Direct and sex-specific enhancement of bone formation and calcification by sex steroids in fetal mice long bone in vitro biochemical and morphometric study

The study was carried out to examine the direct effect of the sex hormones 17β-estradiol (E₂) and testosterone on the modeling of cultured fetal mouse long bones separated according to their sex. The culture system used allowed for the simultaneous assessment of bone growth, mineralization, and resorption on each bone. Bones from 16-day-old male and female mouse fetuses were cultured in BGJ medium, supplemented with either 10% fetal calf serum or 4 mg/ml BSA (serum-free medium) for 48 h. The bones were harvested, and their length; the length of their diaphyses; their hydroxyproline, calcium, and phosphorus contents; and their ⁴⁵Ca release were measured. Histomorphometric analyses on midlongitudinal sections of bones from parallel experiments were also performed. The results indicate that in medium supplemented with 10% fetal calf serum, E₂ had a dose-dependent stimulatory effect on bone formation and mineralization at 10^-7 and 10^-9 M, with no effect on bone resorption. This effect was specific to bones from female mice and to E₂, since 17-α-estradiol had no effect. Testosterone had similar effects specific to bones from male mice, resulting in the stimulation of bone formation and mineralization at 10^-7- and 10^-9-M concentrations. These effects were absent when serum-free medium was used. E₂ and testosterone had an anabolic effect on endochondral and periosteal bone formation and mineralization, but no effect on bone resorption. This effect is dependent on the presence of a serum factor(s).