A direct effect of 24,25-(OH)2D3 and 1,25-(OH)2D3 on the modeling of fetal mice long bones in vitro.

To examine the effects of 24,25-(OH)2D3 and 1,25-(OH)2D3 on fetal long bone modeling the radii and ulnae of 16 day fetal mice were grown in vitro for 2 days. Their growth, mineralization, and resorption were assessed by measuring diaphyseal length, calcium and phosphorus content, hydroxyproline-protein ratios, and the release of incorporated 45Ca. The results showed that 24,25-(OH)2D3 at concentrations of 10(-10)-10(-8) M stimulated the growth of the bones as indicated by their increased diaphyseal length, periosteal bone area, and hydroxyproline content. Calcium and phosphorus content was significantly increased; 45Ca release was unaltered. Bones incubated in media containing 10(-6) M 24,25-(OH)2D3 responded in a similar fashion to bones incubated in media containing 10(-10)-10(-8) M 1,25-(OH)2D3, with inhibition of bone growth as indicated by reduced diaphyseal length, periosteal bone area, hydroxyproline-protein ratios, and calcium and phosphorus content; 45Ca release was significantly increased. Neither metabolite affected total bone length. The results suggest a role for 24,25-(OH)2D3 in the growth of fetal mice bones in vitro and also confirm the findings from previous studies that 1,25-(OH)2D3 and high concentrations of 24,25-(OH)2D2 stimulate bone resorption.