Prostaglandin production by calvariae from sham operated and oophorectomized rats: effect of 17 beta-estradiol in vivo.

The mechanism by which estrogen inhibits bone resorption in vivo is not known. Since prostaglandin E2 (PGE2) is a potent stimulator of bone resorption in vitro, we tested the hypothesis that estrogens might affect bone indirectly by inhibiting endogenous PGE2 synthesis. Cultured parietal bones from 7- to 9-week-old rats showed a gradual release of immunoreactive PGE2 in vitro. Oophorectomy resulted in a two-fold increase in PGE2 release. Treatment in vivo with low doses of 17 beta-estradiol or high doses of 17 alpha-estradiol 26 h and 2 h prior to sacrifice inhibited bone PGE2 release in vitro. Addition of 17 beta-estradiol to calvariae in vitro did not affect PGE2 release, whereas cortisol inhibited PGE2 release.