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  • 1
    ISSN: 1432-0878
    Keywords: Trophoblastic cells ; Spiral artery ; Extracellular matrix ; Uterus ; Macaca fascicularis (Primates) ; Macaca mulatta (Primates)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The processes by which trophoblast cells invade and modify the walls of the uteroplacental arteries of macaques during the course of gestation were examined. Antibodies to cytokeratins were employed to identify trophoblast, anti-desmin antibody to identify smooth muscle, and antibodies to type IV collagen, laminin, and fibronectin to examine changes in extracellular matrix distribution in the arterial wall. During early gestation, endovascular trophoblast adhered to the arterial wall, often in an asymmetrical distribution. As trophoblast cells moved outwardly into the tunica media, the basement membrane underlying the endothelium was lost, as indicated by gaps in the layer when stained for type IV collagen and laminin. Trophoblast cells became sequestered in the vessel wall where they hypertrophied and became surrounded by a capsule containing type IV collagen and laminin. As the trophoblast cells became established in the vessel wall, the muscular layer of the artery became discontinuous. Throughout gestation it was common for trophoblast cells to invade the vessel intimal layer and share the lining of the artery with typical endothelial cells. This general disposition of endovascular and intramural trophoblast persisted into late gestation. In addition, and contrary to the results of earlier studies of macaques, we identified trophoblastic invasion and modification of myometrial segments of the uteroplacental arteries in later gestation. We also found evidence of interstitial trophoblast cells among the stromal cells of the endometrium, especially during early gestation.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 274 (1993), S. 135-144 
    ISSN: 1432-0878
    Keywords: Trophoblast ; Uterus ; Veins ; Basement membrane ; Placenta ; Macaca fascicularis (Primates) ; Macaca mulatta (Primates)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Trophoblast cells invade and modify the uterine vasculature to provide circulation of maternal blood through the placenta. Although evidence indicates fundamental differences between trophoblast modification of arteries and veins, interactions between trophoblast cells and uterine veins have not been addressed. In this report we describe the processes by which trophoblast cells invade and restructure uterine veins during placentation in the macaque. Antibodies were used to identify trophoblast, endothelium, and basement membranes. During early gestation, trophoblast migrated from the trophoblastic shell and, by intravasation, replaced portions of the wall and endothelium of veins in the vicinity of the shell; this is in contrast to invasion by extravasation reported for the arteries in this species. These areas had discontinuous endothelial basement membranes and the endothelial cells were variably hypertrophied. Deeper portions of veins were not invaded; this too is in contradistinction to the spiral arteries where trophoblastic modification extends to the myometrial segments. Later in gestation, those portions of veins interacting with trophoblast were contained within the trophoblastic shell or situated such that one side abutted the shell. These regions of the veins were lined by endothelium, but it could not be determined whether this represented re-endothelialization of regions formerly lined by trophoblast or if these endothelial cells were never displaced.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 709-725 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The radiation-induced polymerization of methyl methacrylate was investigated with radiation sources of cobalt 60 and accelerated electrons at dose rates up to 3 Mrads/sec. Extrapolation of previous rates of polymerization at dose rates of 0.01-200 rads/sec coincided with the present results, the rates being approximately proportional to the square root of the dose rate throughout the entire set of dose rates measured. The molecular weights seemed to be independent of dose rate at the highest dose rates investigated. A combination of high polymer with a much higher molecular weight than expected was formed, together with a substantial portion of low molecular weight polymer. The reason for this behavior is not clear at this time. The G(M·) calculated from the molecular weights and fraction of polymer and resin was 6.0, which approaches that reported in previous investigations at low dose rates. There was no significant effect of air on the polymerization kinetics of methyl methacrylate at above 1 Mrad/sec. Nitrogen also did not influence the measured rates. Conversions to polymer were not substantially reduced by the presence of inhibitor at above 1.26 × 105 rads/sec. Water did not influence the rates of polymerization, except at the highest temperature (50°C) investigated. A large posteffect was observed in sealed degassed ampoules after 25% conversion to polymer. Only 3.4% additional polymer was formed in 24 hr after irradiation in the presence of air. The activation energy for the electron beam polymerization of methyl methacrylate was about 7.0 kcal/mole. This value, considering the complications in technique such as beam heating, did not differ from literature data enough to suggest any mechanistic difference in the polymerization at high dose rates.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 6 (1968), S. 1-25 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of biopolymerization on nucleic acid templates is discussed. The model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation. Each growth center [growing chain end plus enzyme(s)] moves one template site at a time, but blocks L adjacent sites. Solutions are found for the probability nj(t) that a template has a growing center that occupies the sites j  -  L + 1,…, j at time t. Two special sets of solutions are considered, the uniform-density solutions, for which nj(t) = n, and the more general steady-state solutions, for which dnj(t)/dt = 0. In the uniform-density case, there is an upper bound to the range of rates of polymerization that can occur. Corresponding to this maximum rate, there is one uniform solution. For a polymerization rate less than this maximum, there are two uniform solutions that give the same rate. In the steady-state case, only L = 1 is discussed. For a steady-state polymerization rate less than the maximum uniform-density rate, the steady-state solutions consist of either one or two regions of nearly uniform density, with the density value(s) assumed in the uniform region(s) being either or both of the uniform-density solutions corresponding to that polymerization rate. For a steady-state polymerization rate equal to or slightly larger than the maximum uniform-density rate, the steady-state solutions are nearly uniform to the single uniform-density solution for the maximum rate. The boundary conditions (rate of initiation and rate, of release of completed chains from the template) govern the choice among the possible solutions, i.e., determine the region(s) of uniformity and the value(s) assumed in the uniform region(s).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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