GLOMERULAR SIZE-SELECTIVITY DURING PROTEIN OVERLOAD IN THE RAT

Differential glomerular permeability to macromolecules as a function o f their size (size permselectivity) is altered in experimental models of proteinuric renal disease. Size permselectivity during protein over -load proteinuria was examined using urinary clearances of neutral dex trans in anesthetized Wistar-Furth rats. The animals were studied 3-4 h after the last of six twice-a-day intraperitoneal injections of eith er bovine serum albumin (BSA) or ovalbumin (OA) or of vehicle alone (c ontrols). Glomerular filtration rates did not differ significantly amo ng the three groups. OA-treated (n = 4) and control (n = 5) rats had v irtually identical fractional dextran clearances over almost the entir e molecular size range from 18 to 58 angstrom Stokes-Einstein radius. In contrast, BSA-treated rats (n = 5) had elevated fractional clearanc es for medium-sized dextrans with the increases reaching statistical s ignificance at radii of 40 angstrom (+22.7% vs. control) and 44 angstr om (+20.4%). Fractional clearances for BSA-treated rats returned to co ntrol values for larger dextrans. These findings demonstrate a signifi cant size permselectivity defect in BSA overload, although not in OA o verload.