The effects of PGE2 on mineralized bone nodule formation were studied in fetal rat calvarial (RC) cells in vitro. Continuous exposure of RC cells to 3 x 10(-8) M PGE2 induced a twofold increase in mineralized bone nodule formation and a 1.5-fold increase in alkaline phosphatase (ALPase) activity without affecting RC cell growth. These stimulatory effects were evoked by concentrations of 3 x 10(-9)-3 x 10(-6) M PGE2 and the maximal effect was observed with 3 x 10(-8) M PGE2. The in vitro effects of PGE2 were evident when RC cells were exposed to it on days 8-14 and 8-21, which correspond to the post-confluent culture stage, but no effects were observed when the cells were exposed on days 1-7, the growth stage. The ALPase activity was also higher (1.2-1.4-fold) when 3 x 10(-8) M PGE2 was added during the post-confluent stage. In order to determine the effect of PGE2 during the mineralization phase of bone nodules in the presence of a large population of osteoprogenitor cells, RC cells were exposed to dexamethasone for 7 days before PGE2 was added during the post-confluent stage. A significantly higher percentage of nodules mineralized were observed with 3 x 10(-8)-3 x 10(-9) M PGE2 (1.6- and 1.4-fold, respectively), than in control cultures. Analysis of the mineral-related proteins by EDTA extraction of bone nodules followed by electrophoresis and Stains-All staining revealed an increased total amount of osteopontin extracted from the mineralized matrix after PGE2 treatment.(ABSTRACT TRUNCATED AT 250 WORDS)