Abstract Although the consumption of tea has been associatedwith beneficial cardiovascular effects, (–)-epigallocatechin- 3-gallate (EGCG), the most abundant catechinin this beverage has shown seemingly contradictory actionson vascular tissues, for example vasorelaxant activity that could contribute favourably to prevention of cardiovascular disease, and contractile activity that could act in the
opposite direction. The purpose of the present work was to study the contractile effects of EGCG on isolated rat thoracic aorta rings and its effects on the cytosolic free[Ca2+] ([Ca2+]i) measured with fura-2 in cultured rat aortic mooth muscle cell line.In partially depolarised (15 mM KCl) aortic rings EGCG (30–300 μM), (±)-BAY K 8644 (0.1 μM) and thapsigargin (1 μM) induced a Ca2+-dependent,  elium-independent contraction associated with [Ca2+]i elevation in RASMC.EGCG enhanced the responses elicited by (±)-BAY K 8644 and thapsigargin both in aortic rings and in RASMC.Nifedipine totally inhibited the (±)-BAY K 8644-induced contraction, but only partially blocked the contractile responses to EGCG and thapsigargin, while SKF 96365 abolished both responses. The effects of these channel
blockers were associated with a decrease in [Ca2+]i in RASMC. Re-introduction of Ca2+ in the medium after depletion of intracellular Ca2+ stores with thapsigargin in a Ca2+-free solution elicited a contraction of aortic rings and an increase in [Ca2+]i in RASMC. In both cases, this response was partially sensitive to nifedipine, abolished by SKF 96365 and clearly enhanced by EGCG. These results suggest that EGCG induces a transient endothelium-independent contraction in the rat aorta, probably by increasing smooth vascular cell  embrane permeability to Ca2+ through both non-specific and dihydropyridine-sensitive Ca2+ channels.words Catechins · (–)-Epigallocatechin-3-gallate ·Rat aorta · Vascular smooth muscle cells · Fura-2 Introduction Tea is rich in a subclass of flavonoids, i.e. the catechin derivatives or flavan-3-ols, the most abundant of which are (–)-epigallocatechin-3-gallate (EGCG), (–)-epigallocatechin,–)-epicatechin-3-gallate, (–)-epicatechin, (+)-gallocatechin and (+)-catechin, with EGCG having the highest concentration (Graham 1992). All these catechins are absorbed by humans and can be detected in plasma at low concentrations after a single administration of solid extract (Nakagawa et al. 1997) or drinking tea for 2 days (Yang et al. 1998). Bioavailability of catechins in humans after oral nsumption is considered to be only a small percentage of the amount ingested (Warden et al. 2001) and the maximum plasma concentration depends on the amount of flavan- 3-ol ingested (and can be 0.3–7 μM for EGCG; see for example, Ullmann et al. 2003). Beneficial effects of tea consumption on coronary heart disease have been associated frequently with the antioxidant properties of epicatechin derivatives (Ishikawa et al. 1997; Hertog et al. 1997; Álvarez et al. 2002), although other actions may also be implicated. Green tea polyphenols, and specifically EGCG, have been linked to inhibition of platelet aggregation (Deana et al. 2003) and a certain antiproliferative activity on vascular cells (Locher et al. 2002), including A7r5 rat aortic smooth muscle cell line (Chen et al. 2000). In addition, the vasorelaxant effects of purified, green tea epicatechin derivatives have also been reported in rat mesenteric artery (Huang et al.