oxitocin

Oxytocin, sometimes rendered as oxitocin in some languages, is a peptide hormone and neuropeptide produced in the hypothalamus and released from the posterior pituitary into the bloodstream. It is a nine‑amino‑acid (nonapeptide) molecule featuring a disulfide bond that links two cysteine residues, a structure conserved across mammals. Oxytocin is also produced within certain brain neurons, where it can act as a central neurotransmitter.

In the body, oxytocin is released in response to physiological stimuli such as uterine stretch, cervical stimulation, and nipple stimulation, as well as emotional and stress cues. Peripherally, it binds to oxytocin receptors—G protein–coupled receptors found in a variety of tissues, most notably the uterine smooth muscle and mammary glands. The hormone’s half‑life in blood is relatively short, and it is cleared by the liver and kidneys.

Key physiological roles include promoting uterine contractions during labor and facilitating milk ejection (let‑down) during breastfeeding via myoepithelial cells surrounding milk ducts. In addition, oxytocin influences social behaviors, including maternal bonding, trust, recognition, and pair bonding, with central effects modulated by estrogen levels that upregulate oxytocin receptor expression in the brain.

Clinical use of oxytocin involves synthetic forms used to induce or augment labor and to control postpartum hemorrhage. Brand names such as oxytocin or its analogs are administered intravenously or intramuscularly. Potential adverse effects include uterine tachysystole, fetal distress, and, with prolonged high doses, hyponatremia due to antidiuretic activity.

Historically, oxytocin was isolated and its sequence determined in the mid‑20th century, with full chemical synthesis achieved in the early 1950s by Vincent du Vigneaud, a breakthrough for which he received the Nobel Prize in Chemistry in 1955.