OBJECTIVE To study the effect of agmatine (Agm) on carotid sinus baroreflex. METHODS The functional parameters of baroreflex were measured by perfusing the carotid sinus in anesthetized rats. RESULTS (1) Agm 1, 5, and 10 mmol/L shifted the functional curve of carotid sinus baroreflex to the right and upwards in a concentration-dependent manner with a reduction in peak slope and a reflex decrease in mean arterial pressure, indicating that Agm exerted an inhibitory effect on the carotid baroreflex. (2) The inhibitory effect of Agm (5 mmol/L) on baroreflex was eliminated by pretreatment with idazoxan (Ida, 0.1 mmol/L), an alpha2-adrenoceptor (alpha2-AR) and imidazoline receptor (IR) antagonist, and partially blocked by yohimbine (Yoh, 15 micromol/L), a selective alpha2-AR antagonist. (3) NG-nitro-L-arginine methyl ester (L-NAME, 500 micromol/L), an NOS inhibitor, did not affect the inhibitory effect of Agm. CONCLUSIONS Agm inhibits carotid baroreflex via IR and alpha2-AR.