Modulation of the rat adrenal medulla norepinephrine secretion in a sodium-free medium by atrial natriuretic factor

The effects of atrial natriuretic factor (ANF) on [3H]norepinephrine ([3H]NE) release evoked by a sodium-free medium (SFM) were studied. Experiments were performed in rat adrenal medulla slices incubated in vitro. Results showed that [3H]NE release evoked by the omission of Na+ was decreased by 10 nM ANF. In addition, when the Ca2+ was omitted from the SFM, NE output was partially diminished. Nevertheless, if ANF was added to SFM/Ca(2+)-free medium (CFM), NE secretion showed no modifications compared with SFM/CFM. Present results raise the hypothesis that two mechanisms could be involved in NE output evoked by a SFM in the rat adrenal medulla: one independent of and the other dependent on the extracellular calcium. Moreover, ANF only diminished NE secretion evoked by SFM dependent on extracellular calcium and did not modify calcium-independent NE release.