INHIBITORY EFFECT OF 17-BETA-ESTRADIOL ON PROSTAGLANDIN-E2-INDUCED PHOSPHOINOSITIDE HYDROLYSIS IN OSTEOBLAST-LIKE CELLS

We examined the effect of estradiol on PGE2-induced phosphoinositide hydrolysis and cAMP production in cloned osteoblast-like MC3T3-E1 cells. 17-beta-Estradiol pretreatment significantly inhibited the formation of inositol phosphates induced by 10-mu-M PGE2 in a dose-dependent manner between 1 pM and 10 nM. This effect of 17-beta-estradiol was dependent on the time of pretreatment and submaximum inhibition was observed at 4 h. However, 17-beta-estradiol had little effect on the formation of inositol phosphates induced by 20 mM NaF, a GTP-binding protein activator. The cAMP production induced by PGE2 was not influenced by 17-beta-estradiol. These results suggest that 17-beta-estradiol modulates the signal transduction by PGE2 and that the effect seems to be exerted between PGE2 receptor and the GTP-binding protein coupled to phospholipase C in osteoblast-like MC3T3-E1 cells.