[Effect of estrogens on arterial physiology and mechanisms of their atherosclerosis-protective effect in animals]. / Effect des oestrogènes sur la physiologie artérielle et mécanismes de son effet athéroprotecteur chez l'animal.

ABSTRACT

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