EVIDENCE FOR A LOCAL-ACTION OF GROWTH-HORMONE IN EMBRYONIC TOOTH DEVELOPMENT IN THE RAT

Studies in non-dental embryonic tissues have suggested that an interac tion between growth hormone and its receptor may play a role in growth and development before the foetal pituitary gland is competent. This study reports the distribution of growth hormone, its receptor and bin ding protein in developing rat tooth germs from embryonic day 17 to 21 and postnatal day 0 using antibodies specific for each of these prote ins. Pour foetal rats were processed at each time point (E17, E18, E20 /21 and postnatal day 0). Following routine fixation and paraffin embe dding, sections were treated with antisera to rat growth hormone, rat growth hormone binding protein and growth hormone receptor Localizatio n of antibody/antigen complexes was subsequently visualized by additio n of biotinylated IgG and reaction with streptavidin peroxidase and di aminobenzidine. Assessment of the level of staining was qualitative an d based on a subjective rankings ranging from equivocal to very strong staining. Overall, growth hormone and its binding protein were locate d both in the cellular elements and throughout the extracellular matri x, whereas the growth hormone receptor showed an exclusively intra-cel lular location All three proteins were detectable in cells of the dent al epithelium and mesenchyme at the primordial bud stage (E17) which o ccurs prior to expression of pituitary growth hormone. At the cap stag e of odontogenesis (E18-19), numerous cells in both the dental epithel ium and mesenchyme were intensely immunoreactive for growth hormone, i ts binding protein and receptor. In the succeeding early bell stage (E 20-21), most of the mesenchymal cells in the dental pulp were mildly p ositive for these proteins, while the dental epithelium and adjacent m esenchyme were more immunoreactive. At the Late bell stage (postnatal day 0), all three proteins were localized in dental epithelium, differ entiating mesenchymal cells the cuspal surface facing the epithelial-m esenchymal interface, preodontoblasts, and odontoblasts forming dentin e. From these observations, immunoreactive growth hormone, its recepto r and binding protein appear to be expressed in odontogenic cells unde rgoing histodifferentiation, morphodifferentiation and dentinogenesis in a cell-type and stage specific pattern throughout embryonic tooth d evelopment, This suggests the possibility that growth hormone, or a gr owth hormone-like protein, plays a paracrine/autocrine role in tooth d evelopment in utero.