Atrial natriuretic factor modifies noradrenaline release in a sodium-free medium

1. The effects of atrial natriuretic factor (ANF) on 3H-noradrenaline (3H-NA) release evoked by a sodium-free medium (SFM) were studied. The experiments were carried out in rat hypothalamic slices incubated in vitro. 2. ANF (1, 10 and 100 nM) decreased NA release evoked by the omission of sodium in a concentration-dependent way. When calcium was omitted from a SFM, NA output was partially diminished. However, if ANF was added to the SFM/calcium free medium NA secretion showed no modifications. 3. Present results suggest that, in rat hypothalamus, NA release evoked by Na+ omission is divided into two fractions: one independent of and the other dependent on extracellular calcium. In addition, ANF modifies NA release evoked by SFM dependent on extracellular calcium.