Abstract
If some otherwise suitable substance could be found which was completely removed from the blood on one passage through the kidneys, its blood clearance would be a measure of renal blood flow. If the substance were either (a) absent from the blood cells or (b) fixed in the cells during a passage through the kidney, its plasma clearance would be a measure of renal plasma flow (RPF). Diodrast (D) has been proposed by Smith and collaborators 1 , 2 , 3 as meeting or very nearly meeting the conditions that it is completely removed on passing active renal tissue and that it is absent from the cells. We find on trained, unanesthetized renal explant dogs, with D 4 and inulin 5 analyses of urine and of renal vein and arterial (or leg vein) whole blood, plasma and cells, that D plasma clearance departs considerably from RPF independently measured and we have established the factors which bring about this discrepancy.
1. Diodrast in cells. The statement of Smith 1 that D is absent from dog cells is based upon essentially complete recoveries from plasma of D added to drawn blood. We confirm this finding but find that after intravenous administration the ratio
averages 0.62, with extremes 0.48 to 0.73. The average is of 18 observations with plasma levels from 1.51 to 11.50 mg I per 100 cc; the value of the ratio is independent of plasma iodine (I) level, I being a measure of D.
2. Diodrast contribution to urine by cells. Even though we have shown that the cells contain a large proportion of the D, one could still use D plasma clearance as a measure of RPF (if plasma D extraction were complete) provided all the cell D stayed in the cells on passing the kidney.
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