Chen Z Y, Su Y L, Lau C W, Law W I, Huang Y
Department of Biochemistry, Chinese University of Hong Kong, Shatin.
Eur J Pharmacol. 1999 Jun 11;374(1):41-7. doi: 10.1016/s0014-2999(99)00291-5.
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.
