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Glomerular and postglomerular permselectivity to anionic dextrans in the dog
Glomerular (G) and postglomerular (PG) capillary permselectivity to anionic dextran markers was investigated using the multiple-indicator-dilution (MID) technique in anesthetized mongrel dogs (n = 14). A bolus of solutes that included sulfated [3H]dextran (SO4d) homogeneous fractions 15.0-28.5 A Stokes-Einstein radius, 125I-albumin (plasma reference), [14C]inulin (G reference), and creatinine (interstitial reference) was injected into the left renal artery. Serial samples of left renal venous and urine outflows were rapidly collected. Sulfated [3H]dextran was 100% recovered, indicating no secretion or reabsorption. The urine recovery of the extracellular indicators was a measure of G extraction (EG). Mean EGSO4d/EGi (+/- SD) ranged from 0.82 +/- 0.03 to 0.48 +/- 0.02 for SO4d's 15.0-28.5 A and was invariant with renal plasma flow (F). These values were 30-50% less than the fractional EG for neutral [3H]dextrans. Postglomerular capillary extraction (EPG) was calculated from the renal vein outflow curve upslope ratios. EPGso4d/EPGcreat varied inversely with F, confirming PG diffusion limitation. Mean permeability-surface area (PS) product ratios PSSO4d/PSi (+/- SD) ranged from 0.98 +/- 0.01 to 0.55 +/- 0.04 for SO4d's 15.0-28.5 A and were consistently larger than values for neutral [3H]dextrans of the same molecular size. In contrast to G charge limitation to anionic solute flux, the PG capillaries demonstrate an increase in apparent permeability to anionic relative to neutral dextrans.
Glomerular (G) and postglomerular (PG) capillary permselectivity to anionic dextran markers was investigated using the multiple-indicator-dilution (MID) technique in anesthetized mongrel dogs (n = 14). A bolus of solutes that included sulfated [3H]dextran (SO4d) homogeneous fractions 15.0-28.5 A Stokes-Einstein radius, 125I-albumin (plasma reference), [14C]inulin (G reference), and creatinine (interstitial reference) was injected into the left renal artery. Serial samples of left renal venous and urine outflows were rapidly collected. Sulfated [3H]dextran was 100% recovered, indicating no secretion or reabsorption. The urine recovery of the extracellular indicators was a measure of G extraction (EG). Mean EGSO4d/EGi (+/- SD) ranged from 0.82 +/- 0.03 to 0.48 +/- 0.02 for SO4d's 15.0-28.5 A and was invariant with renal plasma flow (F). These values were 30-50% less than the fractional EG for neutral [3H]dextrans. Postglomerular capillary extraction (EPG) was calculated from the renal vein outflow curve upslope ratios. EPGso4d/EPGcreat varied inversely with F, confirming PG diffusion limitation. Mean permeability-surface area (PS) product ratios PSSO4d/PSi (+/- SD) ranged from 0.98 +/- 0.01 to 0.55 +/- 0.04 for SO4d's 15.0-28.5 A and were consistently larger than values for neutral [3H]dextrans of the same molecular size. In contrast to G charge limitation to anionic solute flux, the PG capillaries demonstrate an increase in apparent permeability to anionic relative to neutral dextrans.