Moxonidine displays a presynaptic alpha-2-adrenoceptor-dependent synergistic sympathoinhibitory action at imidazoline-1 receptors. 
The function of presynaptic imidazoline-1 receptors (I1-R) in the heart remains unclear.  In rat hearts, UK14.304 and moxonidine reduced norepinephrine (NE) release.  AGN192403 had no influence on NE, whereas rilmenidine, agmatine, rauwolscine, and efaroxan increased NE.  These effects of moxonidine and rilmenidine were not affected by AGN192403 adminstration.  Conversely, after pretreatment with UK14.304, only moxonidine displayed a pronounced inhibitory action on NE release (sensitive to AGN192403), indicating a synergistic inhibitory action at I1-R under conditions of a stimulated alpha2-adrenergic autoinhibition.