Resistance of ascending vasa recta to transport of water.
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.
Pallone
T L
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Division of Nephrology, M. S. Hershey Medical Center of Pennsylvania State University, Hershey 17033.
D000818:Animals; D001692:Biological Transport; D001834:Body Water / Q000378:metabolism*; D002196:Capillaries / Q000378:metabolism; D003911:Dextrans; D005260:Female; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives*; D005452:Fluoresceins; D007679:Kidney Medulla / Q000098:blood supply*; D008833:Microcirculation; D051381:Rats; D011919:Rats, Inbred Strains; D014655:Vascular Resistance
D003911:Dextrans; D005452:Fluoresceins; C015219:fluorescein isothiocyanate dextran; D016650:Fluorescein-5-isothiocyanate