INHIBITION OF RABBIT AORTIC ANGIOTENSIN-II (AII) RECEPTOR BY CV-11974, A NEW NONPEPTIDE-AII ANTAGONIST

The angiotensin II (AII) antagonistic action of CV-11974 yl)biphenyl-4 -yl!methyl!benzimidazole-7-carboxylic acid) was investigated in an AII -receptor binding assay using rabbit aortic membranes and an All-induc ed contraction assay using rabbit aortic strips. A single class of I- 125!AII-(Sar1,Ile8) binding sites was found in the membranes with a di ssociation constant (K(d)) of 0.15 nM and a receptor concentration (B( max)) of 86.9 fmol/mg protein. CV-11974 markedly reduced K(d) without affecting B(max). The specific binding of I-125!AII-(Sar1, Ile8) in t his preparation was inhibited competely by CV-11974 the inhibition co nstant (K(i)) = 0.64 nM!, DuP 753 an angiotensin Il type I (AT1) rece ptor-selective antagonist! (K(i) = 51 nM) and EXP3174 (an active metab olite of DuP 753) (K(i) = 6.8 nM), but was not affected by PD123177 (a n AT2 receptor-selective antagonist). These results suggest that the s ingle binding site in rabbit aortic membranes is an AT1 receptor subty pe. The affinity of CV-11974 to these AT1 receptors was approximately 80 and 10 times higher than that of DuP 753 and EXP3174, respectively. CV-11974 showed no appreciable affinity for the AT2 receptors found i n bovine cerebellum. In the in vitro functional study, CV-11974 marked ly reduced the AII-induced maximal contractile response of rabbit aort ic strips (pD'2 = 9.97). In contrast, Compound 7-H, which lacks the ca rboxyl group at the benzimidazole ring of CV-11974, inhibited the cont raction in a competitive manner. The inhibition by CV-1 1974 was long lasting. These results suggest that CV-11974 is a potent and long-acti ng AT1 receptor-selective, competitive antagonist. The carboxyl group at the benzimidazole ring plays an important role in the interaction b etween CV-1 1974 and the AT1 receptor.