Permeability of the loop of Henle, vasa recta, and collecting duct to water, urea, and sodium

Abstract

The permeability of the loops of Henle, collecting ducts, and vasa recta were studied by free-flow perfusion. When anti-diuretic hormone (ADH) was absent the diffusional permeability coefficient for tritiated water (THO) in the descending limb (DL) was 119 [plus or minus] 14 (SE) cm sec-1 X 10"5, ascending limb (AL) 50 [plus or minus] 4.5 collecting duct (CD) 45 [plus or minus] 3.1, and vasa recta (VR) at least 192 [plus or minus] 20. ADH increased the value for collecting ducts to 87 [plus or minus] 7 without changing the other values. The diffusional permeability coefficients for urea were DL 13 [plus or minus] 3.0; AL 14 [plus or minus] 2.0; CD 20 [plus or minus] 1.3; and VR 47 [plus or minus] 3.3. ADH increased the permeability of the CD (30 [plus or minus] 2.4) without affecting the other structures. The permeability of the descending limb changed before the hairpin bend. Net water flux was DL 58 [plus or minus] 6.2 nliters cm"2 milliosmol-1 min"1, AL 4.4 [plus or minus] 1.1; CD (no ADH) 4.2 [plus or minus] 2.2; CD (ADH) 30 [plus or minus] 2.6. All parts of the nephron were relatively impermeable to mannitol but were permeable to urea. NaCl did not enter the collecting duct or ascending limb but entered the descending limb of Henle''s loop. These observations are consistent with what would be predicted if the driving force of the countercurrent system were a Na pump in the ascending limb of the loop of Henle, although such a pump was not demonstrated in this preparation.