IGF-1 LR3

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a 83-amino acid recombinant analog of native IGF-1, engineered with a 13-amino acid N-terminal extension and an arginine substitution at position 3. These modifications reduce binding to IGF-binding proteins (IGFBPs) by ~1000-fold and extend half-life to 20–30 hours versus native IGF-1's 12–15 minutes. It is approximately three times more potent than native IGF-1 in anabolic signaling.

IGF-1 LR3 binds to the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase, with high affinity. Receptor activation triggers autophosphorylation and downstream signaling through two primary pathways: the PI3K/Akt/mTOR axis, which drives protein synthesis, suppresses protein degradation, and promotes cell survival; and the MAPK/ERK pathway, which stimulates cell proliferation and differentiation. The near-complete bypass of IGFBPs — which normally sequester native IGF-1 in circulation — means systemically administered IGF-1 LR3 is substantially more bioavailable at tissue IGF-1R. Satellite cell activation in skeletal muscle is a key mechanism for hypertrophic adaptation. IGF-1 LR3 also exhibits insulin-like metabolic activity at high concentrations, activating insulin receptors and driving glucose uptake into muscle tissue.

IGF-1 LR3 is an established research tool in cell biology and metabolic research. In vitro studies consistently demonstrate potent proliferative and anabolic effects in myoblast and fibroblast cell lines. Rodent studies show accelerated muscle hypertrophy, enhanced satellite cell proliferation, and improved recovery from muscle injury. Human pharmacokinetic data from recombinant IGF-1 therapy (mecasermin) provides indirect mechanistic evidence; no controlled human trials specific to IGF-1 LR3 have been published as of 2026. Hypoglycemia risk at higher doses is documented in both animal and human IGF-1 research.

Peptides commonly paired with IGF-1 LR3 for synergistic effects.