Plasma estriol and its conjugates following oral and vaginal administration of estriol to postmenopausal women: correlations with gonadotropin levels.

I Schiff, D Tulchinsky, K J Ryan, S Kadner, M Levitz

Index: Am. J. Obstet. Gynecol. 138(8) , 1137-41, (1980)

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Abstract

A study was designed to compared the metabolic fate and the biologic effects of 4 mg of estriol (E3) administered either orally or vaginally to six postmenopausal women. Blood samples were collected every hour for 6 hours and five different estriol fractions as well as gonadotropins were measured. Vaginal E3 administration resulted in a decline of 45% in luteinizing hormone (LH) levels and 17% in follicle-stimulating hormone (FSH) levels at 6 hours after treatment (p < 0.05). In contrast, the administration of 4 mg of E3 orally did not produce a decline of LH and FSH, despite the fact that the serum levels of E3-3-sulfate, E3-3-sulfate-16-glucosiduronate, estriol-3-glucosiduronate, and estriol-16-glucosiduronate were all fourfold to 24-fold higher after oral administration than after vaginal estriol administration. However, since the levels of unconjugated E3 were higher after the vaginal than after the oral administration of estriol, we conclude that only unconjugated E3 suppresses gonadotropins.