Buy Protein Supplement & Muscle Growth Peptide Follistatin-315 (1mg / vial) Powder Online   What is Follistatin 315? Follistatin is a secreted protein that binds to ligands of the TGF-Beta family and regulates their activity by inhibiting their access to signaling receptors. It was originally discovered as activin antagonists whose activity suppresses expression and secretion of the pituitary hormone FSH (follicle …