Sequentially combined hormone replacement therapy reduces impedance to flow within the uterine and central retinal arteries in healthy postmenopausal women

OBJECTIVE: The purpose of this study was to investigate the long-term effects of combined hormone replacement therapy on the impedances of the uterine, central retinal, and ophthalmic arteries in healthy postmenopausal women. STUDY DESIGN: In a prospective controlled study we randomly assigned 30 healthy postmenopausal women (mean age, 52 +/- 3 years) to 2 groups. Women in the hormone replacement therapy group (n = 15) received 1 mg micronized 17beta-estradiol daily sequentially combined with 5 or 10 mg dydrogesterone for 14 days of each 28-day cycle during 12 months and 2 mg 17beta-estradiol combined with 10 mg dydrogesterone thereafter for a period of 3 months. The control group (n = 15) received no treatment. Color Doppler ultrasonography was used to measure the impedance to flow (pulsatility index) within the uterine, central retinal, and ophthalmic arteries in the 17beta-estradiol phase at baseline and after 3, 12, and 15 months. RESULTS: With respect to values in the control group, 12 months of hormone replacement therapy was associated with a significantly lower (by 39%) mean pulsatility index of the uterine artery (decrease from baseline of 25% in hormone replacement therapy group and increase of 14% in control group) and a significantly lower (by 29%) mean pulsatility index of the central retinal artery (decrease of 9% in hormone replacement therapy group and increase of 20% in control group). After 3 months this effect was already evident. During hormone replacement therapy the reductions in mean pulsatility index values of the uterine and central retinal arteries with respect to baseline were larger (both P =.002) in the women with high pretreatment pulsatility index values than in those with low pretreatment values. The baseline pulsatility index of the uterine artery correlated positively with age and with duration of amenorrhea (r = 0.42, P =. 01; r = 0.48, P =.008; respectively). CONCLUSION: These results suggest that 12 months of sequentially combined hormone replacement therapy with a low dose of estradiol (1 mg) lowers arterial impedance in specific vascular territories. These data may help in understanding the effects of hormone replacement therapy on the cerebral circulation.