RENAL CLEARANCES OF GRASS POLYSACCHARIDE: OBSERVATIONS ON GLOMERULAR POROSITY AND ON THE RELATION OF THIS FUNCTION TO PROTEINURIA IN RENAL DISEASE

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Abstract
Renal plasma clearances of a polysaccharide isolated from Italian rye grass with a mean mol. wt. of about 5400 were measured in dogs and human beings. The observations in dogs indicated that the material was not all freely filterable through the glomerulus. The ratio of polysaccharide clearance (Cp) to creatinine clearance (Ccr) was less than unity and decreased in successive clearance periods, apparently because of the more rapid excretion of the more filterable component(s) of the polysaccharide. In normal human beings, the ratio of Cp to mannitol clearance (CM) averaged 1.1, indicating that the polysaccharide was freely filterable with a renal clearance equal to that of inulin. The human glomerulus is apparently a less retentive filter than that of dogs. Observations in patients with hypertensive disease yielded a mean Cp/CM of 0.98, indicating that about 10% of the residual glomerular bed has become impermeable to the polysaccharide, while still permeable to mannitol. In patients with primary glomerular disease still lower ratios were found. These were interpreted as resulting from decreased glomerular porosity and were considered to confirm by functional means, the severe anatomical changes which would be found in the glomerular capillaries in these conditions. Assuming the ratio Cp/CM to be a measure of relative glomerular porosity, glomerular porosity is found to decrease as proteinuria increases in hypertensive and primary glomerular renal disease. From this it seems to follow the mechanism of such proteinuria is more probably glomerular than tubular.

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