Renal Extraction of PAH and of Diodrast-I¹³¹ as a Function of Arterial Red Cell Concentration

¹ From the Department of Physiology, Harvard Medical School, Boston, Massachusetts

The cell separation theory of renal hemodynamics predicts that the renal extraction of substances secreted by the tubules should vary with the concentration of red cells in arterial blood. This prediction has been tested in anesthetized cats and dogs breathing oxygen. The renal extractions of PAH and of trace concentrations of Diodrast-I¹³¹ were found to be smooth and reversible functions of the arterial red cell concentration. The transfer maxima of these substances were unaffected by removal of red cells and the extraction ratios decreased as a function of arterial hematocrit ratio even when the renal plasma flow was maintained constant. The results indicate that at low red cell concentrations about 50% of the renal plasma flow bypasses the tubular elements of the kidney. According to the cell separation theory this extra-tubular flow of plasma takes place through a short circulation which normally contains a cell-rich moiety of the blood.

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