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  • 1
    ISSN: 0300-9629
    Keywords: Amphibia ; Pseudophryne corroboree ; ammonia ; nitrogen excretion ; nitrogen metabolism during development ; ornithine-urea cycle ; urea
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1433-0431
    Keywords: Schlüsselwörter Gelenkknorpelzellen • Hydrostatischer ¶Druck • Alginat • Sauerstoffpartialdruck •¶Redifferenzierung ; Key words Articular chondrocytes • Hydrostatic ¶pressure • Alginate • Oxygen partial-pressure • Redifferentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary One of the goals in the field of tissue engineering is the development of artificial cartilage for the treatment of cartilage defects. Therefore autologous chondrocytes are seeded on different artificial matrices to test their possible use as implants (resorption, antigenicity, toxicity and their integration in the tissue). One of the main problems in these experiments is that usually the amount of available chondrocytes is too low for treating large-scale defects or for comparing different matrices. An in-vitro-multiplication of the cells is needed which causes the chondrocytes to dedifferentiate and become fibroblast-like. Therefore parameters which induce a redifferentiation are of great interest. The objective of this study was to determine the influence of intermittent hydrostatic pressure and low oxygen partial pressure on the redifferentiation of dedifferentiated bovine articular chondrocytes in monolayer and three-dimensional alginate bead culture. The redifferentiation process was monitored by immunocytochemical detection of newly synthesized collagen type II. The viability of the cells was determined by the trypanblue exclusion test. The chondrocytes were dedifferentiated by a two week culture in plastic flasks with an oxygen level of 20 %. After this they were subcultured in monolayer or three-dimensional alginate culture and subjected to three different stimuli for three weeks in order to redifferentiate: 1.) 20 % O2 (= 20,26 kPa Po2) + 5 % CO2 + 75 % N2; 2.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2; 3.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2 + 8 h/d of intermittent hydrostatic pressure (frequency: 3 bar absolute for 30 min and 1 bar absolute for 2 min). In the monolayer there was no detectable collagen type II found by immunocytochemistry under either of the three culture conditions. Therefore a redifferentiation of dedifferentiated chondrocytes was not possible in monolayer cultures with the tested parameters. In the three-dimensional alginate culture there was no immunocytochemical staining of collagen type II found in the beads cultured with 20 % oxygen. With 5 % oxygen we found a strong collagen type II-production by chondrocytes throughout the whole bead. The intermittent hydrostatic pressure combined with 5 % oxygen lead to a decreased collagen type II-production compared to cells subjected to 5 % oxygen only. Also chondrocytes closer to the edge of these beads were more often immunopositive and seemed to produce more immunoreactive collagen type II. The viability of the chondrocytes in the alginate culture was close to 90 % after three weeks. Our experiments showed that oxygen partial pressure is an important parameter in the cultivation of articular chondrocytes. Reduced partial oxygen pressure promoted or induced the redifferentiation of dedifferentiated chondrocytes in alginate culture.
    Notes: Zusammenfassung Im Bereich des sog. „tissue engineering“ wird derzeit an einem künstlichen Knorpelersatz gearbeitet, der zur Deckung von Defekten im Gelenkknorpel verwendet werden soll. Meist werden dabei verschiedene künstliche Matrices in vitro mit autologen Chondrozyten besiedelt und auf ihre Verwendbarkeit als Implantat (Resorbierbarkeit, Antigenität, Toxizität und Integration in bestehendes Gewebe) hin untersucht. Oft ist bei diesen Untersuchungen die zur Verfügung stehende autologe Knorpelzellmenge zu gering, um größere Defekte behandeln oder verschiedene Matrices miteinander vergleichen zu können. Daher ist eine In-vitro-Vermehrung der Chondrozyten notwendig, bei der die Zellen jedoch gleichzeitig dedifferenzieren und fibroblastenartig werden. Deshalb ist es von Interesse, Parameter zu untersuchen, die eine Redifferenzierung induzieren. Das Ziel dieser Untersuchung war es, den Einfluss von intermittierendem hydrostatischem Druck und niedrigem Sauerstoffpartialdruck auf die Redifferenzierung von Rindergelenkknorpelzellen im Monolayer und in dreidimensionaler (3-D-)Alginatkultur zu testen. Der Redifferenzierungsprozess wurde durch immunzytochemischen Nachweis von Typ-II-Kollagen überprüft. Die Vitalität der Zellen wurde mit Hilfe des Trypan-Blau-Ausschlusstests bestimmt. Die Chondrozyten wurden durch 2wöchige Kultur in Plastikflaschen bei 20 % O2 dedifferenziert. Danach wurden sie als Monolayer oder 3-D-Alginatkultur subkultiviert und für 3 Wochen 3 unterschiedlichen Stimuli zum Zwecke der Redifferenzierung ausgesetzt: 1.) 20 % O2 (= 20,26 kPa Po2) + 5 % CO2 + 75 % N2; 2.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2; 3.) 5 % O2 (= 5,07 kPa Po2) + 5 % CO2 + 90 % N2 + 8 h intermittierende hydrostatische Druckbelastung (Frequenz: 30 min Belastung bei 3 bar absolut und 2 min Entlastung bei 1 bar absolut) pro Tag. Im Monolayer konnte nach 3 Wochen für keine der 3 Kulturbedingungen immunzytochemisch neusynthetisiertes Typ-II-Kollagen nachgewiesen werden. Daher scheint eine Redifferenzierung der dedifferenzierten Chondrozyten im Monolayer unter den untersuchten Bedingungen nicht möglich zu sein. In der 3-D-Alginatkultur wurde bei den bei 20 % O2 gehaltenen Chondrozyten kein immunzytochemisch detektierbares Typ-II-Kollagen gefunden. Bei 5 % O2 war eine starke Typ-II-Produktion in der gesamten Kugel zu verzeichnen. Im Vergleich zu diesen zeigten Chondrozyten aus Kugeln, die zusätzlich noch mit intermittierendem hydrostatischem Druck behandelt wurden, eine geringere Typ-II-Kollagenproduktion (sowohl im Bezug auf die Menge der Immunfärbung als auch auf die Anzahl der Typ-II-produzierenden Zellen) und eine Häufung der positiven Zellen im Randbereich der Kugel. Die Vitalität der Zellen in den Alginatkugeln lag nach 3 Wochen bei ca. 90 %. Unsere Untersuchungen haben gezeigt, dass der Sauerstoffpartialdruck ein wichtiger Parameter in der Kultivierung von Gelenkknorpelzellen darstellt. Ein reduzierter Sauerstoffpartialdruck förderte oder induzierte die Redifferenzierung von dedifferenzierten Chondrozyten in Alginatkultur.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 119 (1929), S. 171-187 
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Haemophilia 9 (2003), S. 0 
    ISSN: 1365-2516
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary. We conducted a retrospective survey of our experience with central venous access devices (CVADs) implanted in children with haemophilia seen at the Vanderbilt Hemostasis–Thrombosis Clinic from 1986 to 2000. Following discussion with parents on the merits and risks associated with the use of CVADs for immune tolerance induction or factor prophylaxis, catheters were inserted under sterile technique in the operating room. One nurse provided demonstration and teaching about catheter care and access. Thirty central venous catheters were inserted in 22 children. Our survey revealed that the two most common complications associated with central venous catheters were bacteraemia and thrombosis. We found a sepsis rate of 0.30/1000 catheter-days or one episode of bacteraemia for every 3346 days of catheter use. The thrombosis rate of our cohort was 0.13/1000 catheter-days or one episode of thrombosis for every 7529 days of catheter use. Uncomplicated venous access is essential in children with severe haemophilia who require prophylaxis or immune tolerance induction. While infection was the most common complication observed in our series, we experienced a lower overall infection rate than several reported series. Catheter thrombosis and subsequent obstruction may occur as a result of intraluminal fibrin deposits. We conclude that the use of implantable central venous catheters is an effective method for accessing children with haemophilia. We accept that the benefits of CVADs in the treatment of paediatric haemophilia patients outweigh the previously documented risks. Future prospective studies should be designed to define all associated risks and to determine effective strategies to reduce them.
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  • 5
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sinistral ovariectomy in the Japanese quail resulted in some hypertrophy of the rudimentary right gonad in about 80% of the cases. The hypertrophied right gonads were composed of cords of epithelial origin, fat laden cells and a connective tissue stroma containing masses of lymphocytes. Neither cortical tissue nor germ cells were found in any of the gonads. In some cases regeneration of a testis-like tissue was seen on the site of removed left ovary. This, however, did not alter the effects of ovariectomy on rudimentary right gonad, accessory sex organs, plumage or sexual behavior. Neither Wolffian nor Müllerian ducts exhibited hormonal stimulation in poulards showing hypertrophy of right gonad with exception of the latter in two poulards. Early orchiectomy inhibited growth and differentiation of the cloacal gland. This organ revealed no noticeable stimulation in poulards showing hypertrophied right gonads. Castration produced no significant changes in plumage of males. Similarly, sinistral ovariectomy did not effect the first juvenile, but the second juvenile, adult winter and summar plumages changed to the male type. However, the plumage of some of these poulards began to revert to the female character as early as 10 to 12 weeks following ovariectomy. The behavior of capons and poulards revealed no conspicuous difference and neither showed any masculine behavior. The average weight of adult females was 20 to 30 gm above that of adult males whereas that of capons was above normal males and that of poulards below normal females. The average weight of capons was somewhat above that of poulards.
    Additional Material: 1 Ill.
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  • 8
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The purpose was to determine the sites, times and frequency of mitotic activity in primordial germ cells in the white Leghorn chick embryo during the period of migration. Colchicine was employed to facilitate the identification of dividing germ cells in embryos ranging in age from 18 hours to five days of incubation (stages 3-27). An increase in the number of germ cells was observed during the period of migration, due primarily to proliferation of intraembryonic cells, since no significant increase in the number of extra-embryonic germ cells was seen during this period. The number of germ cells during this period ranged from 43 at 18 hours to 2211 at 120 hours. Two periods of intense proliferation were observed, the first between 48 and 72, the second between 96 and 120 hours. This coincided with a simultaneous increase in the number of germ cells during these periods. Dividing germ cells were present in the extraembryonic blood vessels anterior, lateral and posterior to the embryo at 28, 48 and 72 hours and within the intra-embryonic circulatory network at 48, 72, 96 and 120 hours. At 72, 96 and 120 hours, dividing germ cells were numerous in the tissues of the dorsal mesentery adjacent to the developing gonads and within the gonads. Dividing germ cells were also located in head mesenchyme, limb buds and mesenchyme surrounding the notochord-neural tube complex. Dividing germ cells were found in the chick embryo throughout the entire migratory period.
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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