Local administration of IGF-I stimulates the growth of mandibular condyle in mature rats

Abstract

Aim: To evaluate the effects of local injection of insulin-like growth factor I (IGF-I) on the growth of mandibular condyle in mature rats.

Materials and methods: Sixteen 15 week-old male rats were used in this study. In the experimental group, IGF-I at a concentration of 50 μg/ml was injected into articular capsules of the condyle, while rats in the control group were injected with equal volume of physiological saline. These injections were performed three times at 7 day intervals, and all of the rats were killed on the 7th day after the last injection. Tetracycline and calcein were used for vital staining. After death, the condyles were extracted and undecalcified ground sections were prepared for histological and histomorphometric observations. The thickness of the cartilaginous layer of the condyle, the percentage of bone area in the subchondral cancellous bone layer and the amount of endochondral bone growth in the condyle were measured. The significance of the difference in these measurements between IGF-I and control group was evaluated.

Results: An increase in the thickness of the cartilaginous layer, and a decrease in the percentage of bone area in the subchondral cancellous bone layer was recognized in IGF-I treated condyle. The amount of endochondral bone growth in the experimental group was greater than that in the control group.

Conclusion: The local injection of IGF-I into mature condyle seemed to reactivate the process of endochondral bone formation and induced actual bone growth in mature condyle.

Keywords:

• Endochondral bone formation
• insulin-like growth factor-I
• local administration
• mandibular condyle
• rat

Acknowledgments

This work was supported by a Grant-in-Aid for Scientific Research (No. 10671926) from the Japanese Ministry of Education, Science, Culture and Sports.