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Peptide hormone (insulin superfamily)

Relaxin

Relaxin (H2 relaxin) is a peptide hormone of the insulin superfamily, built from A and B chains linked by disulfide bonds.

By The Peptides Codex Editorial TeamIndividual review date not recorded

Page data last changed: . Chemistry registry snapshot: . Registry refreshes and identity assessments are separate from scientific content review.

Length
n/a
Class
Peptide hormone (insulin superfamily)
Function
RXFP1 receptor agonist; vasodilation and tissue remodeling
Context
Reproductive and cardiovascular physiology research

An insulin-family hormone with A and B chains that remodels connective tissue and dilates blood vessels.

Also known as: H2 relaxin · RLN2 · serelaxin (analog)

Part of the Foundational & therapeutic peptides cluster

Overview

Relaxin (H2 relaxin) is a peptide hormone of the insulin superfamily, built from A and B chains linked by disulfide bonds. Circulating relaxin-2 acts at the RXFP1 receptor and is studied for roles in reproductive physiology, extracellular-matrix remodeling and vasodilation. This page is educational and not medical advice.

Source & context

Biological / chemical source: Encoded by the RLN2 gene (corpus luteum, placenta, heart)

Primary research or clinical context: Reproductive and cardiovascular physiology research

Structure and receptor

Mature relaxin is a heterodimer of a 24-residue A chain and a 29-residue B chain joined by three disulfide bridges, produced from prorelaxin. It signals mainly through the leucine-rich GPCR RXFP1, structurally echoing insulin while acting on entirely different pathways.

Physiological roles

Relaxin softens connective tissue, remodels the extracellular matrix and increases lung perfusion, and it is a potent vasodilator with anti-fibrotic effects. A recombinant analog, serelaxin, has been investigated in acute heart-failure research, illustrating interest in the relaxin-RXFP1 axis.

Structure & chemistry

Molecular identity & reference confidence

Source-supported reference

Reference values are taken from the cited molecular record or curated profile. A database match is not independent laboratory verification; modifications, counter-ions, and formulations can change the measured mass.

Molecular form
Relaxin (source record; form not independently established)
Species
Not established by this molecular identity audit
Termini (N / C)
Not specified / Not specified

Average reference mass

Reference policy updated: 2026-10-05

Molecular formula
C256H408N74O74S8
Average reference mass
≈ 5,963
Identifiers

Chemistry values: PubChem, IUPHAR/BPS Guide to Pharmacology · fetched 2026-09-06.

Clinical development snapshot

ClinicalTrials.gov lists 31 registered studies with “Relaxin” as an intervention (snapshot 2026-10-01). A registry footprint is not evidence of efficacy or approval.

Registered studies
31
Highest phase reached
Phase 4
Active in latest 100
7
Most recent update
2026-09-30
Most recently updated studies
NCTTitlePhaseStatusUpdated
NCT06808165Relaxin and Placental Volume in Placenta Accreta Spectrum—completed2026-09-30
NCT03449251A Series of Pilot Studies to Evaluate the haemoDynamic and mEtabolic Effects oF apelIn aNd rElaxinPhase 2active not recruiting2026-09-30
NCT06561035Reduce Opiate Exposure With ACL SurgeryPhase 3enrolling by invitation2026-09-15
NCT06299826A Phase IIb Study of AZD5462 in Patients With Chronic Heart FailurePhase 2completed2026-07-08
NCT06264310To Evaluate the Safety, Tolerability and Efficacy of R2R01 Combined With SOC as Compared to SOC Alone in OutpaPhase 2completed2026-06-22
NCT07625553Study of the Relaxin Agonist R2R01 in Patients at High Risk for Cardiac Surgery Associated- Acute Kidney InjurPhase 2recruiting2026-06-04
See all on ClinicalTrials.gov →
Concentration math

Relaxin — reconstitution calculator

Enter how much peptide is in the vial and how much diluent (e.g. bacteriostatic water) is added. The tool returns the resulting solution concentration — and, for any amount you type, the volume it corresponds to. This is educational arithmetic, not a dosing recommendation.

Reference form: Relaxin (source record; form not independently established)Average reference mass: 5,963 Da

Syringe graduation
Solution concentration
5 mg/mL5,000 mcg/mL
mcg

Enter an amount to see the volume it corresponds to.

Educational concentration mathematics only. This tool does not recommend a dose, amount, or protocol, and nothing here is medical advice. Many peptides are not authorized by Health Canada for human use — see our reconstitution and bacteriostatic-water guides for context.

Open the Relaxin calculator on its own page →

FAQ about Relaxin

What is Relaxin?+

Relaxin (H2 relaxin) is a peptide hormone of the insulin superfamily, built from A and B chains linked by disulfide bonds. Circulating relaxin-2 acts at the RXFP1 receptor and is studied for roles in reproductive physiology, extracellular-matrix remodeling and vasodilation. This page is educational and not medical advice.

What Canadian product status is recorded for Relaxin?+

Canadian product status for Relaxin has not been verified in this profile. No verified record here does not mean no authorization exists. Status depends on the product, formulation and use; consult Health Canada's product records.

What is the typical length of Relaxin?+

Relaxin is not a classic amino-acid chain peptide in the same sense; see the profile for classification details.

Related peptides

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TB-500
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TB-500 is the synthetic, N-acetylated heptapeptide Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), corresponding to residues 17–23 of thymosin β4, the protein's actin-binding motif. It first appeared as a veterinary preparation and is sold as a research chemical; its metabolism has been characterised in rats. A 2026 rat tendon study reported benefits with vendor-labelled TB-500 whose sequence was not characterized, so it does not establish efficacy of Ac-LKKTETQ. The fragment has no published human efficacy data. No product-specific authorization record has been verified in this profile; human trial registration does not establish approval. Its first registered human trial began recruiting in 2026.
Tirzepatide
Incretin dual agonist
Tirzepatide is a 39-amino-acid synthetic peptide (C225H348N48O68, ≈4,814 Da) that activates both the GIP and GLP-1 receptors. Its backbone is derived from GIP, with an exendin-4-like C-terminal tail, Aib residues at positions 2 and 13, and a C20 fatty diacid on Lys20 that binds albumin for a half-life of about 5 days. Approved as Mounjaro (type 2 diabetes, 2022) and Zepbound (weight management, 2023; obstructive sleep apnoea, 2024).
Retatrutide
Incretin triple agonist
Retatrutide (LY3437943) is an investigational 39-amino-acid peptide (C221H342N46O68, ≈4,731 Da) that activates three receptors — GIP, GLP-1 and glucagon. It shares its GIP-based scaffold and exendin-4 tail with tirzepatide, adds α-methyl-leucine and a second Aib, and carries a C20 fatty diacid on Lys17 for a half-life of about 6 days. In phase 2 it produced a mean weight change of −24.2% at 48 weeks; phase 3 trials are ongoing and it is not yet approved.

References & further reading

  1. 1.Weiss (1984). Relaxin. Annu Rev Physiol
  2. 2.Martin et al. (2019). Cardioprotective actions of relaxin. Mol Cell Endocrinol
  3. 3.Bani (2020). Recombinant human H2 relaxin (serelaxin) as a cardiovascular drug: aiming at the right target. Drug Discov Today
  4. 4.Weiss (1983). Relaxin. Clin Perinatol
  5. 5.Patil et al. (2017). Relaxin family peptides: structure-activity relationship studies. Br J Pharmacol
  6. 6.Goldsmith et al. (2009). Relaxin in human pregnancy. Ann N Y Acad Sci
  7. 7.Du (2022). Cardioprotection Achieved Through Overexpression of Relaxin Receptors. JACC Basic Transl Sci
  8. 8.Praveen et al. (2019). Single chain peptide agonists of relaxin receptors. Mol Cell Endocrinol
  9. 9.GeneCards — RLN2 gene (Relaxin 2)
  10. 10.PMC — The complex binding mode of H2 relaxin to its receptor RXFP1
  11. 11.Wikipedia — Relaxin
Disclaimer: Educational content only. Not medical advice. Not instructions for human use. Research peptides and unapproved products may be restricted or illegal to market for human consumption in your jurisdiction. Consult qualified professionals and applicable law.
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