Insulin-like growth factor-1, Long R3 Long [R3] Insulin-like growth factor-I (IGF-1 Long [R3]) is a human recombinant, single-chain, non-glycosylated 83 amino acid polypeptide. It is a human IGF-1 analog containing the complete human IGF-1 sequence with the substitution of an arginine (Arg or R) for glutamic acid (Glu or E) at position 3 (hence R3) and a 13 amino acid extender peptide at the N- term. This analog has been engineered with the express purpose of increasing biological activity. IGF-1 Long [R3] significantly more potent than IGF-1 in vitro and in vivo. The increased potency is also due to the significantly reduced binding of IGF-1 Long [R3] to all IGF-binding proteins. These binding proteins normally inhibit the biological effects of the IGFs. IGF-1 stands for insulin-like growth factor. It is a natural substance that is produced in the human body and is at its highest natural level during puberty. During puberty the IGF-1 is responsible for the natural muscle growth that occurs during those years. There are many different things that IGF-1 does in the human body. Among the most positive effects are: . increased amino acid transport to cells. increased glucose transport. increased protein synthesis. decreased protein breakdown. increased RNA synthesis .