Urine concentration during solute diuresis in potassium‐depleted rabbits. Evidence for a defect in tubular sodium transport

Abstract

SUMMARY1. The relationship between osmolal clearance (Cosm) and the reabsorption of solute-free water by the kidney (T-H0) was examined during 10% mannitol and 2-3 % saline diuresis in normal and potassium-depleted rabbits.2. In normal rabbits at osmolal clearances close to 3 0 ml./min, TcH0 during mannitol diuresis was 0-87 + 0-06 ml./min and during saline diuresis 119 + 0 07 ml./min. The mean difference in Tc20 Of 0-32 + 0.05 ml./min was highly significant (P < 0*001).3. In one group of potassium-depleted rabbits with a reduction in maximal urinary concentration, Tc20 during both mannitol and saline diureses was reduced significantly below normal and the increment in TH20 normally seen during saline diuresis was abolished.4. In a second group of potassium-depleted rabbits maximal urinary concentration (1253 + 88 m-osmole/kg H20) was not significantly different from that in normal rabbits (1272 + 116 m-osmole/kg H20). In these animals, Tc20 at osmolal clearances close to 3 0 ml./min was not significantly different during mannitol diuresis (0-83 + 0 07 ml./min) from that in normal animals, whereas it was reduced significantly during saline diuresis (0.89 + 0-07 ml./min, P < 0.001) and the difference in Te20 normally seen between mannitol and saline diuresis was abolished.5. The inability to increase TH0 during saline diuresis above that achieved during mannitol appears to be the earliest manifestation of the concentrating defect associated with potassium depletion. It probably results from an impairment of sodium transport by the ascending limb of the loop of Henle. This is supported by the fact that potassium-depleted rabbits excreted a greater percentage of the filtered load of sodium than did normal controls.