A micropuncture study of the renal concentrating defect of potassium depletion

Abstract

In order to study the renal concentrating defect of potassium depletion, tubular fluid osmolality and segmental water reabsorption were measured in surface nephrons of K-deficient rats and normal controls, using micropuncture methods. The osmolality of proximal and distal tubular fluid was found to follow the same pattern as in normal rats. Many of the proximal TF/PIn ratios and almost all of the distal TF/PIn ratios were higher in the K-deficient rats than in the normals. The data from the early distal tubule suggest that sodium chloride transport by the ascending limb of Henle's loop is not markedly impaired. Delivery of fluid to the collecting ducts was diminished, thus exlcuding the possibility that increased volume flow to this segment is responsible for the concentrating defect. The finding of elevated proximal TF/PIn ratios suggests that delivery of solute to the loops of Henle may be chronically decreased. This could account for low concentrations of sodium and urea in the medullary interstitium and thus play an important contributing role in the hyposthenuria of potassium depletion.