Vasorelaxant effects of purified green tea epicatechin derivatives in rat mesenteric artery

The effects of four epicatechin derivatives, (-) epicatechin, (-) epicatechin gallate, (-) epigallocatechin and (-) epigallocatechin gallate, isolated from jasmine green tea, on the contractions were studied in mesenteric arteries isolated from male Sprague-Dawley rats. All four derivatives (30-500 mu M) noncompetitively reduced the contractile response to phenylephrine in concentration-dependent manner with epigallocatechin gallate being the most potent. The relaxant effects of epicatechin derivatives were unaffected by the ATP-sensitive K+ channel blocker glibenclamide (3 mu M) or the Ca2+-activated K+ channel blocker charybdotoxin (100 nM). Four epicatechin derivatives also reduced the sustained contractions induced by phenylephrine (1 mu M) and endothelin I (5 nM) in normal Krebs solution, whilst they did not relax the phorbol 12-myristate 13-acetate (TPA, 2 mu M)-contracted arteries in the absence of extracellular Ca2+. In arteries contracted with 60 mM K+, each of epicatechins caused a relaxation. However, epicatechin derivatives did not affect the transient contraction induced by 100 mu M caffeine in Ca2+-free solution. The present results suggest that epicatechin derivatives from green tea leaves relaxed rat mesenteric arteries probably by inhibiting Ca2+ influx. The protein kinase C-dependent contractile pathway and intracellular Ca2+ release may not be involved.