Vasorelaxant effect of euxanthone in the rat thoracic aorta.
This study was undertaken to investigate the effect of euxanthone on isolated rat thoracic aorta. Euxanthone concentration-dependently relaxed high K(+)-induced sustained contractions with IC(50) values of 32.28+/-1.73 muM and this inhibition was antagonized by increasing the Ca(2+) concentration in the medium. These results indicated that euxanthone may have calcium antagonistic property. Euxanthone also relaxed norepinephrine (NE)-induced sustained contractions with IC(50) values of 32.50+/-2.15 muM and this relaxant effect was unaffected by the removal of endothelium or by the presence of propranolol, indomethacin, glibenclamide or N(omega)-nitro-l-arginine. Moreover, euxanthone inhibited both the phasic and tonic contractions induced by NE in a concentration-dependent manner and showed more potent inhibition on phasic contraction (P<0.01). Pre-treatment with euxanthone inhibited vascular contraction induced by phorbol 12, 13-dibutyrate (PDBu), a protein kinase C (PKC) agonist, in either the presence or absence of Ca(2+) in the solution with IC(50) values of 20.15+/-1.56 and 18.30+/-1.62 muM, respectively. However, when the tissues were treated with euxanthone after the PDBu-induced contraction had reached a steady state, the tension was not affected by euxanthone. This study also showed that the inhibitory effect of pre-treatment of euxanthone was more potent than the post-treatment after the tension had reached a steady state. These results suggested that the vasorelaxation of euxanthone may be through multiple pathways involved PKC-mediated signal pathway and calcium-independent pathway besides the direct inhibition of calcium influx and its vasorelaxant effect is more active on calcium-independent pathway and more sensitive to the initial stage of contraction.[1]References
- Vasorelaxant effect of euxanthone in the rat thoracic aorta. Fang, L.H., Mu, Y.M., Lin, L.L., Xiao, P.G., Du, G.H. Vascul. Pharmacol. (2006) [Pubmed]
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