Fibroid and myometrial steroid receptors in women treated with gonadotropin-releasing hormone agonist leuprolide acetate.

The reduction in uterine and fibroid volume associated with the chronic administration of a gonadotropin-releasing hormone agonist (GnRH-a) is thought to be secondary to the analogue induced hypoestrogenic state. Our hypothesis was that the concentration of bioactive estrogen receptors (ER) and progesterone receptors (PR) may be important in the regulation of fibroid growth. The purpose of this study was to determine ER and PR content in fibroids and myometria from women pretreated with GnRH-a compared with controls. Tissue was obtained from 20 premenopausal women with uterine fibroids who were randomized to receive either leuprolide acetate depot, 3.75 mg intramuscularly every 28 days for four injections (n = 10) or placebo (n = 10) before myomectomy. The mean fibroid ER and PR content was significantly greater than the mean myometrial ER and PR content. The mean fibroid ER content for GnRH-a-treated patients was significantly greater than in placebo-treated patients (143.3 +/- 22.8 versus 36.1 +/- 14.3 fmol/mg). The mean fibroid PR and the mean myometrial ER and PR content were not significantly different between treatment groups. Clinically, the significant increase in fibroid ER may be an explanation for the rapid regrowth of fibroids observed after the cessation of GnRH-a therapy.