Background and aim: The mechanisms by which estradiol dilates arterial vessels are still unclear. Our aim was to study if estradiol enhances endothelium-dependent vasodilation in an experimental model of human arteries in vitro, and if this effect is nitric oxide mediated.
Methods: Using organ bath chambers, we studied 18 arterial rings obtained from left internal mammary arteries during coronary artery bypass grafting surgery. Response to acetylcholine was evaluated at baseline and after the addition of estradiol 10-6 mol/l to the medium, both in the presence or absence of a nitric oxide synthase inhibitor (L-NNA 10-4 mol/l).
Results: Estradiol significantly enhanced the relaxation of the arterial rings in response to acetylcholine (52 +/- 20% after estradiol versus 42 +/- 22% at baseline; n = 10; p = 0.02). However, endothelium-dependent vasodilation relaxation after estradiol addition was not enhanced in the presence of L-NNA (47 +/- 25% after estradiol versus 38 +/- 22% at baseline; n = 8; p = NS).
Conclusions: Estradiol in vitro enhances endothelium-dependent vasodilation of internal human mammary artery rings; this effect is blunted after the addition to the medium of a nitric oxide inhibitor. Therefore, the vasodilator properties of estradiol at the studied dosage depend on the nitric oxide pathway.