Functional oxytocin receptors discovered in human osteoblasts

Undifferentiated or differentiated human trabecular bone cells with osteogenic capacity in primary culture express oxytocin receptors (OTRs). OTR expression then persists upon differentiation to an osteoblast phenotype. A human epithelial osteosarcoma cell line, Saos-2, also expresses OTRs. Expression was determined both at mRNA and protein levels. Functional OTRs are evidenced by an increase in intracellular calcium concentration, [Ca2+](i), in response to 10 nM oxytocin (OT). An oxytocin antagonist (OTA) blocked this effect, demonstrating specificity for OT. OT also stimulated prostaglandin E-2 (PGE(2)) synthesis in both confluent undifferentiated and differentiated human trabecular bone cells. This is the first report of OTR mRNA and protein expression and of prescribed OT signal pathways in osteoblastic cells. Since PGE(2) has been shown to increase bone turnover in favor of bone formation, OT may be a new class of a bone anabolic agent.