PI3K/Akt & MAPK Anabolic Signaling
Insulin-like Growth Factor 1 Long Arginine 3
IGF-1 LR3 (Insulin-like Growth Factor 1 Long Arginine 3) is a recombinant analog of human insulin-like growth factor 1 (IGF-1), engineered to have significantly enhanced potency and a dramatically extended half-life compared to the native hormone. The "LR3" designation refers to two key modifications: an N-terminal extension of 13 amino acids and a glutamate-to-arginine substitution at position 3.
Native IGF-1 is rapidly sequestered by IGF-binding proteins (IGFBPs) in the circulation, resulting in a half-life of approximately 10–20 minutes. IGF-1 LR3's modifications reduce its affinity for IGFBPs by approximately 1,000-fold, extending its effective half-life to approximately 20–30 hours and dramatically amplifying its biological activity compared to the native hormone.
IGF-1 LR3 is an 83-amino-acid recombinant protein consisting of the full 70-amino-acid sequence of human IGF-1 with a 13-amino-acid N-terminal extension and a Glu³ → Arg substitution. The molecular weight is 9,117.60 Daltons, making it considerably larger than most research peptides in this catalog.
The N-terminal extension and Arg³ substitution are the structural basis for the compound's reduced IGFBP binding: the extension sterically interferes with IGFBP interaction, while the Arg³ substitution disrupts a key IGFBP binding epitope. These modifications preserve full IGF-1 receptor (IGF-1R) binding affinity while dramatically reducing sequestration.
IGF-1 LR3 exerts its effects by binding to the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase expressed on virtually all cell types. IGF-1R binding triggers receptor autophosphorylation and activation of two major downstream signaling cascades: the PI3K/Akt pathway and the MAPK/ERK pathway.
The PI3K/Akt pathway is the primary mediator of IGF-1's anabolic effects: Akt activation phosphorylates and inhibits FOXO transcription factors (reducing protein catabolism), activates mTORC1 (stimulating protein synthesis and cell growth), and promotes glucose uptake via GLUT4 translocation. The MAPK/ERK pathway drives cell proliferation and differentiation, particularly in muscle satellite cells and other progenitor populations.
The combination of reduced protein catabolism, increased protein synthesis, and enhanced glucose uptake creates a strongly anabolic cellular environment that has made IGF-1 LR3 a widely used tool in cell culture and preclinical research.
IGF-1 LR3 is a modified version of Insulin-like Growth Factor 1 (IGF-1), a hormone your liver naturally produces in response to growth hormone. Think of it this way: growth hormone is the command, and IGF-1 is the messenger that actually carries out most of the instructions throughout the body. LR3 is an engineered version designed to stay active much longer than natural IGF-1.
Natural IGF-1 is quickly deactivated in the bloodstream by binding proteins (IGFBPs). IGF-1 LR3 has a modified sequence that dramatically reduces this binding, extending its active half-life from about 15 minutes to approximately 20–30 hours. During that extended window, it activates IGF-1 receptors on muscle, bone, and organ cells, triggering protein synthesis, cell growth, and glucose uptake.
IGF-1 is one of the most important anabolic hormones in the human body — it's the primary mediator of growth hormone's effects on tissue. By creating a version that stays active far longer than the natural form, researchers can study IGF-1 signaling with much greater experimental control. It's also a key tool in muscle biology and metabolic research.
IGF-1 LR3 is a potent research compound that operates at the intersection of growth hormone biology, muscle physiology, and metabolic regulation. Its extended half-life makes it a powerful research tool but also means its effects persist much longer than natural IGF-1. It is a research-only compound prohibited by WADA.
Activates mTORC1 to stimulate protein synthesis, inhibits FOXO-mediated catabolism, and promotes GLUT4-mediated glucose uptake.
Drives cell proliferation and differentiation, particularly in muscle satellite cells and other progenitor populations.
Akt-mediated FOXO phosphorylation suppresses the expression of atrophy genes (MuRF1, atrogin-1), reducing protein catabolism.
N-terminal extension and Arg³ substitution dramatically reduce IGFBP binding, extending bioavailability and receptor engagement duration.
2 cited studies — model, sample size, outcome, and effect size from published literature.
| Study | Model | Sample | Outcome | Effect Size | Level |
|---|---|---|---|---|---|
Tomas FM, et al. (1993) Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic … PubMed | Rodent (rat) — catabolic model | n=40 | IGF-1 LR3 produced greater muscle mass preservation than native IGF-1 | ~2× greater anabolic effect vs. native IGF-1 at equivalent doses | Animal |
Firth SM & Baxter RC. (2002) Cellular actions of the insulin-like growth factor binding proteins PubMed | Review — in vitro + in vivo | Review | Confirmed IGF-1 LR3 bypasses IGFBP binding, extending half-life and bioavailability | Half-life: ~20–30 hours vs. ~12 minutes for native IGF-1 | In Vitro |
Growth Research
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| Peptide Class | Recombinant IGF-1 analog (83 amino acids) |
| Molecular Weight | 9,117.60 Da |
| Key Modifications | 13-AA N-terminal extension; Glu³→Arg substitution |
| IGFBP Binding | ~1,000-fold reduced vs. native IGF-1 |
| Half-life | ~20–30 hours (vs. 10–20 min for native IGF-1) |
| Available Sizes | 1mg vials |
| Form | Lyophilized powder |
| Purity | ≥99% (third-party tested) |
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Purchase IGF-1 LR3 at Purgo LabsMedical Disclaimer: All content on this site is for educational and research purposes only. Research peptides are not FDA-approved for human use. Always consult a qualified healthcare professional before considering any peptide or supplement protocol. Nothing on this site constitutes medical advice, diagnosis, or treatment.
