Oxytocin

Parturition, lactation, and social bonding from a 9-residue peptide.

EndogenousEstablished

Identity

Class: Cyclic nonapeptide (9 aa)
Source: Hypothalamus (PVN/SON); released from the posterior pituitary
Receptor: Oxytocin receptor (OXTR), a class A GPCR

Key properties

Molecular weight

~1,007.2 Da

Half-life (native)

~1–6 min

Model dosing

Approximate values for the native hormone. Engineered analogs are often deliberately larger and far longer-acting.

Mechanism

Synthesized in the hypothalamus and released from the posterior pituitary, oxytocin drives uterine contraction in labor and milk ejection in lactation, and acts centrally in social and affiliative behavior. It differs from vasopressin by only two amino acids.

Reference notes

Oxytocin and vasopressin differ by just two residues yet act on distinct receptor families.
Its central (behavioral) and peripheral (reproductive) roles reflect receptor distribution, not different ligands.
It is a textbook example of how small sequence differences encode large functional ones.

Selected literature

Curated peer-reviewed reviews, sourced from PubMed. Selected for relevance, not exhaustive — open any entry on PubMed for the full record and its primary citations.

1.The physiology and pharmacology of oxytocin in labor and in the peripartum period · American journal of obstetrics and gynecology, 2024 · PMID 38462255
2.Oxytocin, Neural Plasticity, and Social Behavior · Annual review of neuroscience, 2021 · PMID 33823654