Oxytocin
Oxytocin is a nine-amino-acid peptide hormone made in the hypothalamus and released from the posterior pituitary, with a disulfide-bridged ring structure. It regulates uterine contraction and milk ejection, and synthetic oxytocin (Pitocin) is FDA-approved.
Overview
Oxytocin is a neurohypophyseal hormone produced mainly by neurons in the paraventricular and supraoptic nuclei of the hypothalamus and released into the bloodstream from the posterior pituitary. Its best-known physiological roles are stimulating uterine contractions during labor and triggering milk ejection during breastfeeding. It also acts as a neuromodulator within the brain. In 1953, Vincent du Vigneaud's group reported the synthesis of oxytocin, the first synthesis of a polypeptide hormone, work recognized by the 1955 Nobel Prize in Chemistry.
Synthetic oxytocin is an established medicine, approved in the United States as Pitocin and used in obstetric settings. Separately, oxytocin has been widely studied in neuroscience and psychiatry for its role in social behavior, often using intranasal formulations in research. Results in that area have been mixed, and findings from early small studies have not consistently replicated in larger trials.
Structure
Oxytocin is a nonapeptide with the sequence Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 (CYIQNCPLG-NH2). A disulfide bond between Cys1 and Cys6 forms a six-residue ring, followed by a three-residue tail with a C-terminal glycinamide. Oxytocin differs from the related hormone vasopressin at two positions. The disulfide is essential for activity and is a key quality attribute. Pharmaceutical oxytocin is commonly described as an acetate salt.
Mechanism
Oxytocin acts through the oxytocin receptor (OXTR), a G protein-coupled receptor that signals mainly through Gq and phospholipase C, increasing intracellular calcium. In the uterus, receptor expression rises markedly near term, increasing sensitivity to oxytocin and supporting coordinated contractions. In the mammary gland, oxytocin contracts myoepithelial cells to eject milk. In the brain, oxytocin released from hypothalamic neurons acts on receptors in regions involved in social behavior, stress and reward. At higher concentrations oxytocin can also activate vasopressin receptors, reflecting the structural similarity between the two hormones.
Research
Obstetric use
Synthetic oxytocin is approved and widely used in obstetrics. Its clinical use is governed by product labeling and obstetric guidelines and is not described here. Research in this area continues on topics such as receptor desensitization during prolonged exposure and the comparison of oxytocin with longer-acting analogues such as carbetocin, which is approved in some countries. Research also examines dosing variability between institutions, though protocols are outside the scope of this page.
Social behavior research
Animal research, particularly in prairie voles and rodents, linked oxytocin signaling to pair bonding, maternal behavior and social recognition. This work prompted many human studies, often using intranasal oxytocin, examining trust, emotion recognition and social cognition. Early positive findings drew wide attention, but later analyses identified small samples and replication problems, and the overall picture is now considered uncertain. Effect sizes were often small.
Psychiatric and developmental research
Oxytocin has been studied in randomized trials in autism spectrum disorder, schizophrenia, anxiety and other conditions. A large trial in children and adolescents with autism did not find a benefit on social function compared with placebo. These results illustrate that effects observed in small or laboratory studies did not translate to consistent clinical benefit, and these uses remain investigational. Trial results remain mixed.
Metabolism and other research
Oxytocin has also been investigated in relation to appetite, energy balance and bone metabolism in animal models and small human studies. These are early findings. An additional research challenge is how much peripherally administered oxytocin reaches the brain, which remains debated. Small trials examining appetite and food intake have reported mixed results. Measurement of oxytocin in blood is also technically difficult, as different assays can give very different values, which complicates interpretation of observational studies.
Regulatory status
Synthetic oxytocin is FDA-approved, marketed in the United States as Pitocin, for specific obstetric indications set out in its labeling. Uses outside those indications, including social or psychiatric applications, are investigational. Oxytocin is also approved in many other countries under various names. For sport, check the current WADA Prohibited List.
Status changes often. See the regulatory tracker for dated updates.
Quality and identity testing
An oxytocin certificate of analysis should confirm identity by mass spectrometry against the expected mass shown on this page and report HPLC purity. The disulfide bond must be correctly formed: the reduced, linear form is about 2 Da heavier, and disulfide-linked dimers or oligomers can also occur. Deamidation of Gln or Asn (+1 Da), the C-terminal acid variant, and related impurities described in pharmacopoeial monographs should be considered. Salt form and net peptide content should be reported. Pharmacopoeial methods exist for oxytocin and provide useful benchmarks.
Open Oxytocin in the sequence analyzer to see the expected [M+H]+ and multiply charged ions for an MS identity check (set the N-acetyl, amide and disulfide options to match).
For a walkthrough of each section of a certificate, see how to read a COA.
Storage and stability
Lyophilized oxytocin should be stored sealed and protected from light and moisture, at -20 °C for research material. Oxytocin in solution is temperature-sensitive and degrades through deamidation and disulfide-related reactions; this is why pharmaceutical oxytocin products carry specific storage requirements in their labeling. For lab solutions, keep them cold, aliquot them, avoid repeated freeze-thaw cycles and avoid basic pH.
Download the Oxytocin data sheet (PDF): sequence, masses, expected MS ions and handling on one printable page.
Latest research
The newest PubMed-indexed papers that mention Oxytocin in their title or abstract, retrieved through Europe PMC and refreshed automatically. Inclusion is not an endorsement of a paper's findings.
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Frequently asked questions
Is oxytocin a peptide?
Yes. Oxytocin is a peptide hormone made of nine amino acids, with a disulfide bond between two cysteines that forms a ring. It is produced in the hypothalamus and released from the posterior pituitary. It was the first polypeptide hormone to be synthesized, by Vincent du Vigneaud's group in 1953.
Is oxytocin FDA approved?
Yes. Synthetic oxytocin is FDA-approved and marketed in the United States as Pitocin for specific obstetric indications. Other uses studied in research, such as effects on social behavior or psychiatric conditions, are investigational and are not approved indications. Related analogues, such as carbetocin, are approved in some other countries.
What is the difference between oxytocin and vasopressin?
Oxytocin and vasopressin are closely related nonapeptide hormones released from the posterior pituitary. Both have a disulfide-bridged ring and a C-terminal glycinamide, and they differ at two amino acid positions. Oxytocin acts mainly on the uterus, mammary gland and brain, while vasopressin regulates water retention by the kidney and blood vessel tone. They can partly cross-activate each other's receptors.
Related compounds
- Kisspeptin-10
Kisspeptin-10 is the C-terminal decapeptide of kisspeptin, the product of the KISS1 gene. It activates the kisspeptin receptor (KISS1R, also called GPR54) and is studied as a regulator of gonadotropin-releasing hormone and reproductive hormones.
- PT-141 (bremelanotide)
PT-141, or bremelanotide, is a cyclic heptapeptide melanocortin receptor agonist derived from melanotan II. It was FDA-approved in 2019 as Vyleesi for hypoactive sexual desire disorder in premenopausal women.
- VIP (vasoactive intestinal peptide)
Vasoactive intestinal peptide (VIP) is a 28-amino-acid neuropeptide of the secretin-glucagon family that acts on VPAC1 and VPAC2 receptors. It regulates smooth muscle, secretion and immune function, and synthetic VIP (aviptadil) has been studied clinically.
References
- du Vigneaud V, Ressler C, Swan JM, et al. The synthesis of an octapeptide amide with the hormonal activity of oxytocin. J Am Chem Soc. 1953. Find on PubMed
- PubMed: all indexed literature on Oxytocin
- ClinicalTrials.gov: registered studies mentioning Oxytocin
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