Increases in osteocalcin after ovariectomy are amplified by LPS injection: strain differences in bone remodelling

1. LPS (Escherichia coli serotype 0111:B4, 300 micrograms/mouse IP) increases serum osteocalcin in normal female C57B16 mice from 2 to 6 hr after its injection, with peak levels at 2-4 hr after LPS. 2. Both basal and LPS-stimulated serum osteocalcin were markedly inhibited by dexamethasone (10 mg/kg IP). 3. When observed 3 hr after LPS injection, serum osteocalcin was increased by ovariectomy (OVX) (with respect to sham-operated mice) and this increase was amplified in LPS-treated mice. This increase in osteocalcin was maximal 14 days after OVX, whereas urinary deoxypyridinoline cross-link levels were increased at all observation times (11-28 days). 4. All these changes were also observed in Balb/c mice but their magnitudes were consistently lower than those in C57B16 mice. 5. We propose that, (1) osteocalcin is a useful marker of bone remodelling in mice and the precision of measurement of changes in its levels after OVX is increased by LPS treatment and (2) C57B16 mice give greater magnitude and more consistent changes in both serum osteocalcin and urinary deoxypyridinoline cross-links after OVX, and may be a better strain for development of an in vivo model of post-menopausal osteoporosis.