What IGF-1 LR3 is
IGF-1 LR3 — Long R3 insulin-like growth factor 1 — is an engineered analogue of native IGF-1 with two changes: an arginine substituted at position 3 in place of glutamate, and a 13-residue extension at the N-terminus, giving 83 residues against native IGF-1’s 70. Both changes serve one purpose, and it is not receptor binding.
- IGF-1 LR3Arg³ substitution plus a 13-residue extension
- IGF-1 receptorReduced affinity for IGF binding proteins
- PI3K/Akt and MAPKLonger free half-life than native IGF-1
- Growth and cell-culture modelsPreclinical
Mechanism as described in published research. Nothing here describes an effect in a person — these compounds are supplied for laboratory research use only.
Binding-protein evasion
In circulation, the overwhelming majority of IGF-1 is not free — it is bound to IGF binding proteins (IGFBPs), which control its availability and half-life. For a researcher this is a serious confounder: administer native IGF-1 and most of it is immediately sequestered, so the effective concentration at the receptor is neither known nor controlled.
The Arg3 substitution markedly reduces IGFBP affinity while leaving receptor binding largely intact. The result is an analogue that stays substantially free, which makes the delivered concentration far more interpretable. That is the entire design rationale, and it is why LR3 appears in research where native IGF-1 would make the result difficult to read.
Because it acts downstream of the GH axis rather than on it, LR3 is often examined against upstream tools such as modified GRF(1–29) and ipamorelin, separating receptor-level effects from axis-level ones.
What the literature covers
Research areas include:
- IGF-1 receptor signalling — PI3K/Akt and MAPK pathways.
- IGFBP interaction — how binding-protein affinity governs availability.
- Cell proliferation and differentiation models.
- Axis versus receptor study design — LR3 downstream against secretagogues upstream.
Identity and verification
IGF-1 LR3 has the molecular formula C400H625N111O115S9 and a molecular weight of 9117.6 g/mol (CAS 143045-27-6). Identifiers matter more here than in most categories: research compounds are sold under trade names, development codes and abbreviations that do not always refer to the same molecule, and a formula is unambiguous where a name is not.
The lot we currently hold measured 99.87% for the 1 mg (lot 261807), tested by Freedom Diagnostics. The certificate is published in full, including the raw chromatogram and mass spectrum — so the number can be read off the underlying trace rather than taken on trust.
We use two laboratories because purity and identity are different questions. Vanguard Laboratory is ISO/IEC 17025:2017 accredited (A2LA #6377.01.01) and reports chromatographic purity and net quantity with a stated measurement uncertainty. Freedom Diagnostics reports HPLC-UV purity together with LC-MS identity confirmation — the test that catches a substituted compound rather than merely an impure one. A sample can be 99% pure and still be the wrong molecule. How we test →
Handling, reconstitution and storage
IGF-1 LR3 ships lyophilized — freeze-dried to a solid and sealed under vacuum — which is what makes it stable in transit rather than a solution racing a clock. Reconstitute with bacteriostatic water, added slowly down the inside wall of the vial rather than directly onto the powder, then swirled gently. Do not shake: mechanical shear is one of the few things that reliably degrades a peptide in the lab.
Final concentration is a function of the volume added, not of the compound, so the same vial can be prepared at very different concentrations. The reconstitution calculator works out the volume for a target concentration and the reconstitution guide covers the procedure. Store lyophilized vials at −20 °C (−4 °F) protected from light; refrigerate once in solution, and see the storage and stability guide for how long reconstituted material holds.
Common questions
What does LR3 mean?
Long R3: a 13-residue N-terminal extension ("Long") and an arginine substituted at position 3 ("R3"). Native IGF-1 has 70 residues; LR3 has 83.
Why substitute arginine at position 3?
It sharply reduces affinity for IGF binding proteins while leaving receptor binding largely intact. Native IGF-1 is mostly sequestered by those proteins, so the effective concentration is unknown; LR3 stays substantially free and is therefore far more interpretable in an experiment.
Is IGF-1 LR3 the same as mecasermin?
No. Mecasermin is recombinant native IGF-1. LR3 is the engineered analogue with the Arg3 substitution and N-terminal extension — a different molecule with a different molecular weight.
How does LR3 relate to growth hormone secretagogues?
It acts downstream of the GH axis, at the IGF-1 receptor, rather than stimulating GH release upstream. Comparing the two is how a study separates receptor-level effects from axis-level ones.
Where to get it
Buy research-grade IGF-1 LR3 — independently tested, certificate published, shipped from Miami with cold-chain packaging. Current pricing for every size is on the price list, and we ship worldwide.
Research use only
Everything referenced here is supplied strictly for laboratory research. These compounds are not drugs, foods, cosmetics or medical devices, are not for human or veterinary use, and are not approved for diagnostic or therapeutic application. Mechanisms are described as studied in preclinical and laboratory research; nothing above describes dosing, treatment or clinical outcome.
