The effect of vasopressin on renal tubular 22Na efflux in the rat.

1. Paired tracer microinjections of [3H]inulin and 22Na were performed at late proximal and early distal puncture sites in water diuresis and during vasopressin-induced antidiuresis in anaesthetized rats. Vasopressin caused a sixfold increase in Na and a fourfold increase in K excretion without significant changes in renal haemodynamics. 2. 22Na-recovery from late proximal injections increased nearly fivefold (from 0.98+/- 0.16 to 4.76 +/- 0.66%, P less than 0.001). A significant correlation could be detected between changes in sodium excretion and changes in late proximal 22Na recovery. Vasopressin had no significant effect on 22Na recovery from early distal injections. 3. These results suggest that vasopressin inhibits active salt reabsorption within the loop of Henle.