Premenopausal women are known to have a much lower risk of coronary heart disease than age-matched men, with the incidence of risk increasing after the onset of menopause. Accumulating evidence suggests that this protection is due to oestrogen (Guetta et al. 1997), and men and women consuming a phytoestrogen-rich diet have a lower risk of cardiovascular disease (Anthony et al. 1997). These latter compounds have a similar structure to oestrogen and thus protection may be conferred via similar mechanisms. The present study has compared the actions of 17β-oestradiol and phytoestrogens on mitogen-activated protein kinase (MAPK) and nitric oxide (NO) production in endothelial cells cultured from human umbilical cord veins (Wyatt et al. 2002), obtained with the approval of the patient and local ethics committee.

Effects of short (2 min) exposure to 17β-oestradiol (but not 17α-oestradiol), genistein, daidzein and its metabolite equol were studied. Intracellular cGMP levels served as an index of NO production (inhibitable by the NOS inhibitor L-NAME, 100 µM). Low (0.1 µM) concentrations of 17β-oestradiol and phytoestrogens stimulated NO release 1- to 2-fold without elevating intracellular Ca²⁺. 17β-Oestradiol, daidzein and equol also acutely (2 min) phosphorylated p42/p44^MAPK at concentrations of 1-100 nM. Activation of p42/p44^MAPK was inhibited by U0126 (1 µM, 30 min pretreatment), an inhibitor of MEK, the upstream activator of p42/p44^MAPK, but unaffected by L-NAME. In order to determine whether the actions of phytoestrogens were mediated via the classical oestrogen receptors α and β, cells were pretreated with ICI 182,780 (10 µM, 30 min) or tamoxifen (10 µM, 60 min). Neither of these oestrogen receptor antagonists affected NO production in response to genistein, daidzein, equol or 17β-oestradiol.

The present study establishes that, in addition to 17β-oestradiol, dietary phytoestrogens can acutely stimulate p42/p44^MAPK and NO production in human fetal endothelial cells in vitro. L-NAME has no effect on MAPK phosphorylation, whereas inhibition of this signalling pathway by U0126 suggests that in these cells activation of MAPK pathway may be upstream of endothelial NO synthase.

This work was supported by a BHF PhD Studentship.