OXTR

OXTR is the class A GPCR for oxytocin - the nine-residue cyclic neuropeptide that drives uterine contraction, lactation, social bonding, pair bond formation, fear extinction, and maternal behavior. It is the most direct pharmacological handle on prosocial neural circuits and the canonical target for labor induction/augmentation. Oxytocin (as Pitocin/Syntocinon) is one of the most widely administered peptide drugs in obstetrics. OXTR agonism is under clinical investigation for autism spectrum disorder, PTSD, social anxiety, and Prader-Willi syndrome. Every scaffold targeting the oxytocin/vasopressin system, social behavior, or labor pharmacology routes through this card.

OXTR (chromosome 3p25.3, 389 aa) is a Gq/11-primary class A GPCR with significant Gi/o coupling in some cellular contexts. Oxytocin (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH₂, 1–6 disulfide ring) binds the orthosteric pocket formed by TM2, TM3, TM5, TM6, TM7, and ECL2, with a conserved ECL1-ECL2 disulfide (Cys112–Cys187) stabilizing the binding vestibule. Mg²⁺ coordination enhances oxytocin binding affinity in some assays. Signaling: Gq/11 → PLC-β → IP3/DAG → intracellular Ca²⁺ (uterine contraction, milk ejection) + PKC → MAPK/ERK (proliferation, dendritic remodeling); Gi/o → ↓cAMP in CNS neurons; PI3K-AKT. β-arrestin → internalization + sustained ERK. OXTR expression in uterus increases >100-fold from early pregnancy to term under estrogen/progesterone control, driving labor sensitivity. CNS expression is dense in amygdala (central nucleus), hypothalamic PVN/SON, hippocampus, and nucleus accumbens - circuits governing fear, social memory, reward, and oxytocin's own autocrine/paracrine release. OXTR also functions in cardiac myocytes (cardioprotection), osteoblasts/osteoclasts (bone metabolism), and immune cells (anti-inflammatory). SNP rs53576 (A/G in OXTR) associates with individual differences in social cognition and anxiety-related traits. OXTR is closely related to AVPR1A/1B (V1 vasopressin receptors) - oxytocin has ~10-fold selectivity for OXTR over V1R; at high doses, cross-reactivity contributes to vasopressin-like antidiuresis.

Approved: synthetic oxytocin (Pitocin/Syntocinon SC/IV) for labor induction and postpartum hemorrhage prevention; approved worldwide. Atosiban (cyclic nonapeptide OXTR/AVPR antagonist) is approved in Europe for acute tocolysis in preterm labor. Intranasal oxytocin is widely studied but not approved for psychiatric indications - clinical trial results have been inconsistent, partly due to heterogeneous CNS delivery. MVT-602 (kisspeptin analog, Phase 2) engages OXTR indirectly via GnRH pulsatility. For peptide research, the tractable recipes are: [Thr⁴,Gly⁷]-OT (carbetocin analog template) with C-terminal PEGylation for sustained uterotonic action vs. repeat oxytocin bolus; cyclic disulfide-locked oxytocin analogs with ring size variants (8, 9, 10 membered) to probe the binding pocket geometry and tune OXTR vs. AVPR1A selectivity; biased OXTR agonists that favor Gs/cAMP (prosocial CNS) over Gq/Ca²⁺ (uterine contraction) to separate social anxiety indication from labor side effects; and OXTR/AVPR1A dual-selective peptides for Prader-Willi syndrome where the social and anxiolytic effects of both receptors may contribute to the therapeutic effect.