The imidazoline-preferring receptor.

Evidence gathered over the past ten years supports the existence of subtypes of alpha 2-adrenoceptors. A receptor which resembles the alpha 2-adrenoceptor, called the imidazoline-preferring receptor (IPR), is virtually insensitive to catecholamines but binds selectively imidazolines and oxazolines such as idazoxan and rilmenidine. In contrast, the catecholamine-preferring alpha 2-adrenoceptor is preferentially activated by catecholamines including alpha-methylnorepinephrine and epinephrine and is antagonized selectively by rauwolscine. In addition to different pharmacological profiles to agonists and antagonists, the IPR and alpha 2-adrenoceptors show differences in anatomical distribution and molecular properties. The evidence has been drawn primarily from in vitro physiological and radioligand binding studies, but is gradually extending into in vivo and even clinical studies.