MGF is generated from the IGF-I gene through alternative splicing, exhibiting distinct 3' exons compared to either the liver or systemic type (IGF-IEa). In humans, it has a 49 base pair insert, while in rodents, it has a 52 base pair insert located within the E domain of exon 5. This insertion leads to a shift in the reading frame, resulting in a unique carboxy terminal sequence different from that of systemic IGF-IEa. MGF shares the same 5' exons with other IGF isoforms that encode the IGF-I ligand-binding domain. The processing of the pro-peptide produces a mature peptide that plays a role in enhancing protein synthesis. Additionally, there is evidence indicating that the carboxy-terminal of the MGF peptide functions independently as a growth factor, promoting the division of mononucleated myoblasts or satellite (stem) cells, thus increasing their availability for local repair.
MGF seemingly has a dual function, similar to other IGF-I isoforms, in that it both enhances protein synthesis and activates satellite cells. However, MGF's role in activating satellite cells is likely more significant since most of the mature IGF-I will originate from IGF-IEa during the latter phase of repair. Despite this, research has demonstrated that MGF effectively induces muscle hypertrophy; experiments involving the introduction of MGF cDNA into a plasmid vector via intramuscular injection have observed a 20% increase in muscle weight within two weeks, attributed to growth in muscle fiber size. Other studies using a viral construct with the liver type of IGF-I have shown a 25% increase in muscle mass, although this took over four months to manifest (Musaro et al. 2001). Therefore, MGF's dual role in facilitating satellite cell activation and promoting protein synthesis indicates that it is significantly more effective than the liver type or IGF-IEa at inducing rapid hypertrophy.
The peptide is typically administered at a dosage of 200-400 mcg per day and works synergistically with other substances such as IGF and PEG.