In recent years, the age of children entering puberty is getting lower and the incidence of central precocious puberty is increasing. It is known that melatonin plays an increasingly important role in regulating animal reproduction, but the specific role and mechanism of melatonin in regulating the initiation of puberty remain unclear. The purpose of the current study was to investigate the effect of subcutaneous melatonin injection on pubertal development in female mice and its mechanism of action. Female mice that were 22 days old received 1 mg/kg doses of melatonin subcutaneously every day for 10, 15 and 20 days. The vaginal opening was checked daily. Hematoxylin and eosin (HE) stain was used to determine the growth of the uterus and ovaries. Enzyme-linked immunosorbent assay (ELISA) was used to determine the levels of follicle-stimulating hormone (FSH), gonadotropin-inhibiting hormone (GnIH), and gonadotropin-releasing hormone (GnRH) in serum. By using RT-PCR and Western blotting, the mRNA and protein expression of the hypothalamus GnRH, GnIH, Kisspeptin (Kp), Proopiomelanocortin (POMC), Neuropeptide Y (NPY), as well as G protein-coupled receptor 147 (GPR147) were identified. The findings demonstrated that melatonin could suppress ovarian follicle and uterine wall growth as well as delay vaginal opening, decrease serum levels of GnRH and FSH and increase levels of GnIH. Melatonin increased GnIH and GPR147 expression in the hypothalamus in comparison to the saline group, while decreasing the expression of GnRH, Kisspeptin, POMC, and NPY. In conclusion, exogenous melatonin can inhibit the onset of puberty in female mice by modulating the expression of hypothalamic GnRH, GnIH, Kisspeptin, POMC and NPY neurons and suppressing the hypothalamic–pituitary–gonadal axis.
MG has a special molecular structure, and MG is an important chemical intermediate with promising applications. AgÀ Ce/ ZrO 2 catalysts with different contents were prepared for hydrogenation of DMO to MG by equal volume impregnation. The content of Ag and the type of additives were screened. According to the effects of different additives on the conversion rate of DMO and the selectivity of MG, Ce was finally selected as the optimal additive metal. These were characterized by XRD, XPS, BET, H 2 -TPR. The addition of Ce helps the catalyst to form more oxygen vacancies and Ag 2 O is more easily reduced to Ag monomers. The performance test results of the catalyst showed that the addition of appropriate amount of Ce has a certain promotion effect on the hydrogenation performance of the catalyst, The yield of MG using the 8AgÀ Ce 1 /ZrO 2 catalyst was significantly better than that of the Ag/ZrO 2 catalyst.
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