Solute and water flows in thin limbs of Henle's loop in the hamster kidney.

MARSH, DONALD J. Solute and water flows in thin limbs of Henle’s loop in the hamster kidney. Am. J. Physiol. 218(3) : 824433 1. 1970. -Collections were made from two sites in single thin limbs on the surface of the exposed hamster papilla. There was no change of the inulin TF/P along the first millimeter of thin ascending limb, a result that rules out hypotheses of hypertonic urine formation requiring the loops to remove water from the interstitium. In the same specimens osmolality, Na+, and K+ concentrations fell as fluid flowed from the bend of the loop up the ascending limb, but there was net urea entry into the tubular fluid. These results were interpreted as support for the countercurrent-multiplier hypothesis. Similar experiments in descending limbs revealed net entry of urea to tubular fluid as it flowed down toward the bend, but were inconclusive on the question of net entry of NaCl. Urea concentration in tubular fluid at the bend was lower than in adjacent vasa recta blood, so that all urea movement can be accounted for by passive movement down concentration gradients. ity and NaCl concentrations to values lower than in adjacent descending limbs, which simply equilibrate with the interstitial fluid.