Renin is a crucial enzyme in the renin-angiotensin system, and the inhibition of its activity is considered as a useful approach to the treatment of hypertension. The inhibitory effect of catechinrelated compounds on renin was investigated in this work. It was found that epigallocatechin gallate (EGCg) possessed the strongest activity with an IC 50 value of 44.53 μM and acted in an uncompetitive manner. Gallated catechins exerted higher inhibition than the ungallated forms, and gallic acid exhibited an inhibitory potency close to that of epicatechin gallate (ECg). Results indicated that the galloyl moiety and ortho-trihydroxy phenyl structures might be favorable for the renin-inhibitory activity of these compounds.Hypertension is significantly associated with the incidence of various cardiovascular diseases. The renin-angiotensin system (RAS) plays an important role in regulating blood pressure in animals, and its inhibition has been well established as an approach to the treatment of hypertension (15). In this system, renin (EC 3.4.23.15) and angiotensin I-converting enzyme (ACE; EC 3.4.15.1) are two key enzymes. Renin can cleave the N-terminus of angiotensinogen to yield angiotensin I, which is an inactive peptide and may further be processed by ACE to produce angiotensin II, a potent vasoconstrictor. Since the conversion catalyzed by renin is the rate-limiting step, it is thought that direct renin inhibition could lead to better suppression of high blood pressure than ACE inhibition can (2). Although many ACE inhibitors derived from foodstuffs have been identified in the past (7), only a few reports on natural renin inhibitors were available (6,11,20,21). Studies have supported that polyphenol-containing materials such as black and green tea (14), red wine (12), cocoa extract (5, 17) and azuki bean seed coats (13) could reduce blood pressure in several experimental hypertensive models. The mechanisms underlying this effect were proposed to be attributable to vasodilator action, the attenuation of vascular oxidative stress and inflammation, and the ability to reduce arginase-2 activity (18), as well as the inhibitory effect against ACE (1, 3). Nevertheless, to date, not much attention has been paid to their potential renin-inhibitory activities. Recently, researchers found that saponins (8, 20, 21), baicalin (6), and the polyphenolic extracts of two green leafy vegetables (2) showed renin-inhibitory activities, which thus suggested the promising prospect of discovering polyphenolic compounds as candidates for renin inhibitors. Catechins represent a major class of polyphenols and are widely distributed in plants. There are four principal kinds of catechins, that is, epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate; the beneficial effects of these compounds on health have been continually studied (4, 10). In the present work, we investigated whether catechin-related compounds could exert renin-inhibitory activities in vitro and also primarily elucidated their structure-act...