Micropuncture study of composition of loop of Henle fluid in desert rodents

Abstract

Using micropuncture techniques, fluid was collected from loops of Henle at the tip of the renal papilla in anesthetized hamsters and Psammomys, and its composition compared with that of collecting duct urine. The osmolalities of the two fluids were essentially the same. Sodium and attendant anions constituted 64% and urea 19% of the osmotically active solute in loop fluid. In collecting duct urine, urea was the major solute present, and sodium was present in low concentration. Inulin ratios indicated that 9% of the filtered water reached the tip of these loops at a time when 0.9% was in the final urine. The data support the countercurrent hypothesis for urine formation.