What is IGF-1 LR3? Receptor-model note

Research-use notice: This article is laboratory and educational information only. It is not medical or legal advice, and it does not include how-to-use instructions. BlueNex Labs materials are research use only and are not intended for human or veterinary use. Research-use-only labelling is not a Health Canada authorization.

Publication status: Prepared for the BlueNex Labs Research Knowledge Centre. Literature and library notes checked September 25, 2026. Primary papers and the public COA library can change; verify the lot report in hand before an assay.

IGF-1 LR3 is the catalogue nickname for long arginine-3 insulin-like growth factor-I, written in the 1992 literature as Long [Arg3]-IGF-I. Francis, Ross, Ballard, and colleagues described recombinant fusion analogues in the Journal of Molecular Endocrinology (PMID 1378742). The construct that later analytical notes describe as an 83-residue chain carries a 13-residue N-terminal extension and replaces a glutamate near the start of mature IGF-I with arginine. There is no IGF-1 LR3 shop SKU on this site. This page does not offer a vial, a price, or a certificate.

Why the extension and the arginine were introduced

IGF-I in serum and in many culture media is held by IGF-binding proteins. Those proteins change how much of the ligand reaches the type-1 IGF receptor. The GroPep-era analogues were built to lower binding-protein affinity while remaining receptor ligands. Francis and colleagues compared Long IGF-I, Long [Gly3]-IGF-I, and Long [Arg3]-IGF-I with IGF-I and with des(1–3)IGF-I. In L6 rat myoblasts, which secrete binding proteins, the long analogues were more potent than IGF-I on protein synthesis, DNA synthesis, and protein-breakdown readouts. In chicken embryo fibroblasts, which did not secrete detectable binding proteins into the medium, Long [Arg3]-IGF-I was less potent than IGF-I. The order flipped with the medium. That flip is the result to remember. A single "more potent" sentence without the cell line is a mis-citation.

Later work, including receptor-binding comparisons cited back to that paper, treats the arginine substitution as the change that most reduces binding-protein affinity, with a modest drop in receptor affinity relative to IGF-I. Affinity ratios belong in the paper. They are not a specification printed on a research vial, because this shop does not sell the analogue.

Names that are easy to conflate

Mecasermin is an authorized IGF-I medicine in some jurisdictions. It is not this analogue. DES(1–3)IGF-I is a truncated IGF-I, not the long extension. Full-length IGF-I is 70 residues in the usual mature count, not 83. A label that says only "IGF" is incomplete. The 83-residue long [Arg3] construct, the 70-residue [Arg3] construct after the extension is cleaved, and native IGF-I are three analytical targets. Mass spectrometry is how a laboratory tells them apart. This site does not publish that mass because it does not sell the material.

Growth-hormone secretagogues on the catalogue are a different class again. CJC-1295 without DAC with ipamorelin, sermorelin, and tesamorelin are discussed at GHRH or ghrelin receptors. They are not IGF-I analogues. Their certificates do not document LR3. For the hub that says this explicitly, see secretagogue research peptides.

Culture use, without copying a medium recipe

Cell-culture groups use the analogue when they want an IGF-I receptor signal that binding proteins in the serum do not sequester as strongly. That is a methods choice inside a serum-free or low-protein medium the laboratory already validated. Francis and colleagues' potency order is the caution: if the line does not secrete binding proteins, the analogue can be less active than IGF-I, not more. Put the cell line and the binding-protein status in the notebook. Do not take a nanogram-per-millilitre figure from a supplier page. This note deliberately omits one.

Protein-breakdown and DNA-synthesis readouts in the 1992 myoblast table are assay endpoints. They are not clinical language, and they are not repeated here as promises.

Documentation and the empty library row

The certificates library has no IGF-1 LR3 anchor. A purchasing checklist that requires a lot report cannot be satisfied by a secretagogue PDF or by this article. How to read a peptide COA still tells a receiver how to compare an observed mass with a calculated mass when a file exists. For this name, the honest study-file entry is "not supplied by BlueNex Labs."

Neighbouring research-only notes are AOD-9604 and follistatin-344. For the muscle-biology category note, see peptides in muscle-biology laboratory models. None of those URLs is a product page.

Legal frame

IGF-I analogues advertised for human administration are treated as drugs. Health Canada's approach to research-use labelling is summarized in Are research peptides legal in Canada?. A research-use-only sentence does not authorize possession for personal use, and this company does not provide administration guidance. Anti-doping rules may also list IGF-I analogues. This article does not advise athletes.

Canada fulfilment facts, Interac e-Transfer, Canada Post Xpresspost, the Burnaby desk, and the weekend scan gap, apply to SKUs that are actually listed. They are collected in the provincial fulfilment FAQ. They are not an offer to ship IGF-1 LR3.

What to write when a reference says only LR3

Expand the nickname before you file the paper. Long [Arg3]-IGF-I, 13-residue extension, glutamate-to-arginine substitution, PMID 1378742, and the cell line in the potency table. If the reference is actually about cleaved [Arg3]-IGF-I without the extension, say that instead. The two constructs were both made in the same program and they are not the same mass. A purchasing nickname that collapses them will not survive an analytical review.

Binding-protein status of the medium is the second required line. The 1992 potency order reversed when the fibroblasts did not secrete detectable binding proteins. Copying the myoblast order into a fibroblast method is a citation error, not a minor omission. This page cannot tell you which medium your line needs. It can tell you that the paper already showed both directions.

Secretagogue SKUs remain available for laboratories whose protocol names those receptors. Linking them here is a boundary, not a suggestion to substitute. If the protocol names IGF-1 LR3 and the catalogue does not list it, the correct procurement result is "not stocked," written in the same file as the PMID.

Frequently asked questions

Does BlueNex Labs sell IGF-1 LR3?

No. There is no IGF-1 LR3 shop SKU and no Product Offer. Secretagogue vials on the catalogue are different molecules.

What did Francis and colleagues mean by Long Arg3 IGF-I?

A 1992 paper describes an IGF-I analogue with a 13-residue N-terminal extension and arginine in place of glutamate near the start of the IGF-I sequence. Later analytical notes describe the mature analogue as an 83-residue chain. Identity is that construct, not the letters LR3 alone.

Why do culture papers report different potency orders?

Francis and colleagues found a higher potency than IGF-I in lines that secrete IGF-binding proteins, and a lower potency than IGF-I in chicken embryo fibroblasts that did not secrete detectable binding proteins. The result depends on the medium. It is not a catalogue specification.

Can this page be cited as a method?

No. Concentrations and exposure times stay in the paper you are replicating and in your own SOP. This note does not list them as instructions.

Catalogue cross-reference

Receptor-class context for stocked GHRH and ghrelin ligands, which are not this analogue, is the secretagogue hub. For the COA method note, see how to read a peptide COA.

This page does not offer a vial, a price, or a Product Offer. Neighbouring materials that do have catalogue SKUs are listed on the research catalogue under their own names. A shared freezer box is not a shared certificate. Research use only. Not for human or veterinary use.