Formononetin, an isoflavone, relaxes rat isolated aorta through endothelium-dependent and endothelium-independent pathways

Abstract

We evaluated the vasorelaxation effects of formononetin, an isoflavone/phytoestrogen found abundantly in Astragalus mongholicus Bunge, on rat isolated aorta and the underlying mechanisms involved. Cumulative administration of formononetin, genistein, daidzein and biochanin A relaxed phenylephrine-preconstricted aorta. Formononetin and biochanin A caused a similar magnitude of relaxation whereas daidzein was least potent. Mechanical removal of endothelium, L-NAME (100 microM) and methylene blue (10 microM) suppressed formononetin-induced relaxation. Formononetin increased endothelial nitric oxide (NO) synthase (eNOS), but not inducible NO synthase, activity with an up-regulation of eNOS mRNA and p-eNOS(Ser1177) protein expression. In endothelium-denuded preparations, formononetin-induced vasorelaxation was significantly reduced by glibenclamide (3 microM) and iberiotoxin (100 nM), and a combination of glibenclamide (3 microM) plus iberiotoxin (100 nM) abolished the relaxation. In contrast, formononetin-elicited endothelium-independent relaxation was not altered by ICI 182,780 (10 microM, an estrogen receptor (ER alpha/ER beta) antagonist) or mifepristone (10 microM, a progesterone receptor antagonist). In single aortic smooth muscle cells, formononetin caused opening of iberiotoxin-sensitive Ca(2+)-activated K(+) (BK(Ca)) channels and glibenclamide-sensitive adenosine triphosphate (ATP)-dependent K(+) (K(ATP)) channels. Thus, our results suggest that formononetin caused vascular relaxation via endothelium/NO-dependent mechanism and endothelium-independent mechanism which involves the activation of BK(Ca) and K(ATP) channels.

Vasorelaxant and antihypertensive effects of formononetin through endothelium-dependent and -independent mechanisms

“…L-NAME, a NOS inhibitor, inhibits the relaxation of formononetin, indicating that the vasorelaxant activity of formononetin is related to NO release. Similar findings are reported elsewhere [9] . The vasorelaxant effect of PGs is realized through increasing intracellular cAMP levels [35] .…”

“…Our experimental results show that formononetin can relax the arteries pre-contracted by vasoconstrictors, indicating that the antihypertensive activities of formononetin maybe stem from the vasorelaxant activity. This is in concert with the previous findings that formononetin relaxes rat isolated aorta [9] and some isoflavones have vasorelaxant activities [15] . We have found that mesenteric artery is more sensitive to formononetin than abdominal aorta and renal artery in precontraction by phenylephrine, and meanwhile mesenteric artery is one of peripheral arteries which contribute more resistance than aorta in hypertension, and therefore we chose to study the vasorelaxant mechanism of formononetin on mesenteric artery.…”

“…In our experiments, propranolol, glibenclamide, tetraethylammonium and BaCl 2 did not affect the endothelium-independent relaxant response to formononetin in rat mesenteric arteries, suggesting that the K + channels and β-adrenoceptors are not involved in the vascular relaxation processes, which is in accordance with the previous findings that K + channel inhibitors did not affect the relaxation of genistein and zearalanone, two phytoestrogens, in rabbit coronary arteries [38] . By contrast, Wu et al proposed that formononetin caused opening of iberiotoxin-sensitive Ca 2+ -activated K + channels and glibenclamide-sensitive adenosine triphosphate (ATP)-dependent K + channels in rat aorta [9] . This discordance may lie in the different responses of mesenteric artery and aorta to drugs [39] .…”

“…They have attracted much attention because of their potential beneficial role in prevention and treatment of cardiovascular diseases, bone metabolism disorders, breast cancers, Vasorelaxant and antihypertensive effects of formononetin through endothelium-dependent and -independent mechanisms and menopausal symptoms [5][6][7][8][9] . Isoflavones are a class of phytoestrogens naturally sourced from legumes such as soy beans and red clover [10] .…”

“…Medicinal herbs containing formononetin have been used to treat cardiovascular diseases including hypertension in Asia for centuries [23] . Recently, Wu et al reported that formononetin has a vasorelaxant activity in isolated rat aorta rings [9] . However, the antihypertensive activity of formononetin and its vasorelaxant effect on arteries in different regions have not yet been studied.…”