Effect of cold exposure of free water reabsorption in hydropenic man.

With clearance technique, changes in tubular reabsorption of solute free water (TcH2O), were studied in a group of 9 healthy hydropenic volunteers during a cold stress of 1 h at +15 degrees C. Increases were found in TcH2O and in fractional excretion of sodium and osmoles during cold. Since TcH2O was used as an index of sodium reabsorption in the ascending limb of Henle's loop, the findings indicated that under the conditions used in this study, the concentrating ability of the kidney was not negatively influenced by cold, despite a significant increase in arterial pressure. It is suggested that the reabsorption by the ascending limb of the loop was increased secondary to a reduced proximal tubular reabsorption of sodium.