Glomerular function in advanced human diabetic nephropathy.

Intrinsic membrane properties of the glomerular capillary wall were evaluated in 20 diabetic patients, who had heavy proteinuria and reduced GFR, and in 15 healthy control subjects. The glomerular sieving coefficients were determined for narrow dextran fractions with molecular radii between 20 and 64 A. GFR determinants were directly measured or indirectly estimated. These quantities were then subjected to a theoretical analysis based upon (1) a mathematical model of glomerular ultrafiltration and (2) a pore model of transmembrane solute transport. The results indicated that in patients with diabetic nephropathy and glomerular ultrafiltration coefficient (0.02 vs. 0.16 ml . sec-1 . mm Hg-1 . 1.73m-2), effective pore area-to-pore length (2.6 x 10(6) vs. 20.0 x 10(6) cm), and mean pore radius (56.8 vs. 58.0 A) are all reduced relative to normal control subjects. It is suggested that (1) hypofiltration in advanced diabetic nephropathy results, in part, from reduction of the surface area available for filtration, while (2) proteinuria is a consequence of either loss of electrostatic barrier function, of isolated focal disruptions within the glomerular filtration barrier, or a combination thereof.