p-iodo-Clonidine (hydrochloride) is a partial agonist of the alpha 2-adrenergic receptor [1].
The adrenergic receptors are G protein-coupled receptors that are targets of the catecholamines, especially norepinephrine and epinephrine. There are two main groups of adrenergic receptors: α receptors and β receptors. α2-adrenergic receptor is a Gi coupled receptor, which causes a decrease in neurotransmitter release, as well as a decrease of cAMP activity resulting in smooth muscle contraction [1].
p-iodo-Clonidine (hydrochloride) is a partial agonist of the alpha 2-adrenergic receptor. Clonidine is an antihypertensive α2-adrenergic receptor agonist. PIC had minimal agonist activity in inhibiting adenylate cyclase in platelet membranes through α2-adrenergic receptor, but it increased platelet aggregation induced by ADP with EC50 value of 1.5 μM. PIC also inhibited epinephrine-induced aggregation with IC50 value of 5.1 μM. PIC competed for [3H]bromoxidine binding with Ki value of 1.0 nM. PIC bound to the alpha 2B-AR in NG-10815 cell membranes with Kd value of 0.5 +/- 0.1 nM [1].
Reference:
[1]. Gerhardt MA, Wade SM, Neubig RR. p-[125I]iodoclonidine is a partial agonist at the alpha 2-adrenergic receptor. Mol Pharmacol. 1990 Aug;38(2):214-21.