17-BETA-ESTRADIOL INCREASES CALCIUM CONTENT IN FETAL MOUSE PARIETAL BONES CULTURED IN SERUM-FREE MEDIUM ONLY AT PHYSIOLOGICAL CONCENTRATIONS

Using a bone organ culture system that shows mineralization in vitro, we investigated whether 17 beta-estradiol dose-dependently increases c alcium 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), ins ulin (6 mu g/mL), and transferrin (6 mu g/mL) for 4-5 days, Under thes e culture conditions, the calcium content of the cultured bones (at di ssection 34.0 +/- 4.6 mu g/bone [mean +/- SD], n = 50) increased by 15 -20 mu g during 4-5 days of culture, 17 beta-Estradiol increased the c alcium content significantly at 10(-12) to 10(-11) mol/L, but not at l ower (10(-13) mol/L) or higher (10(-10) to 10(-9) mol/L) concentration s, 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 ha d ho significant effect on Ca-45 release from prelabeled parietal bone s, Furthermore, light- and electron-microscopic examinations revealed that bone mineralization proceeded through formation of matrix vesicle s, without any metastatic or dystrophic calcification, These in vitro findings suggest that 17 beta-estradiol elicits small, but reproducibl e, direct effects on calcium content in the parietal bones not only in female but also in male fetal mice at physiological-free E(2) concent rations (10(-12)-10(-11) mol/L), which is attainable in serum of norma l human subjects, In contrast to in vivo studies, pharmacological dose s of 17 beta-estradiol had no anabolic effect on parietal bones, The m echanism of such a biphasic effect of estrogens remains to be elucidat ed.