Encyclopedia

Somatropin is recombinant human growth hormone (rhGH) -- a bioidentical, 191-amino-acid copy of the growth hormone naturally secreted by the anterior pituitary. It is FDA-approved under multiple brand names for a specific list of growth-disorder and deficiency indications, and separately (as Serostim) for HIV-associated wasting. Unlike the GH secretagogues elsewhere in this encyclopedia (e.g., ipamorelin, CJC-1295, GHRP-6), somatropin supplies growth hormone directly rather than stimulating the pituitary to release its own.

Somatropin is produced via recombinant DNA technology (typically in E. coli or mammalian expression systems) and is structurally identical to the major isoform of endogenous human growth hormone: a 191-amino-acid, single-chain polypeptide with four cysteine residues forming two intrachain disulfide bonds. Multiple manufacturers market essentially identical or near-identical rhGH products under different brand names (Genotropin, Humatrope, Norditropin, Saizen, Nutropin, Omnitrope, Zomacton), with Serostim licensed specifically for HIV-associated wasting. It binds the growth hormone receptor (GHR), a class I cytokine receptor that dimerizes upon ligand binding and activates JAK2-STAT5 intracellular signaling, driving hepatic IGF-1 production and direct anabolic and metabolic effects across multiple tissues. FDA-approved indications include growth hormone deficiency and specific growth disorders in children (idiopathic and organic GHD, Turner syndrome, Prader-Willi syndrome, small for gestational age, Noonan syndrome, SHOX deficiency, chronic renal insufficiency) and growth hormone deficiency in adults (childhood-onset or adult-onset, from pituitary tumors, surgery, radiation, or trauma), plus HIV-associated wasting/cachexia (Serostim). It is a distinct entry from the shorter, injectable GH secretagogue peptides in this encyclopedia -- somatropin is the hormone itself, not a stimulator of its release, and it is a fully approved prescription drug with an extensive body of clinical evidence, unlike the research-chemical secretagogues.

Mechanism of Action

Binds the growth hormone receptor (GHR), a class I cytokine receptor, causing receptor dimerization and activation of JAK2-STAT5 intracellular signaling. This drives hepatic and peripheral IGF-1 production and directly promotes protein synthesis, lipolysis, and tissue growth. Effects include increased linear growth in children, and in adults a shift in body composition toward more lean mass and less fat mass, along with effects on bone density and lipid metabolism; supraphysiologic doses can raise blood glucose, cause fluid retention, and cause joint pain.