Background: Postmenopausal estrogen replacement, with or without progestins, has been related to lower cardiovascular risks.
Objective: We investigated whether the actions of estrogen on vascular resistance contribute to this cardioprotective effect.
Design and methods: In a 6-month double-blind study, pre- and post-treatment blood pressure, cardiac index, total vascular resistance index and plasma catecholamine responses during baseline and mental stressors were compared in 69 women (including 19 with mild hypertension but no history of heart disease). Women were randomized to receive either conjugated estrogens alone, estrogens plus medroxyprogesterone, or placebo.
Results: Both groups on active hormone replacement showed similar decreases in vascular resistance and modest blood pressure reductions, which differed from the unchanged responses of those on placebo (P< 0.05) after 3 and 6 months of treatment. Hypertensive women showed greater reductions in vascular resistance than normotensives (P< 0.05) and their blood pressure reductions tended to be larger. Women receiving hormone replacement showed increased stroke volume and cardiac index at 6 months, particularly among hypertensives and those receiving medroxyprogesterone (P < 0.05). Hormone replacement was also related to decreases in plasma norepinephrine. Finally, in 33 women receiving hormone replacement, significant 5 and 3% decreases in echocardiographic measures of left ventricular mass index and relative wall thickness were evident at 6 months (P < 0.05), while 20 placebo-treated women showed no reliable echocardiographic improvements (P= NS).
Conclusions: These findings suggest that estrogen-mediated reductions in hemodynamic load on the heart may contribute to the reduced risk of cardiovascular events in relatively healthy postmenopausal women who use hormone replacement.