Kawasoko S

Effects of insulin-like growth factor-I on nasopremaxillary growth under different masticatory loadings in growing mice

It is well accepted that reduced masticatory function induced by a diet with soft physical consistency causes alterations in the craniofacial morphology in growing animals. It is assumed that these alterations are associated with reduced proliferative activity of osteoblasts on the bone surface, indicating a significant role for mechanical stimuli mediated by various local growth factors including insulin-like growth factor-I (IGF-I). Here, the effects of IGF-I on the linear growth of nasal and premaxillary bones subjected to different masticatory loadings were examined. The length of the nasal bone and the width of the premaxilla were measured. These dimensions were significantly greater in mice fed a solid diet than in mice fed a granulated diet. In animals treated with IGF-I, the nasal bone length and premaxillary width increased significantly in a subgroup receiving a solid diet, but these changes were not found in a similar group fed a granulated diet. No statistically significant differences in these dimensions were found between solid-diet mice injected with saline and granulated-diet group injected with IGF-I. It is concluded that IGF-I induces nasal and premaxillary growth, and that its effect is enhanced or accelerated by increased mechanical masticatory loading.

Recruitment of osteoclasts in the mandibular condyle of growing osteopetrotic (op/op) mice after a single injection of macrophage colony-stimulating factor

The purpose was to elucidate histological changes in the mandibular condyle and ramus in growing osteopetrotic (op/op) mice after a single injection of macrophage colony-stimulating factor (M-CSF). M-CSF (5 microg) was injected into 6-, 11-, 26-, 56- and 86-day-old op/op mice, and the mice were killed 4 days after the injection. In normal mice, the condyle was substantially wider than the ramus beneath it, and enlargement and ossification of the condyle occurred after weaning. These changes were not found in the uninjected and injected op/op mice, the condyles of which were occupied by hypertrophic cartilage cells, and the hypertrophic cell layer was thicker and more irregular in the arrangement of epiphyseal cell columns. In spite of the lack of bone resorption in uninjected and injected op/ op mice, ossification of the mandibular ramus occurred, but later than that of normal mouse. The number of tartrate-resistant acid phosphatase-positive cells in the injected op/op and normal mice approached a maximum at 30 days and then gradually decreased up to 90 days of age, although the numbers were substantially different for all ages. The uninjected op/op mice had no visible osteoclasts until 15 days and their number then increased significantly from 60 to 90 days of age. These results were considered due to the difference in biological responses of bony structures to M-CSF injection in the op/op mice. The influences of mechanical stimuli from masticatory functions, which are deficient in op/op mice, might also be responsible for the differences in bony architecture between the op/op and normal mice.