Abstract: Objective The purpose of this paper is to observe the expression levels of duodenal TPH1 and LRP5 as well as the level of serum 5-HT in SD male rats of different months, and analyze their changes with the increase of age and the correlation with aging bone mass loss. Methods 6 male SD rats at the age of 2, 6, 12, 15 and 18 months respectively (30 in total) were selected in this study for each group and they were grouped according to their ages so as to simulate the physiological aging model. RT-PCR and Westernblot methods were employed respectively in this study to detect the mRNA and the expression of protein level of duodenal TPH1, LRP5 in rats of different months. Moreover, the ELISA method was used to check the level of serum 5-HT and the Dual-energy bone mineral density method was used to determine the bone mineral density of rats’ femur in vitro. Results Both the expression level of the duodenal TPH1mRNA and protein as well as the level of serum 5-HT increased with the growth of the age, but they showed the negative correlation with the aging bone mass loss（P＜0.001）. Conclusion The enterogenous 5-HT and the expression of TPH1, which is the key enzymes for the speed limit, play an important role in the aging bone mass loss, and they might become the new potential treatment and intervention targets for senile osteoporosis.

Key words: LRP5, TPH1, 5-HT, senile osteoporosis