EFFECTS OF INSULIN ON IN-VITRO BONE-FORMATION IN FETAL-RAT PARIETAL BONE

We examined the effects of insulin on bone formation including the min eralizing process. Twenty-day fetal rat parietal bones were cultured f or 96 h on grids in a serum-free medium. For the precise assessment of bone formation, histomorphometry, with an image analyzing system, was used to measure the areas of mineralized bone and bone matrix, and th e numbers of osteoblasts and osteoclasts. In order to confirm the effe cts of insulin on bone mineralization, the calcium content of the bone and the release of previously incorporated Ca-45 into the medium were measured. Insulin, at a concentration of 10(-6) M or higher, increase d the areas of mineralized bone and bone matrix, and the number of ost eoblasts. Osteoclasts were seldom observed in bones on day 0 or in bon es treated with insulin. In bones treated with insulin at a concentrat ion of 10(-6) M, the calcium content of bone increased. At an insulin concentration of 10(-7) M or higher, the dry weight of decalcified bon e increased. Lactate production in the medium increased dose-dependent ly. The inhibited release of Ca-45 in bones indicated that insulin act s by increasing calcium retention. We demonstrated that insulin has an effect on bone-forming and bone-resorbing cells to enhance the bone f orming process from matrix formation to mineralization.