Contractions of the SHR aorta to high doses of epigallocatechin gallate are due to vasoconstrictor prostanoids

Abstract

OBJECTIVE: Regular consumption of green tea is believed to be beneficial for the cardiovascular system. However, high concentrations of epigallocatechin gallate (EGCG), a catechin of green tea, cause contractions of the aorta of spontaneously hypertensive rats (SHR). The present studies were designed to investigate the mechanisms underlying these EGCG-induced contractions. METHODS: Isometric tension was measured in isolated aortic rings from 36-weeks-old male SHR. The release of prostanoids end-products was measured with enzyme immunoassay kits. The intracellular reactive oxygen species (ROS) concentration was measured by confocal microscopy. RESULTS: From 10(–6) to 10(–4) M, EGCG induced concentration-dependent contractions in preparations with and without endothelium. These contractions were abolished by cyclooxygenase (COX) inhibitor indomethacin or the thromboxane-prostanoid (TP) receptor antagonist S18886, and reduced by antioxidants. The release of prostaglandin F1α, prostaglandin F2α and thromboxane B2 was significantly increased by 10(–4) M EGCG. A burst of ROS was observed upon exposure to 10(–4) M of EGCG. CONCLUSIONS: The EGCG-induced contractions involve the production of ROS, activation of COX, production of prostanoids and stimulation of TP receptors. This study indicates a possible adverse effect of EGCG administration and tea consumption at high concentrations.