Biological significance of agmatine, an endogenous ligand at imidazoline binding sites

Many publications have shown that imidazoline derivatives such as clonidine, moxonidine or rilmenidine reduce sympathetic tone via a central mechanism and that as a result they reduce plasma catecholamines and blood pressure. This reduction in blood pressure appears not to be regulated via peripheral, presynaptically localized receptors, since neither catecholamine depletion by reserpine, or since neither catecholamine destruction of the nerve endings with 6-hydroxydopamine produces a notable weakening of the clonidine-induced blood pressure reduction.