Modulation of prostaglandin E₂-induced Ca²⁺ influx by steroid hormones in osteoblast-like cells

In osteoblast-like MC3T3-E1 cells, we previously reported that prostaglandin E₂ (PGE₂), a potent bone resorbing agent, stimulates Ca²⁺ influx (H. Tokuda, M. Miwa, Y. Oiso and O. Kozawa, Cell Signal 1992; 4: 261-266). In this study, we examined the effects of various hormones belonging to the steroid hormone superfamily on PGE₂ -induced Ca²⁺ influx in MC3T-E1 cells. 1,25-Dihydroxyvitamin D₃ [1,25-(OH)₂D₃], an active form of vitamin D₃, dexamethasone and retinoic acid significantly inhibited the PGE₂-induced Ca²⁺ influx in a dose-dependent manner in these cells. The effects of these hormones were dependent on the time of pretreatment and submaximum inhibitions were observed at 6 h. In contrast, 24,25-dihydroxyvitamin D₃ [24,25-(OH)₂D₃], an inactive form of vitamin D₃, 17 β-estradiol, progesterone, testosterone and triiodothyronine had little effect on the PGE₂-induced Ca²⁺ influx in these cells. These results suggest that, in the steroid hormone superfamily, 1,25-dihydroxyvitamin D₃, glucocorticoid and retinoic acid modulate bone metabolism through the inhibition of Ca²⁺ influx induced by PGE₂ in osteoblast-like cells.