Binding of epidermal growth factor and insulin in cells of bone and tooth as revealed by radioautography

In vivo binding assays using radioautography were employed to visualize epidermal growth factor (EGF) and insulin receptors in bone and the enamel organ of the rat. The same method was used to study the internalization of EGF within cells of bones and the enamel organ.EGF receptors were observed in three different cell types of bone: a macrophage-like cell, a rough endoplasmic reticulum rich cell and a poorly differentiated cell. No binding of EGF was observed in osteoblasts or in osteoclasts. In the incisor tooth, EGF receptors were found in all the cellular layers of the enamel organ. A functional paracrine type relationship was shown between the papillary layer cells and the covering ameloblasts. EGF receptors were also observed in the ligamentous periodontal ligament and in the stratum germinativum of the gingiva.The radioautographic method permitted not only the detection of insulin receptors in bone cells, but also the identification of cells in the osteoblastic lineage at different stages of maturation. Insulin receptors were found in the cells of the osteoblastic lineage, in endothelial cells and in capillary associated macrophage-like cells. In the incisor tooth, insulin receptors were present in endothelial cells in the maturation zone papillary layer of the enamel organ.Finally, the penetration of insulin within cartilage, prebone and bone, predentin and dentin and enamel was observed