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 microM) non-competitively reduced the contractile response to phenylephrine in a 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 microM) or the Ca2+-activated K+ channel blocker charybdotoxin (100 nM). Four epicatechin derivatives also reduced the sustained contractions induced by phenylephrine (1 microM) and endothelin I (5 nM) in normal Krebs solution, whilst they did not relax the phorbol 12-myristate 13-acetate (TPA, 2 microM)-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 microM 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.
Huang
Y
Y
Department of Physiology, Chinese University of Hong Kong, Shatin, NT. yu-huang@cuhk.edu.hk
Zhang
A
A
Lau
C W
CW
Chen
Z Y
ZY
D000818:Animals; D002392:Catechin / Q000737:chemistry / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013662:Tea; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*
D013662:Tea; D014662:Vasoconstrictor Agents; D002392:Catechin