The Impact Of Estrogen On The Prepubertal Female Rats, Hypothalamic Gnrh Expression And Secretion

Background In recent years, the incidence of precocious puberty increased, precocious puberty may Damage both mental behavior and physical development of children. Researeh has indieated the existence of Environmental Estrogens, They can serve as estrogen receptor (ER) ligand and activate the ER, The estrogen levels of the prepubertal children may affect the time to start puberty. Since the priming of puberty is date from the increase of the secretion of Hypothalamic gonadotropin-releasing hormone (GnRH), GnRH is a vital neurohormone to start the hypothalamus - pituitary - gonadal (HPG) axis , GnRH pulse to the pituitary portal circulation and stimulate the synthesis and release of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH).,but the mechanisms of the initiation, activation and maintenance of hypothalamic GnRH neurons on the onset of puberty still remains unclear at present.Objeetive In this experiment, the estrogen-induced precocious puberty rats as models, the gene synthesis and Hormone secretion of hypothalamic GnRH were measured during the prepubertal Period of rats, Moreover,the effect of exogenous estrogen on the onset of puberty and expression and secretion of GnRH were explored in rat hypothalamus.the result provide a theoretical basis for further studying the pathogenesis and treatment of precocious puberty.Methods Methods Fifty Female rats were divided into normal group, short-term control group, short-term E2 group, long-term control group and long -term E2 group. Rats except those in normal group,were subcutaneously administered drug once a day at 15 days of age individually, 17β-estradiol were administered to rats in the short-term E2 group and the long -term E2 group while the two control groups were only treated with vehicles(sesame oil), respectively. The two short-term groups were administered drugs for 5 days and the two long-term groups were treated for 13 days. the vaginal opening were examined. The content of GnRH in culture solution was determined with ELISA before and after the slices were stimulating with high KCL to observe the change of GnRH biosynthesis in hypothalamus. The expression of hypothalamic GnRH mRNA were assayed by real time-PCR.Results Compared with normal group, the vaginal opening in the groups which were administered 17β-estradiol were ahead of time[(24.7±1.227d,24.9±1.165d) vs (33.12±1.409d) P < 0. 05];before stimulated by high KCL, the secretion of GnRH in normal group were more than other groups [(1.39±0.08μg/L) vs(1.21±0.21μg/L,1.22±0.06μg/L,1.24±0.09μg/L) P < 0. 05] ,after stimulated the secretion of GnRH in all groups increased. the secretion of GnRH in short-term control group were fewer than that in short-term E2 group and normal group[(6.75±0.47μg/L) vs (7.47±0.85μg/L,7.44±0.45μg/L) P < 0. 05] ;the expression of hypothalamic GnRH mRNA in normal group increased(8.17±6.64μg/L P < 0. 05).Conclusions Estrogen may accelerate the stimulation of hypothalamus - pituitary - ovary axis by increasing the secretion of GnRH, and affect the pubertal development.