Effects of local administration of insulin-like growth factor-I on mandibular condylar growth in rats.

Endochondral bone formation observed at the mandibular condyle is regulated by various growth factors including insulin-like growth factor-I (IGF-I). In this paper, we describe a method for the local administration of IGF-I to the bilateral mandibular articular cavities of 3- and 12-week-old rats, and the effects of IGF-I on endochondral bone formation by histomorphometric techniques. In 3-week-old IGF-I-treated rats, three days after administration, an increase in bone tissue was found in the area of the subchondral cancellous bone layer. In 12-week-old IGF-I-treated rats, three days after administration, an increase in the thickness of the condylar cartilage and a decrease in bone tissue were observed in the area of the subchondral cancellous bone layer. This study revealed that the local administration of IGF-I on mandibular condyle caused different histological changes between growth and maturation periods. These results indicated that the effects of IGF-I on endochondral bone formation in the mandibular condyle were age-dependent.