Effects of 1.25 Dihydroxyvitamin D3 and Calcitonin on Fracture Healing in Adult Rats

Through its effects on the intestinal mucosa, 1.25 dihydroxyvitamin D3 (1.25(OH),D3), the physiologically active vitamin D metabolite, is of decisive importance for calcium (Ca) and phosphorus (P) homeostasis. It protects the skeleton from mineral loss during a marginally low Ca intake* and maintains a serum level of Ca and P which is necessary for the mineralization of osteoid. In a state of vitamin D deficiency there is a block of the formation of mature bone and although the deposition of osteoid is not impaired6 the healing of fractures is likely to be.’ However, 1.25(OH2D3 has also been found to increase bone mass in rats given an adequate supply of vitamin D.3 Since fracture healing means the formation of new bone tissue, a trophic effect of 1.24(OH)2D3 on bone might also result in a more rapid callus formation. Calcitonin lowers the serum levels of Ca and P and thereby counteracts the effects of 1.25(OH),D3. It also decreases bone resorption,6 which will be increased as a result of very high levels of 1.25(OH)& There are divergent reports in the literature as to