24,25-Dihydroxycholecalciferol induces the growth of chick cartilage in vitro

Recent studies have indicated that 24R,25-dihydroxycholecalciferol [24R,25(OH)2D3] induces development of endochondral bone. It binds specifically to cytoplasmic and nuclear receptors in epiphyseal cartilage cells. In the present investigation we report the effects of 24R,25(OH)2D3 in comparison to other active vitamin-D metabolites on cell growth. This study was performed on micro-mass cell cultures which were prepared from 4.5-day-old embryonic chick skeletal mesenchyme: this culture consists of a high proportion of chondrocytes. Twelve nM 24R,25(OH)2D3 induces a 2-fold increase in [3H] thymidine incorporation into DNA after 24 h of treatment. Other metabolites, either at this or higher concentrations, had no significant effect. [3H]-leucine incorporation into protein and ornithine decarboxylase (ODC) activity were also enhanced only by 24R,25(OH)2D3 at 12 nM (2.4- and 2.0-fold, respectively). These results present supporting evidence for the specific role of 24R,25 (OH)2D3 in the growth and differentiation of developing cartilage cells.