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  • 1
    Electronic Resource
    Electronic Resource
    Uncoupled regulation of leukotriene C4 synthase in platelets from aspirin-intolerant asthmatics and healthy volunteers after aspirin treatment (2002)
    Oxford, UK : Blackwell Science Ltd
    Clinical & experimental allergy 32 (2002), S. 0 
    Details
    ISSN: 1365-2222
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background We have reported that thromboxane A2 induces suppression of leukotriene (LT) C4 synthase activity in human platelets.Aim In the present study, we describe a mechanism whereby aspirin treatment can lead to increased formation of LTC4, which is a potent bronchoconstrictor and inflammatory mediator. This mechanism is also demonstrated to be present in platelets from aspirin-intolerant asthmatics (AIA).Methods The effect of arachidonic acid or platelet agonists on LTC4 synthase activity was investigated in platelets obtained from healthy volunteers, aspirin-intolerant asthmatics or aspirin-tolerant asthmatics after in vivo treatment or in vitro pre-incubation with aspirin.Results Incubation of normal platelets with arachidonic acid or collagen provoked approximately 50% reduction of platelet LTC4 synthase activity, as determined by the conversion of LTA4 to LTC4. However, the inhibitory effect of arachidonic acid or collagen was not observed after oral administration of aspirin prior to collection of the platelets. Arachidonic acid-induced inhibition of LTC4 synthase activity was totally abolished in platelets collected from peripheral blood already 30 min after aspirin ingestion but was fully restored in platelets collected 3 to 7 days after the administration of aspirin. Treatment of platelet suspensions with aspirin in vitro dose-dependently counteracted the suppressive effect of arachidonic acid on LTC4 formation, with total reversal at approximately 40 µm. In contrast, the major aspirin metabolite, salicylic acid did not alter arachidonic acid-induced reduction of LTC4 synthase activity. Similarly, LTC4 synthase activity in platelets from AIA and aspirin-tolerant asthmatics (ATA) was reduced by approximately 50% after pre-treatment with arachidonic acid in vitro. Again the inhibitory effect was abolished when platelets were pre-incubated in the presence of aspirin.Conclusion The results indicate that oral aspirin administration can lead to uncoupling of thromboxane A2-dependent negative feedback mechanisms, which may normally restrict the production of cysteinyl leukotrienes. This mechanism can be of potential interest in aspirin-induced asthma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2222.2002.01531.x
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  • 2
    Electronic Resource
    Electronic Resource
    Bidirectional supply of glutamine maintains enterocyte ATP content in the in vitro Ussing chamber model (2000)
    Springer
    International journal of colorectal disease 15 (2000), S. 291-296 
    Details
    ISSN: 1432-1262
    Keywords: Ussing chamber Glutamine Energy metabolism Intestinal mucosa Epithelial resistance Permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Glutamine is the principal energy source for enterocytes, but it is not known whether parenteral or enteral supplementation is most beneficial to gut integrity. The aim of this study was to evaluate the effects of glutamine in uni- or bidirectional supply on the viability of intestinal mucosa of starved rats during incubation in Ussing chambers. Segments of jejunum from rats starved for 48 h were randomly mounted in Ussing chambers with three nutrient solutions: Krebs buffer without glutamine; 6 mM glutamine added to the mucosal side; 6 mM glutamine added to the mucosal side and 0.6 mM glutamine to the serosal side. ATP content of the mucosa, electrophysiology, and 51Cr-ethylenediaminetetraacetate (EDTA) permeability were studied during 180 min of incubation. The addition of glutamine to both sides of the stripped mucosa improved ATP levels compared to the Krebs solution (P〈0.05), and the addition of glutamine resulted in an increase in short circuit current (P〈0.05). No significant differences were seen in 51Cr-EDTA permeability or epithelial electrical resistance. Glutamine supplementation to both the luminal and serosal side in the Ussing chamber was more effective than luminal glutamine only in maintaining ATP levels of intestinal mucosa. Bidirectional supplementation of glutamine might improve intestinal energy metabolism and viability in in vitro studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003840000258
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  • 3
    Electronic Resource
    Electronic Resource
    Spatial variations of incoming longwave radiationin Göteborg, Sweden (2000)
    Springer
    Theoretical and applied climatology 67 (2000), S. 181-192 
    Details
    ISSN: 1434-4483
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Summary  A measurement programme was conducted in Göteborg Sweden, to examine the spatial variations of incoming longwave irradiance on calm, cloudless nights. Both regional and local spatial variations were examined. Incoming longwave irradiance data was obtained from mobile car transects, and at a fixed site on a building roof at the city centre. Ancillary data included sky view factor at various transect locations, and balloon soundings of air temperature and humidity on one night. Measurements revealed that on average, incoming longwave irradiance at the fixed urban site was 11 W m −2 higher than at the rural station, with varying differences for intervening sites. Bulk apparent sky emissivity was higher at the most rural station compared to the fixed urban site, by about 0.03 on average. Nighttime balloon measurements and a sensitivity analysis with a radiative transfer model argue that the bulk apparent sky emissivity differences stem mainly from the temperature structure of the lower boundary layer which changes markedly from rural to urban areas. A good relationship was found between sky view factor and incoming longwave irradiance for a range of urban and park locations. The relationship applies to both individual nights and average data. Using a simple obstruction model, canyon wall temperatures are derived, and the relationship between sky view factor and wall temperature is examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007040070007
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    Paper (German National Licenses)
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