Inhibition of Renal Tubular Sodium Reabsorption by Hypernatremia*

Abstract

In a recent study (1), we confirmed the obser- vation of Bresler (2) and Toussaint and Vereer- straeten (3) that tubular sodium reabsorption (TNa) in dogs increases following plasma sodium (PNa) elevation. However, when the increase in filtered sodium (FNa) that usually accompanied an elevated PNa was eliminated by reducing glo- merular filtration rate (GFR) with an aortic clamp, hypernatremia appeared to inhibit rather than stimulate TNa. Similar results have been ob- tained by Blythe and Welt (4), who found that sodium excretion during the infusion of hypertonic saline was above control when filtered sodium was reduced below control by inflating a balloon in the inferior vena cava. The micropuncture studies of Giebisch, Klose, and Windhager (5) in rats have also demonstrated that TNa is de- creased by hypertonic saline infusions.