Clonidine is a centrally acting α2-adrenergic receptor agonist that decreases peripheral vascular resistance by centrally inhibiting sympathetic nerve activity. In isolated mesenteric arteries precontracted with norepinephrine, clonidine induces relaxation at 10 μM. It can also open K+ channels and hyperpolarize mensenteric artery plasma membrane at this concentration. The antihypertensive effects of clonidine have also been attributed to its agonism of the imidazoline (I1) receptor (Ki = 4-8 nM), which mediates the sympatho-inhibitory actions of imidazolines to lower blood pressure.
