Temporal Changes in Ovarian Gonadotropin-Releasing Hormone
mRNA Levels by Gonadotropins in the Rat
Sung Ho Lee, Eun-Seob Song, Sun Kyeong Yu, Changmee Kim, Dae Kee Lee,
Wan Sung Choi l and Kyungjin Kim*
Department of Molecular Biofogy and SRC for Cell Differentiation, Seoul National University,
Seoul 150-742, Korea; IDepartment of Anatomy, College of Medicine, Gyeongsanf; National
University, Chinju 660-280, Korea
(Recei·. cd on December 29, 1993) The present study examines whether gonadotropins are involved in the regulation of ovarian
GnRH gene expression and how ovarian GnRH gene expression temporalJy correlates with
alterations in hypothalamic GnRH, pituitary LH~ gene expression in respons to gonadotropins.
Hypothalamic and ovarian GnRH mRNA and pituitary LH~ mRNA levels were determined
by respective RNA-blot hybridizations, and ovarian GnRH and estradiol contents and serum
LH levels were measured by respective radioimmunoassays. Three animal models such as 1)
PMSG-treated, 2) PMSG and heG-treated immature rats and 3) proestrous stage of adult
rats were used. Immature rats (25-days old) were administered with PMSG (10 iu) at 10:00
hand 48 h later with heG (10 iu) to induce ovulation. In the PMSG-injected model, hypothalamic GnRH mRNA levels were markedly augmented about 9-fold at 50 h, and pituitary LH
mRNA 3-fold at 52 h after PMSG administration. Serum LH levels were increased to the
preovulatory surge levels at 56 h, and ovarian GnRH mRNA levels were augmented 4-fold
at 60 h after PMSG injection. Administration of heG also induced a marked enhancement
in ovarian GnRH mRNA levels in comparison to the values shown in both intact and PMSGtreated rats at 52 hand 54 h, respectively. In the proestrous stage of normal adult rats,
pituitary LH~ mRNA levels were peaked at 16:00 h. The preovulatory LH surge was evident
at 4 h before increment in ovarian GnRH mRNA levels as shown in PMSG-treated rats.
The present study clearly showed the sequential increase in hypothalamic GnRH mRNA, pituitary LH~ mRNA and ovarian GnRH mRNA levels, indicating that ovarian GnRH may play
a possible role in the control of follicular maturation and the ovulation process.