The Effect And Mechanism Of Leptin, And Leptin Receptor On The Ovariectomic Rat's Bone Metabolism

OBJECTIVE: To investigate the effect of ovariectomy, leptin, and leptin receptor on the female ovariectomic rat's bone metabolism and to explore the possible mechanism of leptin on bone through the cell culture of osteoblast.in order to provide new way of prevention and treatment for postmenopausal osteoporosis.METHOD : Eighty Wistar female rats,aged 6-month-old,were divided into four groups randomly:sham rats fed with ordinary diet,sham rats fed with nourished diet, ovariectomized rats fed with ordinary diet, ovariectomized fed with nourished diet.After 2 months' feeding,detect the concentration of leptin and leptin receptor in serum by ELISA,the weight of the rats,the fat mass inside the abdominal cavity,the bone mineral density (BMD) by DEXA,and the norphometry of bone were measured.After the osteoblastic cultivation,we measured .the proliferation and apoptosis through the MTT method and the flow cytometer,the expression about OB-Ra mRNA, OB-Rb mRNA and STAT3 mRNA by RT-PCR,the activity about STAT3 with its corresponding gene.RESULT:1. The vaginal cytology of ovariectomic group showed no oestrous cycle.An area of the uterus transverse section was deceased in ovariectomic group significantly.The depth of endometrium and its epithelia,the area percentage of endometric gland in ovariectomic group were smaller than those in sham surgical group.2. The body weight in ovariectomic group was increased obviously, specially in ovariectomic rats fed with nourished diet. Nourished diet induced the fat mass inside the abdominal cavity increased.The fat mass was positively correlated with the concentration of leptin in two nourished groups,and was positively correlated with BMD and the percentage of bone trabecula area in sham rats fed with the nourished diet groups.And the fat mass was negatively correlated with BMC in ovariectomized rats fed with the nourished diet group. In ovariectomized rats fed with the nourished diet group,the negative correlation between leptin and BMD existenced, the correlation between leptin and BMD was positive in the other three groups. The proliferation and apoptosis of osteoblasts among the four groups were no differences statistically.3. The tendency of the concentration of leptin receptor in serum was the same as the concentration of leptin in serum. The tendency of the ratio of leptin and leptin receptor was the same as the change of fat mass.There were no correlation between leptin and leptin receptor.After correlation analysis,the positive correlation was observed between LEP/LEPR and BMC.LEP/LEPR was positively correlated with the diameter and the percentage of bone trabecula area in sham rats fed the nourished diet ,and it was negatively correlated with spacing of bone trabecula. LEP/LEPR was positively correlated with diameter of bone trabecula in sham rats fed with nourished diet ,and the leptin receptor' concentration was positively correlated with the spacing of bone trabecula.In ovariectomized rats fed the nourished diet,the negative correlation between LEP/LEPR and BMD,BMC were existenced.The positive correlation between LEP/LEPR and diameter of bone trabecula in sham rats fed with the nourished diet. The correlation between leptin receptor and BMD was negative in sham rats fed with ordinary diet.There were long and short leptin receptor on osteoblasts,and showed no expression of OB- Rb mRNA,20% in sham rats fed with nourished diet, 60% in the ovariectomizd rats fed with nourished diet.4. The expression of STAT3 mRNA and the result of EMSA were the similar tendency:the nourished diet groups' were lower than the corresponding ordinary diet groups',and the ovariectomic groups'were lower than the sham groups'.There was no correlation between OB-Ra and STAT3.CONCLUSION:1. The castrated animal model was successfully established. Ovariectomy may cause the decrease of the cortical bone mass.While the increased body weight after ovariectomy perhaps slow the decrease of bone mass partly.2. The nourishment was the main factor of the body fat increasing,especially after ovariectomy. Furthermore,the fat mass was positively correlated with the weight.3. The leptin was induced by adipocyte.But the increasing of the fat mass couldn't following the increasing of the concentration of leptin.The ratio of leptin and leptin receptor was increased. The body fat regulated the bone metabolism by the ratio of leptin and leptin receptor.4. The body fat may regulate the bone metabolism through the leptin system.The effect of leptin on bone was outside partial function when the body fat affect pimping. When the body fat increased gradually, the axis function of leptin increased also. After the fat mass exceeded the threshold ,the effect of leptin on bone was regarded the axis function as principle, repressing the bone formation,and leptin and amount of bones present negatively related.