Relaxing Effects of Phytoestrogen α-Zearalanol on Rat Thoracic Aorta Rings in Vitro

The aim of this research is to investigate the vasorelaxing effects and mechanisms involved in the phytoestrogen α-zearalanol (α-ZAL) in rat thoracic aortas rings. Intact or endothelium denuded rat thoracic aortas rings were put in individual organ chamber to observe the endothelium-dependent or independent vasorelaxing effects of α-ZAL (10-10-10-5 M). The thoracic aortas rings were pre-contracted with phenylephrine. The relaxing effects of α-ZAL were observed and the influence of Nω-nitro-Larginine methylester (L-NAME, NOS inhibitor), methylene blue (MB, guanylate cyclase inhibitor), charybdotoxin (ChTX, Ca2+-activated K+ channel blocker), glibenclamide (ATP-sensitive K+ channel blocker), (–) BayK8644 (L-type Ca2+ channel agonist) and ICI182,780 (estrogen receptor antagonist) were pre-incubated with α-ZAL, respectively, to explore the possible mechanisms involved in this vasorelaxation. Furthermore, the Phospho-eNOS expression and cGMP level in the aortas tissue were detected by Western blot and radioimmunity, respectively; the NO level in perfusate was assaied by chromatometry. Our result showed that α-ZAL (10-10-10-5 M) induced both endothelium-dependent and -independent relaxation of rat thoracic aortas rings. The vasorelaxing effects of α-ZAL were dosedependent whether the endothelium was intact or not. In endothelium-intact aortas rings, α-ZALinduced vasorelaxation might be inhibited by L-NAME, MB, charybdotoxin, glibenclamide and (–) BayK8644, but not ICI182,780. (–) BayK8644 could also inhibit α-ZAL-induced vasorelaxation in endothelium-denuded aortas rings.10-7-10-5 M α-ZAL might induce the Phospho-eNOS expression in thoracic aorta tissue, increase the NO level in perfusate and cGMP content in thoracic aorta tissue. Meanwhile, L-NAME might decrease both NO and its downstream cGMP level. Methylene blue might decrease the level of cGMP. These results suggest that α-ZAL induces a partly endothelium-dependent relaxation of rat thoracic aortas rings; the possible mechanisms involved in this rapid vasorelaxation include activation of eNOS/NO/cGMP pathway, opening of VSMCs ATP-sensitive and Ca2+-activated K+ channels through secretion of EDHF from endothelium. Furthermore, this relaxation also appears to be mediated by both direct and indirect inhibition of voltage-dependent Ca2+ channel of VSMCs, while it is not concerned with activation of estrogen receptor.