A Comparative Study On The Curative Effect Of Day And Night Injection Of Melatonin In The Treatment Of Osteoporosis

Objective:To explore the difference in the efficacy of intraperitoneal injection of exogenous melatonin at different times of day and night in the treatment of osteoporosis.Methods:In this study,40 SD rats were reared.10 rats were randomly selected into the Sham operation group(Sham group,n=10).The ovaries of the remaining 30 rats were removed by bilateral ovariectomy.Continue feeding for 3 months after surgery.The success of the model was identified by Micro-CT,HE staining and Masson staining.After the models were established successfully,the ovariectomized rats were randomly divided into three groups:no special treatment group after ovariectomy(OVX group,n=10),daytime melatonin injection group(OVX+DMLT group,n=10)and nighttime melatonin injection group(OVX+NMLT group).At the preset time point,Administer equal doses(30mg/kg/d)of melatoin to each group.After three months of treatment,the rats were sacrificed and their femur and medullary cavity contents were collected.Bone mineral density and trabecular bone were detected by Micro-CT and histology.Changes of bone formation-related proteins(OC,OPG and RUNX2)in molecular biology were detected by Western-blot.The maximum compressive force that each group of bone tissue can bear was measured by the compressiven experiment.Results:Two ovariectomized rats died after the operation.Before the administration of the ovariectomized rats,the imaging parameters BV/TV,Tb.N,Conn.D of the OVX group were significantly lower than those of the Sham group(P<0.05).HE staining showed that the ovariectomized rats had significantly lower bones volume than the Sham group.After melatonin administration in ovariectomized rats,the BV/TV,Tb.N,Conn.D of OVX+DMLT group and OVX+NMLT group were higher than those of OVX group(P<0.05),and the upward trend was more obvious in OVX+DMLT group comparing with OVX+NMLT group(P<0.05).The highest Tb.sp in the OVX group was significantly different from other groups.The Tb.Sp of the OVX+NMLT group was higher than that of the OVX+DMLT group,and both groups were higher than the Sham group.The Tb.Sp of the OVX+DMLT group was not significantly different from that of the Sham group.Histologically,the area of red connective tissue in the OVX group was significantly less than that in the other groups in HE staining.In the comparison of the OVX+DMLT group and the OVX+NMLT group,the area of red connective tissue was more dense in the OVX+DMLT group,but still lower than that in the SHAM group.In Masson staining,the light blue connective tissue in the OVX group was more sparse compared with other groups(P<0.05),and the light blue connective tissue in the OVX+DMLT group was more dense than that in the OVX+NMLT group.In the Western-blot experiment,the expression levels of RUNX2,OPG and OC in the OVX+DMLT group and the OVX+NMLT group were significantly increased compared with those in the OVX group,and were all lower than those in the SHAM group.The increase in OVX+DMLT group was greater,and the expression level was statistically compared with that in OVX+NMLT group.The value of the maximum crushing force experienced by the Sham group was the largest.This was followed by the OVX+DMLT group and the OVX+NMLT group.The maximum compressive force that the OVX+DMLT group could bear was higher than that of the OVX+NMLT group,and it was statistically significant(P<0.05).Conclusion:The experimental results show that daytime injection of melatonin is more beneficial to promote bone formation and inhibit bone resorption than nighttime injection of melatonin.Thus,osteoporosis can be treated more effectively.