Oral estrogen replacement therapy increases forearm reactive hyperemia accompanied by increases in serum levels of nitric oxide in postmenopausal women

The present study sought to determine the correlation between rite vasodila tor response of forearm resistance vessels and the circulating levels of ni tric oxide (NO) after the administration of oral estrogen for 12 weeks to p ostmenopausal women. We classified postmenopausal women into two groups: those treated with conj ugated equine estrogen (0.625 mg daily) orally for 12 weeks (n = 24) or tho se who received no treatment (control group, n = 8). Forearm blood flow was measured using strain-gauge plethysmography during hyperemia to evaluate e ndothelium-dependent vasodilation, and after sublingual nitroglycerin admin istration to evaluate endothelium-dependent vasodilation. Serum levels of n itrite/nitrate (metabolites of NO) and lipid parameters were measured. Basal forearm blood flow, body weight and heart rate were similar in each g roup. After 12 week of estrogen administration, the maximal forearm blood f low response during reactive hyperemia and the serum level of nitrite/nitra te each showed a significant increase from 26.9 +/- 1.9 to 37.9 +/- 3.5 ml/ min per 100 ml tissue (p < 0.01), and from 25.2 +/- 2.2 to 37.5 +/- 3.7 (mu )mol/l (p < 0.05), respectively. No increases were seen in controls. The ch anges in forearm blood flow after sublingual nitroglycerin were similar bef ore and after 12 weeks of estrogen administration. The increase in maximal forearm bloodflow with reactive hyperemia was significantly correlated with the increase in nitrite/nitrate in the group administered estrogen (r = 0. 48, p < 0.05). There war no significant correlation between maximal forearm blood flow with reactive hyperemia, nor any change in serum lipids, blood pressure or other parameters. In conclusion, the 12-week administration of oral estrogen increased forear m reactive hyperemia in postmenopausal women, probably via an increase in t he production of NO.