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 μM) 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 μM) or the Ca²⁺-activated K⁺ channel blocker charybdotoxin (100 nM). Four epicatechin derivatives also reduced the sustained contractions induced by phenylephrine (1 μM) and endothelin I (5 nM) in normal Krebs solution, whilst they did not relax the phorbol 12-myristate 13-acetate (TPA, 2 μM)-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 μM 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.