Potent oxytocin receptor (OTR) antagonist. Inhibits oxytocin-induced increase in Ca2+ concentration in myometrial cells in vitro (IC50 = 5 nM) Activates NF-κB and MAPK pathways in human amnion via Gαi signaling, resulting in pro-inflammatory effects. Inhibits oxytocin-induced uterine contractions in vivo and in vitro. Effective in a rat preterm labor model. MW (observed): 994.19.