title: Endothelium-dependent contraction and direct relaxation induced by baicalein in rat mesenteric artery.
abstract: The vascular effect of purified baicalein from Scutellaria baicalensis Georgi (Huangqin) was examined in rat isolated mesenteric arteries. Baicalein exerts both contractile and relaxant effects on the U46619-, phenylephrine- or high K+-contracted endothelium-intact arteries. In endothelium-denuded arteries, the contractile response to baicalein (0.3-10 microM) was absent while the relaxant response to baicalein (30-300 microM) remained. Pretreatment with 100 microM N(G)-nitro-L-arginine (L-NNA) or 3 microM methylene blue abolished the baicalein-induced contraction while 10 microM indomethacin or 100 nM BQ610 had no effect. Pretreatment with baicalein (3-10 microM) significantly attenuated the relaxation induced by acetylcholine or by A23187. In contrast, baicalein did not affect the sodium nitroprusside-induced relaxation in endothelium-denuded arteries. Baicalein also concentration dependently inhibited the contractile response to 1 microM phorbol 12,13-diacetate (PDA) in Ca2+-free solution. Baicalein had little effect on the contractile response to 60 mM K+ or to 10 mM caffeine in endothelium-denuded arteries. The baicalein-induced relaxation was unaffected by 1 microM glibenclamide or by 3 mM tetraethylammonium ions in endothelium-denuded arteries. These results indicate that baicalein at low concentrations caused a contractile response and inhibited the endothelium-dependent relaxation, probably through inhibition of endothelial nitric oxide (NO) formation/release. At higher concentrations, baicalein relaxed the arterial smooth muscle partially through inhibition of the protein kinase C-mediated contractile mechanism.
authors.affiliation: Department of Biochemistry, Chinese University of Hong Kong, Shatin.
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Chen
authors.forename: Y L
authors.initials: YL
authors.lastname: Su
authors.forename: C W
authors.initials: CW
authors.lastname: Lau
authors.forename: W I
authors.initials: WI
authors.lastname: Law
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004730:Endothelium, Vascular / Q000502:physiology*; D044950:Flavanones; D005419:Flavonoids / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D010703:Phorbol Esters / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D044950:Flavanones; D005419:Flavonoids; D010703:Phorbol Esters; C008874:phorbol-12,13-diacetate; D002110:Caffeine; C006680:baicalein; D011188:Potassium; D005905:Glyburide; D002118:Calcium