Unraveling efficiency-limiting processes in organic solar cells by ultrafast spectroscopy - impact of chemical structure and morphology on photophysics and efficiency

Diese Arbeit widmet sich der Untersuchung der photophysikalischen Prozesse, die in Mischungen von Elektronendonoren mit Elektronenakzeptoren zur Anwendung in organischen Solarzellen auftreten. Als Elektronendonoren werden das Copolymer PBDTTT-C, das aus Benzodithiophen- und Thienothiophene-Einheiten besteht, und das kleine Molekül p-DTS(FBTTh2)2, welches Silizium-überbrücktes Dithiophen, sowie fluoriertes Benzothiadiazol und Dithiophen beinhaltet, verwendet. Als Elektronenakzeptor finden ein planares 3,4:9,10-Perylentetracarbonsäurediimid-(PDI)-Derivat und verschiedene Fullerenderivate Anwendung. PDI-Derivate gelten als vielversprechende Alternativen zu Fullerenen aufgrund der durch chemische Synthese abstimmbaren strukturellen, optischen und elektronischen Eigenschaften. Das gewichtigste Argument für PDI-Derivate ist deren Absorption im sichtbaren Bereich des Sonnenspektrums was den Photostrom verbessern kann. Fulleren-basierte Mischungen übertreffen jedoch für gewöhnlich die Effizienz von Donor-PDI-Mischungen.rnUm den Nachteil der PDI-basierten Mischungen im Vergleich zu den entsprechenden Fulleren-basierten Mischungen zu identifizieren, werden die verschiedenen Donor-Akzeptor-Kombinationen auf ihre optischen, elektronischen und strukturellen Eigenschaften untersucht. Zeitaufgelöste Spektroskopie, vor allem transiente Absorptionsspektroskopie (TA), wird zur Analyse der Ladungsgeneration angewendet und der Vergleich der Donor-PDI Mischfilme mit den Donor-Fulleren Mischfilmen zeigt, dass die Bildung von Ladungstransferzuständen einen der Hauptverlustkanäle darstellt.rnWeiterhin werden Mischungen aus PBDTTT-C und [6,6]-Phenyl-C61-buttersäuremethylesther (PC61BM) mittels TA-Spektroskopie auf einer Zeitskala von ps bis µs untersucht und es kann gezeigt werden, dass der Triplettzustand des Polymers über die nicht-geminale Rekombination freier Ladungen auf einer sub-ns Zeitskala bevölkert wird. Hochentwickelte Methoden zur Datenanalyse, wie multivariate curve resolution (MCR), werden angewendet um überlagernde Datensignale zu trennen. Zusätzlich kann die Regeneration von Ladungsträgern durch Triplett-Triplett-Annihilation auf einer ns-µs Zeitskala gezeigt werden. Darüber hinaus wird der Einfluss des Lösungsmitteladditivs 1,8-Diiodooctan (DIO) auf die Leistungsfähigkeit von p-DTS(FBTTh2)2:PDI Solarzellen untersucht. Die Erkenntnisse von morphologischen und photophysikalischen Experimenten werden kombiniert, um die strukturellen Eigenschaften und die Photophysik mit den relevanten Kenngrößen des Bauteils in Verbindung zu setzen. Zeitaufgelöste Photolumineszenzmessungen (time-resolved photoluminescence, TRPL) zeigen, dass der Einsatz von DIO zu einer geringeren Reduzierung der Photolumineszenz führt, was auf eine größere Phasentrennung zurückgeführt werden kann. Außerdem kann mittels TA Spektroskopie gezeigt werden, dass die Verwendung von DIO zu einer verbesserten Kristallinität der aktiven Schicht führt und die Generation freier Ladungen fördert. Zur genauen Analyse des Signalzerfalls wird ein Modell angewendet, das den gleichzeitigen Zerfall gebundener CT-Zustände und freier Ladungen berücksichtigt und optimierte Donor-Akzeptor-Mischungen zeigen einen größeren Anteil an nicht-geminaler Rekombination freier Ladungsträger.rnIn einer weiteren Fallstudie wird der Einfluss des Fullerenderivats, namentlich IC60BA und PC71BM, auf die Leistungsfähigkeit und Photophysik der Solarzellen untersucht. Eine Kombination aus einer Untersuchung der Struktur des Dünnfilms sowie zeitaufgelöster Spektroskopie ergibt, dass Mischungen, die ICBA als Elektronenakzeptor verwenden, eine schlechtere Trennung von Ladungstransferzuständen zeigen und unter einer stärkeren geminalen Rekombination im Vergleich zu PCBM-basierten Mischungen leiden. Dies kann auf die kleinere Triebkraft zur Ladungstrennung sowie auf die höhere Unordnung der ICBA-basierten Mischungen, die die Ladungstrennung hemmen, zurückgeführt werden. Außerdem wird der Einfluss reiner Fullerendomänen auf die Funktionsfähigkeit organischer Solarzellen, die aus Mischungen des Thienothienophen-basierenden Polymers pBTTT-C14 und PC61BM bestehen, untersucht. Aus diesem Grund wird die Photophysik von Filmen mit einem Donor-Akzeptor-Mischungsverhältnis von 1:1 sowie 1:4 verglichen. Während 1:1-Mischungen lediglich eine co-kristalline Phase, in der Fullerene zwischen den Seitenketten von pBTTT interkalieren, zeigen, resultiert der Überschuss an Fulleren in den 1:4-Proben in der Ausbildung reiner Fullerendomänen zusätzlich zu der co kristallinen Phase. Transiente Absorptionsspektroskopie verdeutlicht, dass Ladungstransferzustände in 1:1-Mischungen hauptsächlich über geminale Rekombination zerfallen, während in 1:4 Mischungen ein beträchtlicher Anteil an Ladungen ihre wechselseitige Coulombanziehung überwinden und freie Ladungsträger bilden kann, die schließlich nicht-geminal rekombinieren.

Absence of histamine-induced nitric oxide release in the human radial artery: implications for vasospasm of coronary artery bypass vessels

Radial artery (RA) bypass grafts can develop severe vasospasm. As histamine is known to induce vasospasm, its effect on RA was assessed compared with the classic bypass vessels internal mammary artery (MA) and saphenous vein (SV). The vessels were examined in organ chambers for isometric tension recording. Histamine induced contractions on baseline; the sensitivity was higher in RA and SV than MA. After precontraction with norepinephrine, histamine did not evoke relaxations of RA but induced relaxations of MA and less of SV at lower concentrations; it induced contractions at higher concentrations, reaching similar levels in all three vessels. Indomethacin did not affect the response of MA and RA but potentiated relaxations and reduced contractions of SV. Endothelium removal, N(omega)-nitro-L-arginine methyl ester (L-NAME), or the H2-receptor blocker cimetidine did not affect the response of RA, but inhibited relaxations and enhanced contractions in MA and inhibited relaxations in SV; in the latter, only L-NAME enhanced contractions. Real-time PCR detected much lower expression of endothelial H2-receptor in RA than MA or SV. Western blots revealed similar endothelial nitric oxide (NO) synthase expression in all three vessels. Relaxations to acetylcholine were identical in RA and MA. Thus histamine releases NO by activating the endothelial H2-receptor, the expression of which is much lower in RA than MA or SV. H2-receptor activation also releases prostaglandins in SV, partially antagonizing NO. The lack of histamine-induced NO production represents a possible mechanism of RA vasospasm.

Erythropoietin enhances oxygenation in critically perfused tissue through modulation of nitric oxide synthase

The aim of this study was to investigate the effect of human recombinant erythropoietin (EPO) on the microcirculation and oxygenation of critically ischemic tissue and to elucidate the role of endothelial NO synthase in EPO-mediated tissue protection. Island flaps were dissected from the back skin of anesthetized male Syrian golden hamsters including a critically ischemic, hypoxic area that was perfused via a collateralized vasculature. Before ischemia, animals received an injection of epoetin beta at a dose of 5,000 U/kg body weight with (n = 7) or without (n = 7) blocking NO synthase by 30 mg/kg body weight L-NAME (Nomega-nitro-L-arginine methyl ester hydrochloride). Saline-treated animals served as control (n = 7). Ischemic tissue damage was characterized by severe hypoperfusion and inflammation, hypoxia, and accumulation of apoptotic cell nuclei after 5 h of collateralization. Erythropoietin pretreatment increased arteriolar and venular blood flow by 33% and 37%, respectively (P < 0.05), and attenuated leukocytic inflammation by approximately 75% (P < 0.05). Furthermore, partial tissue oxygen tension in the ischemic tissue increased from 8.2 to 15.8 mmHg (P < 0.05), which was paralleled by a 21% increased density of patent capillaries (P < 0.05) and a 50% reduced apoptotic cell count (P < 0.05). The improved microcirculation and oxygenation were associated with a 2.2-fold (P < 0.05) increase of endothelial NO synthase protein expression. Of interest, L-NAME completely abolished all the beneficial effects of EPO pretreatment. Our study demonstrates that, in critically ischemic and hypoxic collateralized tissue, EPO pretreatment improves tissue perfusion and oxygenation in vivo. This effect may be attributed to NO-dependent vasodilative effects and anti-inflammatory actions on the altered vascular endothelium.

Comparison of the toxicity of diesel exhaust produced by bio- and fossil diesel combustion in human lung cells in vitro

Alternative fuels are increasingly combusted in diesel- and gasoline engines and the contribution of such exhausts to the overall air pollution is on the rise. Recent findings on the possible adverse effects of biodiesel exhaust are contradictive, at least partly resulting from the various fuel qualities, engine types and different operation conditions that were tested. However, most of the studies are biased by undesired interactions between the exhaust samples and biological culture media. We here report how complete, freshly produced exhausts from fossil diesel (B0), from a blend of 20% rapeseed-methyl ester (RME) and 80% fossil diesel (B20) and from pure rapeseed methyl ester (B100) affect a complex 3D cellular model of the human airway epithelium in vitro by exposing the cells at the air–liquid interface. The induction of pro-apoptotic and necrotic cell death, cellular morphology, oxidative stress, and pro-inflammatory responses were assessed. Compared to B0 exhaust, B20 exhaust decreased oxidative stress and pro-inflammatory responses, whereas B100 exhaust, depending on exposure duration, decreased oxidative stress but increased pro-inflammatory responses. The effects are only very weak and given the compared to fossil diesel higher ecological sustainability of biodiesel, it appears that – at least RME – can be considered a valuable alternative to pure fossil diesel.

Studies on the interaction of NADPH cytochrome P-450 reductase and cytochromes P-450

Chemical modification of cytochrome P-450 reductase was used to determine the involvement of charged amino acids in the interaction between the reductase and two forms of cytochrome P-450. Acetylation of 11 lysine residues of the reductase with acetic anhydride yielded a 20-40% decrease in the K$\sb{\rm m}$ of the reductase for cytochrome P-450b or cytochrome P-450c. Modification of carboxyl groups on the reductase with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and methylamine, glycine methyl ester, or taurine as nucleophiles inhibited the interaction with the cytochromes P-450. We were able to modify 4.0, 7.9, and 5.9 carboxyl groups using methylamine, glycine methyl ester, and taurine, respectively. The apparent K$\sb{\rm m}$ for cytochrome P-450c or cytochrome P-450b was increased 1.3 to 5.2 fold. There were varied effects on the V$\sb{\rm max}$. There was no significant change in the conformation of the reductase upon chemical modification. These results strongly suggest that electrostatic interactions as well as steric constraints play a role in the binding and electron transfer step(s) between the reductase and cytochrome P-450. Cytochrome P-450 protected 0.8 moles of carboxyl residues on the reductase from being modified with EDC. These protected amino acids on the reductase are presumably involved in binding to cytochrome P-450. The specific peptide containing these amino acids has been identified. ^

Glutamate and nitric oxide as regulatory transmitters in developing rabbit retina

Glutamate is the major excitatory neurotransmitter in the retina and serves as the synaptic messenger for the three classes of neurons which constitute the vertical pathway--the photoreceptors, bipolar cells and ganglion cells. In addition, the glutamate system has been localized morphologically, pharmacologically as well as molecularly during the first postnatal week of development before synaptogenesis occurs. The role which glutamate plays in the maturing visual system is complex but ranges from mediating developmental neurotoxicity to inducing neurite outgrowth.^ Nitric oxide/cGMP is a novel intercellular messenger which is thought to act in concert with the glutamate system in regulating a variety of cellular processes in the brain as well as retina, most notably neurotoxicity. Several developmental activities including programmed cell death, synapse elimination and synaptic reorganization are possible functions of cellular regulation modulated by nitric oxide as well as glutamate.^ The purpose of this thesis is to (1) biochemically characterize the endogenous pools of glutamate and determine what fraction exists extracellularly; (2) examine the morphological expression of NO producing cells in developing retina; (3) test the functional coupling of the NMDA subtype of glutamate receptor to the NO system by examining neurotoxicity which has roles in both the maturing and adult retina.^ Biochemical sampling of perfusates collected from the photoreceptor surface of ex vivo retina demonstrated that although the total pool of glutamate present at birth is relatively modest, a high percentage resides in extracellular pools. As a result, immature neurons without significant synaptic connections survive and develop in a highly glutamatergic environment which has been shown to be toxic in the adult retina.^ The interaction of the glutamate system with the NO system has been postulated to regulate neuronal survival. We therefore examined the developmental expression of the enzyme responsible for producing NO, nitric oxide synthase (NOS), using an antibody to the constitutive form of NOS found in the brain. The neurons thought to produce the majority of NO in the adult retina, a subpopulation of widefield amacrine cells, were not immunoreactive until the end of the second postnatal week. However, a unique developmental expression was observed in the ganglion cell layer and developing outer nuclear layer of the retina during the first postnatal week. We postulate NO producing neurons may not be present in a mature configuration therefore permitting neuronal survival in a highly glutamatergic microenvironment and allowing NO to play a development-specific role at this time.^ The next set of experiments constituted a functional test of the hypothesis that the absence of the prototypic NO producing cells in developing retina protects immature neurons against glutamate toxicity. An explant culture system developed in order to examine cellular responses of immature and adult neurons to glutamate toxicity showed that immature neurons were affected by NMDA but were less responsive to NMDA and NO mediated toxicity. In contrast, adult explants exhibited significant NMDA toxicity which was attenuated by NMDA antagonists, 2-amino-5-phosphonovaleric acid (APV), dextromethorphan (Dex) and N$\rm\sp{G}$-D-methyl arginine (metARG). These results indicated that pan-retinal neurotoxicity via the NMDA receptor and/or NO activation occurred in the adult retina but was not significant in the neonate. (Abstract shortened by UMI.) ^

Plant strengtheners enhance parasitoid attraction to herbivore-damaged cotton via qualitative and quantitative changes in induced volatiles

BACKGROUND Herbivore-damaged plants release a blend of volatile organic compounds (VOCs) that differs from undamaged plants. These induced changes are known to attract the natural enemies of the herbivores and therefore are expected to be important determinants of the effectiveness of biological control in agriculture. One way of boosting this phenomenon is the application of plant strengtheners, which has been shown to enhance parasitoid attraction in maize. It is unclear whether this is also the case for other important crops. RESULTS The plant strengtheners BTH [benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester] and laminarin were applied to cotton plants, and the effects on volatile releases and the attraction of three hymenopteran parasitoids, Cotesia marginiventris, Campoletis sonorensis and Microplitis rufiventris, were studied. After treated and untreated plants were induced by real or simulated caterpillar feeding, it was found that BTH treatment increased the attraction of the parasitoids, whereas laminarin had no significant effect. BTH treatment selectively increased the release of two homoterpenes and reduced the emission of indole, the latter of which had been shown to interfere with parasitoid attraction in earlier studies. Canonical variate analyses of the data show that the parasitoid responses were dependent on the quality rather than the quantity of volatile emission in this tritrophic interaction. CONCLUSION Overall, these results strengthen the emerging paradigm that induction of plant defences with chemical elicitors such as BTH could provide a sustainable and environmentally friendly strategy for biological control of pests by enhancing the attractiveness of cultivated plants to natural enemies of insect herbivores. © 2014 Society of Chemical Industry

Less is More: Treatment with BTH and Laminarin Reduces Herbivore-Induced Volatile Emissions in Maize but Increases Parasitoid Attraction

Chemical plant strengtheners find increasing use in agriculture to enhance resistance against pathogens. In an earlier study, it was found that treatment with one such resistance elicitor, BTH (benzo-(1, 2, 3)-thiadiazole-7-carbothioic acid S-methyl ester), increases the attractiveness of maize plants to a parasitic wasp. This surprising additional benefit of treating plants with BTH prompted us to conduct a series of olfactometer tests to find out if BTH and another commercially available plant strengthener, Laminarin, increase the attractiveness of maize to three important parasitic wasps, Cotesia marginventris, Campoletis sonorensis, and Microplitis rufiventris. In each case, plants that were sprayed with the plant strengtheners and subsequently induced to release volatiles by real or mimicked attack by Spodoptera littoralis caterpillars became more attractive to the parasitoids than water treated plants. The elicitors alone or in combination with plants that were not induced by herbivory were not attractive to the wasps. Interestingly, plants treated with the plant strengtheners did not show any consistent increase in volatile emissions. On the contrary, treated plants released less herbivore-induced volatiles, most notably indole, which has been reported to interfere with parasitoid attraction. The emission of the sesquiterpenes (E)-β-caryophyllene, β-bergamotene, and (E)-β-farnesene was similarly reduced by the treatment. Expression profiles of marker genes showed that BTH and Laminarin induced several pathogenesis related (PR) genes. The results support the notion that, as yet undetectable and unidentified compounds, are of major importance for parasitoid attraction, and that these attractants may be masked by some of the major compounds in the volatile blends. This study confirms that elicitors of pathogen resistance are compatible with the biological control of insect pests and may even help to improve it.

Estudio técnico-económico de una planta de producción de biodiesel

Se explica las posibles razones que han obligado a varias de las plantas de biodiésel en España a cerrar a pesar de estar siendo auspiciadas por la Unión Europea y fomentadas, mediante normativas específicas y ayudas sustanciales en cada uno de los países miembros, a fin de reforzar la utilización de los biocarburantes, como energía alternativa a los combustibles fósiles, debido a las ventajas medioambientales y sociopolíticas que conllevan. Para ello se ha empezado realizando un estudio del sector y de su funcionamiento así como de la evolución reciente del mercado tanto en Europa como en España. Posteriormente se ha modelizado una planta de biodiesel tipo desde las primeras fases de su construcción hasta su puesta en funcionamiento, para, a continuación analizar su desarrollo haciendo especial hincapié en la evolución de las principales variables económicas anteriormente estudiadas que han llevado finalmente a tener que cerrarla por falta de rentabilidad. El proceso de producción del biodiésel desde aceites vegetales y grasas animales mantiene un fuerte crecimiento en los mercados de la Unión Europea al igual que en Estados Unidos y Canadá. La producción de biodiésel se ha incrementado rápidamente en los últimos años, ya que es una alternativa renovable a los carburantes, como el petróleo o el diésel. La producción por trasesterificación de aceites vegetales y grasas animales, dan al biodiésel una densidad, un punto de encendido, viscosidad, estabilidad a la oxidación similares al diésel. Estas propiedades permiten a la mezcla de biodiésel poder usarlo en motores convencionales sin necesidad de grandes modificaciones. El objetivo fundamental de este proyecto es, dentro de un entorno económico hostil, explicar el posible porqué de la situación de las plantas de biodiésel en España, haciendo un análisis de la viabilidad económico – financiera de una planta de producción de biodiésel. La instalación de la que parte el presente proyecto es la de una planta, situada en la provincia de Jaén, con una capacidad de producción de 100 000 t/año, con una previsión de funcionamiento continua y con una vida útil estimada de 15 años. Una vez finalizado el estudio económico, se ha valorado el impacto del mercado en el funcionamiento de la planta, tanto a nivel internacional debido a la competencia desleal, como nacional, debido a las ayudas en los cultivos. Se deduce que la rentabilidad de una planta de biodiésel es relativamente positiva pero viene dada por un gran número de variables internas y externas que hacen un negocio inestable y poco rentable. ABSTRACT It explains the possible reasons that have forced several biodiesel plants in Spain to close in spite of being sponsored by the European Union and promoted by specific regulations and substantial aid in each of the member countries to strengthen the use of biofuels as alternative energy to fossil fuels because of the environmental and sociopolitical involving VII For this we have begun a study of the sector and its operation as well as the recent market developments in Europe and in Spain. Later was modeled biodiesel plant type from the early stages of construction to commissioning, to then analyze its development with particular emphasis on the evolution of the main economic variables that have been previously studied eventually have to close by unprofitability. The processes and production of biodiesel (methyl ester) from vegetable oil and animal fat feedstocks remain a strong growth market in the European Union as well as the United States and Canada. Biodiesel production has increased rapidly in this last years as producers sought a renewable alternative to petroleum fuel. Produced by the trans-esterification of vegetable oils and animal fats, biodiesel has similar density, flash point, viscosity, oxidation stability to petroleum diesel. These similarities enable biodiesel blends to be used in conventional diesel engines without significant modifications. This proyect gives an overview of current developments with regard to biodiesel technology, the Spain biofuel market, and national biofuel policies, looking at closely the economic-financial feasibility of a biodiesel production plant. The installation, situated at Linares (Jaén), has a production capability of 100 000 t/year. The operation estimated is constant and with a product life of 15 years. Finished the part destined to the economic view of this project, it has been considered the adverse effects on the overall performance and the financial situation of the industry. It follows form the study that biodiesel plant´s profitability is relatively high, but it is given by a large numbers of variables, internals and externals, which have made an unviable and unsustainable business.

Biokerosene from Babassu and Camelina Oils: production and properties of their blends with fossil kerosene

Babassu and camelina oils have been transesterified with methanol by the classical homogeneous basic catalysis method with good yields. The babassu fatty acid methyl ester (FAME) has been subjected to fractional distillation at vacuum, and the low boiling point fraction has been blended with two types of fossil kerosene, a straight-run atmospheric distillation cut (hydrotreated) and a commercial Jet-A1. The camelina FAME has been blended with the fossil kerosene without previous distillation. The blends of babassu biokerosene and Jet-A1 have met some of the specifications selected for study of the ASTM D1655 standard: smoke point, density, flash point, cloud point, kinematic viscosity, oxidative stability and lower heating value. On the other hand, the blends of babassu biokerosene and atmospheric distillation cut only have met the density parameter and the oxidative stability. The blends of camelina FAME and atmospheric distillation cut have met the following specifications: density, kinematic viscosity at −20 °C, and lower heating value. With these preliminary results, it can be concluded that it would be feasible to blend babassu and camelina biokerosenes prepared in this way with commercial Jet-A1 up to 10 vol % of the former, if these blends prove to accomplish all the ASTM D1655-09 standards.

Stimulation of renin secretion by nitric oxide is mediated by phosphodiesterase 3

This study aimed to characterize the cellular pathways along which nitric oxide (NO) stimulates renin secretion from the kidney. Using the isolated perfused rat kidney model we found that renin secretion stimulated 4- to 8-fold by low perfusion pressure (40 mmHg), by macula densa inhibition (100 μmol/liter of bumetanide), and by adenylate cyclase activation (3 nmol/liter of isoproterenol) was markedly attenuated by the NO synthase inhibitor nitro-l-arginine methyl ester (l-Name) (1 mM) and that the inhibition by l-Name was compensated by the NO-donor sodium nitroprusside (SNP) (10 μmol/liter). Similarly, inhibition of cAMP degradation by blockade of phosphodiesterase 1 (PDE-1) (20 μmol/liter of 8-methoxymethyl-1-methyl-3-(2-methylpropyl)xanthine) or of PDE-4 (20 μmol/liter of rolipram) caused a 3- to 4-fold stimulation of renin secretion that was attenuated by l-Name and that was even overcompensated by sodium nitroprusside. Inhibition of PDE-3 by 20 μmol/liter of milrinone or by 200 nmol/liter of trequinsin caused a 5- to 6-fold stimulation of renin secretion that was slightly enhanced by NO synthase inhibition and moderately attenuated by NO donation. Because PDE-3 is a cGMP-inhibited cAMP-PDE the role of endogenous cGMP for the effects of NO was examined by the use of the specific guanylate cyclase inhibitor 1-H-(1,2,4)oxodiazolo(4,3a)quinoxalin-1-one (20 μmol). In the presence of 1H-[1,2,4]oxodiazolo[4,3-a]quinoxalin-1-one the effect of NO on renin secretion was abolished, whereas PDE-3 inhibitors exerted their normal effects. These findings suggest that PDE-3 plays a major role for the cAMP control of renin secretion. Our findings are compatible with the idea that the stimulatory effects of endogenous and exogenous NO on renin secretion are mediated by a cGMP-induced inhibition of cAMP degradation.

Calpain is a mediator of preservation-reperfusion injury in rat liver transplantation

Proteases as well as alterations in intracellular calcium have important roles in hepatic preservation-reperfusion injury, and increased calpain activity recently has been demonstrated in liver allografts. Experiments were designed to evaluate (i) hepatic cytosolic calpain activity during different periods of cold ischemia (CI), rewarming, or reperfusion, and (ii) effects of inhibition of calpain on liver graft function using the isolated perfused rat liver and arterialized orthotopic liver transplantation models. Calpain activity was assayed using the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-7-amino-4-methyl coumarin (AMC) and expressed as mean ± SD pmol AMC released/min per mg of cytosolic protein. Calpain activity rose significantly after 24 hr of CI in University of Wisconsin solution and further increased with longer preservation. Activity also increased within 30 min of rewarming, peaking at 120 min. Increased durations of CI preceding rewarming resulted in significantly higher activity (P < 0.01). Calpain activity increased rapidly upon reperfusion and was significantly enhanced by previous CI (P < 0.01). Calpain inhibition with Cbz-Val-Phe methyl ester significantly decreased aspartate aminotransferase released in the isolated perfused rat liver perfusate (P < 0.05). Duration of survival after orthotopic liver transplantation using livers cold-preserved for 40 hr was also significantly increased (P < 0.05) with calpain inhibitor. In conclusion, calpain proteases are activated during each phase of transplantation and are likely to play an important role in the mechanisms of preservation-reperfusion injury.

Lipoxin A4 stable analogs inhibit leukocyte rolling and adherence in the rat mesenteric microvasculature: Role of P-selectin

Three different stable lipoxin A4 (LXA4) analogs (i.e., 16-phenoxy-LXA4-Me, 15-cyclohexyl-LXA4-Me, and 15-R/S-methyl-LXA4-Me) were studied for their ability to modulate leukocyte-endothelial cell interactions in the rat mesenteric microvasculature. Superfusion of the rat mesentery with 50 μmol/liter NG-nitro-l-arginine methyl ester (l-NAME) caused a significant, time-dependent increase in leukocyte rolling (56 ± 8 cells/min; P < 0.01 vs. control) and leukocyte adherence (12.5 ± 1.2 cells/100 μm length of venule; P < 0.01 vs. control) after 120 min of superfusion. Concomitant superfusion of the rat mesentery with 10 nmol/liter of each of three lipoxin analogs consistently and markedly attenuated l-NAME-induced leukocyte rolling to 10 ± 4 (P < 0.01), 4 ± 1 (P < 0.01), and 32 ± 7 (P < 0.05) cells/min, and adherence to 4 ± 0.8 (P < 0.01), 1.1 ± 0.4 (P < 0.01), and 7 ± 0.7 (P < 0.05) cells/100 μm length of venule (16-phenoxy-LXA4-Me, 15-cyclohexyl-LXA4-Me, and 15-R/S- methyl-LXA4-Me, respectively). No alterations of systemic blood pressure or mesenteric venular shear rates were observed in any group. Immunohistochemical up-regulation of P-selectin expression on intestinal venular endothelium was significantly increased (P < 0.01) after exposure to l-NAME, and this was significantly attenuated by these lipoxin analogs (P < 0.01). Thus, in vivo superfusion of the rat mesentery with stable lipoxin analogs at 10 nmol/liter reduces l-NAME-induced leukocyte rolling and adherence in the mesenteric rat microvasculature by attenuating P-selectin expression. This anti-inflammatory mechanism may represent a novel and potent regulatory action of lipoxins on the immune system.

Inhibition of gastric acid secretion by stress: A protective reflex mediated by cerebral nitric oxide

Moderate somatic stress inhibits gastric acid secretion. We have investigated the role of endogenously released NO in this phenomenon. Elevation of body temperature by 3°C or a reduction of 35 mmHg (1 mmHg = 133 Pa) in blood pressure for 10 min produced a rapid and long-lasting reduction of distension-stimulated acid secretion in the rat perfused stomach in vivo. A similar inhibitory effect on acid secretion was produced by the intracisternal (i.c.) administration of oxytocin, a peptide known to be released during stress. Intracisternal administration of the NO-synthase inhibitor, NG-nitro-l-arginine methyl ester (l-NAME) reversed the antisecretory effect induced by all these stimuli, an action prevented by intracisternal coadministration of the NO precursor, l-arginine. Furthermore, microinjection of l-NAME into the dorsal motor nucleus of the vagus nerve reversed the acid inhibitory effects of mild hyperthermia, i.v. endotoxin, or i.c. oxytocin, an action prevented by prior microinjection of l-arginine. By contrast, microinjection of l-NAME into the nucleus tractus solitarius failed to affect the inhibitory effects of hyperthermia, i.v. endotoxin, or i.c. oxytocin. Immunohistochemical techniques demonstrated that following hyperthermia there was a significant increase in immunoreactivity to neuronal NO synthase in different areas of the brain, including the dorsal motor nucleus of the vagus. Thus, our results suggest that the inhibition of gastric acid secretion, a defense mechanism during stress, is mediated by a nervous reflex involving a neuronal pathway that includes NO synthesis in the brain, specifically in the dorsal motor nucleus of the vagus.

Pharmacological and immunohistochemical evidence for a functional nitric oxide synthase system in rat peritoneal eosinophils

Eosinophil migration in vivo is markedly attenuated in rats treated chronically with the NO synthase (NOS) inhibitor Nω-nitro-l-arginine methyl ester (l-NAME). In this study, we investigated the existence of a NOS system in eosinophils. Our results demonstrated that rat peritoneal eosinophils strongly express both type II (30.2 ± 11.6% of counted cells) and type III (24.7 ± 7.4% of counted cells) NOS, as detected by immunohistochemistry using affinity purified mouse mAbs. Eosinophil migration in vitro was evaluated by using 48-well microchemotaxis chambers and the chemotactic agents used were N-formyl-methionyl-leucyl-phenylalanine (fMLP, 5 × 10−8 M) and leukotriene B4 (LTB4, 10−8 M). l-NAME (but not d-NAME) significantly inhibited the eosinophil migration induced by both fMLP (54% reduction for 1.0 mM; P < 0.05) and LTB4 (61% reduction for 1.0 mM; P < 0.05). In addition, the type II NOS inhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine and the type I/II NOS inhibitor 1-(2-trifluoromethylphenyl) imidazole also markedly (P < 0.05) attenuated fMLP- (52% and 38% reduction for 1.0 mM, respectively) and LTB4- (52% and 51% reduction for 1.0 mM, respectively) induced migration. The inhibition of eosinophil migration by l-NAME was mimicked by the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a] quinoxalin-1-one (0.01 and 0.1 mM) and reversed by either sodium nitroprusside (0.1 mM) or dibutyryl cyclic GMP (1 mM). We conclude that eosinophils do express NO synthase(s) and that nitric oxide plays an essential role in eosinophil locomotion by acting through a cyclic GMP transduction mechanism.