Role of oestrogens in vascular physiology and mechanisms of their atheroprotective effect in animal models

Two isoforms of oestrogen receptors (alpha and beta) have been identified i n the cells of the arterial wall, and heterogeneity of their expression acc ording to the animal species, the vascular beds and the sex has been report ed. Oestrogens can thus directly influence the vascular physiology through a 'genomic' mechanism, but 'extra-genomic' mechanisms responsible for a sho rt-term effect have also been suggested. Oestrogens potentiate endothelium- dependent relaxation through an increase in nitric oxide bioavailability (i ncrease in its production and/or decrease in its degradation by superoxide anion according to the vascular beds). Endothelial 'dysfunction' (abnormali ty of the endothelium-dependent vasodilation) occurs in atheromatous arteri es. Oestrogen replacement prevents and even corrects this endothelial dysfu nction. In monkeys, this beneficial effect of oestrogens is not altered by coadministration of progesterone, but is abolished by coadministration of m edroxyprogesterone. Finally, oestrogens prevent fatty streak deposit, and t he mechanisms of this atheroprotective effect are being studied.