Glucocorticoids stimulate resorption in fetal rat parietal bones in vitro

The effect of glucocorticoids on bone resorption was examined in a serum-free mineralizing organ culture system derived from 20 day fetal rat parietal bones. Bone resorption was assessed by prelabeling the fetal rats in utero with 45Ca and determining the daily release of 45Ca into the medium of cultured bones. During the first 24 h of treatment a transient stimulation of bone resorption was found; 4.5 +/- 0.3% of the total 45Ca was released into the medium with 1 nM corticosterone and 4.1 +/- 0.2% with 10 nM corticosterone compared to 2.9 +/- 0.2% in control bones. Treatment with 1 and 10 nM dexamethasone for 24 h also showed an increase in 45Ca release compared to control bones. During the same time period 45Ca release was 6.9 +/- 1.4% with 10 nM parathyroid hormone. At later time points 100 and 1000 nM corticosterone inhibited 45Ca release, but 1 and 10 nM corticosterone values were similar to controls. At 24 h the number of osteoclasts per mm2 tissue in bone lacunae was significantly elevated with 1-100 nM corticosterone and 10 nM parathyroid hormone compared to control bones. In control bones 0.10 +/- 0.05 osteoclasts per mm2 of tissue were found, but 0.59 +/- 0.21 osteoclasts per mm2 were seen with 10 nM corticosterone and 1.50 +/- 0.34 with 10 nM parathyroid hormone. An additional assay of bone resorption, the release of lysosomal beta-glucuronidase into the medium was also elevated in glucocorticoid and parathyroid hormone-treated cultures.(ABSTRACT TRUNCATED AT 250 WORDS)