Free water reabsorption during solute diuresis in normal and potassium-depleted rats

Abstract

Free water reabsorption (TcH2O) was studied in rats during massive hypsrtonic saline and mannitol diuresis, to determine whether a "limit" for TcH2O could be demonstrated. Since TcH2O vs osmolar clearance (Cosm) was linear as Cosm rose to the highest levels obtainable, it is concluded that the sodium transport system in the ascending limb of the loop of Henle is unsaturable up to the highest rate of sodium delivery to the loop of Henle which can be achieved in the intact animal. To determine the effect of increasing sodium delivery to the loop on the concentrating defect of K depletion, TcH2O was studied during solute diuresis in K-depleted rats. The slope of the regression of TcH2O vs. Cosm in K-depleted rats during saline diuresis of 0. 33 was significantly lower than the slope of 0. 52 in normal rats. Inulin clearances were similar in all groups. The data are best explained by an intrinsic defect in sodium transport in the ascending limb of the loop of Henle in K-depleted rats.