title: Potentiating effects on contractions by purified baicalin and baicalein in the rat mesenteric artery.
abstract: The effects of purified baicalin and baicalein from the traditional Chinese herb, Huangqin, on contractions induced by phenylephrine, U46619, and high extracellular K+ were investigated in isolated rat mesenteric arteries. Both baicalin (1-100 microM) and baicalein (1-50 microM) potentiated the contractile response to phenylephrine in a concentration-related manner. Both flavonoids (10 microM) also enhanced the U46619- or 40 mM K+-induced contractions. Baicalein (100-300 microM) reduced the phenylephrine-induced tone. Prazosin at 1 microM did not affect U46619-induced contraction in the absence and presence of baicalein or baicalin. Neither baicalin (1-100 microM) nor baicalein (1-100 microM) affected the basal tension. Removal of the functional endothelium abolished the potentiating effects of baicalin and baicalein in arteries preconstricted by both constrictors. Pretreatment of endothelium-intact rings with 100 microM N(G)-nitro-L-arginine also potentiated phenylephrine- or U46619-induced contraction but completely inhibited the effects of baicalin and baicalein. Pretreatment with 1 mM L-arginine reversed the enhancing effect of baicalin but not of baicalein on phenylephrine-evoked contraction. Pretreatment with 10 microM baicalin or 10 microM baicalein significantly reduced the endothelium-dependent relaxation induced by acetylcholine or ionomycin. These results indicate that both baicalin and baicalein potentiated the evoked contractile response, likely through inhibition of nitric oxide formation and/or release in the endothelium.
authors.affiliation: Department of Physiology, Chinese University of Hong Kong, Shatin.
authors.forename: S Y
authors.initials: SY
authors.lastname: Tsang
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Chen
authors.forename: X Q
authors.initials: XQ
authors.lastname: Yao
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D004357:Drug Synergism; D004365:Drugs, Chinese Herbal / Q000494:pharmacology*; D044950:Flavanones; D005419:Flavonoids / Q000302:isolation & purification / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014662:Vasoconstrictor Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology
chemical_list: D004365:Drugs, Chinese Herbal; D044950:Flavanones; D005419:Flavonoids; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; C038044:baicalin; C006680:baicalein; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001120:Arginine; D000109:Acetylcholine