AJP - Renal Physiology, Vol 242, Issue 1 1-F7, Copyright © 1982 by American Physiological Society
Methodologic considerations in the study of glomerular ultrafiltration
R. W. Osgood, H. J. Reineck and J. H. Stein
Over the past decade numerous studies have detailed the dynamics of
glomerular ultrafiltration. Observations in a unique strain of
Munich-Wistar rats, which afford the direct measurement of intraglomerular
capillary hydrostatic pressure, have determined that under normal
physiologic conditions these animals are in a state of filtration
equilibrium. Both mathematical models based on this observation and
experimental evidence indicate that under these circumstances the primary
determinant of glomerular filtration rate (GFR) is the rate of glomerular
plasma flow. In addition, this state of filtration equilibrium provides a
condition in which changes in the product of glomerular surface area and
glomerular capillary hydraulic conductivity (ultrafiltration coefficient)
have no influence on glomerular filtration rate. Similarly, changes in
glomerular hydrostatic pressure have a relatively small influence on GFR.
These conclusions represent a marked alteration of the previously held
concepts of the determinants of GFR. Unfortunately, studies in other
strains of rats and in other animal species, particularly the dog, have led
to the conclusion that filtration disequilibrium is the normal physiologic
condition. The validity of this conclusion, however, is made uncertain by
methodologic necessities that may lead to erroneous physiologic
measurements of the determinants of GFR. In the present Editorial Review we
examine the data reflecting on the applicability of filtration equilibrium
to mammalian species. In addition, we summarize two new in vitro techniques
for the further study of the dynamics of glomerular ultrafiltration.
