Determination of glomerular intracapillary and transcapillary pressure gradients from sieving data

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Abstract
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.