PD 123319 (ditrifluoroacetate) is a potent, selective AT2 angiotensin II receptor antagonist with IC₅₀ of 34 nM. IC50 & Target: IC50: 34 nM (AT2 Receptor)^[1] In Vitro: PD 123319 is shown to discriminate between two subclasses of AII receptors in many different tissues. ¹²⁵I-AII specifically label two classes of binding sites for AII in a membrane preparation of bovine adrenal glomerulosa cells. The first class (DuP-753 sensitive) represents approximately 85% of the total binding sites for AII and possesses a high affinity (IC₅₀ of 92.9 nM) for DuP-753. PD-123319 does not have any effect on ¹²⁵I-AII binding to this site. The second class of binding sites is more sensitive to PD-123319, with an IC₅₀ of 6.9 nM, and has a much lower affinity for DuP-753 (IC₅₀ around 10 microM)^[2].