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  • 1
    ISSN: 1432-2013
    Keywords: Kidney (Physiology) ; Glomerulus (Hemodynamics or Permeability) ; Membranes (Physiology) ; Capillaries Permeability ; Macromolecular Systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Determination of glomerular intracapillary and transcapillary pressure gradients from sieving data. A biomathematical model is described to calculate the intracapillary and transcapillary glomerular pressure gradients from the sieving coefficients (Φ: fractional clearances/GFR) of macromolecules such as polyvinylpyrrolidone (PVP). Two differential equations have been developed. The first one calculates local values for GFR in terms of local values forPGC (intracapillary hydrostatic pressure) and π (oncotic pressure). The second equation calculates the clearance of PVP equimolecular fractions, the sieving equations previously described (24) being used to derive the concentrations of PVP in the filtrate (c 2). Two variants of the second equation have been considered, assuming the filtrate in contact with the membrane either “well stirred” or “unstirred” (constantc 2 and localc 2 gradient models respectively). Computer simulations have been used to illustrate how the sieving curve is modified when the five parameters on which depends the shape of the curve are changed one by one. The sieving curve relates Φ toa s (hydrodynamically equivalent molecular radius). The determining parameters are: $$\overline {GFP}$$ , the mean effective glomerular filtration pressure, ε, the slope of the intracapillary pressure,FF, the filtration fraction,Cp 0, the protein concentration in arterial plasma andr, the pore radius which is the only structural parameter involved when one assumes the glomerular membrane crossed by cylindrical pores of uniform size and length. The shape of the sieving curve is modified significantly enough by changing $$\overline {GFP}$$ ,FF andr within reasonable limits, to make it possible to derive $$\overline {GFP}$$ andr from experimental sieving data for macromolecules such as PVP or dextrans.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2013
    Keywords: Angiotensin II ; Renal hemodynamics ; Glomerular permeability ; Macromolecules (sieving)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of the intrarenal infusion of synthetic A sn 1, val 5 angiotensin II (AII) (from 0.38 to 1 μg min−1) on the determinants of glomerular filtration have been studied. The intracapillary and transcapillary pressure gradients along the capillaries, together with 2 parameters characterizing the porosity of the membrane in terms of pore theory (r, radius of the pores and Ap/1, total pore area per unit of path length) were calculated from the analysis of the sieving curve of I125 PVP molecules (polyvinylpyrrolidone) according to a biomathematical model previously described. A II increased PGC, the intracapillary hydrostatic pressure, but more at the efferent end of the capillaries. Filtration pressure equilibrium was maintained. A II also decreased the water permeability coefficient,K f , by decreasing Ap/1,r remaining constant. Our results were compared to those obtained from the direct measurements of PGC, using micropuncture techniques in hydropenic and plasma loaded rats. The complete agreement between the two approaches confirms the validity of the method based on the analysis of the sieving data of neutral macromolecules to calculate the determinants of GFR.
    Type of Medium: Electronic Resource
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