Oxytocin is a nine-amino-acid neuropeptide made mainly in the hypothalamus and released from the posterior pituitary. It is one of the best-studied signaling peptides in physiology. Classic work focused on its peripheral roles, and research now extends to social behavior, stress responses, and receptor pharmacology. Because it is small, well characterized and has a single well-defined receptor, oxytocin is a common reference ligand in neuroendocrine and GPCR research.
BioSim supplies oxytocin for laboratory research only. It is not for human or veterinary use, and nothing here is guidance on administration to people or animals.
Structure and Basic Properties
Oxytocin has the sequence Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, with a disulfide bridge between the two cysteines that forms a six-residue ring and a three-residue amidated tail. Its CAS number is 50-56-6 and its molecular weight is about 1007 Da.
Arginine vasopressin (AVP) has almost the same structure, differing at only two positions: phenylalanine replaces isoleucine at position 3, and arginine replaces leucine at position 8. That close similarity is why the two peptides cross-react at each other’s receptors, a point that matters in experimental design.
Where Oxytocin Is Made and Released
The major site of oxytocin gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to stimuli such as suckling, parturition or certain kinds of stress, the processed peptide is released from the posterior pituitary into the circulation, and it is also released within these nuclei. Oxytocinergic neurons project widely through the central nervous system, and the peptide is also made in peripheral tissues, including the uterus, placenta, corpus luteum, testis and heart (Gimpl & Fahrenholz, 2001).
The Oxytocin Receptor
The oxytocin receptor (OXTR) is a typical class I (rhodopsin-like) G protein-coupled receptor that couples mainly through Gq proteins to phospholipase C-beta. Its high-affinity state requires both magnesium ions and cholesterol, which probably act as allosteric modulators, and the agonist-binding region differs from the antagonist-binding site (Gimpl & Fahrenholz, 2001). Receptor expression and function are strongly regulated by gonadal and adrenal steroids, which the review’s authors described as one of the most remarkable and least understood features of the system.
Coupling is broader than Gq alone. Using a bioluminescence resonance energy transfer (BRET) biosensor, researchers found that oxytocin directly engaged and activated Gq and all the Gi/o subtypes at the human receptor. Peptide analogs with substitutions at key residues showed biased activation of particular G protein subtypes, and two of them activated only Gi1 or Gi3, did not recruit β-arrestins and did not cause receptor internalization (Busnelli et al., 2012). This makes the oxytocin system a useful model for studying functional selectivity, often called biased agonism.
Classic Physiological Roles
The classic actions of oxytocin are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation (Gimpl & Fahrenholz, 2001). Oxytocin receptors are also found in the kidney, heart, thymus, pancreas and adipocytes, and in the rat oxytocin acts with atrial natriuretic peptide to promote sodium and potassium excretion. Its roles in reproduction-related functions such as the estrous cycle, follicle luteinization and ovarian steroidogenesis are also documented in animal studies.
Social Behavior and Memory Models
Rodent studies have made oxytocin central to research on social recognition. Social memory in rodents depends mainly on olfactory cues and is measured as a decrease in investigation during repeated encounters with the same animal. Male mice lacking the oxytocin gene (Oxt-/-) failed to develop social memory, while their olfactory detection of non-social stimuli, spatial memory and behavioral inhibition appeared intact. Oxytocin, but not vasopressin, rescued social memory in the knockout mice, and an oxytocin antagonist produced a social amnesia-like effect in wild-type mice (Ferguson et al., 2000).
These results support the view that social memory has a neural basis distinct from other forms of memory, and they established the knockout mouse as a standard model. The same study noted that pharmacological results with oxytocin vary with route and paradigm, which is a reason to report both carefully.
Oxytocin and Vasopressin Cross-Reactivity
Because the two peptides differ at only two residues, oxytocin can activate vasopressin receptors (V1a, V1b and V2) and vasopressin can activate OXTR, with potencies that differ by receptor and species. A review of agonists and antagonists for these receptors stresses receptor selectivity and species differences, provides receptor data on widely used peptide and nonpeptide ligands as a guide for their use, and notes that peptide agonists and antagonists remain very widely used research tools (Manning et al., 2012).
| Property | Oxytocin | Arginine vasopressin |
|---|---|---|
| Sequence | Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2 | Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2 |
| Disulfide | Cys1-Cys6 | Cys1-Cys6 |
| Main receptor | OXTR (Gq, also Gi/o) | V1a, V1b, V2 |
| Cross-reactivity | Can activate vasopressin receptors | Can activate OXTR |
| Key reference | Gimpl & Fahrenholz, 2001 | Manning et al., 2012 |
Experimental Design Notes
- Use selective tools. Pair oxytocin with a selective OXTR antagonist and, where relevant, a vasopressin receptor antagonist to confirm which receptor mediates an effect (Manning et al., 2012).
- Check species. Ligand affinity and selectivity can differ between rodent and human receptors.
- Control steroid status. Because OXTR expression is steroid dependent (Gimpl & Fahrenholz, 2001), the sex, estrous stage or hormonal state of the animals or cells can change results.
- Choose readouts that match the pathway. Calcium mobilization and IP accumulation track Gq signaling, while BRET sensors or cAMP assays can capture Gi/o coupling (Busnelli et al., 2012).
For wider context, see our guide to neuropeptides in research, the overview of peptide receptor signaling and our Reproductive and Melanocortin Research category.
Handling in the Lab
Oxytocin’s disulfide bond and C-terminal amide are important for activity. Store lyophilized vials as labeled, reconstitute with a suitable sterile diluent, aliquot stock solutions, avoid repeated freeze-thaw cycles and protect solutions from heat and light. Our storage and stability guide covers these steps.
Frequently Asked Questions
Why does oxytocin affect vasopressin receptors?
The two peptides differ at only two of nine positions, so each can bind the other’s receptors to some degree. Selective antagonists help separate the effects (Manning et al., 2012).
Does the oxytocin receptor signal only through Gq?
No. Gq is the main pathway, but oxytocin also activated all the Gi/o subtypes in BRET studies (Busnelli et al., 2012).
How do I confirm the identity of my lot?
Every BioSim lot is third-party tested, with identity confirmed by mass spectrometry. Available certificates are published on our COA page.
References
- Busnelli M, Saulière A, Manning M, et al. (2012). Functional selective oxytocin-derived agonists discriminate between individual G protein family subtypes. The Journal of biological chemistry, 287(6), 3617-29. PMID: 22069312 · DOI: 10.1074/jbc.M111.277178
- Ferguson JN, Young LJ, Hearn EF, et al. (2000). Social amnesia in mice lacking the oxytocin gene. Nature genetics, 25(3), 284-8. PMID: 10888874 · DOI: 10.1038/77040
- Gimpl G, Fahrenholz F (2001). The oxytocin receptor system: structure, function, and regulation. Physiological reviews, 81(2), 629-83. PMID: 11274341 · DOI: 10.1152/physrev.2001.81.2.629
- Manning M, Misicka A, Olma A, et al. (2012). Oxytocin and vasopressin agonists and antagonists as research tools and potential therapeutics. Journal of neuroendocrinology, 24(4), 609-28. PMID: 22375852 · DOI: 10.1111/j.1365-2826.2012.02303.x
Research These Compounds: Oxytocin 5mg and Oxytocin 10mg from BioSim Peptides: 99%+ purity, every lot third-party tested with identity confirmed by mass spectrometry, and available certificates published on our COA page. For laboratory research use only. Not for human consumption.
