Biologic Effects of Transdermal Estradiol

Abstract

We conducted a dose-response study in 23 postmenopausal women to compare the physiologic effects of transdermal estradiol and oral conjugated equine estrogens. The doses studied were 25, 50, 100, and 200 micrograms of transdermal estradiol per 24 hours, and 0.625 and 1.25 mg of oral conjugated estrogens. Transdermal estradiol increased circulating concentrations of estradiol and estrone. Oral conjugated estrogens also raised the levels of estrogen, particularly estrone. Both preparations lowered gonadotropin levels, decreased the percentages of vaginal parabasal cells, increased the percentage of superficial cells, and lowered urinary calcium excretion. The effects of 0.625 and 1.25 mg of oral estrogens were similar to those of 50 and 100 micrograms of transdermal estradiol per 24 hours, respectively. Oral estrogens significantly increased circulating levels of renin substrate, sex-hormone-binding globulin, thyroxine-binding globulin, and cortisol-binding globulin; transdermal estradiol had no effect. The higher dose of oral estrogens had favorable effects on concentrations of low-density and high-density lipoproteins, but transdermal estradiol did not. Neither preparation affected any of the four clotting factors studied. These data indicate that transdermal estradiol can elicit many of the desirable actions of estrogen while avoiding the pharmacologic effects of oral estrogens on hepatic proteins.