AJP - Renal Physiology, Vol 245, Issue 1 41-F47, Copyright © 1983 by American Physiological Society
Effect of volume expansion and plasma chloride on function of the loop segment
B. B. Booker, R. H. Williams and R. G. Luke
To determine the effect of acute volume expansion and changes in plasma
chloride on fluid and chloride uptake in superficial loop segments of rats,
this segment was microperfused in vivo at 22 nl/min with a fluid containing
Na 145, Cl and 36Cl 130, and HCO3 15 meq/liter during hydropenia and after
acute volume expansion with 0.15 M NaCl, 0.15 M NaHCO3, or an isotonic
bicarbonate Ringer (Cl 106 meq/liter) solution. Fractional fluid, chloride,
and 36Cl reabsorption and early distal chloride concentration did not
change during maintained hydropenia (time control) or during volume
expansion with NaCl (plasma chloride 120 meq/liter) or bicarbonate Ringer
solution (plasma chloride 104 meq/liter). Absolute and fractional
reabsorption of chloride and 36Cl increased, without change in fluid
reabsorption, and early distal chloride diminished after infusion of NaHCO3
(plasma chloride 90 meq/liter). It is concluded that acute volume
expansion, per se, has no effect on either net fluid or net chloride
absorption in the superficial loop segment at the load studied.
Hypochloremia is associated with increased net reabsorption of chloride and
an increased unidirectional efflux of chloride from the loop segment during
acute volume expansion, most likely due to a gradient effect on the thick
ascending limb of the loop of Henle.
