Differential effects of transdermal estradiol and sequential progestogens on impedance to flow within the uterine arteries of postmenopausal women.

OBJECTIVE: To investigate the relationship between estradiol (E2), progestogen, and impedance to blood flow in the uterine artery. SUBJECTS: Twelve postmenopausal women treated for two cycles with transdermal E2, 0.05 mg/d, with either norethindrone acetate, 0.7 mg, or medroxyprogesterone acetate, 10 mg added sequentially. MEASUREMENTS: Transvaginal ultrasonography and color flow imaging were used to measure the pulsatility index in the uterine arteries before and during the E2-only and combined E2/progestogen phases. RESULTS: The mean pulsatility index fell to 53% of its pretreatment value within 12 days E2 administration (P < or = 0.0001) and was 66% of its pretreatment value in the combined phase (P < 0.005). Similar changes were seen in cycle 2. Time since menopause was correlated with the pretreatment pulsatility index (r = 0.674, P < 0.05) and change in pulsatility index on treatment (r = 0.856, P < 0.001). CONCLUSION: Gonadal hormones have a profound effect on arterial tone in postmenopausal women; this action may help explain some of the beneficial effects of estrogen on arterial disease risk.