LEVELS OF HYPOTHALAMIC PROOPIOMELANOCORTIN mRNA AND ESTROGEN BINDING SITES DURING PREOVULATORY GnRH SURGE IN RAT
YANG Shu Ping ①\ \ HE Lian Fang ②\ YU Jin ① ( ① OB/GYN Hospital,Shanghai Medical University, Shanghai 200011, China) ( ② Department of Neurobiology,Shanghai Medical University, Shanghai 200032, China)
To examine change in gene expression of POMC and its relationship with changes in levels of serum estradiol, binding sites of estradiol, progesterone and GnRH densities in the hypothalamus during the preovulatory LH surge, time course studies were performed in pro estrous rats to determine the levels of serum estrogen, progesterone, GnRH densities in the median eminence(ME), binding sites of estrogen receptor(ER) and progesterone receptor(PR) and levels of Arc POMC mRNA in hypothalamic periarcuate area(Arc). The results showed that levels of serum estrogen increased at 1 400 h in the proestrous( P 0 05) and peaked at 1 600 h when levels of estrogen receptor binding sites and POMC mRNA in the Arc decreased( P 0 05) while Arc progesterone binding sites increased( P 0 05). There was a negative correlation between levels of Arc POMC mRNA and levels of serum estrogen or ME GnRH( P 0 01 and 0 05, respectively) and a positive correlation between levels of Arc POMC mRNA and estrogen binding sites( P 0 01). These results suggest that changes in gene expression of hypothalamic POMC during preovulatory LH surge may be regulated by estrogen and its receptors. The decreased synthesis of hypothalamic β END may be involved in the process of preovulatory GnRH/LH surge.