IGF-1 LR3 Research Guide — Modified Growth Factor for Muscle Science

## Introduction

IGF-1 LR3 (Insulin-Like Growth Factor-1 Long R3) is a genetically engineered analogue of the native insulin-like growth factor 1, a peptide hormone that plays a central role in growth, development, and tissue maintenance. IGF-1 is primarily produced in the liver in response to growth hormone stimulation and circulates systemically.

The Long R3 modification was developed to overcome the limitation of native IGF-1’s short half-life. By adding a 13-amino-acid extension to the N-terminus and substituting arginine at position 3, researchers created an IGF-1 analogue with substantially reduced affinity for IGF binding proteins (IGFBPs), resulting in significantly more free, bioactive peptide and an extended half-life of approximately 20-30 hours.

## Mechanism of Action

IGF-1 LR3 exerts its effects primarily through activation of the IGF-1 receptor (IGF-1R), a transmembrane tyrosine kinase receptor.

**PI3K/Akt Pathway:** IGF-1R activation leads to PI3K recruitment and Akt phosphorylation, which activates mTORC1 driving protein synthesis, inhibits GSK3β, and inactivates pro-apoptotic factors.

**MAPK/ERK Pathway:** Simultaneously, Ras initiates the Raf → MEK → ERK kinase cascade, promoting gene expression programs for cell proliferation, differentiation, and survival.

**Satellite Cell Activation:** IGF-1 LR3 promotes satellite cell proliferation and myogenic differentiation.

## Research Applications

Muscle hypertrophy and protein synthesis research, satellite cell biology, anti-apoptotic research, growth factor signaling cascades, and regenerative medicine protocols.

## Dosage & Administration

Standard dosing: 20-100 mcg per administration, once daily (SubQ or IM). Typical cycles: 4-6 weeks, followed by an off-period.

## Reconstitution Guide

IGF-1 LR3 is supplied as a lyophilized powder. Reconstitute with 1mL bacteriostatic water for a concentration of 1mg/mL (1000 mcg/mL).

- 20 mcg dose = 0.02 mL (2 units)

- 50 mcg dose = 0.05 mL (5 units)

- 100 mcg dose = 0.1 mL (10 units)

Store lyophilized at -20°C for long-term stability. Store reconstituted at 2-8°C.

## Safety & Side Effects

IGF-1 LR3 is classified as preclinical research compound. Hypoglycemia risk at higher concentrations due to insulin receptor cross-reactivity. Listed on WADA Prohibited List.

## References

- PeptideWiki (peptidewiki.co)

- 10 PubMed-indexed studies

- IGF-1 receptor signaling and PI3K/Akt/mTOR pathway literature