Influence of estrogen and progesterone on matrix-induced endochondral bone formation.

The influence of estradiol and progesterone, alone or in combination, on the discrete phases of matrix-induced endochondral bone formation was investigated. Administration of estradiol and progesterone in combination increased mesenchymal cell proliferation, as indicated by [3H] thymidine incorporation into acid precipitable material. However, ornithine decarboxylase (ODC) activity was significantly suppressed by the combination of estradiol and progesterone. Also, this treatment did not influence the 35SO4 incorporation into proteoglycans on day 7. Mineralization of newly induced bone was quantitated by alkaline phosphatase, 45Ca incorporation into bone mineral and calcium content, and was found to be significantly increased by progesterone alone and in combination with estradiol in both matrix-induced plaques and tibial metaphysis. These results demonstrated the stimulatory role of progesterone in combination with estradiol in bone formation and mineralization.