Browsing by Subject "NO"
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Item Amino acids, polyamines, and nitric oxide synthesis in the ovine conceptus(Texas A&M University, 2005-08-29) Kwon, Hyuk JungThe objective of this study was to determine concentrations of amino acids and polyamines as well as nitric oxide (NO) and polyamine synthesis in the ovine conceptus (embryo/fetal and associated placental membrane). Ewes were hysterectomized on Days 30, 40, 60, 80, 100, 120, or 140 of gestation to obtain allantoic and amniotic fluids, intercotyledonary placenta, placentomes and uterine endometrium for the analyses. Alanine, citrulline plus glutamine accounted for about 80% of total α-amino acids in allantoic fluid during early gestation. Serine (16.5 mM) contributed about 60% of total α-amino acids in allantoic fluid on Day 140 of gestation. Maximal ornithine decarboxylase (ODC) and arginase activities and highest rates of polyamine and NO synthesis occured in all tissues on Day 40 of gestation. In ovine allantoic and amniotic fluids, polyamines were most abundant during early (Days 40-60) and late (Days 100-140) gestation, respectively. Activity of guanosine 5??-triphosphate-cyclohydrolase I (GTP-CH), and concentrations of NOS cofactors, tetrahydrobiopterin (BH4) and NADPH (nicotinamide adenine dinucleotide), peaked on Day 40 of gestation in placental and endometrial tissues. In these tissues, NO synthesis was positively correlated with total NOS activity, GTP-CH activity, and concentrations of BH4 and NADPH. The physiological significance of these changes was manifested by undernutrition-induced intrauterine growth retardation (IUGR). Maternal undernutrition (50% of National Research Council nutrient requirements) reduced concentrations of total α-amino acids in fetal plasma and fluids, and retarded fetal growth at both mid (Day 78) and late (Day 135) gestation. Concentrations of polyamines in fetal fluids were lower in underfed ewes than in control-fed ewes. Realimentation of underfed ewes between Days 78 and 135 of gestation increased concentrations of total α-amino acids and polyamines in fetal plasma and fluids, when compared with non-realimented ewes. Results of these studies demonstrate metabolic coordination among the several integrated pathways to enable high rates of polyamine and NO synthesis in the placenta and endometrium during early pregnancy. Collectively, our findings may have important implications for both IUGR and fetal origins of adult disease.Item Astrocyte-derived nitric oxide in manganese neurotoxicity: from cellular and molecular mechanisms underlying selective neuronal vulnerability in the basal ganglia to potential therapeutic modalities(Texas A&M University, 2007-04-25) Liu, XuhongChronic exposure to manganese (Mn) causes the neurodegenerative movement disorder, manganism. A mouse model was developed to elucidate mechanisms involved in the etiology and progression of injury. Twelve-week old female C57Bl/6J mice were exposed to MnCl2 (100 mg/kg/day) by oral gavage daily for 8 weeks. After the experiment striatal dopamine (DA) content was decreased with the manifestation of hypoactivity. A distinct population of neurons was vulnerable to the effects of Mn, including enkephalin (ENK)-positive projection neurons, interneurons expressing neuronal nitric oxide synthetase (nNOS/NOS1), and choline acetyltransferase (ChAT)-expressing interneurons. Activation of surrounding astrocytes occurred with expression of inducible nitric oxide synthase (iNOS/NOS2) and production of nitric oxide (NO)/peroxynitrite (ONOO-). Activated astrocytes were detected primarily near the microvasculature in both the striatum and globus pallidus (GP). It is suggested that Mn exposure may damage the blood-brain barrier (BBB) and induce astrocytosis and NOS2 expression, subsequent NO production may cause the death of adjacent neurons. This hypothesis was also tested in an in vitro co-culture model. Differentiated pheochromocytoma cells (PC12 cells) were co-cultured with primary astrocytes and exposed to Mn and inflammatory cytokines. Mn and cytokines induced NOS2 expression and NO production in astrocytes, which correlated with apoptosis of PC12 cells. Apoptosis of PC12 cells was prevented by overexpression of a phosphorylation-deficient mutant of I????B???? that inhibited NOS2 expression in astrocytes. It is concluded that Mn-and cytokine-dependent apoptosis in PC12 cells requires astrocyte-derived NO and nuclear factor ????B (NF-????B)-dependent expression of NOS2. To explore possible means of interdicting this inflammatory process in astrocytes, a noval pharmacologic ligands of the peroxisome proliferator-activated receptor gamma (PPAR????) agonist, 1,1-Bis(3'-indolyl)-1-(p-trifluoromethylphenyl) methane (DIM-C-pPhCF3) were used in the same co-culture system. DIM-C-pPhCF3 protected PC12 cells from apoptosis through inhibition of NOS2 expression in astrocytes after Mn and cytokines exposure. By contrast, the PPAR???? antagonist, 2-chloro-5-nitrobenzanilide (GW9622), had the opposite effect, increasing both NO production in astrocytes and neuronal injury. It is concluded that PPAR???? is involved in the regulation of NOS2 expression in astrocytes and that agonists of PPAR???? may represent a potential treatment method for Mn neurotoxicity.Item Beneficial effects of dietary L-arginine supplementation to diabetic rats(Texas A&M University, 2004-09-30) Kohli, RiplaDiabetic rats exhibit decrease in plasma arginine, NO synthesis and tetrahydrobiopterin in endothelial cells (EC). Treatment with L-arginine may be beneficial for enhancing NO synthesis in diseases associated with endothelial dysfunction. However, little is known about the mechanism responsible for the stimulatory effect of arginine on endothelial NO synthesis. We hypothesized that dietary arginine supplementation increases BH4 for NO synthesis in EC of diabetic rats, thereby preventing endothelial dysfunction. In experiment I, streptozotocin (STZ) induced-diabetic male Sprague Dawley (SD) rats (a model of type-I diabetes) were individually pair-fed a casein-based diet on the basis of feed intake (per kg body weight) of non-diabetic SD rats. Addition of arginine-HCl or alanine to drinking water for the rats were adjusted daily to ensure isonitrogenous provision per kg body weight. In non-diabetic rats, arginine supplementation increased plasma arginine (144%), plasma insulin (44%), EC arginine (88%), EC BH4 (106%) and EC NO synthesis (80%), compared with alanine treatment. In diabetic rats, arginine supplementation reduced body weight loss (36%), and plasma glucose (54%), and increased plasma arginine (110%), plasma insulin (209%), EC arginine (173%), EC BH4 (128%) and EC NO synthesis (125%), compared with alanine treatment. In experiment II, male Zucker diabetic fatty (ZDF) rats (a model of type-II diabetes) were individually pair-fed a Purina 5008 diet on the basis of feed intake by alanine-treated diabetic rats (per kg body wt). Addition of arginine-HCl or alanine to drinking water for the rats was adjusted daily to ensure isonitrogenous provision per kg body weight. Arginine supplementation to ZDF rats did not affect plasma glucose and insulin, reduced epidididmal fat (30%), abdominal fat (43%) and body weight gain (18%), and increased plasma arginine (273%), EC arginine (197%), EC BH4 (120%) and EC NO synthesis (122%), compared with alanine-treated ZDF rats. These results show that dietary L-arginine supplementation increases BH4 and NO synthesis in EC of both STZ-diabetic and ZDF rats. Strikingly, arginine treatment prevented hyperglycemia in STZ-diabetic SD rats and reduced obesity in ZDF rats. Collectively, results demonstrate that oral administration of arginine is beneficial for both type-I and type-II diabetic rats.Item NOx reduction with the use of feedlot biomass as a reburn fuel(2009-05-15) Goughnour, Paul GordonCoal fired power plants produce NOx at unacceptable levels. In order to control these emissions without major modifications to the burners, additional fuel called reburn fuel is fired under rich conditions (10-30 % by heat) after the coal burners. Additional air called overfire air (about 20 % of total air) is injected in order to complete combustion. Typically reburn fuel is natural gas (NG). From previous research at TAMU, it was found that firing feedlot biomass (FB) as reburn fuel lowers the NOx emission at significant levels compared to NG. The present research was conducted to determine the optimum operating conditions for the reduction of NOx. Experiments were performed in a small scale 29.3 kW (100,000 BTU/hr) reactor using low ash partially composted FB (LA PC FB) with equivalence ratio ranging from 1 to 1.15. The results of these experiments show that NOx levels can be reduced by as much as 90% - 95 % when firing pure LA PC FB and results are almost independent of. The reburn fuel was injected with normal air and then vitiated air (12.5 % O2); further the angles of reburn injector were set normal to the main gas flow and at 45-degrees upward. For LA PC FB no significant changes were observed; but high ash PC FB revealed better reductions with 45-degrees injector and vitiated air. This new technology has the potential to reduce NOx emissions in coal fired boilers located near cattle feedlots and also relieves the cattle industry of the waste.Item Polarization modulation infrared reflection absorption spectroscopy for heterogeneous catalytic applications at elevated pressures(Texas A&M University, 2005-08-29) Ozensoy, EmrahThis dissertation focuses on bridging the pressure and complexity gap between heterogeneous catalysis and surface science by introducing new instrumental tools that can operate under catalytically relevant conditions (i.e. atmospheric pressures and temperatures higher than room temperature). Thus, some of the few detailed examples of the polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) as an in situ vibrational spectroscopic tool for the elevated-pressure investigation of gas/solid interfaces on planar single crystal model catalyst systems were presented in this work. Furthermore, for the first time in the literature, PM-IRAS technique was applied to study complex multi-component model catalyst structures exhibiting three dimensional morphologies such as metal nanoparticles deposited on a metal-oxide thin film. In order to achieve a molecular understanding of the properties of CO+NO catalytic reaction at elevated temperatures and pressures on Pd based catalysts, adsorption trends of each of the reactant molecules were studied separately on Pd (111). The adsorption properties of CO/Pd (111) and NO/Pd (111) systems both under UHV conditions and at elevated pressures were discussed in a comparative manner to highlight the pressure dependent behavioral differences between these two probe molecules by emphasizing the risks of extrapolating UHV trends to elevated pressure regimes. CO+NO reaction mechanism and kinetics was also studied on Pd (111) by in situ PM-IRAS. Factors affecting the conversion and the selectivity of the Pd (111) model catalyst towards CO+NO reaction at elevated pressures were discussed. Formation of isocyanate containing species?? was also observed and the catalytic implications of this observation was elaborated. Finally, design and characterization of a complex model catalyst composed of supported Pd nano-particles was investigated using CO adsorption at elevated pressures. Catalytic activity of the defect sites on the supported Pd nano-particles towards CO dissociation was demonstrated and compared with Pd (111) to elucidate the significance of the surface morphology of the active sites in a catalytic reaction.Item Selective catalytic reduction (SCR) of nitric oxide (NO) with ammonia over vanadia-based and pillared interlayer clay-based catalysts(Texas A&M University, 2004-09-30) Oh, Hyuk JinThe selective catalytic reduction (SCR) of nitric oxide (NO) with ammonia over vanadia-based (V2O5-WO3/TiO2) and pillared interlayer clay-based (V2O5/Ti-PILC) monolithic honeycomb catalysts using a laboratory laminar-flow reactor was investigated. The experiments used a number of gas compositions to simulate different combustion gases. A Fourier transform infrared (FTIR) spectrometer was used to determine the concentrations of the product species. The major products were nitric oxide (NO), ammonia (NH3), nitrous oxide (N2O), and nitrogen dioxide (NO2). The aim was to delineate the effect of various parameters including reaction temperature, oxygen concentration, NH3-to-NO ratio, space velocity, heating area, catalyst arrangement, and vanadium coating on the removal of nitric oxide. The investigation showed that the change of the parameters significantly affected the removals of NO and NH3 species, the residual NH3 concentration (or NH3 slip), the temperature of the maximum NO reduction, and the temperature of complete NH3 conversion. The reaction temperature was increased from the ambient temperature (25?C) to 450 ?C. For both catalysts, high NO and NH3 removals were obtained in the presence of a small amount of oxygen, but no significant influence was observed from 0.1 to 3.0% O2. An increase in NH3-to-NO ratio increased NO reduction but decreased NH3 conversions. For V2O5-WO3/TiO2, the decrease of space velocity increased NO and NH3 removals and broadened the active temperature window (based on NO > 88% and NH3 > 87%) about 50?C. An increase in heating area decreased the reaction temperature of the maximum NO reduction from 350 to 300?C, and caused the active reaction temperature window (between 250 and 400?C) to shift toward 50?C lower reaction temperatures (between 200 and 350?C). The change of catalyst arrangements resulted slight improvement for NO and NH3 removals, therefore, the change might contribute to more gas removals. The catalyst with extra vanadium coating showed higher NO reductions and NH3 conversions than the catalyst without the extra vanadium coating.Item The effects of cycle-to-cycle variations on nitric oxide (NO) emissions for a spark-ignition engine: Numerical results(Texas A&M University, 2004-11-15) Villarroel, MilivoyThe objectives of this study were to 1) determine the effects of cycle-to-cycle variations (ccv) on nitric oxide (NO) emissions, and 2) determine if the consideration of ccv affects the average NO emission as compared to the mean cycle NO emission. To carry out the proposed study, an engine simulation model was used. The simulation determines engine performance and NO emissions as functions of engine operating conditions, engine design parameters, and combustion parameters. An automotive, spark-ignition engine at part load and 1400 rpm was examined in this study. The engine cycle simulation employed three zones for the combustion process: (1) unburned gas, (2) adiabatic core region, and (3) boundary-layer gas. The use of the adiabatic core region has been shown to be especially necessary to capture the production of nitric oxides which are highly temperature dependent. Past research has shown that cyclic variations in combustion cause ccv of burn duration, ignition delay and equivalence ratio. Furthermore, literature has shown that variations of these three input parameters may be approximated by a normal frequency distribution. Using the mean and standard deviation, and a random number generator, input values were tabulated for the ignition delay, burn duration and equivalence ratio. These three input parameters were then used to simulate cyclic variations in the combustion process. Calculated results show that cyclic variations of the input parameters cause the cycle-by-cycle NO emissions to increase and decrease by as much as 59% from the mean cycle NO of 3,247 ppm. The average NO emission resulting from ccv was 4.9% less than the mean cycle NO emission. This result indicates that cyclic variations must be considered when calculating the overall NO emissions.