Oxytocin

What is Oxytocin?

Oxytocin is a cyclic nonapeptide with the sequence Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH₂ (CYIQNCPLG-NH₂), molecular formula C₄₃H₆₆N₁₂O₁₂S₂, molecular weight 1007.19 g/mol, CAS 50-56-6. A disulphide bridge between the cysteine residues at positions 1 and 6 closes the molecule into a twenty-atom ring that gives it its constrained cyclic architecture, and the C-terminus is a primary amide rather than a free carboxyl. The sequence and proposed structure were published by du Vigneaud, Ressler and Trippett (J Biol Chem, 1953), and the first synthesis was reported the same year by du Vigneaud and colleagues (J Am Chem Soc, 1953), work recognised with the Nobel Prize in Chemistry in 1955. Oxytocin is one of the most heavily studied neuropeptides in existence, with a literature spanning social behaviour, pair bonding, stress response, peripheral receptor pharmacology and structural biology, and it is a licensed human pharmaceutical in several injectable formulations. Because of that licensed status, the material supplied here is positioned strictly as an analytical research reagent: it is provided as lyophilised powder for in-vitro laboratory research use only, it is not a pharmaceutical product, and no therapeutic use is suggested or implied.

Oxytocin vs Vasopressin

Oxytocin and arginine vasopressin are the two cyclic nonapeptides of the posterior pituitary, and they are the standard comparator pair in neuropeptide pharmacology because they differ at only two residues. Vasopressin carries phenylalanine at position 3 and arginine at position 8 (CYFQNCPRG-NH₂), where oxytocin carries isoleucine and leucine, yet the two ligands diverged into largely separate receptor systems: oxytocin acts principally at the oxytocin receptor (OXTR), while vasopressin acts at the V1a, V1b and V2 receptors, with measurable cross-binding at higher concentrations, as catalogued by Gimpl and Fahrenholz (Physiol Rev, 2001) and reviewed alongside the receptor genetics by Donaldson and Young (Science, 2008). The experimental consequence is that the two cannot be treated as interchangeable tools. Researchers select oxytocin when the design concerns OXTR pharmacology, reproductive-tissue receptor biology or the social behaviour and pair bonding literature, and vasopressin when fluid balance, vascular tone or male-biased social recognition endpoints are in question. Residues 3 and 8 are also the obvious handles for analogue design, since subtype selectivity traces to exactly those side chains.

Oxytocin Research Applications

Oxytocin is studied along four main lines of research. The receptor pharmacology line uses oxytocin as the reference agonist at OXTR, a class A G-protein-coupled receptor coupled through Gq/11 and phospholipase C, with binding, cAMP and calcium mobilisation assays in OXTR-transfected cell lines following the framework set out by Gimpl and Fahrenholz (Physiol Rev, 2001) and updated by Jurek and Neumann (Physiol Rev, 2018). The structural biology line was opened by the crystal structure of the human receptor in complex with a ligand (Waltenspühl et al., Sci Adv, 2020), which makes oxytocin a benchmark ligand for receptor structure work. The behavioural neuroscience line covers pair bonding and social behaviour, built on prairie vole pharmacology (Insel and Hulihan, Behav Neurosci, 1995; Insel and Young, Nat Rev Neurosci, 2001; Donaldson and Young, Science, 2008). The stress and human social cognition line spans hypothalamic-pituitary-adrenal axis interaction work (Grinevich and Neumann, Mol Psychiatry, 2021) and controlled human experiments on trust behaviour (Kosfeld et al., Nature, 2005), a strand whose replication record is contested (Nave et al., Perspect Psychol Sci, 2015). Peripheral receptor pharmacology, myometrial contraction and mammary myoepithelial biology complete the picture.

Reconstitution Guide

Allow the vial to reach room temperature, then sterilise the rubber stopper of both the peptide vial and the bacteriostatic water vial with an alcohol swab. Slowly draw your bacteriostatic water into a sterile insulin syringe, then inject it gently down the inner glass wall of the peptide vial, never directly onto the lyophilised powder. Once added, gently swirl the vial in a slow circular motion until fully dissolved. Never shake or vortex, agitation accelerates oxidation of the disulphide bridge. The solution should be clear and colourless. The material in this vial is an analytical research reagent, not a pharmaceutical product: it must be handled in a laboratory setting and is not supplied for, and must not be used for, human or veterinary administration. Label the vial with the reconstitution date and refrigerate immediately.

See our full peptide reconstitution guide and reconstitution calculator for step-by-step protocol.

Storage Instructions

Lyophilised vials should be stored at -20°C, protected from light and moisture, and remain stable for up to 24 months. Once reconstituted with bacteriostatic water, store the solution at 2-8°C and use within approximately 4 weeks, preparing single-use aliquots at -20°C for longer storage. The disulphide bridge between Cys1 and Cys6 is the degradation route to design against: oxidation and disulphide scrambling generate the dimer and related species that resolve as new peaks on RP-HPLC, and repeated freeze-thaw cycles accelerate both. Keep vials tightly sealed with minimal headspace, aliquot rather than repeatedly accessing one stock, and handle under sterile laboratory conditions throughout. Supplied for in-vitro research use only.

Frequently Asked Questions

Research References

• The sequence of amino acids in oxytocin, with a proposal for the structure of oxytocin (du Vigneaud, Ressler and Trippett, J Biol Chem, 1953)
• The oxytocin receptor system: structure, function, and regulation (Gimpl and Fahrenholz, Physiol Rev, 2001)
• Oxytocin, vasopressin, and the neurogenetics of sociality (Donaldson and Young, Science, 2008)
• Crystal structure of the human oxytocin receptor (Waltenspühl et al., Sci Adv, 2020)

Related Research Compounds

• → DSIP 5mg
• → Kisspeptin-10
• → Bacteriostatic Water 10ml