Purpose: To measure the effect of long-term clinical hormone replacement therapy on brachial artery vasomotor responses, and to compare these responses in premenopausal and postmenopausal women.

Patients and Methods: We studied 23 postmenopausal women, including 18 who were evaluated prior to starting clinically indicated oral hormone replacement therapy. Twelve postmenopausal women received estrogen alone, the other 6 were treated with estrogen/medroxyprogesterone combinations. Eleven premenopausal volunteers served as a comparison group. Change in brachial artery diameter in response to postischemic hyperemic flow and sublingual nitroglycerin was measured by ultrasound.

Results: The 18 postmenopausal subjects receiving hormone replacement showed a progressive improvement in their postischemic vasodilation. Mean (±SD) postischemic vasodilation was 0.4% ± 7.1% prior to estrogen replacement. There were significant increases in postischemic vasodilation of 4.8% ± 6.6% after 1 month and 8.3% ± 3.4% after 6 months of estrogen replacement. The response to nitroglycerin was similar at all time points studied. Women with the most abnormal responses to hyperemic flow at baseline demonstrated the greatest improvement after 6 months of hormone replacement therapy. Premenopausal and postmenopausal subjects differed in their response to hyperemic flow, with premenopausal women showing 5.8% vasodilatation compared with a 0.6% vasodilation in postmenopausal women (P = 0.046).

Conclusions: Endothelial function is abnormal in many postmenopausal women compared with premenopausal women, and in some postmenopausal women it can be enhanced by estrogen replacement therapy. This effect may increase with prolonged use.