Muscle & growth hormone
IGF-1 LR3: published research
Also known as Long R3 insulin-like growth factor-1
A modified form of IGF-1, the growth factor that carries much of growth hormone's effect on tissue. Thirteen extra amino acids and one swapped amino acid make it bind less to the proteins that normally hold IGF-1 back, so it stays active longer. It is widely used in cell culture and studied in animal growth models.
Evidence at a glance
3 studies 2001–2002
- 2 Animal study
- 1 Cell study
What researchers look at
- Growth models
- IGF signalling
- IGF binding proteins
- Cell culture
What is still unknown
There are no controlled human studies; all published data come from cells and animals.
Animal studies
2- Animal study
In finishing pigs, a 4-day infusion of LongR3 IGF-I lowered plasma IGFBP-3 and hepatic class 2 IGF-I mRNA without changing liver or kidney IGFBP-3 mRNA; the authors infer a direct suppressive effect on the pigs' growth-hormone axis.
Dunaiski V, et al. Short-term infusion of LongR(3) insulin-like growth factor (IGF)-I decreases hepatic IGF-I mRNA but not IGF binding protein-3 mRNA expression in pigs. General and Comparative Endocrinology. 2002. PMID 12030778
- Animal study
In artificially reared newborn pigs, infused Long R3 IGF-I did not change weight gain when milk was restricted, but with unlimited milk it increased daily weight gain in the second 9 days of infusion, alongside higher milk intake.
Dunshea FR, et al. Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs. The British Journal of Nutrition. 2002. PMID 12067429
Cell studies
1- Cell study
In in-vitro-produced cow embryos, Long R3 IGF-I most strongly stimulated early cleavage and gave blastocysts with the most cells, while native IGF-I better supported later development; Long R3 also raised IGFBP-2 and IGF-I receptor mRNA.
Prelle K, et al. Insulin-like growth factor I (IGF-I) and long R(3)IGF-I differently affect development and messenger ribonucleic acid abundance for IGF-binding proteins and type I IGF receptors in in vitro produced bovine embryos. Endocrinology. 2001. PMID 11181549
Short summaries of published studies, with links to the original papers. Results in animals or cells may not apply to people. This is not medical advice and not a guide to use.