Induction of osteocalcin gene expression in vitro by progesterone.

The effect of progesterone on osteocalcin gene expression was investigated in order to understand how progesterone acts on osteoblast in vitro. For this purpose, fetal rat calvarial osteoblasts were cultured in the medium containing 10(-9) M-10(-6) M progesterone respectively for two weeks while the cells progressing differentiation. Northern blot analysis showed that progesterone increased the level of osteocalcin mRNA in a dose-dependent manner. Among those doses of progesterone employed in this study, only 10(-6) M hormone caused a significant induction of osteocalcin gene expression (2.3 fold, P < 0.01). Our results demonstrated for the first time that the osteocalcin gene expression is regulated by progesterone. In addition, the results obtained from our study provides a good evidence for the direct effect of progesterone on osteoblast in vitro.