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 17 β-estradiol (E2) reduced BRSA by enhancing the elaboration of an inhibitory factor of BRSA in a dose-dependent manner, and 10-9 M 17 β -E2 showed a significant effect. Neither 17 α -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. © 1993 Academic Press, Inc.