Effects of Glucocorticoids on Fetal Rat Bone Collagen Synthesis in Vitro*

Abstract

Effects of glucocorticoids on bone collagen synthesis were examined in organ cultures. Fetal rat calvaria were incubated with [3H]proline during the last 2 h of culture; [3H] proline incorporation into collagenase-digestible (CDP) and noncollagen protein (NCP) was measured using purified bacterial collagenase. Cortisol (0.03-3 μM) increased incorporation of label after 24 h, although CDP was affected more than NCP. Cortisol did not alter collagen synthesis in freshly explanted bones cultured for 3 h. The stimulatory effect was seen at high and low concentrations of unlabeled proline and was not associated with increased incorporation of [3H]thymidine into DNA or [3H]uridine into RNA; release of labeled collagen from bone to medium was unaffected by cortisol. Dexamethasone (9α-fluoro- 11β,17α,21-trihydroxy- 16α-methylpregna- l,4-diene-3,20-dione; 1 nM), corticosterone, and cortexolone (17α,21-dihydroxy-4-pregnene- 3,20-dione; 0.1 μM) increased collagen synthesis after 24 h; epicortisol (11α,17α,21-trihydroxy-4-pregnene-3,20-dione) and deoxycorticosterone were ineffective. Cortexolone did not alter the stimulatory effect of cortisol. Cortisol, added for the last 3, 24, or 48 h of a 96-h culture, increased collagen synthesis; cortisol treatment for 96 h produced a dose-related inhibition of incorporation of [3H]proline into CDP and NGP and reduced the incorporations of [3H]thymidine into DNA and [33H]uridine into RNA. Dexamethasone and cortexolone decreased [3H]proline incorporation after 96 h, and cortexolone did not alter the cortisol response. After 96 h of treatment with cortisol, histological examination showed decreased numbers of osteoblasts and fibroblasts. We conclude that cortisol and related glucocorticoids have two different effects on bone collagen synthesis in vitro. Collagen synthesis is stimulated in short term cultures, suggesting that physiological concentrations of glucocorticoids may maintain the differentiated function of osteoblasts. The long term effect is to inhibit collagen and NCP synthesis, possibly due to inhibition of precursor cell proliferation.