Effects of prostaglandins on rat calvarial bone-cell calcium

Abstract

Prostaglandin E 2 (PGE 2) over the concentration range 10 −5–10 −7M stimulated calcium uptake in osteoclastic-enriched populations isolated by sequential collagenase digestions of newborn rat calvaria. This effect was on initial calcium uptake occurring at 5 min at 37 °C but was not present when isotopic equilibrium was approached (60 min). Prostacyclin (PGI 2, PGE 1 and PGF 2α) stimulated osteoclastic calcium uptake in a similar manner, but with slightly smaller effects than PGE 2. Under identical conditions, significant effects of PG were not observed in osteoblastic cells isolated from the same bones by extended collagenase digestions. Combined treatment with PGE 2 and parathyroid hormone (PTH) at concentrations which produced no individual effects resulted in a significant increase in calcium uptake in osteoclastic cells. During a 48-h culture period, osteoblastic populations released significantly greater amounts of PGE 2 than osteoclastic populations. Pre-incubation for 1 h at 37 °C with the prostaglandin cyclo-oxygenase antagonists, indomethacin and flufenamic acid, had no effect on calcium uptake in osteoclastic cells, but resulted in significant decreases in osteoblastic cells. The PGE 2-induced increase in calcium uptake on osteoclastic cells was not altered by indomethacin or flufenamic-acid pretreatment. However, after treatment with these inhibitors, a significant response to PGE 2 was observed in osteoblastic cells.