ABSTRACT-The pharmacological properties of 2-butyl-4-(methylthio)-1- [[2 [[[(propylamino)carbonyl] amino] sulfonyl](1,1 biphenyl)-4-yl]methyl]-1H-imidazole-5-carboxylate (HR720), a novel non-peptide angiotensin (Ang) II type I (AT1) receptor antagonist, were characterized in both in vitro and in vivo systems. In vitro autoradiography using 125I-[Sar1,IIe8]Ang II as a ligand revealed that HR720 competitively inhibited the specific binding of the ligand to the adrenal cortex. The IC50 value for the adrenal cortex was 1.5 x 10-8 M, and the IC50 for medulla was 1.4 x 10-6 M. Similar results were obtained in the adrenal cortex with CV-11974, a known potent AT1-receptor antagonist. Since AT1 receptors are known to predominate in the adrenal cortex and AT2-receptors in the adrenal medulla, it is considered that HR720 is highly selective for AT, receptors. HR720 inhibited the Ang II-induced contraction of isolated rabbit aortic strips and hu man gastroepiploic arteries in a noncompetitive manner, pD'2=9.40 and 9.62 for rabbit aorta and human artery, respectively. With CV-11974, pD'2 values of 9.84 in isolated rabbit aorta and 10.00 in human artery were obtained. HR720 did not affect the norepinephrine-, serotonin or KCl-induced contraction even at a concentration of 1 x 10-5 M. In anesthetized hamsters, HR720 induced a dose-dependent inhibition of the pressure response to Ang II. The potency of HR720 to antagonize the Ang II-induced pressure response was similar to that of CV-11974. These results demonstrate that HR720 is a potent and selective AT1 -receptor antagonist.
Keywords:Renin-angiotensin system, Angiotensin II, Receptor, Antagonist, Isolated vesselThe renin-angiotensin system (RAS) plays a critical role in blood pressure regulation and in fluid and electrolytes homeostasis; it is also involved in the pathogenesis of many cardiovascular diseases (1, 2). The RAS consists of a cascade of enzymatic reactions leading to formation of angiotensin (Ang) II which is a powerful vasoconstrictor. The angiotensin converting enzyme (ACE) inhibitors have clearly demonstrated the beneficial effect of pharmacological inhibition of the RAS in the treatment of hypertension and congestive heart failure (3). Recent studies have suggested that ACE inhibitors effectively prevented the progression of atherosclerosis in high cholesterol loaded rabbit aorta (4, 5) and inhibited the progression of renal damage in the rat model of chronic renal failure (6, 7), indicating the involvement of Ang II in such pathological disorders. However, there are many reports on the unwanted side effects of ACE inhibitors such as cough and angioedema resulting from the lack of * To whom correspondence should be addressed .specificity of ACE inhibitors for Ang I (8, 9). Moreover, ACE inhibitors interfere with the kinin metabolism (10). Recent studies have demonstrated that Ang II can also be formed in non-ACE-dependent manner in several species of animals including humans (11-13). In view of these limitations of ACE inhibitors, selective blocking of Ang I...