GLOMERULAR SIZE-SELECTIVITY DURING PROTEIN OVERLOAD IN THE RAT

Differential glomerular permeability to macromolecules as a function of 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 dextrans in anesthetized Wistar-Furth rats. The animals were studied 3-4 h after the last of six twice-a-day intraperitoneal injections of either bovine serum albumin (BSA) or ovalbumin (OA) or of vehicle alone (controls). Glomerular filtration rates did not differ significantly among the three groups. OA-treated (n = 4) and control (n = 5) rats had virtually identical fractional dextran clearances over almost the entire molecular size range from 18 to 58 angstrom Stokes-Einstein radius. In contrast, BSA-treated rats (n = 5) had elevated fractional clearances for medium-sized dextrans with the increases reaching statistical significance at radii of 40 angstrom (+22.7% vs. control) and 44 angstrom (+20.4%). Fractional clearances for BSA-treated rats returned to control values for larger dextrans. These findings demonstrate a significant size permselectivity defect in BSA overload, although not in OA overload.