Inhibitory effects of harvested proximal tubular fluid on Jv and delta cNa during acute saline volume expansion in the rat.

The present micropuncture experiments were carried out in male Wistar rats during isotonic saline volume expansion (VE) to explore the relative importance of peritubular physical forces and tubular factors on proximal tubular Na transport. Isotonic volume flux, measured by the shrinking drop technique was reduced from 3.53 +/- 0.09 X 10(-4) . mm3 . mm-2 . s-1 with the artificial fluid to 1.79 +/- 0.1 with harvested autologous proximal tubular fluid (HTF) (49%), but only to 2.77 +/- 0.1 (78% of control) with artificial tubular solution (AS), both during volume expansion. delta cNa was reduced from a control of 18.0 +/- 2.2 mmol . kg-1 -14.5 +/- 2.0 with AS (81%) and 10.0 +/- 2.4 with HTF (56%) during VE. Thus both isotonic volume flux as well as delta cNa were reduced to the same degree by saline VE. These results and those obtained previously with mannitol-saline VE, indicate the presence of a factor in harvested proximal tubular fluid of volume expanded rats which inhibits sodium and water transport independent of peritubular osmolarity.