Effects of 1,24 dihydroxyvitamin D3 and calcitonin on fracture healing in adult rats.

Calcitonin and 1.25(OH)2D3 have opposite effects on the serum concentrations of Ca and P, as well as on bone resorption, and can be observed in the process of healing of standardized fracture in adult rats. The rats given 1.25(OH)2D3 had a stronger fracture callus and slightly less pronounced postfracture osteopenia. Calcitonin did not significantly influence the fracture healing but had a pronounced effect in preventing the osteopenia. The effects of 1.25(OH)2D3 are believed to be indirect, i.e., through the changes in the serum Ca X P product, whereas the osteopenia preventing action of calcitonin may come from direct effect on bone.