IGF-1 LR3 Research Guide: Long-Arg3 IGF-I Overview

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For laboratory research use only.

What is IGF-1 LR3? IGF-1 LR3 (Long R3 IGF-I) is an 83-amino-acid analog of insulin-like growth factor-I with a 13-residue N-terminal extension and arginine in place of glutamic acid at position 3. These changes reduce binding to IGF-binding proteins, so more free ligand reaches the IGF-1 receptor in many experimental systems. It is a growth-factor receptor ligand, not a SARM and not a GH secretagogue. Explicit SARMs supplies IGF-1 LR3 1mg for laboratory research use only.

IGF-1 LR3 (Long Arg3 insulin-like growth factor-I) is an IGF-I analog engineered to alter interactions with IGF-binding proteins. It is a growth-factor receptor ligand, not a GH secretagogue.

Why LR3 exists

Native IGF-I is a 70-residue peptide whose availability is shaped by high-affinity IGF-binding proteins. Experimental systems showed that endogenous IGFBPs can inhibit IGF-I effects in cells (IGFBP inhibition of IGF-I). Long Arg3 variants incorporate an N-terminal extension and an Arg substitution at position 3 that reduce binding-protein association in biochemical descriptions, increasing free ligand availability in many culture conditions.

Direct experimental traces of LR3IGF-I

Physiological delivery studies reported preferential intestinal delivery of long[Arg3] IGF-I over IGF-I in preweaning piglets, illustrating how the analog can behave differently from native IGF-I even in whole-animal contexts (LR3IGF-I delivery study). Analytical toxicology work has detected His-tagged Long-R3-IGF-I in illicit products, underscoring both the analog’s real-world appearance and the need for analytical confirmation of identity (Long-R3-IGF-I detection).

Axis placement

GH secretagogues act upstream of pituitary GH release. IGF-I analogs act downstream at IGF1R. Conflating those levels confuses both methods and purchasing. IGF-1 LR3 belongs with growth-factor tools. Native IGF-I papers do not automatically validate every LR3 conclusion, and LR3 papers do not validate every “IGF” nickname on a shelf.

Frequently asked questions

What is the function of IGF-1 LR3 in research?

IGF-1 LR3 is used as an IGF-1 receptor (IGF1R) ligand in cell-culture and animal research, including studies of growth-factor signaling and as a supplement in cell-culture media. Because it binds IGF-binding proteins weakly, it is often chosen when binding-protein interference would confound results.

Why is IGF-1 LR3 described as having a longer half-life than IGF-1?

Native IGF-I is largely held by IGF-binding proteins, which shape how long it stays available. The LR3 modifications reduce that binding-protein association, which is why the analog is described in research literature as longer-acting than native IGF-I in experimental models.

Is IGF-1 LR3 a SARM?

No. IGF-1 LR3 is a peptide growth-factor analog that acts at the IGF-1 receptor. SARMs are small non-steroidal molecules that act at the androgen receptor. Browse our research peptides or SARMs collections separately.

What does “IGF IR3” mean?

“IGF IR3” is a common misspelling of IGF-1 LR3, where LR3 stands for Long R3: the N-terminal extension (Long) plus the arginine (R) substitution at position 3.

How does IGF-1 LR3 relate to GHRP-2 and GHRP-6?

They sit at different points of the GH–IGF axis. GHRP-2 and GHRP-6 act upstream at the pituitary ghrelin receptor, while IGF-1 LR3 acts downstream at IGF1R. See our GHRP-2 and GHRP-6 research overviews. IGF-1 LR3 1mg is for research use only.


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