A direct effect of 24,25‐(OH) 2 D 3 and 1,25‐(OH) 2 D 3 on the modeling of fetal mice long bones in vitro

To examine the effects of 24,25‐(OH) 2 D 3 and 1,25‐(OH) 2 D 3 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 45 Ca. The results showed that 24,25‐(OH) 2 D 3 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; 45 Ca release was unaltered. Bones incubated in media containing 10 −6 M 24,25‐(OH) 2 D 3 responded in a similar fashion to bones incubated in media containing 10 −10 ‐10 −8 M 1,25‐(OH) 2 D 3 , with inhibition of bone growth as indicated by reduced diaphyseal length, periosteal bone area, hydroxyproline‐protein ratios, and calcium and phosphorus content; 45 Ca release was significantly increased. Neither metabolite affected total bone length. The results suggest a role for 24,25‐(OH) 2 D 3 in the growth of fetal mice bones in vitro and also confirm the findings from previous studies that 1,25‐(OH) 2 D 3 and high concentrations of 24,25‐(OH) 2 D 3 stimulate bone resorption.