OT-R antagonist 1 inhibits oxytocin-evoked intracellular Ca2+ mobilization (IC50 = 8 nM). OT-R antagonist 1 is a new effective and selective nonpeptide low molecular weight OT-R antagonist.

OT-R antagonist 1 inhibits IP3-Synthesis, rat OT-R (IC50=0.03 uM). OT-R antagonist 1 inhibits phosphodiesterase IV (IC50 = 6.1 μM, a value about 300-fold higher than the affinity for OT-R). OT-R antagonist 1 competitively inhibits binding of [3H]oxytocin and the peptide antagonist 125I-ornithine vasotocin analog to human and rat oxytocin receptor expressed in human embryonic kidney 293-EBNA or Chinese hamster ovary cells with nanomolar potency. OT-R antagonist 1 displays a very clean selectivity profile with specific interaction with OT-R. Selectivity against vasopressin receptor subtypes is >6-fold for V1a and >350-fold for V2 and V1b[1][4].

OT-R antagonist 1 significantly inhibits spontaneous uterine contractions in pregnant rats near term when administered intravenously or orally. Oxytocininduced contraction of isolated rat uterine strips is blocked by OT-R antagonist 1 (pA2 = 7.82). OT-R antagonist 1(single administration; i.v. or oral routes) causes dose-dependent inhibition of contractions elicited by repeated injections of oxytocin (ED50 = 3.5 mg/kg i.v. and 89 mg/kg p.o., respectively), in anesthetized nonpregnant rats [1]