Objective:To examine the interaction between i.c.v. administration of endothelin and brain natriuretic peptide (BNP) on vasopressin (AVP) secretion in unanesthetized, freely moving rats.Methods:i.c.v. cannulation and femoral artery catheterization were performed 7-8 days and 2 days before the experiment, respectively. Endothelin and BNP were injected into the third ventricle through the guide cannula. One millilitre of blood was collected for AVP measurement 30 min before and 10 min after i.c.v. injection.Results:Central administration of endothelin (20 or 40 pmol/2 (µl) dose-dependently evoked the elevation of plasma AVP levels. Preinjection of BNP (0.2 or 1 nmol/3 µl, i.c.v.) dose-dependently attenuated central endothelin (40 pmol/2 µl)-induced plasma AVP secretion.Conclusions:We have already reported that BNP attenuated central endothelin-induced pressor response and plasma catecholamine secretion. Taken together, the results indicate that BNP attenuated central endothelin-induced pressor response, at least partially, by suppressing sympathetic nervous system activation and plasma AVP secretion.