Effect of oestrogens on arterial physiology and mechanisms of its atheroprotective action in the animal.

The two isoforms (alpha and beta) of the oestrogen receptor were identified in arterial wall cells. The heterogeneity of their expression is considere d according to vascular regions and gender. Oestrogens can have a direct in fluence on vascular physiology through a "genomic" mechanism of action, alt hough "extragenomic" mechanisms allowing very short-term hormonal action ar e also possible. Oestrogens potentiate endothelium-dependent relaxation by increasing the bioavailability of nitrogen monoxide (higher production and/ or lesser degradation by the superoxide anion as a function of vascular bed s). The atheromatous artery is the site of endothelial "dysfunction" (an an omaly of endothelium-dependent vasodilatation), which can be prevented and even corrected by administration of oestradiol. In the monkey, this benefic ial effect of oestrogens is not alte red by addition of progesterone, but a bolished by the addition of medroxyprogesterone. Finally, oestrogens preven t formation of the fatty streak. Studies of the mechanism(s) of this effect are now in progress.