The effects of endothelin-3 (ET-3) on changes in renal hemodynamics, urine formation, and norepinephrine (NE) overflow induced by renal nerve stimulation (RNS) were examined in anesthetized dogs. RNS at a low frequency (0.5-2.0 Hz) produced significant decreases in urine flow (UF), urinary excretion of sodium (UNaV), and fractional excretion of sodium (FENa), and increased the NE secretion rate (NESR) without affecting systemic or renal hemodynamics. RNS at a high frequency (2.5-5.0 Hz), which diminishes renal hemodynamics by causing renal vasoconstriction, affected urine formation and NESR more potently than did low-frequency RNS. When ET-3 (2.0 ng/kg/min) was infused into the renal artery, there was a slight and transient increase in renal blood flow (RBF); this response was followed by a gradual reduction. ET-3 infusion tended to increase the basal levels of UF without affecting UNaV, indicating the excretion of hypotonic urine with administration of this peptide. During ET-3 infusion, low-frequency RNS-induced antidiuretic action was significantly attenuated. Simultaneously, increase in NESR elicited by low-frequency RNS was markedly suppressed. Qualitatively similar results were observed in the case of high-frequency RNS. In addition, high-frequency RNS-induced decreases in the glomerular filtration rate (GFR) and the filtration fraction (FF) were suppressed by ET-3 infusion. These findings suggest that ET-3 suppresses renal responses to stimulated renal noradrenergic neurotransmission by inhibiting the release of NE. These findings, together with our previous findings, suggest that ET-3 (and/or ET-1) functions as an inhibitory modulator of the renal noradrenergic nervous system through the prejunctional ETB-receptor mechanism.