Introduction: Emodin, an important active component of traditional Chinese herbs including rhubarb,exerts obvious anti-tumor, anti-bacterial, and anti-inflammatory effects.Recently: it is reported that emodin possesses a vasodilatory effect.However, the effects of emodin on the atrial natriuretic peptide (ANP) release have not yet been identified.It is well known that ANP, first discovered in the heart, is involved in the control of cardiovascular function and water and sodium balance.ANP is also known to possess anti-inflammatory, antioxidative, anti-proliferative, and lipolytic properties.The purpose of the present study was to identify the effects of emodin on the plasma levels of ANP and atrial secretory function.Methods: Experiments were performed in vivo and in vitro models.Emodin (100 mg/kg·day-1) was administered orally for 14 days in rats.hn vitro experiments:experiments were performed in perfused beating rabbit left atria.The change in ANP concentration was measured by a specific radioimmunoassay.Extracellular fluid translocation, transmural atrial clearance of 3H-inulin, was measured.The changes in atrial mechanical dynamics, atrial stroke volume and pulse pressure, were chased during the experiments.Results: Oral administration of emodin resulted in an increase in plasma levels of ANP.Emodin increased atrial myocyte ANP release concomitantly with a decrease in stroke volume and intra-atrial pulse pressure in a concentration-dependent manner.The emodin-induced changes were attenuated by atropine, a muscarinic receptor antagonist, and nifedipine, an L-type Ca2+ channel antagonist.Tetraethylammonium (TEA),a non-selective K+ channels blocker, attenuated the emodin-induced increase in ANP release but not the atrial dynamics.Inhibition ofATP-sensitive K+ channels with glibenclamide, had no effects on the emodin-induced atrial dynamics and secretory function.Conclusions: These findings indicate that emodin increases plasma levels of ANP and enhances atrial ANP secretion via activation of muscarinic receptors and K+ channels in experimental animals.