Appearance of osteoclasts by injections of lipopolysaccharides in rat periodontal tissue

The effect of lipopolysaccharides (LPS) on periodontal tissue was studied in 11-week-old Wistar rats. Four injections of 500 micrograms LPS induced marked osteoclastic alveolar bone resorption, whereas no alveolar bone resorption occurred after four injections of physiological saline. The osteoclast count increased progressively during the four injections of 500 micrograms LPS. After eight injections, however, the osteoclast count fell from the maximum level after four injections, although osteoclasts continued to increase in size and demonstrate an increased number of nuclei. Comparison of the osteoclast number between a series of four injections of 5, 50 or 500 micrograms LPS each revealed a dose-dependent increase. This strongly suggests LPS induction of osteoclastic bone resorption in vivo. Combined use of indomethacin, a prostaglandin synthesis inhibitor, with LPS injections inhibited both the LPS-induced alveolar bone resorption and osteoclast increase, suggesting a possible participation of prostaglandins in osteoclast-mediated bone resorption.