AJP - Renal Physiology, Vol 260, Issue 3 303-F310, Copyright © 1991 by American Physiological Society
Resistance of ascending vasa recta to transport of water
T. L. Pallone
Division of Nephrology, M. S. Hershey Medical Center of Pennsylvania State University, Hershey 17033.
A study was undertaken to determine the effect of increasing capillary
pressure on volume flux in ascending vasa recta (AVR). In one experiment
(group I), AVR were blocked by a single injection of paraffin wax and
subjected to free-flow microperfusion at 10 nl/min. Collected fluid was
obtained from the perfused vessels by micropuncture. In a second experiment
(group II), AVR segments were isolated between two paraffin blocks and
perfused at 10 nl/min. In group II, the collection pipette was pressurized
to 0, 10, or 20 mmHg. Transmembrane volume flux was determined by measuring
the change in concentration of fluorescein isothiocyanate-labeled dextran
(2 x 10(6) mol wt) from perfusate to collected fluid. In group I,
measurements revealed a capillary pressure of 10.3 +/- 0.5 (SE) mmHg and
volume flux of 4.3 +/- 1.0 nl.mm-1.min-1. In group II, volume flux was 1.8
+/- 1.3, 5.9 +/- 1.0, and 11.2 +/- 1.1 nl.mm-1.min-1 at collection
pressures of 0, 10, or 20 mmHg, respectively. Based on these data and an
AVR diameter of 20 microns, AVR hydraulic conductivity is between 12.5 x
10(-6) and 18.7 x 10(-6) cm.s-1.mmHg-1. The papillary AVR have a high
hydraulic conductivity. This is consistent with their role as the sole
conduit for removal of water from the papillary interstitium.
