The Extraction Fraction of p-Aminohippurate in the Superficial and Deep Venous Drainage Area of the Cat Kidney

Abstract

At plasma concentrations below 40 μg/ml the average extraction fraction of PAH was 0.95 in the superficial drainage area (consisting of approximately the outer half of the cortex), and 0.82 in the deep drainage area (the inner cortex + the medulla). Loading with Ringer's fluid, mannitol solution or plasma generally resulted in a decrease in the extraction fraction of both areas. The two extraction fractions fell to 0.86 and 0.64, respectively. The incompleteness of the extraction cannot be attributed to admixture of blood from the fibrous and fatty capsules of the kidney or to impurities in the PAH preparations. The erythrocytes showed a very low permeability to PAH; correction of renal venous plasma concentrations for diffusion of PAH from erythrocytes to plasma is unnecessary in the cat.—The Reubi principle of calculating the medullary plasma flow as the difference between the total renal plasma flow and the clearance of PAH is misleading in the cat, as it presumes complete extraction in cortical tissue.