Leptin effects on the hypothalamic-pituitary-gonadal axis by activating proopiomelanocortin neurons-- Correlation between regulatory effects and duration

摘要

BACKGROUND:Leptin preserves reproductive functions by stimulating hypothalamic-pituitary-gonadal axis activities at different levels.Some interneurons play an important role in leptin regulation of the gonadal axis.It remains uncertain whether leptin regulates reproductive functions by activating proopiomelanocortin (POMC) neurons.OBJECTIVE:To investigate leptin effects on secretory function of the neuroendocrine-gonadal axis by activating POMC neurons and to observe and verify the relationship between leptin effects and various time points.DESIGN,TIME AND SETTING:The randomized,controlled,animal study was performed at the Basic Institute of Chengde Medical University and the Research Room of Reproductive Immunology of National Research Institute for Family Planning from June to September 2008.MATERIALS:Leptin (Peprotech,USA),α-melanocyte stimulating hormone and rabbit anti-POMC polyclonal antibody (SC-20148) (Santa Cruz Biotechnology,USA),follicle stimulating hormone,luteinizing hormone,and gonadotropin releasing hormone enzyme-labeled immunosorbent assay (ELISA) kit (ADL,USA) were used in the present study.METHODS:A total of 60 healthy,female,adult,Wistar rats received 17 β-estradiol for 5 consecutive days at 15 days after ovariectomy.The rats were randomly assigned to physiological saline (n=35),leptin (n=35),and α-melanocyte stimulating hormone (n=20) groups.MAIN OUTCOME MEASURES:Changes in gonadotropin releasing hormone,luteinizing hormone,and follicle stimulating hormone were compared following intraventricular injection of physiological saline,leptin,and α-melanocyte stimulating hormone at various time points.Changes in POMC mRNA and protein expression in the hypothalamus were measured following physiological saline and leptin injection via the lateral ventricle.RESULTS:Compared to the physiological saline group,leptin and α-melanocyte stimulating hormone affected secretion in the hypothalamus-pituitary axis.Leptin affected secretion of gonadotropin releasing hormone,luteinizing hormone,and follicle stimulating hormone,whereas α-melanocyte stimulating hormone inhibited secretion of these hormones.Compared to the physiological saline group,POMC mRNA expression was significantly increased in the hypothalamus at 2 and 4 hours after leptin injection (P 0.05).POMC protein expression was significantly increased in the hypothalamus at 4 and 6 hours after leptin injection (P < 0.05).CONCLUSION:Leptin affects secretory function of the neuroendocrine-gonadal axis through combined effects on POMC neurons and other pathways.Results suggested that the regulatory effects of POMC neurons were later compared to other neurons.