to nitrate. Phenotypic and phylogenetic characterization of the new strain PS88 showed that it represents a previously unknown species of the genus Pseudomonas, closely related to Pseudomonas fluorescens and Pseudomonas putida. The heterotrophic, obligately aerobic strain PS88 was not able to denitrify or nitrify; however, strain PS88 oxidized NO to nitrate. NO was not reduced to nitrous oxide (N2O). Nitrogen dioxide (NO2) and nitrite (NO2 ) as possible intermediates of NO oxidation to nitrate (NO3 ) could not be detected. NO oxidation was inhibited under anoxic conditions and by high osmolarity, but not by nitrite. NO oxidation activity was inhibited by addition of formaldehyde, HgCl2, and antimycin, and by autoclaving or disintegrating the cells, indicating that the process was enzyme-mediated. However, the mechanism remains unclear. A stepwise oxidation at a metalloenzyme and a radical mechanism are discussed. NO oxidation in strain PS88 seems to be a detoxification or a co-oxidation mechanism, rather than an energy-yielding process. Received: 15 November 1995 / Accepted: 24 February 1996  相似文献   

6.
Nitrogen oxides (NOx) are important components of ambient and indoor air pollution and are emitted from a range of combustion sources, including on-road mobile sources, electric power generators, and non-road mobile sources. While anthropogenic sources dominate, NOx is also formed by lightning strikes and wildland fires and is also emitted by soil. Reduced nitrogen (e.g., ammonia, NH3) is also emitted by various sources, including fertilizer application and animal waste decomposition. Nitrogen oxides, ozone (O3) and fine particulate matter (PM2.5) pollution related to atmospheric emissions of nitrogen (N) and other pollutants can cause premature death and a variety of serious health effects. Climate change is expected to impact how N-related pollutants affect human health. For example, changes in temperature and precipitation patterns are projected to both lengthen the O3 season and intensify high O3 episodes in some areas. Other climate-related changes may increase the atmospheric release of N compounds through impacts on wildfire regimes, soil emissions, and biogenic emissions from terrestrial ecosystems. This paper examines the potential human health implications of climate change and N cycle interactions related to ambient air pollution.  相似文献   

7.
ABSTRACT

Ammonia oxidizing bacteria extract energy for growth from the oxidation of ammonia to nitrite. Ammonia monooxygenase, which initiates ammonia oxidation, remains enigmatic given the lack of purified preparations. Genetic and biochemical studies support a model for the enzyme consisting of three subunits and metal centers of copper and iron. Knowledge of hydroxylamine oxidoreductase, which oxidizes hydroxylamine formed by ammonia monooxygenase to nitrite, is informed by a crystal structure and detailed spectroscopic and catalytic studies. Other inorganic nitrogen compounds, including NO, N2O, NO2, and N2 can be consumed and/or produced by ammonia-oxidizing bacteria. NO and N2O can be produced as byproducts of hydroxylamine oxidation or through nitrite reduction. NO2 can serve as an alternative oxidant in place of O2 in some ammonia-oxidizing strains. Our knowledge of the diversity of inorganic N metabolism by ammonia-oxidizing bacteria continues to grow. Nonetheless, many questions remain regarding the enzymes and genes involved in these processes and the role of these pathways in ammonia oxidizers.  相似文献   

8.
Microbial removal of nitrogen monoxide (NO) under aerobic conditions   总被引:13,自引:0,他引:13  
Nitrogen oxide gas (NOx), consisting of nitrogen monoxide (NO) and nitrogen dioxide (NO2), at a low concentration corresponding to that on roads as a result of exhaust from automobiles, was supplied for 25 days through a laboratory-scale biofilter packed with soil as a packing material. The removal efficiency of NO2 by soil was almost 100%, and the removal efficiency of NO was 60% on average and 86% at maximum. By using -irradiated soil as a packing material, NO2 was completely removed mainly by adsorption onto or absorption into the packing material. However, the removal efficiency of NO in the sterilized soil was only 20%, suggesting that NO in soil was removed microbiologically under aerobic conditions.  相似文献   

9.
Gaseous NO2 as a regulator for ammonia oxidation of Nitrosomonas eutropha   总被引:8,自引:0,他引:8  
Cells of Nitrosomonas eutropha strain N904 that were denitrifying under anoxic conditions with hydrogen as electron donor and nitrite as electron acceptor were unable to utilize ammonium (ammonia) as an energy source. The recovery of ammonia oxidation activity was dependent on the presence of NO2. Anaerobic ammonia oxidation activity was observed in a helium atmosphere supplemented with 25 ppm NO2 after 20 h. Ammonia oxidation activity was detected after 2–3 days using an oxic atmosphere with 25 ppm NO2. In contrast, ammonia consumption started after 8–9 days under oxic conditions without the addition of NO2; in this case, small amounts of NO and NO2 were detected and their concentrations increased with increasing ammonia oxidation activities. Hardly any ammonia oxidation was detected when nitrogen oxides were removed by intensive aeration. It would seem, therefore, that NO2 is the master regulatory signal for ammonia oxidation in Nitrosomonas eutropha. Anaerobic ammonia oxidation activity was inhibited by the addition of NO. This inhibition was partly compensated by either increasing the NO2 concentration or by using 2,3-dimercapto-1-propane-sulfonic acid as a NO binding substrate. DMPS was inhibitory to nitrification under oxic conditions, while increased amounts of NO or NO2 led to increased oxidation activities.  相似文献   

10.
The distribution of anaerobic ammonium oxidation (anammox) in nature has been addressed by only a few environmental studies, and our understanding of how anammox bacteria compete for substrates in natural environments is therefore limited. In this study, we measure the potential anammox rates in sediment from four locations in a subtropical tidal river system. Porewater profiles of NOx (NO2 plus NO3) and NO2 were measured with microscale biosensors, and the availability of NO2 was compared with the potential for anammox activity. The potential rate of anammox increased with increasing distance from the mouth of the river and correlated strongly with the production of nitrite in the sediment and with the average concentration or total pool of nitrite in the suboxic sediment layer. Nitrite accumulated both from nitrification and from NOx reduction, though NOx reduction was shown to have the greatest impact on the availability of nitrite in the suboxic sediment layer. This finding suggests that denitrification, though using NO2 as a substrate, also provides a substrate for the anammox process, which has been suggested in previous studies where microscale NO2 profiles were not measured.  相似文献   

11.
The nr1 soybean (Glycine max [L.] Merr.) mutant does not contain the two constitutive nitrate reductases, one of which is responsible for enzymic conversion of nitrite to NOx (NO + NO2). It was tested for possible nonenzymic NOx formation and evolution because of known chemical reactions between NO2 and plant metabolites and the instability of nitrous acid. It did not evolve NOx during the in vivo NR assay, but intact leaves did evolve small amounts of NOx under dark, anaerobic conditions. Experiments were conducted to compare NO3 reduction, NO2 accumulation, and the NOx evolution processes of the wild type (cv Williams) and the nr1 mutant. In vivo NR assays showed that wild-type leaves had three times more NO3 reducing capacity than the nr1 mutant. NOx evolution from intact, anerobic nr1 leaves was approximately 10 to 20% that from wild-type leaves. Nitrite content of the nr1 mutant leaves was usually higher than wild type due to low NOx evolution. Lag times and threshold NO2 concentrations for NOx evolution were similar for the two genotypes. While only 1 to 2% of NOx from wild type is NO2, the nr1 mutant evolved 15 to 30% NO2. The kinetic patterns of NOx evolution with time weré completely different for the mutant and wild type. Comparisons of light and heat treatments also gave very different results. It is generally accepted that the NOx evolution by wild type is primarily an enzymic conversion of NO2 to NO. However, this report concludes that NOx evolution by the nr1 mutant was due to nonenzymic, chemical reactions between plant metabolites and accumulated NO2 and/or decomposition of nitrous acid. Nonenzymic NOx evolution probably also occurs in wild type to a degree but could be easily masked by high rates of the enzymic process.  相似文献   

12.
Nitric oxide (NO) plays an important role in a number of physiologic processes. Evidence exists that NO, which stimulates soluble guanylate cyclase and enhances cyclic guanosine monophosphate (cGMP) levels, may inhibit platelet activation. In contrast, during platelet activation induced by different agonists, synthesis of NO in platelets occurs. In these studies, production of the stable end-products of NO-nitrite and nitrate (NOx) in human platelets, stimulated by different doses of lipopolysaccharide from Proteus mirabilis (LPS; endotoxin), has been evaluated. LPS is a weak platelet agonist that may activate various steps of platelet activation with the generation of reactive oxygen species. The mechanism of platelet activation induced by the endotoxin is not known. The aim of the present study was to measure the level of nitrite and NOx in blood platelets treated with LPS and to examine the level of nitrotyrosine in platelet proteins caused by LPS. Our results show that LPS at a low concentration (6.8 ng/ml) caused a decrease (approximately 80%) in the NOx level, whereas at higher concentrations (13.6 and 25 ng/ml) it induced an increase in the NOx level (approximately 210% and 260%, respectively). Our results indicate that LPS, like other agonists (thrombin, platelet-activating factor), can stimulate NO production in platelets. After incubating platelets with LPS, we also observed a distinct increase in platelet protein nitration (3-nitrotyrosine).  相似文献   

13.
The mechanism of anaerobic reduction of NO2? to N2O in a photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans, was investigated. With ascorbate-reduced phenazine methosulfate (PMS) as the electron donor, the nitrite reductase of this photodenitrifier reduced NO2? to NO and a trace amount of N2O. With dithionite-reduced benzyl viologen as the electron donor, the major product of NO2? reduction was NH2OH, and a trace amount of N2O was also produced. The nitrate reductase itself had no NO reductase activity with ascorbate-reduced PMS. It was concluded that the essential product of NO2? reduction by the purified nitrite reductase is NO. Chromatophore membranes stoichiometrically produced N2O from NO2? with any electron donor, such as dithionite-redduced benzyl viologen, ascorbate-reduced PMS or NADH/FMN. The membranes also contrained activity of NO reduction of N2O with either ascorbate-reduced PMS or duroquinol. The NO reductase activity with duroquinol was inhibited by antimycin A. Stoichiometric production of N2O from N2? also was observed in the reconstituted NO2? reduction system which contained the cytochrome bc1 complex, cytochrome c2, the nitrite reductase and duroquinol as the electron donor. The preparation of the cytochrome bc1 complex itself contianed NO reductase activity. From these results the mechanism of NO2? reduction to N2O in this photodenitrifier was determined as the nitrite reductase reducing NO2? to NO with electrons from the cytochrome bc1 complex, and NO subsequently being reduced, without release, to N2O with electrons from the cytochrome bc1 complex by the NO reductase, which is closely associated with the complex.  相似文献   

14.
The effect of snow cover on surface-atmosphere exchanges of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide (NO2); note, here ‘NO2’ is used as surrogate for a series of oxidized nitrogen gases that were detected by the used monitor in this analysis mode) was investigated at the high elevation, subalpine (3,340 m asl) Soddie site, at Niwot Ridge, Colorado. Vertical (NO + NO2) concentration gradient measurements in interstitial air in the deep (up to ~2.5 m) snowpack were conducted with an automated sampling and analysis system that allowed for continuous observations throughout the snow-covered season. These measurements revealed sustained, highly elevated (NO + NO2) mixing ratios inside the snow. Nitrogen oxide concentrations were highest at the bottom of the snowpack, reaching levels of up to 15 ppbv during mid-winter. Decreasing mixing ratios with increasing distance from the soil–snow interface were indicative of an upwards flux of NO from the soil through the snowpack, and out of the snow into the atmosphere, and imply that biogeochemical processes in the subnival soil are the predominant NO source. Nitrogen dioxide reached maximum levels of ~3 ppbv in the upper layers of the snowpack, i.e., ~20–40 cm below the surface. This behavior suggests that a significant fraction of NO is converted to NO2 during its diffusive transport through the snowpack. Ozone showed the opposite behavior, with rapidly declining levels below the snow surface. The mirroring of vertical profiles of ozone and the NO2/(NO + NO2) ratio suggest that titration of ozone by NO in the snowpack contributes to the ozone reaction in the snow and to the ozone surface deposition flux. However, this surface efflux of (NO + NO2) can only account for a minor fraction of ozone deposition flux over snow that has been reported at other mid-latitude sites. Neither (NO + NO2) nor ozone levels in the interstitial air showed a clear dependence on incident solar irradiance, much in contrast to observations in polar snow. Comparisons with findings from polar snow studies reveal a much different (NO + NO2) and ozone snow chemistry in this alpine environment. Snowpack concentration gradients and diffusion theory were applied to estimate an average, wintertime (NO + NO2) flux of 0.005–0.008 nmol m−2 s−1, which is of similar magnitude as reported (NO + NO2) fluxes from polar snow. While fluxes are similar, there is strong evidence that processes controlling (NO + NO2) fluxes in these environments are very different, as subnivial soil at Niwot Ridge appears to be the main source of the (NO + NO2) efflux, whereas in polar snow (NO + NO2) has been found to be primarily produced from photochemical de-nitrification of snow nitrate.  相似文献   

15.
A pure culture of the obligately lithoautotrophic ammonia-oxidizer Nitrosomonas eutropha was grown in a laboratory-scale bioreactor with complete biomass retention. The air supply was supplemented with nitrogen dioxide (NO2; 25 or 50 ppm) or nitric oxide (NO; 25 or 50 ppm). Compared to cultures grown without these nitrogenous oxides, the addition of NO2 or NO to the culture resulted in a significant increase of the nitrification rate, specific activity of ammonia oxidation, growth rate, and maximum cell densities. In contrast, the growth yield slightly decreased in the presence of NO or NO2. Maximum cell densities of about 2 × 1010 cells ml–1 and a maximum nitrification rate of about 221 mmol NH4 + l–1 day–1 were obtained after 3 weeks in the presence of 50 ppm NO2. Furthermore, in the stationary phase about 50% of the nitrite produced was aerobically denitrified to dinitrogen (N2) and traces of nitrous oxide (N2O). When cells were supplemented with NO, a high rate of aerobic denitrification occurred only during the first days of the exponential growth phase. Received: 12 May 1997 / Accepted: 10 November 1997  相似文献   

16.
Cells of Nitrosomonas eutropha grown under anoxic conditions with hydrogen as electron donor and nitrite as electron acceptor were initially unable to oxidize ammonia (ammonium) and hydroxylamine when transferred to oxic conditions. Recovery of ammonia and hydroxylamine oxidation activity was dependent on the presence of NO2. Under oxic conditions, without addition of NO2, ammonia consumption started after 8 – 9 days, and small amounts of NO and NO2 were detectable in the gas atmosphere. Removing these nitrogen oxides by intensive aeration, ammonia oxidation activity decreased and broke off after 15 days. Addition of gaseous NO2 (25 ppm) led to a fast recovery of ammonia oxidation (3 days). Simultaneously, the arrangement of intracytoplasmic membranes (ICM) changed from circular to flattened vesicles, the protein pattern revealed an increase in the concentration of a 27 and a 30 kDa polypeptide, and the cytochrome c content increased significantly.  相似文献   

17.
The dose- and time-response effects of sequential 3 h+3 h NO→NO2 day time exposures [0–9 μl l?1 (ppm) NO, 0–7.5 μl l?1 NO2] followed by 3 h+3 h NO→NO2 night-time exposures (0–9.5 μl l?1 NO, 0–9 μl l?1 NO2) on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian (‘Rachovo’) half-sib families and for two populations, one from the FRG (‘Westerhof’) and one from the GDR (‘Schmiedefeld’) of Norway spruce [Picea abies (L.) Karst.], all in their 4th growing season. In a second exposure series the exposure sequence was reversed. None of the treatments induced needle scorching. The higher NOx (NO or NO2) concentrations reduced photosynthesis and transpiration within 1 h. The physiology of the different spruce types was affected significantly differently, the most sensitive spruce having its photosynthesis suppressed 6.6 times and its transpiration 5.5 times more than the most tolerant. ‘Westerhof’ was more sensitive to NO2 than the average ‘Rachovo’ half-sibs. The gradients of different photosynthesis and transpiration sensitivities among the half-sibs (and ‘Westerhof’) demonstrated a significant, positive, mutual correlation, but significant negative correlations with the gradient of novel decline symptoms among their parents growing in Danish forests. The relative photosynthesis and transpiration sensitivies may thus serve as diagnostic parameters for laboratory selection of the most resistant trees to novel spruce decline. The average NO2 flux density was three times larger than the average NO flux density. Only for NO2 and in light was stomatal NOx uptake larger than the total NOx uptake. Both night transpiration and dark respiration were stimulated by high concentrations of night NOx, preceded by day NOx exposures.  相似文献   

18.

Background

Low Emission Zones (LEZs) are areas where the most polluting vehicles are restricted from entering. The effectiveness of LEZs to lower ambient exposures is under debate. This study focused on LEZs that restricted cars of Euro 1 standard without appropriate retrofitting systems from entering and estimated LEZ effects on NO2, NO, and NOx ( = NO2+NO).

Methods

Continuous half-hour and diffuse sampler 4-week average NO2, NO, and NOx concentrations measured inside and outside LEZs in 17 German cities of 6 federal states (2005–2009) were analysed as matched quadruplets (two pairs of simultaneously measured index values inside LEZ and reference values outside LEZ, one pair measured before and one after introducing LEZs with time differences that equal multiples of 364 days) by multiple linear and log-linear fixed-effects regression modelling (covariables: e.g., wind velocity, amount of precipitation, height of inversion base, school holidays, truck-free periods). Additionally, the continuous half-hour data was collapsed into 4-week averages and pooled with the diffuse sampler data to perform joint analysis.

Results

More than 3,000,000 quadruplets of continuous measurements (half-hour averages) were identified at 38 index and 45 reference stations. Pooling with diffuse sampler data from 15 index and 10 reference stations lead to more than 4,000 quadruplets for joint analyses of 4-week averages. Mean LEZ effects on NO2, NO, and NOx concentrations (reductions) were estimated to be at most −2 µg/m3 (or −4%). The 4-week averages of NO2 concentrations at index stations after LEZ introduction were 55 µg/m3 (median and mean values) or 82 µg/m3 (95th percentile).

Conclusions

This is the first study investigating comprehensively the effectiveness of LEZs to reduce NO2, NO, and NOx concentrations controlling for most relevant potential confounders. Our analyses indicate that there is a statistically significant, but rather small reduction of NO2, NO, and NOx concentrations associated with LEZs.  相似文献   

19.
Reduced nitric oxide (NO) production and bioactivity is a major contributor to endothelial dysfunction. Animal data suggest that improvements in endothelial function in response to aerobic exercise training may depend on the duration of the training program. However, no studies have examined changes in NO (as assessed by the major NO metabolites, nitrate and nitrite, NOx) after long-term training in humans. In addition, aging may impair the ability of the vasculature to increase NO with exercise. Thus, we determined whether 24 weeks of aerobic exercise training increases plasma NOx levels in sedentary older adults. We also examined changes in forearm blood flow (FBF) at rest and during reactive hyperemia as a measure of vasomotor function. Plasma NOx levels were measured in 82 men and women using a modified Griess assay. FBF was assessed in a subset of individuals (n = 15) using venous occlusion plethysmography. After 24 weeks of exercise training, there were significant improvements in maximum oxygen consumption, HDL cholesterol, triglycerides, and body fat. Changes in plasma NOx levels ranged from ?14.83 to +16.69 μmol/L; however, the mean change overall was not significant (?0.33 ± 6.30 μmol/L, p = 0.64). Changes in plasma NOx levels were not associated with age, gender, race, HDL cholesterol, triglycerides, body weight, body fat, or maximal oxygen consumption. There were also no significant changes in basal FBF, peak FBF, hyperemic response, total hyperemic flow, or minimum forearm vascular resistance with exercise training. In conclusion, improvements in plasma NOx levels and FBF are not evident after long-term training in older adults.  相似文献   

20.

Background

Nitrate and nitrite (jointly referred to herein as NOx) are ubiquitous environmental contaminants to which aquatic organisms are at particularly high risk of exposure. We tested the hypothesis that NOx undergo intracellular conversion to the potent signaling molecule nitric oxide resulting in the disruption of endocrine-regulated processes.

Methodology/Principal Findings

These experiments were performed with insect cells (Drosophila S2) and whole organisms Daphnia magna. We first evaluated the ability of cells to convert nitrate (NO3 ) and nitrite (NO2 ) to nitric oxide using amperometric real-time nitric oxide detection. Both NO3 and NO2 were converted to nitric oxide in a substrate concentration-dependent manner. Further, nitric oxide trapping and fluorescent visualization studies revealed that perinatal daphnids readily convert NO2 to nitric oxide. Next, daphnids were continuously exposed to concentrations of the nitric oxide-donor sodium nitroprusside (positive control) and to concentrations of NO3 and NO2 . All three compounds interfered with normal embryo development and reduced daphnid fecundity. Developmental abnormalities were characteristic of those elicited by compounds that interfere with ecdysteroid signaling. However, no compelling evidence was generated to indicate that nitric oxide reduced ecdysteroid titers.

Conclusions/Significance

Results demonstrate that nitrite elicits developmental and reproductive toxicity at environmentally relevant concentrations due likely to its intracellular conversion to nitric oxide.  相似文献   

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