Oxytocin

Oxytocin is a cyclic nonapeptide, meaning a nine-residue peptide closed into a ring. Its sequence is Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, with a disulfide bridge joining the cysteines at positions 1 and 6 and an amide at the C-terminus. That bridge closes a six-residue ring and leaves a three-residue tail, the architecture shared across the vasopressin and oxytocin nonapeptide family. PubChem catalogues the compound as CID 439302 under CAS number 50-56-6, with molecular formula C43H66N12O12S2 and a molecular weight of 1007.2 g/mol. Research material is supplied as a lyophilized (freeze-dried) solid, commonly as an acetate salt.

In the laboratory oxytocin is the reference ligand used to characterise the oxytocin receptor, OXTR, a class A G protein-coupled receptor. Its usefulness as a standard rests on how completely the molecule is defined: a short, fully sequenced, chemically synthesised peptide with a solved receptor structure and quantified binding data across a related receptor family. It is also the closest structural neighbour of vasopressin, differing at two of nine positions, which makes selectivity an analytical question in binding work. Identity figures above are reconciled against the Certificate of Analysis supplied with the lot.

Oxytocin is an approved drug substance in human medicine in other contexts. It holds no research-use approval, and the material listed here is a synthetic reference peptide, not that approved product.

Oxytocin was isolated from posterior pituitary extracts early in the twentieth century. In 1953 du Vigneaud, Ressler and Trippett reported its amino acid sequence and proposed the ring-and-tail structure still accepted (PubMed 13129273). It was the first polypeptide hormone made by chemical synthesis.

Kimura and colleagues cloned a human oxytocin receptor in 1992, placing it in the class A GPCR family (PubMed 1313946). Gimpl and Fahrenholz reviewed receptor structure, signalling and regulation (PubMed 11274341). Waltenspühl and colleagues reported a crystal structure of the human receptor (PubMed 32832646).

Chemistry and receptor biology are well characterised: sequence, synthesis, cloned receptor, solved structure and comparative affinity data all sit in primary sources. Work downstream of the receptor is more heterogeneous.

Published work describes oxytocin as an agonist at OXTR, a class A G protein-coupled receptor. Activation is reported to couple principally through Gq/11 to phospholipase C beta, mobilising intracellular calcium in cultured cells. Gi/o coupling has also been reported in expression systems (PubMed 11274341).

The useful distinction is with vasopressin, which differs from oxytocin only at positions 3 and 8: isoleucine and leucine against phenylalanine and arginine. Two substitutions do not guarantee selectivity: cross-reactivity between OXTR and the V1a, V1b and V2 receptors is documented. Comparative affinity data across the four receptors have been tabulated (PubMed 18655904).

Comparisons need care: much of this pharmacology comes from heterologous expression systems rather than native tissue, receptor properties differ between species, and reported affinity varies with membrane cholesterol content.

Sealed lyophilized oxytocin is held frozen at -20°C, shielded from light, in its original container. Lyophilized peptides are hygroscopic, so a container reaches ambient temperature before opening, and freeze-thaw cycles are avoided.

The 1-6 disulfide bridge is the feature most sensitive to handling, since reducing conditions and alkaline pH are described routes to disulfide scrambling. Stability for a lot is documented on its Certificate of Analysis.

Reconstitution means returning a lyophilized compound to solution. This entry gives no preparation procedure: solvent, concentration and handling steps belong to a protocol, not to the compound. Oxytocin is handled as aqueous-soluble material.

Lyophilized material takes up atmospheric moisture, degrading gravimetric accuracy, and the acetate counter-ion on most lots contributes mass that is not peptide. Water content and solubility figures appear on the lot Certificate of Analysis.

Identity and purity of research-grade oxytocin are established analytically, usually by reverse-phase HPLC with mass spectrometric confirmation. Verified purity is documented per lot on the Certificate of Analysis. For a disulfide-cyclised nonapeptide the questions that matter most are ring closure, since the reduced linear form differs by two mass units, and disulfide-linked dimers.

Two further impurity classes belong on lot documentation: deamidation of the glutamine and asparagine residues, and residual acetate. Suppliers vary more in salt form and water content than in sequence fidelity.

Oxytocin is studied alongside these compounds.

• Vasopressin.
  Nonapeptide differing at two of nine residues, the structural comparator and main source of cross-reactivity in binding assays.
• PT-141.
  Melanocortin receptor agonist, another short peptide ligand of a class A GPCR.
• Kisspeptin-10.
  KISS1R (GPR54) decapeptide ligand used as a reference agonist in hypothalamic research.

du Vigneaud V, Ressler C, Trippett S (1953). The sequence of amino acids in oxytocin, with a proposal for the structure of oxytocin. J Biol Chem.
PubMed 13129273

Kimura T, Tanizawa O, Mori K, et al. (1992). Structure and expression of a human oxytocin receptor. Nature.
PubMed 1313946

Gimpl G, Fahrenholz F (2001). The oxytocin receptor system: structure, function, and regulation. Physiol Rev.
PubMed 11274341

Chini B, Manning M, Guillon G (2008). Affinity and efficacy of selective agonists and antagonists for vasopressin and oxytocin receptors: an easy guide to receptor pharmacology. Prog Brain Res.
PubMed 18655904

Waltenspühl Y, Schöppe J, Ehrenmann J, et al. (2020). Crystal structure of the human oxytocin receptor. Sci Adv.
PubMed 32832646

Oxytocin is stocked here in one format: a sealed single-compound lyophilized vial. Vials are the only listed format for this compound, and the catalog currently lists one brand at a single 10mg fill. Per-vial strengths are product specifications only. Each lot is batch tested with a published Certificate of Analysis documenting verified purity for that lot.

• Browse all Oxytocin research products
• Real Peptides Oxytocin, 10mg lyophilized vial
• Collections: Research Vials. Documentation: COA and Lab Testing.

These products are sold for Research Use Only and are not intended for human consumption.