Discrepancy between Renal Plasma Flow Values Determined Simultaneously from PAH and Thiosulfate by the Fick Method and Its Significance for Renal Lymph

Abstract

(1) A comparative study of the renal plasma flow was carried out with the Fick principle, employing PAH and sodium thiosulfate at the same time and firstly, keeping the the plasma PAH concentration low, i.e. between 2.01 and 11.6 mg/dl. in normal dogs whose renal vein has been catheterized. Thus C_PAH/E_PAH and C_T/E_T were determined in a total of 31 measurements on 11 dogs and the results were compared. It was found that C_PAH/E_PAH did not agree with C/_TE_T; while C_PAH/E_PAH per unit body weight gave a mean value of 9.60 cc/min/kg., C_T/E_T per unit body weight gave a mean value of 8.02 cc/min/kg., and the two values were significantly different on statistical basis. The ratio of C_PAH/E_PAH to C_T/E_T was 1.25 on the average.
(2) A similar experiment was performed with the same plasma concentration of thiosulfate but with higher PAH concentrations, i.e. 32.5-94.5 mg/dl. A total of 21 determinations of C_PAH/E_PAH and C_T/E_T were done on 7 dogs. C_PAH/E_PAH per unit body weight gave a mean value of 10.00 cc/min/kg. and C_T/E_T per unit body weight gave a mean value of 10.30 cc/min/kg.; two values were not significantly different on statistical basis. In this case C_PAH/E_PAH bore a ratio of 0.98 in respect to C_T/E_T on the average.
(3) The two ratios were significantly different on statistical basis, i.e. 1.25 obtained at low plasma concentrations of PAH on one hand, and 0.98 obtained at higher plasma concentrations of PAH.
(4) From these observations the author infers that a considerable fraction of the administered thiosulfate is carried out of the kidneys other than by way of the glomerulus into urine, i.e. postglomerular loss by way of the renal lymph. According to this view, the observed C_T/E_T does not represent the real renal plasma flow; it should give a value lower than C_PAH/E_PAH determined at low plasma PAH concentration.
This view seems to be supported by the fact that the ratio of C_PAH/E_PAH to C_T/E_T approaches unity, when plasma concentration of PAH is high, i.e. where extraction ratio for PAH approaches the extraction ratio for thiosulfate.