Gonadotropin-releasing hormone (GnRH) and GnRH receptor gene expression in human myometrium and leiomyomata and the direct action of GnRH analogs on myometrial smooth muscle cells and interaction with ovarian steroids in vitro.

The objective of the present study was to determine whether GnRH and GnRH receptor are expressed in myometrium and leiomyomata, and if GnRH analogs alone or in the presence of ovarian steroids can modulate the rate of DNA synthesis, proliferation, and transforming growth factor-beta 1 (TGF beta 1) production in myometrial smooth muscle cells in vitro. Reverse transcription-PCR revealed that leiomyomata, unaffected myometrium, and isolated myometrial smooth muscle cells express GnRH and GnRH receptor messenger ribonucleic acid. Furthermore, in a dose-dependent manner, GnRH agonist (leuprolide acetate) inhibited, but GnRH antagonist [D-pGlu1,D-Phe2,D-Trp3.6] (GnRH-Ant1) stimulated, the rate of [3H]thymidine incorporation into myometrial smooth muscle cells (P < 0.05), whereas GnRH-Ant2 (Ac-D-P-Cl-Phe1.2,D-Trp3,D-Arg6,D-Ala10) had no effect. 17 beta-Estradiol (E2) medroxyprogesterone acetate (MPA), and E2 plus MPA (1 micromol/L) stimulated the rate of DNA synthesis by smooth muscle cells (P < 0.05), which was inhibited by GnRH analogs used at 5 micromol/L (P < 0.05). GnRH analogs had no significant effect on myometrial smooth muscle cell proliferation, with the exception of GnRH-Ant1; however, they inhibited the stimulatory action of E2, MPA, and E2 plus MPA in a time-dependent manner (P < 0.05). These cells also synthesized and released approximately 1.32 +/- 0.02 ng/mL total (active plus latent) TGF beta 1, of which 0.73 +/- 0.02 ng/mL was in an active form. E2, MPA, E2 plus MPA, and GnRH analog treatments resulted in an increase in total TGF beta 1 production, whereas GnRH agonist and GnRH-Ant2, but not GnRH-An1, inhibited active TGF beta 1 (P < 0.05). GnRH analogs also inhibited the action of E2 plus MPA on total and active TGF beta 1 production, whereas GnRH-Ant1 further stimulated E2, MPA, or E2 plus MPA action on active TGF beta 1 production (P < 0.05). The data demonstrate for the first time that GnRH and GnRH receptor messenger ribonucleic acid are expressed in myometrium, leiomyomata, and myometrial smooth muscle cells. The local expression of GnRH and receptor along with the direct action of GnRH analogs on the smooth muscle cell DNA synthesis and TGF beta 1 production suggest an autocrine/paracrine role for GnRH in these tissues, a mechanism that may be involved in leiomyomata regression in women receiving GnRH agonist therapy.