AJP - Renal Physiology, Vol 251, Issue 3 528-F531, Copyright © 1986 by American Physiological Society
Glomerular capillary permeability in developing canines
D. I. Goldsmith, R. A. Jodorkovsky, J. Sherwinter, S. R. Kleeman and A. Spitzer
The changes in glomerular permeability that occur during development were
assessed in 1- and 6-wk-old canines by analyzing dextran-sieving curves
obtained in six animals at each age. The fractional clearance of the
smallest dextran molecules (18 A) was 0.97 +/- 0.02 (+/- SE) in both 1- and
6-wk-old animals, and it became progressively less at larger molecular
sizes. The sieving curves were consistent with an isosporous model of a
glomerular capillary. When axial changes in protein concentration were
included in the mathematical model, the apparent pore radius was 62.7 +/-
1.7 and 61.7 +/- 1.69 A in 1- and 6-wk-old puppies, respectively (P greater
than 0.7). The effects of developmental changes in hydrostatic pressure and
renal blood flow were balanced by the increases in serum protein
concentration and filtration fraction leaving the fractional clearances of
macromolecules unchanged. In contrast, the total cross-sectional pore area
per unit path length (Aw/delta x) increased during this 6-wk period by
approximately 7.5-fold (from 1.39 +/- 0.2 to 10.55 +/- 3.0 10(-5) cm, P
less than 0.0001), and the ultrafiltration coefficient rose from 0.012 +/-
0.002 to 0.093 +/- 0.012 ml X s-1 X mmHg-1 (P less than 0.0001). The
findings reveal constancy of pore size and an increase in total pore area
as a function of age. Analysis by classical pore theory yielded similar
findings. We conclude that the predominant factor determining the rise in
glomerular filtration rate during development is the large increment in
Aw/delta x, which in turn is due to increases in the surface area and pore
density of the glomerular capillaries.
