PD 123319 is shown to discriminate between two subclasses of AII receptors in many different tissues. 125I-AII specifically labeled 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]