BACKGROUND: Leptin may regulate reproductive function via release of hypothalamic neuropeptide Y. However, it is unknown whether this regulatory effect is limited to the hypothalamus. OBJECTIVE: To detect the effect of different dosages of leptin on luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from in vitro cultured rat anterior pituitary cells. DESIGN: Contrast study based on cells. SETTING: This study was performed in the Basic Institute of Chengde Medical College, Chengde City, Hebei Province, China from March to June 2007. MATERIALS: Eighteen female Wistar rats of three months of age, weighing 200-220 g, and of clean grade were used. Leptin was provided by Peprotech Company, DMEM culture medium by Invitrogen Company, and the radioimmunological kit by Beijing Zhongshan Jinqiao Biotechnology Co., Ltd. METHODS: Three glandular organs were regarded as one group for culture of anterior pituitary cells. In the control group, saline was added to the culture medium instead of leptin. In the leptin group, leptin was prepared into different concentrations of 1×10-12, 1×10-11, 1×10-9, 1×10-7, and 1×10-6 mol/L for stimulation of cultured cells. The culture supernatant was obtained at three hours after additional of saline/leptin. MAIN OUTCOME MEASURES: Contents of LH and FSH were detected by radioimmunology. RESULTS: Following leptin stimulation, LH release increased with increasing concentrations of leptin up to 1×10-9 mol/L, where LH release peaked. LH release then progressively decreased with increasing leptin concentrations (P