Endothelium-dependent and direct relaxation induced by ethyl acetate extract from Flos Chrysanthemi in rat thoracic aorta

The aims of the present study were to investigate the vasoactive effects of ethyl acetate extract from Flos Chrysanthemi (FCE) and its mechanisms on the rat thoracic aorta. FCE (9.4-150 mg/L) caused a concentration-dependent relaxation on endothelium-intact rings precontracted with phenylephrine (PE, 10−6 M) or a high level of K+(6 × 10−2 M). By removal of endothelium, the effect was not abolished but reduced significantly. NG-nitro-l-arginine methyl ester (l-NAME) (10−4 M), methylene blue (10−5 M) significantly inhibited the effect of FCE. Meanwhile, NO synthase of aorta in FCE group was markedly elevated versus the control. However, indomethacin did not influence FCE effect. SKF-525A combined with l-NAME had the same effect as l-NAME. Tetraethylammonium, BaCl2, 4-aminopyridine, 5-HD and propranolol also did not influence the vascular effect of FCE, but glibenclamide significantly attenuated its vasodilation. FCE did not reduce PE-induced transient contraction in Ca2+-free medium, but inhibited PE-induced contraction in K+-free solution or Ca2+ caused contraction after PE induced a stable contraction in Ca2+-free solution. It is concluded that FCE induced both endothelium-dependent and -independent relaxation. NO and cGMP-mediated pathway are likely involved in the endothelium-dependent relaxation, whereas inhibition of voltage-dependent Ca2+ channel, receptor-operate Ca2+ channel and activation of KATP contribute in part to the endothelium-independent relaxation.