AJP - Renal Physiology, Vol 241, Issue 3 238-F243, Copyright © 1981 by American Physiological Society
Measurement of nephron filtration in the dog: role of proximal intratubular pressure
D. A. Hartupee, A. H. Gillies and F. G. Knox
Previous studies concerning the measurement of single nephron filtration
rate have shown that collections of proximal tubular fluid, in which an oil
drop is held in a constant position, do not affect intratubular pressure in
the early proximal tubule in the hydropenic rat. Since intratubular
pressures are higher in the dog than the rat, we investigated the effect of
position-controlled collections on proximal pressure and single nephron
filtration rate (SNGFR) in the dog. During position-controlled collections,
early proximal pressure fell 5.8 +/- 0.9 mmHg and SNGFR was 76.3 +/- 5.3
nl/min. During proximal re-collections, in which proximal pressure was
maintained near the free-flow value using a long immobile oil block, SNGFR
was significantly less, 44.4 +/- 5.5 nl/min. For each micropunctured
kidney, SNGFR was also estimated by dividing GFR by the number of glomeruli
(mean, 5.4 +/- 0.5 X 10(5)). Estimated SNGFR (50.9 +/- 6.3 nl/min) was not
significantly different from pressure-controlled SNGFR but was
significantly less than position-controlled SNGFR. Accordingly, in the dog,
early proximal pressure decreases during position-controlled collection of
proximal tubular fluid, resulting in an overestimation of SNGFR. This
artifact can be avoided by controlling the intratubular pressure during
collection of tubular fluid.
