The early postnatal development of the murine mandibular condyle is regulated by endogenous insulin-like growth factor-I

Skeletal growth during the early postnatal period is thought to be GH-independent, and is probably regulated by intrinsic growth factors. We studied the involvement of locally produced insulin like growth factor-I (IGF-I) in the growth of the neonatal mandibular condyle. Immunofluorescence studies revealed intense staining with antibodies to IGF-I in the mandibular condyle of 2-day-old ICR mice. We have also shown that these mandibular condyles contain specific high-affinity binding sites (K(d) = 0.157 nmol/l) for IGF-I (427 fmol/mg). Autoradiographieal studies of iodinated IGF-I revealed that the distribution of the receptors for IGF-I was parallel to that of IGF-I production, mainly in the younger zones of the condyle, namely the chondroprogenitor and the chondroblast cell layers. Immunoinhibition of IGF-I resulted in an almost complete inhibition (-91%) of thymidine incorporation into DNA, as well as in marked degenerative changes in the morphological appearance of the condyle. Our studies support the hypothesis that early postnatal growth is dependent on the paracrine activity of endogenous GH-independent IGF-I.