Oestrogen and progestogen synergistically stimulate human and rat osteoblast proliferation

Oestrogens play an important role in bone metabolism; they preserve bone mass after the menopause. Their action in bone has recently been shown to be, partly, a direct one, as oestrogen receptors and their effects have been demonstrated in bone cells. The role of progestogens in bone metabolism is less clear. In this study it has been shown that 17 beta-oestradiol exerts only a small, although not significant, stimulatory action with regard to SaOS-2 human osteosarcoma cell proliferation. A pure progestogen (Org 2058) has no effect when added alone. In combination with 17 beta-oestradiol, however, it has a highly synergistic action on SaOS-2 cell proliferation. The same effect was observed in primary rat osteoblasts, showing that this synergism is a general phenomenon in osteoblastic cells. High numbers of oestrogen and progestogen receptors have been demonstrated in SaOS-2 cells, indicating that the effects of these steroids are mediated via the normal route of steroid receptors. These data provide a cellular basis for the clinically recognized positive effect of oestrogen/progestogen combinations on bone formation.