Transfer of Na transport inhibition in proximal tubules from saline volume-expanded to nonexpanded rats.

In dual micropuncture experiments the shrinking drop technique was used to measure volume flux with artificial tubular fluid (AF) alternating with harvested tubular fluid (HTF) during saline volume-expanded (VE) and nonexpanded (NE) periods. In VE rats, volume flux (Jv) (nl.mm-1.min-1) with AF was 1.78 +/- 0.08 (means +/- SE) during NE and was reduced to 1.39 +/- 0.09 (P = 0.01) during subsequent VE, whereas with randomly alternating HTF during VE it was 1.07 +/- 0.08 (P less than 0.0001 and less than 0.03, respectively). Jv with HTF from NE rats tested in the VE rats was 1.20 +/- 0.06, which is significantly higher than that measured with their own HTF (Wilcoxon rank, P = 0.05). In NE rats Jv was 1.65 +/- 0.10 and 1.69 +/- 0.10 with AF and HTF and was 1.28 +/- 0.07 (P less than 0.001 from both) with HTF obtained from VE rats. Elemental analysis of reaspirated tubular fluids showed no significant differences in Na or Cl concentrations among any of the fluids. It is concluded that during VE, a transferable Na transport inhibitor appears in proximal tubular fluid, which, together with a changed proximal tubular epithelium, possibly due to physical forces, accounts for proximal tubular Na transport inhibition during VE.