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Computationally efficient algorithms for convection-permeation-diffusion models for blood-tissue exchange (1992)

Bassingthwaighte, James B. ; Chan, I. S. Joseph ; Wang, C. Y.

Springer

Annals of biomedical engineering 20 (1992), S. 687-725

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ISSN: 1573-9686

Keywords: Blood-tissue exchange ; Capillary permeability ; Pharmacokinetics ; Cellular uptake ; Volumes of distribution ; Interstitial space ; Intracellular consumption ; Organ uptake and washout ; Blood flow

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: Abstract Analysis of data on tissue depositions obtained by positron tomographic or NMR imaging, or of multiple tracer outflow dilution curves, requires fitting data with models composed of aggregates of capillary-tissue units. These units account for heterogeneities of flows and multisolute exchanges between longitudinally distributed regions across capillary and cell barriers within an organ. Because the analytic solutions to the partial differential equations require convolution integration, solutions are obtained relatively efficiently by a fast numerical method. Our approach centers on the use of a sliding fluid element algorithm for capillary convection, with the time step set equal to the length step divided by the fluid velocity. Radial fluxes by permeation between plasma, interstitial fluid, and cells and axial diffusion exchanges within each time step are calculated analytically. The method enforces mass conservation unless there is regional consumption. Solution for a 2-barrier, 3-region model, accurate to within 0.5%, are 100 to 1000 times faster than the corresponding, purely analytic solution, and over 10,000 times for a 4-region model. Applications include multiple indicator dilution studies of kinetics of transcapillary exchange and positron emission tomographic studies of the mechanisms of substrate transport into cells of organsin vivo.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02368613

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Pattern of glucose transporter (Glut 1) expression in embryonic brains is related to maturation of bood-brain barrier tightness (1992)

Dermietzel, R. ; Krause, D. ; Kremer, M. ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

American Journal of Anatomy 193 (1992), S. 152-163

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ISSN: 0002-9106

Keywords: Cerebral endothelium ; Development ; Immunocytochemistry ; Rat ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: A constant supply of blood-borne glucose is vital to cerebral metabolism. Although transport of glucose into the nervous tissue, effectively separated from the blood by a functional barrier (the blood-brain barrier, BBB), is one of the essential properties of the cerebral endothelium, little is known about its metabolic regulation and developmental expression in the BBB. In this study we provide evidence by immunocytochemistry that the pattern of the brain endothelial glucose transporter in rat brains (BBB-GT), immunologically homologous with the human hepatoma (G2), human erythrocyte transporter (Glut 1), changes with BBB maturation. While the neuroepithelium at embryonic days 12 and 13 shows a high incidence of immuno-detectable BBB-GT, vascularisation of the cerebral anlage and subsequent development of vascular tightness, as evidenced by intravascularly applied horseradish peroxidase and fluorescinated dextrans, is accompanied by a significant reduction BBB-GT expression in neuroepithelial cells and confinement of BBB-GT expression to the cerebral endothelium. Immunoblots and Northern blots of embryonic brain homogenates corroborate this change in BBB-GT expression in the brain anlage at the time of BBB maturation. However, low molecular weight glucose transporters, presumed to be of non-endothelial origin, are less dramatically reduced. The development of BBB tightness, therefore, seems to play a pivotal role in the pattern of BBB-GT expression during brain differentiation.

Additional Material: 6 Ill.