ATC Group: C02AC Imidazoline receptor agonists

Clonidine has been shown to have both central and peripheral sites of action. With long-term treatment clonidine reduces the responsiveness of peripheral vessels to vasoconstrictor and vasodilator substances and to sympathetic nerve stimulation. Early in treatment, however, blood pressure reduction is associated with a central reduction of sympathetic outflow and increased vagal tone.

Guanfacine is a selective alpha_2A-adrenergic receptor agonist in that it has 15-20 times higher affinity for this receptor subtype than for the alpha_2B or alpha_2C subtypes. Guanfacine is a non-stimulant. The mode of action of guanfacine in ADHD is not fully established.

Moxonidine has been shown to bind selectively to the I₁-imidazoline receptors in the brain stem. These imidazoline-sensitive receptors are concentrated in the rostral ventrolateral medulla, an area which is of crucial importance for central control of the peripheral sympathetic nervous system. The result of this effect on the I₁-imidazoline receptors has been apparent in reduced activity in the sympathetic nerves. (demonstrated for cardiac, splanchnic and renal sympathetic nerves).