title: Epigallocatechin-3-gallate relaxes the isolated bovine ophthalmic artery: involvement of phosphoinositide 3-kinase-Akt-nitric oxide/cGMP signalling pathway.
abstract: The present study investigates the direct action and the underlying mechanism(s) of epigallocatechin-3-gallate (EGCG) vasomotor effects on the bovine isolated ophthalmic artery. Adjacent rings were cut from each artery and mounted in a wire miograph system for isometric recording. Concentration-response curves for EGCG were constructed by adding cumulative concentrations of the drug to arterial rings pre-contracted with 5-HT (1 microM). Effects of mechanical endothelial cell removal and of selective blockers of the nitric oxide (NO)/cGMP pathways were investigated on the EGCG relaxant responses. EGCG relaxed ophthalmic arteries and maximum relaxation was 78.4+/-2.64%. Mechanical removal of endothelium, blockade of soluble guanylyl cyclase by 1H-1,2,4-oxadiazolo [4,3-a]quinoxalin-1-one (ODQ, 1 and 5 microM) or inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine (L-NAME, 50 and 100 microM) reduced significantly the relaxant response to catechin; moreover, the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 100 microM) significantly increased the vasorelaxant responses to EGCG. Relaxation to EGCG was inhibited by iberiotoxin (200 nM), a blocker of big-conductance Ca(2+)-activated K(+) (BK(Ca)) channel, whereas the blockade of K(ATP) channel by glibenclamide (5 microM) and of small-conductance Ca(2+)-activated K(+) (SK(Ca)) channel by apamin (100 nM) elicited no effect. Interestingly, also inhibition of phosphoinositide-3-kinase (PI3K) by wortmannin (100 nM) and of Akt by SH6 (1 microM) markedly decreased the EGCG-evoked vasorelaxation. These data suggest that EGCG induced vasorelaxation in ophthalmic arteries with endothelium-intact via the activation of the NO/cGMP signalling pathway and defined an intriguing role for PI3K and Akt as upstream mediators for activation of NO-mediated relaxant responses.
authors.affiliation: Department Pharmacobiology, Section of Pharmacology, University of Bari, Bari, Italy.
authors.forename: Maria Rosaria
authors.initials: MR
authors.lastname: Romano
authors.forename: Marcello Diego
authors.initials: MD
authors.lastname: Lograno
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002417:Cattle; D006152:Cyclic GMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D008954:Models, Biological; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009880:Ophthalmic Artery / Q000187:drug effects*; D010069:Oxadiazoles / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011810:Quinoxalines / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects; D000077191:Wortmannin
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D000730:Androstadienes; D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D010069:Oxadiazoles; D010455:Peptides; D010716:Phosphatidylinositols; D011810:Quinoxalines; C110881:S-nitro-N-acetylpenicillamine; C483312:phosphoinositide 3-phosphate; D009569:Nitric Oxide; D012701:Serotonin; C064719:iberiotoxin; D002392:Catechin; C045651:epigallocatechin gallate; D051057:Proto-Oncogene Proteins c-akt; D006162:Guanylate Cyclase; D010396:Penicillamine; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester; D000077191:Wortmannin