Resistance of ascending vasa recta to transport of water

Am J Physiol. 1991 Mar;260(3 Pt 2):F303-10. doi: 10.1152/ajprenal.1991.260.3.F303.


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 In group II, volume flux was 1.8 +/- 1.3, 5.9 +/- 1.0, and 11.2 +/- 1.1 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport
  • Body Water / metabolism*
  • Capillaries / metabolism
  • Dextrans
  • Female
  • Fluorescein-5-isothiocyanate* / analogs & derivatives*
  • Fluoresceins
  • Kidney Medulla / blood supply*
  • Microcirculation
  • Rats
  • Rats, Inbred Strains
  • Vascular Resistance*


  • Dextrans
  • Fluoresceins
  • fluorescein isothiocyanate dextran
  • Fluorescein-5-isothiocyanate