Molecular parameters other than size and charge are likely to influence the filtration of macromolecules across the glomerular filter. We have studied, therefore, the glomerular permeability of macro-molecules with widely different molecular configuration such as horseradish peroxidase, a plant glycoprotein with an isoelectric point in the physiologic pH range, and dextran, an uncharged sugar polymer of D-glucopyranose. Simultaneous fractional clearances were determined for both test macromolecules in five Wistar-Furth rats. The results indicate that for a molecular radius of 28.45 Å, as measured by gel filtration, the sugar polymer has a fractional clearance of 0.483 on the average, exceeding that of the protein tracer, with a value of 0.068, by a factor > 7. We conclude that other molecular parameters such as shape, flexibility, and deformability play important roles in the transport of macromolecules across the extracellular matrix that constitutes the glomerular filter.
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