Endometrial effect of oral estriol treatment in postmenopausal women

Estriol is a weak estrogen with a claimed specific action on the epithelium in cervix uteri and vagina and with no or limited ability to induce endometrial proliferation. In a previous pharmacokinetic study we have shown elevated estriol levels for only 2-3 hours after oral administration of the drug. The present study was performed to test if estriol, when given orally in daily divided doses to postmenopausal women, has any effect on the endometrium. Twenty postmenopausal women who had no vaginal bleeding in response to lynestrenol (Orgametil 5 mgX2XV) were treated with 6 mg estriol a day (Ovesterin 2 mgX3), divided into three doses, for 2 up to 3.5 months. When lynestrenol (5 mgX2XV) was given following the estriol treatment periods, 12 women out of 20 experienced a vaginal bleeding and one reported spotting. Endometrial biopsies in ten of these women who had a bleeding were examined histologically. The endometrium was atrophic in four women, proliferative in two, slightly hyperplastic in one and showed signs of weak hormonal activity in one. Two women had secretory endometrium. It is concluded that estriol, administered in a way that gives prolonged elevation of the blood levels, is able to produce the same effect on the endometrium as other estrogens.