Biochemical markers of bone resorption in ovariectomized rats: therapeutic effects of vitamin D metabolites

The changes of bone metabolism in female rats after ovariectomy are similar to the alterations in early post-menopausal women. Vitamin D metabolites, especially the naturally occurring steroid hormone 1,25-dihydroxyvitamin D-3, are known to prevent bone resorption, but show negative side-effects such as hypercalcaemia and hypercalciuria. This study focused on 1 alpha-hydroxyvitamin D-3, on 1 alpha-hydroxyvitamin D-2 and on 1,25-dihydroxyvitamin D-2. The application of 1,25-dihydroxyvitamin D-3, 1 alpha-hydroxyvitamin D-3 and 1,25-dihydroxyvitamin D-3 proved to be effective in decreasing bone resorption in ovariectomized rats. However, these vitamin D metabolites induced the negative side effects of hypercalcemia and hypercalciuria. The application of 1 alpha-hydroxyvitamin D-2 led to an adjustment of markers of bone resorption altered by ovariectomy to the corresponding values of control animals without increasing the values for serum and urinary calcium. This vitamin D metabolite could represent an interesting alternative to 1,25-dihydroxyvitamin D-3, which is the dominating substance in the prophylaxis of postmenopausal osteoporosis with vitamin D metabolites.