Renal water reabsorption during saline and urea osmotic diuresis in the dog

Abstract

Free water reabsorption (T_w^c) was measured in conscious dogs during a long-term, reasonably steady-state osmotic diuresis induced either by sodium salts or by urea. After 4 to 8 hr the original solute was partially replaced by urea or by sodium salts. Both the replacement of sodium salts by urea and the converse procedure were associated with an augmentation in T_w^c. During sodium diuresis T_w^c always fell during the first 2 or 3 hr, a change which appeared unrelated to glomerular filtration rate (GFR) or to osmolar clearance. During the course of urea diuresis T_w^c steadily increased and showed a positive correlation with GFR. A possible basis for such a correlation is discussed.