[3H]DUP 753, a highly potent and specific radioligand for the angiotensin II-1 receptor subtype.

[3H]Dup 753, a nonpeptide angiotensin II (AII) receptor antagonist radioligand, was used to characterize a subtype of AII receptors in rat adrenal cortical microsomes. By Scatchard analysis, a single class of DuP 753 binding sites was found with an affinity of 6.4 nM and a Bmax of 1.3 pmol/mg protein. These sites were saturable and readily reversible. Angiotensin (I, II, III) expressed the same affinities and order of potency for these binding sites as those labeled by [3H]AII for the AII-1 sites. The affinities expressed by nonpeptide AII antagonists were commensurate with their inhibitory potencies on AII-1 receptors. PD123177, an AII-2 specific ligand, and other non-AII peptides showed no inhibitory action. These data together with the differential tissue distribution strongly support our conclusion that [3H]DuP 753 is a potent and highly specific radioligand for the AII-1 receptors.