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GH Secretagogues Research Guide

IGF-1 LR3: Mechanism, Handling & Research Guide

Also known as: IGF-1 LR3, Long R3 IGF-1, LongR3 IGF-I, Long [R3] IGF-I, LR3 IGF-1, LR3, IGF-I LR3, Long Arg3 IGF-1

Key Facts

IGF-1 LR3 is a gh secretagogues research peptide. Extended-activity IGF-1 analogue for cell proliferation and tissue repair research. It is supplied as a lyophilized powder for laboratory and in-vitro research use only — not for human consumption.

Classification IGFBP-resistant long-acting IGF-1 analog (N-terminal 13-aa extension + Arg3 substitution)
Molecular Weight 9117.5 g/mol
CAS Number 946870-92-4
Research Half-Life Substantially longer than native IGF-1 (whose circulating free half-life is only minutes) because of greatly reduced IGFBP binding; commonly cited as on the order of ~20-30 hours, but this figure is approximate and not rigorously established for humans.
Form Lyophilized powder
Research Category GH Secretagogues

What is IGF-1 LR3?

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified 83-amino acid analogue of human IGF-1 in which glutamic acid at position 3 is replaced with arginine, and a 13-amino acid N-terminal extension peptide is added. These modifications significantly reduce binding to IGF-binding proteins (IGFBPs), resulting in a much higher proportion of free, bioactive peptide in circulation compared to native IGF-1. The mechanism of action involves binding to the IGF-1 receptor (IGF-1R), a tyrosine kinase receptor that activates the PI3K/Akt and MAPK/ERK signaling cascades to promote cell proliferation, differentiation, and survival. Research demonstrates that IGF-1 LR3 has approximately 2-3 times the potency of native IGF-1 in cell culture proliferation assays due to its reduced IGFBP sequestration (Francis et al., Journal of Molecular Endocrinology, 1992). In muscle biology research, IGF-1 signaling promotes satellite cell activation and myofiber hypertrophy while simultaneously inhibiting myostatin-mediated atrophy pathways. Studies also indicate IGF-1 LR3 promotes both hyperplasia (new cell formation) and hypertrophy (cell enlargement), distinguishing it from GH secretagogues that primarily drive hypertrophy. Compared to native IGF-1, LR3 has a significantly extended half-life of approximately 20-30 hours versus 12-15 minutes, making it substantially more practical for research applications. Store lyophilized powder at -20C; reconstitute with 0.1M acetic acid or bacteriostatic water and refrigerate at 2-8C, using reconstituted material within 30 days. IGF-1 LR3 is studied by cell biology laboratories, muscle physiology researchers, cancer biology departments investigating IGF-1R signaling, and metabolic research institutions.

IGF-1 LR3 Research Applications

In published and preclinical research, IGF-1 LR3 has been studied across the following areas:

  • Cell proliferation and hyperplasia studies
  • Metabolic and glucose-regulation research
  • Muscle preservation and myostatin inhibition
  • Cellular-aging and senescence research

IGF-1 LR3 in Research: Study Context

The published literature characterizes Long [R3] IGF-1 as an IGF-1 analog engineered with a Glu3-to-Arg substitution plus a 13-amino-acid N-terminal extension that lowers affinity for IGF binding proteins (>100-fold reduction reported by Francis et al., 1992), increasing the free, bioactive fraction and raising in-vitro potency relative to native IGF-1; in-vivo infusion studies (e.g., Dunaiski et al., 1997 in pigs) report it stimulates growth while suppressing endogenous GH, IGF-1, and IGFBP-3. It acts on the IGF-1 receptor and downstream PI3K/Akt and MAPK/ERK pathways in research models. This material is reconstituted with bacteriostatic water (or 0.1 M acetic acid) to a defined mg/mL for laboratory research use only; there is no established human concentration because it is not FDA-approved. Researchers should reference the primary literature and document each lot against its Certificate of Analysis (COA).

How IGF-1 LR3 Compares

Researchers frequently evaluate IGF-1 LR3 alongside related compounds:

  • IGF-1 LR3 vs PEG-MGF — MGF is a local IGF-1 splice-variant E-peptide for satellite-cell research; LR3 is a systemic, IGFBP-resistant full IGF-1 analog.
  • IGF-1 LR3 vs Ipamorelin — Ipamorelin is a GH secretagogue acting upstream on GH release; IGF-1 LR3 acts directly at the IGF-1 receptor, downstream of GH.

IGF-1 LR3 — Frequently Asked Questions

Why is IGF-1 LR3 more potent in cell-culture assays than native IGF-1?
The Arg3 substitution plus the N-terminal extension sharply reduce binding to IGF binding proteins (Francis et al. 1992 reported >100-fold lower IGFBP affinity). With less of the peptide sequestered by IGFBPs, a larger free fraction is available to bind the IGF-1 receptor, which the literature associates with higher in-vitro biological potency relative to wild-type IGF-1.
What did in-vivo infusion studies report?
Infusion studies in pigs (Dunaiski et al. 1997) and guinea pigs reported Long [R3] IGF-1 stimulates organ/body growth while paradoxically lowering plasma endogenous IGF-1, GH, and IGFBP-3 - consistent with negative feedback and reduced IGFBP carriage. These are animal-model findings and do not establish any human effect.
How does IGF-1 LR3 differ from MGF in the research context?
IGF-1 LR3 is a systemically circulating, IGFBP-resistant full IGF-1 analog studied for sustained IGF-1 receptor activation, whereas MGF is a locally acting IGF-1 splice variant (E-peptide) studied for satellite-cell activation at sites of mechanical stress. They model different aspects of IGF-1 biology.
What handling and documentation practices apply?
Reconstitute with bacteriostatic water (or 0.1 M acetic acid for solubility) to a defined mg/mL, keep reconstituted solution refrigerated at 2-8C, avoid repeated freeze-thaw, and protect from light. Confirm identity, mass, and purity for each lot against its Certificate of Analysis before use. For laboratory research use only; not FDA-approved and not for human use.
Is IGF-1 LR3 legal to buy for research?
IGF-1 LR3 is sold in the United States as a research chemical for laboratory and in-vitro use only. It is not approved by the FDA for human use and is not sold for human consumption. Researchers are responsible for compliance with all applicable federal, state, and institutional regulations.
Does IGF-1 LR3 come with a Certificate of Analysis?
Yes. Every batch of IGF-1 LR3 from Elyte Peptides ships with a third-party Certificate of Analysis (COA) documenting identity and HPLC purity (≥98%), so research results can be traced to a verified lot.
What is IGF-1 LR3 and how does it work?
IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is an 83-amino acid analogue of human IGF-1 with an arginine substitution at position 3 and a 13-amino acid N-terminal extension. These modifications dramatically reduce binding to IGF binding proteins (IGFBPs), increasing its bioavailability and half-life compared to native IGF-1. It acts through the IGF-1 receptor to promote cell proliferation, protein synthesis, and glucose uptake in research models.
What research has been done on IGF-1 LR3?
Published research in Endocrinology demonstrated that IGF-1 LR3 has approximately three times the potency of native IGF-1 due to reduced IGFBP sequestration. Studies in the Journal of Cellular Physiology showed modulated myoblast proliferation and differentiation. Additional research has explored its role in satellite cell activation for muscle repair, pancreatic beta-cell proliferation, and neuroprotective mechanisms in CNS injury models.
How does IGF-1 LR3 compare to native IGF-1 or MGF?
Native IGF-1 is rapidly bound by IGFBPs (especially IGFBP-3), reducing its free fraction and bioactivity. IGF-1 LR3's structural modifications keep it largely unbound, resulting in higher and more sustained IGF-1 receptor activation. MGF (Mechano Growth Factor) is a splice variant of IGF-1 that acts locally in damaged tissue. IGF-1 LR3 has a more systemic action profile, making it useful for different research questions.

Research References

  1. Francis GL et al. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol 1992;8(3):213-23.
  2. Dunaiski V et al. Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs. J Endocrinol 1997.
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