Description
IGF-1 LR3 (Insulin-like Growth Factor 1 Long Arginine 3) is a synthetic 83-amino acid analog of natural IGF-1. Two structural modifications distinguish the compound from the native hormone: a substitution of glutamic acid by arginine at position 3 and an N-terminal extension of 13 additional amino acids. These adaptations reduce binding affinity to IGF binding proteins (IGFBPs) by approximately 100- to 1000-fold.
In research models, this provides a central advantage: while native IGF-1 is approximately 99 percent bound by IGFBPs and thereby shielded from receptor activation, IGF-1 LR3 remains bioavailable. The half-life extends from a few minutes (native IGF-1) to 20 to 30 hours in research settings. The compound binds with approximately 2- to 3-fold higher affinity to the IGF-1 receptor (IGF-1R).
Activation of IGF-1R triggers in studies primarily the PI3K/Akt/mTOR signaling pathway, which is regarded as the central mediator of anabolic effects. Secondarily, the MAPK/ERK pathway is activated, which is involved in cell proliferation and differentiation. In muscle research models, activation of satellite cells, increased protein synthesis and muscle fiber hypertrophy have been observed.
IGF-1 LR3 is used in research on muscle hypertrophy, sarcopenia, regeneration and tissue engineering. Due to IGFBP independence, the compound is particularly suitable for studies investigating isolated IGF-1R activation.
You can order IGF-1 LR3 in 10-vial packs at 1mg per vial.
This information is for research and educational purposes only. No medical recommendations.
Risks & Safety
IGF-1 LR3 is considered largely well tolerated per study reports, but due to the direct, IGFBP-independent receptor activation and the long half-life, it has a profile that requires somewhat more attention than pure GH secretagogues.
Observed in research and user reports:
- Injection site: mild redness, pressure or transient irritation at the injection site is the most common observation with subcutaneous use.
- Hypoglycemia risk: IGF-1 has insulin-like effects. The literature describes a risk of low blood sugar (sweating, shaking, grogginess) - the most relevant safety point of this compound.
- Growth of existing tissue: because IGF-1 LR3 strongly activates anabolic, proliferative pathways (PI3K/Akt/mTOR) in studies, the literature discusses a theoretical concern that existing abnormal tissue could also be promoted to grow. No evidence supports this. The point remains part of the research discussion.
- Water retention: transient water retention is occasionally reported, usually dose-dependent.
- No long-term data: robust long-term human studies on research use do not exist. The profile rests primarily on animal and cell models.
This classification does not replace medical advice. Risk and responsibility for any actual use lie entirely with the buyer.
Studies
- 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 - Journal of Molecular Endocrinology 1992: Describes the production of the Long IGF-I analogues, including Long Arg3 IGF-I (LR3): in myoblasts they were more potent than native IGF-I in stimulating protein and DNA synthesis, attributed to their altered interaction with IGF-binding proteins.
- Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats - Biochemical Journal 1992: In rats in a dexamethasone-induced catabolic state, LR3 IGF-I was about 2.5-fold more potent than native IGF-I in its anabolic effect although it binds the type 1 IGF receptor less well, explained by its weak binding to IGF-binding proteins.
- Viral mediated expression of IGF-I in skeletal muscle - PNAS 1998 (Barton-Davis): Classical study on IGF-1 and muscle mass increase.
- Mediation of IGF-1-induced skeletal myotube hypertrophy by PI3K/Akt/mTOR - Nature Cell Biology 2001 (Rommel): Identification of the PI3K/Akt pathway as mediator.
