El proceso de descentralización de la educación en Argentina. Un caso: La provincia de Buenos Aires Formichella, Maria Marta; Rojas, Mara Carolina En el contexto de las transformaciones ocurridas durante las décadas `80 - `90 en América Latina, cabe destacar lo sucedido en el ámbito de la educación pública. En este trabajo se analiza el proceso de descentralización educativa llevado a cabo en la República Argentina, haciendo hincapié en el caso de la Provincia de Buenos Aires.

Reyes's syndrome, encephalopathy, hyperammonemia and acetyl salicylic acid ingestion in a city hospital of Buenos Aires, Argentina Lemberg, Abraham; Fernández, María A.; Coll, Carlos; Rosello, Diego O.; Romay, Salvador; Perazzo, Juan C.; Filinger, Ester Julia Twelve cases of Reye's syndrome are presented with different degrees of encephalopathy, hyperammonemia and hypoglycemia; associated to acetyl salicylic acid (ASA) ingestion. The aim of the present retrospective study was to describe our experience in selected patients with Reye's syndrome associated to the ASA ingestion and to underline the influence of hyperammonemia on Reye's encephalopathy. All the cases presented moderate hyperbilirubinemia, elevated alanine aminotransferase, aspartate aminotransferase with an average of 302±205 UI/L and 285±149 UI/L respectively. Arterial blood ammonia averaged 172.4±71.3 μmol/L and glycaemia averaged 35.2±17.0 mg/ dl. A high mortality was found in our series (41.7%). Considering that encephalopathy is the leading syndrome in these cases, the influence of ammonia on brain tissue was described. Glutamate is an excitotoxic neurotransmitter, capable to produce neuron and astrocyte damage and apoptosis. The presence of ASA could cause the onset of the mitochondrial permeability transition and the mitochondrial swelling in the astrocyte, leading to hyperammonemia. In Reye's syndrome, hyperammonemia and perhaps the increase of glutamate are the leading factors in the mechanism of brain damage and encephalopathy. Aspirin must be carefully administrated and controlled by professionals. Furthermore, parents must be informed about the risks in the use of this drug in children.

Análisis de la coherencia en los textos producidos en clases de Física en el nivel polimodal Domínguez, María Alejandra El trabajo que se comunica forma parte de una investigación más amplia que se centra en el estudio de la negociación de significados en clases de Física, tomando como indicadores los discursos argumentativos que se construyen en ese ámbito. La semiótica es una herramienta que permite analizar, a través de signos, la significación de todo lo que nos rodea. En particular, el estudio de la coherencia es uno de los indicadores para identificar modos de comunicación; no sólo interesa la coherencia manifiesta en el texto, sino también la que es recuperable mediante inferencias. Dado que la coherencia es la organización mínima del texto que permite acceder a otras interpretaciones, se supone que los alumnos deben ser capaces de elaborar discursos argumentativos coherentes para que el docente pueda tener éxito al interpretar el significado de los mismos. Se aspira a indagar si los alumnos son capaces de distinguir la organización global del texto base y elaborar un texto (resumen) que dé cuenta de las macroestructuras pertinentes. Es decir, derivar, por medio de las macrorreglas, proposiciones más generales. Los alumnos que no conseguieran recortar la información que no resulta prescindible, dejarían la incertidumbre en cuanto a si se ha podido captar la estructura global del texto; no se evidencia la utilización de las reglas de construcción y generalización y se encuentran ciertas incoherencias a lo largo de las producciones que se manifiestan en un incorrecto manejo de los mecanismos que operan en la estructura lineal. Se podría pensar en la posibilidad de trabajar la utilización de las reglas y la actividad de resumir, encontrar la estructura global de un texto y expresarla en un nuevo texto coherente.

¿Puede aprenderse química orgánica en la universidad presenciando una clase expositiva?; Can students learn organic chemistry in university being present at a lecture? Lorenzo, Maria Gabriela; Salerno, Alejandra; Blanco, María de Las Mercedes A study about the effect of the teacher´s lectures on students’ possibilities for solving some exercises of organic chemistry is presented. An investigation in context to 455 freshmen students with pencil-and-paper tasks of different complexity and different requirements was performed. The experimental design included the following independent variables: Condition of answering (previous, short-time, long-time), type of question (declarative concept, relational concept, technical and strategical procedure) and chemical contents (conformational analyses, nuclear magnetic resonance). The data were analyzed qualitatively and quantitatively. The responses were classified like correct (from the chemical point of view), incorrect (incomplete, regular, wrong) and not answered. Our results demonstrate that teacher participation is irreplaceable to promote student learning. This effect is not only visible in an increase of correct answers, but on the increase of total responses. Lectures affects principally on the using of technical language, the respect of conventions of chemical notations and on procedures for solving tasks.

New Fluorinated Pyrazol and Uracil Derivatives: Synthesis and Biological Activity Fustero, Santos; Sanz-Cervera, Juan F.; Simón-Fuentes, Antonio; Román, Raquel; Catalán, Silvia; Murguia, Marcelo Cesar Both fluorinated pyrazoles and uracils are compounds that display very interesting biological activity. This chapter reviews recent work or our group in the development of synthetic strategies for the preparation of new examples of these two kinds compounds.

Miedo, (in)seguridad y violencia en el entramado social Capdevielle, Julieta María Desde hace algunos  años el concepto de (in)seguridad cobra relevancia en las agendas mediáticas, y se convierte en una de las preocupaciones más importantes de la población.  Los lugares de enunciación vinculados a las "seguridad" operan, hoy por hoy, como una eficiente maquinaria de producción de visibilidad, credibilidad y, lo fundamental, agenda para el debate. Es así que, las encuestas revelan que, en la actualidad, la primera demanda de las poblaciones de Argentina, México, Brasil, Venezuela y Colombia es, precisamente, la de seguridad cotidiana. En Argentina, específicamente, la triada violencia, seguridad e inseguridad se reactualiza y cobra nuevos sentidos no sólo en los medios masivos de comunicación sino también por la demanda concreta de seguridad a través de prácticas y discursos de un sector de la sociedad.  A lo largo del presente trabajo buscamos analizar cómo ese discurso dominante sobre la inseguridad se filtra en el entramado simbólico de la sociedad y se transforma sedimentándose como sentido común. En esta reflexión nos  interrogamos no sólo por el sentido que se le otorga al concepto de seguridad, sino también por las prácticas concretas que conlleva o produce pensar en términos de esa seguridad. 

Dysregulation of stromal derived factor 1/CXCR4 axis in the megakaryocytic lineage in essential thrombocythemia Salim, Juan Pablo; Goette, Nora Paula; Lev, Paola Roxana; Chazarreta, Carlos Daniel; Heller, Paula Graciela; Alvarez, Clarisa Ester; Molinas, Felisa Concepción; Marta, Rosana Fernanda This study investigated the involvement of chemokines including stromal derived factor 1 (SDF-1), interleukin 8 (IL-8), growth-related oncogene alpha (GRO-a) and their receptors, CXCR4, CXCR2 and CXCR1 in essential thrombocythemia (ET), a chronic myeloproliferative disease characterized by megakaryocytic hyperplasia and high platelet count. Fifty-three ET patients were studied. Plasma levels of SDF-1, IL-8 and GRO-a, evaluated by enzymelinked immunosorbent assay, and flow cytometric analysis of CXCR1 and CXCR2 on the platelet membrane, were found to be normal in ET patients. CXCR4 expression on platelet surface aswell as platelet CXCR4mRNAdetected by real-time reverse transcription polymerase chain reaction, were decreased. Platelet CXCR4 internalization rate was normal while SDF-1-induced platelet aggregation was delayed, decreased or absent. Immunohistochemical staining revealed that megakaryocytes were also affected. CXCR4 decrease was not observed either in peripheral white blood cells or in circulating CD34+ precursors. These results show that CXCR4 is decreased in the megakaryocytic lineage in ET, mainly due to a reduced CXCR4 production, and an abnormal platelet response to SDF-1. This report is the first to describe platelet and megakaryocytic CXCR4 deficiency in a human disease and the presence of this abnormality in a megakaryocytic-related illness highlights the important role of SDF-1/CXCR4 axis in platelet development.

Detection of unintended stress effects based on a metabonomic study in tomato fruits after treatment with carbofuran pesticide. Capabilities of MCR-ALS applied to LC-MS three-way data arrays Sánchez Pérez, I.; Culzoni, Maria Julia; Siano, Gabriel German; Gil García, Magdalena; Goicoechea, Hector Casimiro; Martínez Galera, M. A chemometric strategy based on multivariate curve resolution and alternating least-squares (MCR-ALS) applied to LC-MS three-way data arrays has been developed to perform a metabonomic study in tomato (Lycopersicon esculentum) fruits (cultivar Rambo) following treatment with carbofuran. This methodology has proved to be adequate for the detection of unintended stress effects due to the previous treatment with this pesticide. MCR-ALS was performed on augmented matrices built with the LC-MS three-way data obtained from treated and nontreated samples through the sampling time. The strategy allowed us to obtain the concentration and spectra profiles of the main components (previously estimated with the SVD algorithm) from samples treated with pesticide as well as from blank samples, showing how they vary with time after plants treatment with the pesticide. In addition, a simple resolved mass spectrum was obtained corresponding to the peaks of a particular component in all matrices, thus avoiding ambiguity in the compound identity assignment. Different time profiles were found for some metabolites in treated and nontreated samples, which demonstrate that the presence of pesticide causes changes thorough time in the behavior of certain endogenous tomato metabolites as a result of physiological stress

Interactions between milk whey protein and polysaccharide in solution Perez, Adrián Alejandro; Carrara, Carlos Roberto; Carrera Sánchez, Cecilio; Rodríguez Patino, Juan M.; Santiago, Liliana Gabriela In this work we have studied the interactions between a commercial whey protein concentrate (WPC) and two anionic polysaccharides (sodium alginate, SA, and λ-carrageenan, λ-C) in the aqueous phase. The concentration of WPC at 1.0% and the pH 7.0 of the aqueous phase were maintained constant, while polysaccharides (PS) were evaluated within a 0.0–1.0% concentration range. Interactions between WPC and PS in the aqueous phase were analysed by fluorescence spectroscopy, absorption spectroscopy in the presence of methylene blue (MB), and confocal laser scanning microscopy. The results from these methodologies revealed differences in the molecular dynamics of mixed systems. The nature of the interactions between WPC and PS depended on the PS type, its relative concentration in the aqueous phase and also on the two WPC fractions. Whey protein concentrate/sodium alginate (WPC/SA) mixed systems were distinguished by a tendency to protein aggregation in the aqueous phase and their segregation into separated microdomains. On the other hand, WPC/λ-carrageenan (WPC/λ-C) mixed systems showed a high degree of attractive interactions over the whole range of concentrations. The ultrastructure revealed the existence of hybrid macromolecular entities (biopolymer network). Interaction of WPC and polysaccharide in the aqueous phase has an effect on the adsorption of mixed systems at the air–water interface and on their foaming characteristics.

The cytochrome ba complex from the thermoacidophilic crenarchaeote Acidianus ambivalens is an analog of bc1 complexes Bandeiras, Tiago M.; Refojo, Patricia N.; Todorovic, Smilja; Murgida, Daniel Horacio; Hildebrandt, Peter; Bauer, Christian; Pereira, Manuela M.; Kletzin, Arnulf; Teixeira, Miguel A novel cytochrome ba complex was isolated from aerobically grown cells of the thermoacidophilic archaeon Acidianus ambivalens. The complex was purified with two subunits, which are encoded by the cbsA and soxN genes. These genes are part of the pentacistronic cbsAB-soxLN-odsN locus. The spectroscopic characterization revealed the presence of three low-spin hemes, two of the b and one of the as-type with reduction potentials of + 200, + 400 and + 160 mV, respectively. The SoxN protein is proposed to harbor the heme b of lower reduction potential and the heme as, and CbsA the other heme b. The soxL gene encodes a Rieske protein, which was expressed in E. coli; its reduction potential was determined to be + 320 mV. Topology predictions showed that SoxN, CbsB and CbsA should contain 12, 9 and one transmembrane α-helices, respectively, with SoxN having a predicted fold very similar to those of the cytochromes b in bc1 complexes. The presence of two quinol binding motifs was also predicted in SoxN. Based on these findings, we propose that the A. ambivalens cytochrome ba complex is analogous to the bc1 complexes of bacteria and mitochondria, however with distinct subunits and heme types.

pH-dependent mechanism of nitric oxide release in nitrophorins 2 and 4 Swails, Jason M.; Meng, Yilin; Walker, F. Ann; Marti, Marcelo Adrian; Estrin, Dario Ariel; Roitberg, Adrián Nitrophorins are NO carrier proteins that transport and release NO through a pH-dependent conformational change. They bind NO tightly in a low pH environment and release it in a higher pH environment. Experimental evidence shows that the increase in the NO dissociation equilibrium constant, K d, is due mainly to an increase in the NO release rate. Structural and kinetic data strongly suggest that NPs control NO escape by modulating its migration from the active site to the solvent through a pH-dependent conformational change. NP2 and NP4 are two representative proteins of the family displaying a 39% overall sequence identity, and interestingly, NP2 releases NO slower than NP4. The proposal that NPs' NO release relies mainly on the NO escape rate makes NPs a very peculiar case among typical heme proteins. The connection between the pH-dependent conformational change and ligand release mechanism is not fully understood and the structural basis for the pH induced structural transition and the different NO release patterns in NPs are unresolved, yet interesting issues. In this work, we have used state of the art molecular dynamics simulations to study the NO escape process in NP2 and NP4 in both the low and high pH states. Our results show that both NPs modulate NO release by switching between a "closed" conformation in a low pH environment and an "open" conformation at higher pH. In both proteins, the change is caused by the differential protonation of a common residue Asp30 in NP4 and Asp29 in NP2, and the NO escape route is conserved. Finally, our results show that, in NP2, the conformational change to the "open" conformation is smaller than that for NP4 which results in a higher barrier for NO release.

SK2 channels are required for function and long-term survival of efferent synapses on mammalian outer hair cells Murthy, Vidya; Maison, Stéphane F.; Taranda, Julian; Haque, Nadeem; Bond, Chris T.; Elgoyhen, Ana Belen; Adelman, John P.; Liberman, M. Charles; Vetter, Douglas E. Cochlear hair cells use SK2 currents to shape responses to cholinergic efferent feedback from the brain. Using SK2-/- mice, we demonstrate that, in addition to their previously defined role in modulating hair cell membrane potentials, SK2 channels are necessary for long-term survival of olivocochlear fibers and synapses. Loss of the SK2 gene also results in loss of electrically driven olivocochlear effects in vivo, and down regulation of ryanodine receptors involved in calcium-induced calcium release, the main inducer of nAChR evoked SK2 activity. Generation of double-null mice lacking both the α10 nAChR gene, loss of which results in hypertrophied olivocochlear terminals, and the SK2 gene, recapitulates the SK2-/- synaptic phenotype and gene expression, and also leads to down regulation of α9 nAChR gene expression. The data suggest a hierarchy of activity necessary to maintain early olivocochlear synapses at their targets, with SK2 serving an epistatic, upstream, role to the nAChRs.

Role of the pre-A motif in nitric oxide scavenging by truncated hemoglobin HbN of Mycobacterium Tuberculosis Lama, Amriti; Pawarta, Sudesh; Bidon Chanal, Axel; Anand, Arvind; Gelpi, José Luis; Arya, Swati; Marti, Marcelo Adrian; Estrin, Dario Ariel; Luque, F. Javier; Dikshit, Kanak Mycobacterium tuberculosis truncated hemoglobin, HbN, is endowed with a potent nitric-oxide dioxygenase activity and has been found to relieve nitrosative stress and enhance in vivo survival of a heterologous host, Salmonella enterica Typhimurium, within the macrophages. These findings implicate involvement of HbN in the defense of M. tuberculosis against nitrosative stress. The protein carries a tunnel system composed of a short and a long tunnel branch that has been proposed to facilitate diatomic ligand migration to the heme and an unusual Pre-A motif at the N terminus, which does not contribute significantly to the structural integrity of the protein, as it protrudes out of the compact globin fold. Strikingly, deletion of Pre-A region from the M. tuberculosis HbN drastically reduces its ability to scavenge nitric oxide (NO), whereas its insertion at the N terminus of Pre-A lacking HbN of Mycobacterium smegmatis improved its nitric-oxide dioxygenase activity. Titration of the oxygenated adduct of HbN and its mutants with NO indicated that the stoichiometric oxidation of protein is severalfold slower when the Pre-A region is deleted in HbN. Molecular dynamics simulations show that the excision of Pre-A motif results in distinct changes in the protein dynamics, which cause the gate of the tunnel long branch to be trapped into a closed conformation, thus impeding migration of diatomic ligands toward the heme active site. The present study, thus, unequivocally demonstrates vital function of Pre-A region in NO scavenging and unravels its unique role by which HbN might attain its efficient NO-detoxification ability.

Flexibility study for an MSF desalination plant Tarifa, Enrique Eduardo; Franco, Samuel; Humana, Demetrio; Mussati, Sergio Fabian This work addresses a flexibility study on a multi-stage flash (MSF) desalination plant. When any plant is designed, the engineers define the design for reaching optimal operation under nominal conditions. However, uncertain variables or disturbance cannot be handled to obtain those nominal conditions. For this reason, the design contains control elements for compensating the disturbance effects. This compensation is only possible into a region defined by the characteristics of the process and the control elements. When the actual conditions are out of that region, the compensation is not enough, and the plant is not operable. A flexibility study determines the region into which the process is operable. This information can be useful for determining design modifications to improve the process flexibility. A flexibility study involves a complex mathematical model, which is even more complex for a MSF plant. To perform the task, in this work, a stationary simulator was developed for a real-world case study, and the region exploration was performed by Monte Carlo simulation. Results show, in terms of both robustness and speed of computation, that this approach can be a useful tool.

Features of spin-charge separation in the equilibrium conductance through finite rings Jimenez Rincon, Jose Julian; Aligia, Armando Ángel; Hallberg, Karen Astrid We calculate the conductance through rings with few sites L described by the t-J model, threaded by a magnetic flux Φ and weakly coupled to conducting leads at two arbitrary sites. The model can describe a circular array of quantum dots with large charging energy U in comparison with the nearest-neighbor hopping t. We determine analytically the particular values of Φ for which a depression of the transmittance is expected as a consequence of spin-charge separation. We show numerically that the equilibrium conductance at zero temperature is depressed at those particular values of Φ for most systems, in particular at half filling, which might be easier to realize experimentally.

Estructura de la vegetación y selección de hábitats reproductivos en aves del pastizal pampeano; Vegetation structure and selection of reproductive habitats by Pampas grassland birds Cozzani, Natalia Carolina; Zalba, Sergio Martín La transformación acelerada de los pastizales naturales en tierras destinadas a actividades agrícolas y ganaderas afecta de manera particular a las aves de pastizal, cuya reproducción depende de forma estricta de estos ambientes. En este trabajo estudiamos las especies de aves que anidan en el Parque Provincial Ernesto Tornquist, ubicado al sudoeste de la provincia de Buenos Aires. Durante tres temporadas reproductivas realizamos búsquedas intensivas de nidos, registramos las características de los sitios donde estaban construidos y evaluamos las preferencias de las distintas especies por sectores de pajonales cerrados (dominados por Paspalum quadrifarium y Cortaderia selloana) o por áreas de flechillar (pastizales dominados por especies de Stipa y Piptochaetium). Hallamos 214 nidos construidos en matas de pasto o en el suelo, correspondientes a 12 especies. El 76.65% de los nidos se hallaban en sectores de pajonal, pese a que los pajonales representaban solo el 7.75% del área de trabajo, lo cual refleja una preferencia significativa por estos ambientes. Resultó llamativa la abundancia reducida de nidos de especies como Ammodramus humeralis, Cistothorus platensis y Anthus correndera y la ausencia total de otras, como la perdiz colorada (Rhynchotus rufescens), todas ellas aves obligadas de pastizal, asociadas fundamentalmente a ambientes de flechillar. Nuestros resultados podrían reflejar una vulnerabilidad particular de las aves que anidan en los flechillares, los ambientes más afectados en su estructura por el efecto del pastoreo de grandes herbívoros.; Vegetation structure and selection of reproductive habitats by Pampas grassland birds: The increasing transformation of natural grasslands into agricultural fields affects grassland birds with particular severity, as their breeding success depends strictly on these habitats. This study focuses on bird species that nest in the Ernesto Tornquist Provincial Park in the southwest of Buenos Aires province (Argentina). We conducted intensive nest surveys during three reproductive seasons, recording their site characteristics and evaluating nesting preferences of needlegrass grasslands (dominated by Stipa and Piptochaetium species, "flechillares") and tussock grasslands (dominated by Paspalum quadrifarium and Cortaderia selloana). We found 214 nests, belonging to 12 species, built within grass tussocks or directly on the ground. Paspalum grasslands represent 7.75% of the surveyed area but contained 76.65% of the nests, showing a significant preference for this type of habitat. Low nest abundance of obligate grassland species, typically associated to "flechillares", e.g. Grassland Sparrow (Ammodramus humeralis), Grass Wren (Cistothorus platensis) and Correndera Pipit (Anthus correndera), and the complete absence of Red-winged Tinamou (Rhynchotus rufescens) nests, was particularly worrying. Our results may reflect the particular vulnerability of species nesting in "flechillares", a habitat the structure of which is more deeply affected by big herbivores.

Isolation of Bacteria from Remote High Altitude Andean Lakes Able to Grow in the Presence of Antibiotics Dib, Julian Rafael; Weiss, Annika; Neumann, Anna; Ordoñez, Omar Federico; Estévez, Maria Cristina; Farias, Maria Eugenia High altitude Andean lakes are placed in Puna desert over 4400 above sea level. Completely isolated, they are exposed to extreme environmental factors like high levels of salinity, UV radiation and heavy metals and low concentrations of phosphorus. Nevertheless, they are the habitat of enormous populations of three flamingo species that migrate among these Lakes. Previous reports have determined that bacteria isolated from these environments present high levels of resistance to antibiotics. The aim of this work was to determine the diversity of antibiotic resistant bacteria in water from Andean Lakes and their connection with flamingo enteric biota. Bacteria from water and birds faeces from high altitude Lakes: Laguna (L.) Aparejos, L. Negra, L. Vilama and L. Azul (all are located between 4,200 and 4,600 m altitude) were isolated by plating in five different Antibiotics (ampicillin, 100 microg ml(-1); chloramphenicol, 170 microg ml(-1); colistin , 20 microg ml(-1); erythromycin, 50 microg ml(-1) and tetracycline 50 microg ml(-1)). 56 bacteria were isolated and identified by 16 S rDNA sequencing. Antibiotic resistance profiles of isolated bacteria were determined for 22 different antibiotics. All identified bacteria were able to growth in multiple ATBs. Colistin, ceftazidime, ampicillin/sulbactam, cefotaxime, cefepime, cefalotin, ampicillin and erythromycin were the most distributed resistances among the 56 tested bacteria. The current results demonstrated that antibiotic resistance was abundant and diverse in high altitude Lakes. Also the present article indicates some useful patents regarding the isolation of bacteria able to grow in the present of antibiotics.

Addition to the knowledge of Xylaria (Xylariaceae, Ascomycota) in Santa Catarina, Southern Brazil Trierveiler Pereira, Larissa; Romero, Andrea Irene; Baltazar, Juliano Marcon; Loguercio Leite, Clarice Xylaria specimens have been collected in the State of Santa Catarina, Southern Brazil, since the 19th century, primarily by European naturalists such as Ernst Ule and Alfred Möller. Few comprehensive surveys or Xylaria collections have been made by Brazilians in the State until recently. New knowledge has been gained from the authors' recent survey and examination of specimens from the Florianópolis metropolitan area. Among the species discussed are a new species, Xylaria nigromedullosa, and eleven other species, including X. adscendens, X. allantoidea, X. anisopleura, X. comosa, X. cubensis, X. curta, X. ianthinovelutina, X. magnoliae var. microspora, X. mellissii, X. obovata, and X. telfairii. Most collections were obtained from dead wood, with a few found growing on fallen fruits. Seven species are new records from Santa Catarina and X. magnoliae is a new record for Brazil. Full descriptions, illustrations, and a key to the Xylaria collections now curated in FLOR are provided.

Involvement of nitric oxide synthase in the mechanism of histamine-induced inhibition of Leydig cell steroidogenesis via histamine receptor subtypes in Sprague-Dawley rats Mondillo, Carolina; Pagotto, Romina María del Luján; Piotrkowski, Barbara; Reche, Cecilia; Patrignani, Zoraida Judith; Cymeryng, Cora Beatriz; Pignataro, Omar Pedro The present study was conducted to shed light on the so far unexplored intracellular mechanisms underlying negative modulation of Leydig cell steroidogenesis by histamine (HA). Using the MA-10 cell line and highly purified rat Leydig cells as experimental models, we examined the effect of the amine on biochemical steps known to be modulated by HA, or involved in LH/hCG action. In agreement with previous findings, HA at 10 microM showed a potent inhibitory effect on hCG-stimulated steroid synthesis, regardless of the gonadotropin concentration used. Moreover, HA not only decreased LH/hCG-induced cAMP production but also steroid synthesis stimulated by the permeable cAMP analog dibutyryl cAMP (db-cAMP). Considering the post-cAMP sites of HA action, it is shown herein that HA markedly inhibited db-cAMP-stimulated acute regulatory (STAR) protein expression, as well as steps catalyzed by P450-dependent enzymes, mainly the conversion of cholesterol to pregnenolone by cholesterol side-chain cleavage enzyme (CYP11A). The antisteroidogenic action of HA was blocked by addition of the PLC-inhibitor U73122, and HA significantly augmented IP3 production, suggesting a major role for the PLC/IP3 pathway in HA-induced inhibition of Leydig cell function. Finally, HA increased nitric oxide synthase (NOS) activity, and the NOS inhibitor L-N(G)-nitro-arginine methyl ester (L-NAME) markedly attenuated the effect of the amine on steroid synthesis. On the basis of our findings, HA antagonizes the gonadotropin action in Leydig cells at steps both pre- and post-cAMP formation. NOS activation is the main intracellular mechanism by which HA exerts its antisteroidogenic effects.

Photocatalytic degradation of Dichloroacetic acid: a kinetic study with a mechanistically based reaction model Ballari, Maria de Los Milagros; Alfano, Orlando Mario; Cassano, Alberto Enrique In the present work, a study of the reaction kinetics of the photocatalytic degradation of dichloroacetic acid (DCA) employing UV radiation and titanium dioxide suspensions is reported. This study involved the development of a kinetic model from a proposed complete reaction sequence and estimation of the kinetic parameters from experimental data. The experimental data were obtained using a perfect mixed photoreactor, because the operating conditions were chosen in compliance with restrictive conditions established in a previous work in which the possibility of mass-transfer limitations in slurry reactors was investigated. The significant variables in this study were (1) the initial DCA concentration, (2) the catalyst loading, and (3) the light intensity. Simulation results from the complete reactor mass balance, including radiation transport in the bulk and resistances inside the catalytic particle agglomeration, are in good agreement with  experiments, which provides confidence in the estimation of the kinetic parameters within the range of the explored variables.