IGF-1 LR3 vs HGH 191AA (Somatropin)
IGF-1 LR3 and HGH 191AA occupy different tiers of the same growth axis. HGH 191AA is recombinant human growth hormone, the upstream signal, while IGF-1 LR3 is a long-acting analog of insulin-like growth factor 1, the downstream mediator through which many GH effects are expressed.
Side-by-Side Comparison
| Property | IGF-1 LR3 | HGH 191AA (Somatropin) |
|---|---|---|
| Category | Insulin-like growth factor 1 analog (83 amino acids) | Recombinant human growth hormone (191 amino acids, identical to endogenous hGH) |
| Mechanism of Action | Activates the IGF-1 receptor (tyrosine kinase); Arg3 substitution plus a 13-residue N-terminal extension drastically reduce binding to IGF binding proteins, prolonging free activity | Activates the GH receptor (JAK2/STAT5 signaling); stimulates hepatic IGF-1 production, lipolysis, and protein anabolism |
| Molecular Weight | ~9,111 Da | ~22,124 Da |
| Primary Research Focus | IGF-1 receptor signaling, muscle cell proliferation and differentiation, IGFBP interaction biology | GH axis physiology, body composition, metabolism, GH deficiency models |
| Receptor Target | IGF-1 receptor (with weak insulin receptor cross-reactivity at high concentrations) | Growth hormone receptor |
| Half-Life | ~20-30 hours (IGFBP evasion keeps the analog free and active) | ~2-3 hours subcutaneous (~20 minutes intravenous) |
| Key Research Citations | Francis et al. (1992), J Mol Endocrinol; Tomas et al. (1993), J Endocrinol | Møller & Jørgensen (2009), Endocr Rev |
Key Differences
- HGH 191AA acts at the top of the growth axis, inducing the liver to produce IGF-1; IGF-1 LR3 supplies the downstream effector signal directly at the IGF-1 receptor.
- IGF-1 LR3’s defining modification is IGFBP evasion: native IGF-1 circulates almost entirely bound to binding proteins, while the LR3 analog stays free and active for roughly a day.
- HGH 191AA is sequence-identical to endogenous growth hormone and engages the full breadth of GH effects (lipolysis, IGF-1 induction, protein anabolism); IGF-1 LR3 isolates the IGF-1 receptor arm of that cascade.
- The compounds differ more than twofold in size (~9 kDa vs ~22 kDa) and use unrelated receptor systems, so they are complements in research design, not substitutes.
Research Summary
HGH 191AA and IGF-1 LR3 let researchers interrogate the GH/IGF-1 axis at two different nodes. Recombinant HGH replicates the endogenous upstream hormone, producing the full spectrum of GH receptor effects including hepatic IGF-1 induction. IGF-1 LR3 bypasses that upstream machinery and stimulates the IGF-1 receptor directly, with engineered resistance to IGF binding proteins that extends its active half-life to roughly a day. Studying them separately or together distinguishes which growth-axis effects are GH-receptor-mediated versus IGF-1-receptor-mediated.
What is the difference between IGF-1 LR3 and HGH 191AA?
HGH 191AA is recombinant human growth hormone, identical to the endogenous 191-amino-acid hormone; it acts on the GH receptor and induces the liver to produce IGF-1. IGF-1 LR3 is an engineered IGF-1 analog that acts directly on the IGF-1 receptor and evades IGF binding proteins, giving it a ~20-30 hour active half-life versus hours for GH. They target different receptors at different levels of the same growth axis.
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Disclaimer: All compounds referenced on this page are sold for research and laboratory use only. The comparisons presented are based on published scientific literature and are intended for educational and informational purposes. This content does not constitute medical advice. Researchers should consult primary literature and applicable regulations before designing study protocols.