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 [H-3]norepinephrine ([H-3]NE) release evoked by a sodium-free medium (SFM) were studied. E xperiments were performed in rat adrenal medulla slices incubated in v itro. 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 fr om the SFM, NE output was partially diminished. Nevertheless, if ANF w as added to SFM/Ca2+-free medium (CFM), NE secretion showed no modific ations compared with SFM/CFM. Present results raise the hypothesis tha t 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 th e extracellular calcium. Moreover, ANF only diminished NE secretion ev oked by SFM dependent on extracellular calcium and did not modify calc ium-independent NE release.