Estrogen Stimulates the Elaboration of Cell/Matrix Surface-Associated Inhibitory Factor of Osteoclastic Bone Resorption from Osteoblastic Cells

Osteoblast-like UMR106 cells secreted bone resorption-stimulating activity (BRSA) under stimulation by human parathyroid hormone 1-34. Most of BRSA was associated with cell/matrix surface and could be extracted by 2 M NaCl. Pretreatment with 17β-estradiol (E₂) reduced BRSA by enhancing the elaboration of an inhibitory factor of BRSA in a dose-dependent manner, and 10⁻⁹ M 17β -E₂ showed a significant effect. Neither 17α -E₂ nor dihydrotestosterone showed a similar effect. The inhibitory factor of BRSA was also bound to cell/matrix surface, showed affinity for heparin, and was trypsin- and heat-sensitive. Furthermore, this factor could also inhibit resorption pit formation stimulated by 1,25-dihydroxyvitamin D₃, interleukin (IL)-1α and IL-6. Elaboration of such an inhibitory factor of bone resorption from osteoblasts may play an important role in the protective effect of estrogen against bone resorption.Copyright 1993, 1999 Academic Press