Green Tea Suppresses the Radiation-Induced Increase of the AngiotensinConverting Enzyme & Reactive Oxygen Species in the Aorta of Rats

The consumption of green tea reduces the risk of cardiovascular diseases and suppresses the development of atherosclerosis. The main factor for the initiation and progression of atherosclerosis is an increase in the production of reactive oxygen species (ROS) in vessels. A significant contribution to the increase in ROS production is made by increased concentration of angiotensin II, a product of the angiotensin-converting enzyme (ACE). The effect of green tea on the level of ROS and ACE activity in blood vessels in vivo has not yet been studied. The activity of ACE in aorta sections of rat was determined by measuring the hydrolysis of hippuryl-L-histidyl-L-leucine, and the production of ROS was estimated from the oxidation of dichlorodihydrofluorescein. Green tea inhibited the radiation-induced activation of the ACE in the aorta of rats on intraperitoneal (i.p.) and peroral administration. Six hours after the administration of tea, the activity of ACE in irradiated rats decreased to the control level, and by 24 h after administration, the tea did not almost affect the ACE activity. On i.p. administration, effective doses were lower than on peroral administration. The concentration of orally administered tea that inhibited the ACE activation in irradiated rats by 50% (IC50) was 1 ml of an extract of 2.1 g of tea brewed per 100 ml of water. One milliliter of i.p. administered green tea (1 g per 100 ml of water) completely suppressed the increased ROS production in the aorta of irradiated rats.