Treatment effects of GnRH agonist on the binding of estrogen and progesterone, and the histological findings of uterine leiomyomas.

The changes in the histology and steroid hormone binding capacity of the uterine leiomyomas treated with; GnRH agonists (GnRHa buserelin acetate in, 900 micrograms/day for 16 weeks) were investigated. The occurrence of hyaline degeneration in the myometrium was significantly higher in the GnRHa-treated group than in the control group, and the grade of hyaline degeneration was more advanced in the GnRHa group. After the GnRHa treatment, the Bmax of the estrogen receptor increased significantly in the leiomyomas and myometrium. The Bmax of progesterone receptors in the myometrium decreased significantly and the reduction rates of leiomyomas (% of the initial volumes) measured by MRI correlated (r = 0.775) with the Bmax of progesterone receptors. In summary, GnRHa caused hyaline degeneration of the uterine leiomyomas which were responsible for the shrinkage. The shrunk leiomyomas have the potential for regrowth in response to estrogen as they still have high concentrations of the estrogen receptors.