Oxytocin

Oxytocin is a cyclic nonapeptide hormone produced in the hypothalamus and released from the posterior pituitary. It holds a special place in biochemistry: in 1953 Vincent du Vigneaud's group made oxytocin the first peptide hormone to be both sequenced and chemically synthesised, an achievement recognised by the 1955 Nobel Prize in Chemistry. Its name, from the Greek for swift birth, reflects the uterine activity first observed in pituitary extracts in the early twentieth century.

Oxytocin is approved as a prescription medicine for indications including labour induction and the prevention and management of postpartum haemorrhage. Beyond obstetrics, it is among the most studied neuropeptides in behavioural neuroscience. Animal work, especially in prairie voles, linked oxytocin signalling to maternal behaviour and pair bonding, and these findings triggered a large body of human research on trust, social cognition and stress. Results in human behavioural studies have been inconsistent, and questions about how much peripherally present oxytocin reaches the brain remain unresolved.

Oxytocin binds the oxytocin receptor, a GPCR that couples mainly to Gq/11. In myometrium, receptor activation stimulates phospholipase C, generating inositol trisphosphate and releasing intracellular calcium, which drives smooth muscle contraction. Oxytocin receptor expression in the uterus rises sharply toward term, increasing tissue sensitivity. In the mammary gland, oxytocin contracts myoepithelial cells to produce milk ejection. Centrally released oxytocin acts on receptors in regions such as the amygdala and nucleus accumbens, where it modulates social and stress-related behaviour in animal models. Prolonged exposure causes receptor desensitisation, an effect studied in obstetric research.