In vitro stimulation of bone resorption was observed with the glucocorticoids hydrocortisone and dexamethasone. Dosage-dependent release of 45Ca from neonatal mouse calvarial bones was found for both steroids, with half-maximal responses for hydrocortisone and dexamethasone of 0.3 and 0.08 microM, respectively. Significant release of stable calcium (Ca2+), inorganic phosphate (Pi), and the lysosomal enzyme beta-N-acetylglucosaminidase was noted following treatment of mouse calvariae with either 1 microM hydrocortisone or 1 microM dexamethasone. Additionally, both 1 microM hydrocortisone and 1 microM dexamethasone elicited release of 3H from calvarial bones prelabeled with [3H]proline. The stimulation of bone resorption by the glucocorticoids, as assessed by 45Ca release, was sustained over 120 h of culture. Inhibition of 45Ca release from calvariae treated with either 1 microM hydrocortisone or 0.1 microM dexamethasone was observed with 0.01-30 nM salmon calcitonin (sCT), 0.1 mM acetazolamide, and 0.1 mM of the bisphosphonate AHPrBP. Inhibition of glucocorticoid-induced bone resorption by sCT occurred without "escape from calcitonin-induced inhibition." The 45Ca release stimulated by 1 microM hydrocortisone and 0.1 microM dexamethasone was also inhibited by 10 microM progesterone in a competitive manner and by 1 microM of the antiglucocorticoid RU38486, both of which are modulators of glucocorticoid binding. Prostaglandin E2 (PGE2) formation by 10 nM parathyroid hormone (PTH) in neonatal mouse calvarial bones was inhibited by both 1 microM hydrocortisone and 1 microM dexamethasone, but neither compound altered basal PGE2 formation. Exposure of calvarial bones to the mitotic inhibitors hydroxyurea and mitomycin C inhibited 45Ca release stimulated by 1 microM hydrocortisone and 1 microM dexamethasone. In contrast, addition of 1 ng/ml of recombinant murine granulocyte macrophage colony stimulating factor (rmGM-CSF) had no effect on 45Ca release elicited by the glucocorticoids. These results suggest that hydrocortisone and dexamethasone stimulate osteoclastic resorption in neonatal mouse calvariae by a receptor-mediated mechanism that is dependent on cellular replication.