Gender difference in improvement of endothelium-dependent vasodilation after estrogen supplementation.

Objectives: We examined whether there is a gender difference in the improvement of endothelium-dependent vasodilation after estrogen supplementation.
Background: Estrogen therapy reduces the risk of cardiovascular events in postmenopausal women, and the augmented release of endothelium-derived nitric oxide (NO) by estrogens has been suggested to be one of the mechanisms for the cardioprotective effects of estrogen.
Methods: With ultrasound technique, we measured the diameter and blood flow of the brachial artery at rest, during reactive hyperemia after transient occlusion and after nitroglycerin administration before and after estradiol supplementation in 15 postmenopausal women (mean 63 years) and in 15 men matched for age and risk factors for atherosclerosis.
Results: Estradiol supplementation augmented the flow-mediated vasodilation and serum level of nitrite/nitrate (metabolites of NO) in women (respectively, from mean +/- SEM of 8.0 +/- 0.6% to 12.9 +/- 0.6% [p < 0.01 by analysis of variance (ANOVA)] and from 64.9 +/- 8.7 to 93.7 +/- 9.4 mumol/liter [p < 0.05 by ANOVA]) but not in men (respectively, from 8.1 +/- 0.6% to 8.3 +/- 0.7% and from 57.8 +/- 6.7 to 60.8 +/- 5.4 mumol/liter). The increases in blood flow during reactive hyperemia and in diameter after nitroglycerin administration were not affected by estradiol supplementation in either men or women.
Conclusions: Estradiol supplementation improves endothelium-dependent vasodilation in women, probably because of augmented NO production/release, but not in men. Thus, there may be gender differences in the effects of estrogen therapy on endothelial functions and NO production/release.