17 beta-estradiol increases calcium content in fetal mouse parietal bones cultured in serum-free medium only at...

Using a bone organ culture system that shows mineralization in vitro, we investigated whether 17 beta-estradiol dose-dependently increases calcium content in cultured calvarial bones in serum-free medium. Fetal mouse parietal bones (3 x 3 mm) were cultured in phenol red-free BGJ medium containing phosphate (3-4 mmol/L), calcium (1-1.25 mmol/L), insulin (6 micrograms/ML), and transferrin (6 micrograms/mL) for 4-5 days. Under these culture conditions, the calcium content of the cultured bones (at dissection 34.0 +/- 4.6 micrograms/bone [mean +/- SD], n = 50) increased by 15-20 micrograms during 4-5 days of culture. 17 beta-Estradiol increased the calcium content significantly at 10(-12) to 10(-11) mol/L, but not at lower (10(113) mol/L) or higher (10(-10) to 10(-9) mol/L) concentrations. 17 alpha-Estradiol had no effect. The stimulatory effect of 17 beta-estradiol was completely inhibited by the antiestrogen agent ICI-182,780. The anabolic effect of 17 beta-estradiol was elicited not only in bones from females but also in those from males. 17 beta-Estradiol had no significant effect on 45Ca release from prelabeled parietal bones. Furthermore, light- and electron-microscopic examinations revealed that bone mineralization proceeded through formation of matrix vesicles, without any metastatic or dystrophic calcification. These in vitro findings suggest that 17 beta-estradiol elicits small, but reproducible, direct effects on calcium content in the parietal bones not only in female but also in male fetal mice at physiological-free E2 concentrations (10(-12)-10(-11) mol/L), which is attainable in serum of normal human subjects. In contrast to in vivo studies, pharmacological doses of 17 beta-estradiol had no anabolic effect on parietal bones. The mechanism of such a biphasic effect of estrogens remains to be elucidated.