ARC 239 dihydrochloride is a selective antagonist of α2B adrenoceptor with pKD value of 8.8 . α2B adrenoceptor is a G-protein coupled receptor. α2-adrenergic receptors include three subtypes: α2A, α2B and α2C, which play an important role in regulating neurotransmitter release from adrenergic neurons in the central nervous system and from sympathetic nerves. ARC 239 dihydrochloride is a selective α2B adrenoceptor antagonist. In rat brain, ARC 239 inhibited the binding of 5-HTIA receptor radioligands 8-OH-DPAT and RX 821002 to cortical membranes with Ki values of 63.1 and 136 nM respectively, which suggested that ARC 239 recognized 5-HT1A receptor . Treatment human platelets with ARC 239 significantly inhibited platelet aggregation induced by adenosine diphosphate (ADP), epinephrine and arachidonic acid and increased collagen/epinephrine closure time, which suggested that α2B adrenoceptor play a critical role in platelet aggregation . In cervical samples isolated from pregnant rats, ARC 239 effectively inhibited noradrenaline-stimulated contractions . In C57BL/6 mice with gastric mucosal damage induced by acidified ethanol, ARC 239 (10.4 nM) antagonized gastroprotective effect induced by α2-adrenoceptor agonists .