VASORELAXANT EFFECTS OF PURIFIED GREEN TEA EPICATECHIN DERIVATIVES INRAT MESENTERIC-ARTERY

The effects of four epicatechin derivatives, (-) epicatechin, (-) epic atechin 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 res ponse to phenylephrine in concentration-dependent manner with epigallo catechin gallate being the most potent. The relaxant effects of epicat echin derivatives were unaffected by the ATP-sensitive K+ channel bloc ker glibenclamide (3 mu M) or the Ca2+-activated K+ channel blocker ch arybdotoxin (100 nM). Four epicatechin derivatives also reduced the su stained contractions induced by phenylephrine (1 mu M) and endothelin I (5 nM) in normal Krebs solution, whilst they did not relax the phorb ol 12-myristate 13-acetate (TPA, 2 mu M)-contracted arteries in the ab sence of extracellular Ca2+. In arteries contracted with 60 mM K+, eac h of epicatechins caused a relaxation. However, epicatechin derivative s did not affect the transient contraction induced by 100 mu M caffein e in Ca2+-free solution. The present results suggest that epicatechin derivatives from green tea leaves relaxed rat mesenteric arteries prob ably by inhibiting Ca2+ influx. The protein kinase C-dependent contrac tile pathway and intracellular Ca2+ release may not be involved.