Growth hormone （GH）, also known as somatotropin, is a member of a family of growth factors that includes prolactin, placental lactogens, proliferins, and somatolactin. It is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by somatotropic cells within the lateral wings of the anterior pituitary gland. The pulsatile release of GH into circulation is regulated by the concerted actions of the hypothalamic hormones-GH-releasing hormone （GHRH） and somatostatin （SST） as well as by signals from the periphery-ghrelin and leptin. The human GH cDNA encodes a 217 amino acid （aa.） residue precursor protein with a 26 aa. putative signal peptide. By alternative splicing, at least four isoforms of GH have been identified.