AJP - Renal Physiology, Vol 245, Issue 4 496-F505, Copyright © 1983 by American Physiological Society
Determination of postglomerular permselectivity to neutral dextrans in the dog
C. Whiteside and M. Silverman
The single-pass multiple-indicator-dilution (MID) technique was used to
analyze postglomerular capillary permeability. Anesthetized mongrel dogs (n
= 13) during mannitol diuresis received a pulse injection of 125I-albumin
(plasma reference), [14C]inulin (glomerular reference), creatinine
(interstitial reference), and a homogeneous [3H]dextran molecular weight
marker 6,000-12,000 dalton in the left renal artery. Simultaneous left
renal venous outflow and right and left urine were rapidly sampled. Left
urine recoveries of creatinine, [14C]inulin, and [3H]dextran were
identical, indicating no glomerular solute flux limitation. Progressive
precession of the [14C]inulin and [3H]dextran renal vein curves relative to
creatinine indicated increasing postglomerular limitation to solute flux
proportional to molecular size. The postglomerular solute extraction (EPG)
(renal vein upslope indicator/125I-albumin) varied inversely with
postglomerular renal plasma flow (F), indicating diffusion limitation.
Ouabain infusion into the left renal artery significantly reduced Na
reabsorption but did not alter the EPG of [14C]inulin or [3H]dextran.
Permeability-surface (PS) area products calculated from EPG and F ranged
from 4.86 +/- 0.89 to 0.97 +/- 0.25 (SD) cm X s-1 X 100 g-1 for indicators
5,000-12,000 dalton. [14C]Inulin PS products remained constant for F
greater than or equal to 2.50 ml X s-1 X 100 g kidney-1.
PS[3H]dextran/PS[14C]In (n = 20, F greater than or equal to 2.5 ml X s-1)
was used to calculate an effective postglomerular capillary pore radius, r
= 55.5 +/- 7.6 (SD) A.
