Effect of Estriol Administration on the Hypogonadal Woman

Abstract

To study the biologic effects of estriol, 14 hypogonadal patients received either vaginal or oral estriol. The vaginal administration of 0.5 mg of estriol to five patients resulted in increases of serum unconjugated and conjugated estriol levels which were maximal at 1 and 2 hours following treatment (161 ± 59 [SE] pg/ml and 762 ± 146 pg/ml, respectively). Significant suppression of luteinizing hormone (LH) to 84% and 81% of base line levels was observed at 2 and 3 hours following treatment, respectively (P < 0.05), and significant suppression of follicle-stimulating hormone (FSH) was reached only at 5 hours (P < 0.05). The ingestion of 8 mg of estriol orally caused a minimal increase in the serum unconjugated estriol concentration (from ≤ 25 pg/ml to 75.3 ± 17.4 pg/ml) and a dramatic increase of 600-fold in the serum conjugated estriol concentration (from 0.1 ± 0.01 ng/ml to 62.4 ± 13.8 ng/ml). This was associated with no significant decrease in serum FSH levels and with only a 10% to 15% decrease in LH (P < 0.05). The continued daily ingestion of 8 mg of estriol for 30 days was associated with a further increase in unconjugated estriol concentrations (to 132 ± 28 pg/ml) and a further decrease of serum FSH and LH to 66% and 83% of pretreatment levels, respectively (P < 0.05). A shift to the right in the vaginal maturation index (P < 0.05) was noted at the end of the treatment course and suggested an estrogenic effect on the vaginal epithelium. Estriol is a weak estrogen. Rapid conjugation of the orally administered estriol renders it a weakly potent estrogen. Estriol administered vaginally is conjugated less rapidly than orally administered estriol, thus rendering it more biologically potent.