IGF-I and IGFBP-3 transport in the rat heart.
Boes. Mary M; Dake. Brian L BL; Booth. Barbara A BA; Sandra. Alexander A; Bateman. Mathew M; Knudtson. Kevin L KL; Bar. Robert S RS
Key Findings
- IGF‑1 uptake in the heart drops dramatically when its direct binding sites are blocked
- IGF‑1 bound to IGFBP‑3 still enters the heart at a higher rate than blocked free IGF‑1
- Both direct IGF‑1 sites and IGFBP‑3 binding sites help transport IGF‑1 into heart tissue
Practical Outcomes
- For biohackers, the finding suggests that using IGF‑1 LR3 alone may limit tissue delivery unless it’s paired with binding proteins like IGFBP‑3. Considering formulations that include or mimic IGFBP‑3 could improve cardiac or muscle uptake, but human studies are needed before changing protocols.
Summary
The study shows that in rat hearts, IGF‑1 gets into the tissue through two routes: directly binding to its own sites and via complexes with the carrier protein IGFBP‑3. Blocking IGF‑1’s own sites cuts uptake a lot, while using IGF‑1 bound to IGFBP‑3 still allows a decent amount to get in. This hints that the way IGF‑1 is delivered (free vs. bound) matters for how much reaches heart tissue.
Abstract
Specific binding of IGF-binding protein (IGFBP)-3 was shown to be present in the isolated, beating rat heart. The uptake of perfused (125)I-labeled IGF-I in the beating heart was decreased to 9% by blocking IGF-I binding sites with the IGF-I analog Long R(3) (LR(3)) IGF-I. When LR(3) was perfused with complexes of (125)I-IGF-I. IGFBP-3, uptake of (125)I-IGF-I was decreased to 41%, which was significantly greater than LR(3) and (125)I-IGF-I (41 vs. 9%). These data suggest that both microvessel IGF-I and IGFBP-3 binding sites contribute to the transport of IGF-I in the perfused rat heart. This also suggests a novel and plausible mechanism whereby circulating IGFs reach sites of IGF bioactivity.
Study Information
pubmed
2003
10.1152/ajpendo.00336.2002