Somatropin is recombinant human growth hormone: a 191-amino-acid, single-chain polypeptide identical in sequence to the major form of pituitary-derived human growth hormone (GH).1 Unlike the GH-axis secretagogues grouped in this category (which act upstream to stimulate the body’s own GH release), somatropin is the hormone itself. Note the “191aa” designation distinguishes mature recombinant somatropin from the historical 192-residue methionyl variant (somatrem) that carried an extra N-terminal methionine.2
It is important to be clear about regulatory and research framing. Somatropin is the active ingredient in numerous approved prescription medicines worldwide; recombinant methionyl GH was first introduced in the United States in 1985, the same year distribution of pituitary-extracted GH was suspended after reports of Creutzfeldt-Jakob disease in earlier recipients.2 Material sold for laboratory work is supplied strictly for research use only and is not an approved therapeutic. The data summarized below derive from the published clinical and biochemical literature on the hormone; nothing here is dosing guidance.
Sequence & identity
191-residue single chain · C990H1528N262O300S7 · ~22,124 g/mol · two disulfide bonds (Cys53–Cys165, Cys182–Cys189)1
Somatropin is a folded ~22 kDa four-helix-bundle protein, not a simple linear peptide, so it has no standard small-molecule descriptor. The PubChem record cross-referenced to its CAS (12629-01-5) returns a mismatched small-molecule entry (an unrelated tert-butylcyclooctene mixture, CID 168009821) and is not a valid identifier for the protein; sequence and disulfide assignments here follow UniProt P01241.1
Mechanisms studied
Researchers describe somatropin acting through the cell-surface growth hormone receptor (GHR). Current models report that GHR exists as a preformed dimer at the membrane; hormone binding triggers a conformational change that brings the receptor-associated kinase JAK2 into an active orientation, leading to transphosphorylation and activation of JAK2.3 Activated JAK2 phosphorylates the receptor and recruits STAT5, which dimerizes, translocates to the nucleus, and drives transcription of target genes including IGF1; PI3K-AKT and MAPK pathways are also engaged.3 Many of the systemic effects observed in studies are mediated by GH-induced insulin-like growth factor-1 (IGF-1), produced mainly in the liver, while GH also exerts direct effects such as lipolysis in adipose tissue.4
Dosing in the research literature
The figures below summarise regimens as reported in published research — they are not recommendations or directions for use.
| Source / model | Regimen reported | Notes |
|---|---|---|
| Salomon et al., 1989 (NEJM), adults with GH deficiency4 | 0.07 U/kg body weight per day, administered subcutaneously at bedtime for 6 months in a double-blind, placebo-controlled trial. | Reported in adult GH-deficient patients on stable replacement of other pituitary hormones. Older fixed-dose, weight-based regimen; not usage guidance. |
| UK multicentre somatrem trial, 1987 (Arch Dis Child), children with GH deficiency5 | 4 units three times per week by subcutaneous or intramuscular injection for one year (biosynthetic methionyl GH / somatrem). | Pediatric GH-deficiency study; uses the 192-aa methionyl variant, not the 191-aa form. Historical schedule reported in the literature. |
| Subcutaneous pharmacokinetics (Genotropin prescribing information; Laursen et al., 1993)67 | Not a dose. After subcutaneous injection, peak serum GH (Tmax) is reported at roughly 5-6 hours, and the apparent terminal half-life is ~3 hours — longer than the short half-life seen after intravenous dosing because absorption is rate-limiting. | PK context only. The labeled mean terminal half-life is ~0.4 h (~24 min) after intravenous dosing versus ~3.0 h after subcutaneous dosing. |
Effects observed in research
In controlled trials in adults with diagnosed GH deficiency, six months of recombinant GH replacement was reported to increase lean body mass (mean +5.5 kg) and decrease fat mass (mean −5.7 kg) versus placebo, alongside an increase in basal metabolic rate and lower fasting cholesterol; the investigators concluded GH influences body composition through anabolic and lipolytic actions.4 In children with GH deficiency, recombinant (methionyl) GH was observed to accelerate linear growth: in the UK multicentre trial, 42 of 54 previously untreated children responded with an increase in growth velocity of more than 1.5 cm/year.5 Reported adverse effects in these populations included anti-GH antibody formation (about two-thirds of patients in the somatrem trial developed low-titre antibodies that did not affect the response) and, in the adult studies, fluid-retention-related symptoms.54 These outcomes come from studies in GH-deficient patients; they do not establish effects in individuals with normal GH status, and somatropin is not characterized here for any non-approved use.
Strength of evidence
Evidence grade A. Somatropin is supported by decades of randomized controlled trials and clinical use for defined indications (notably GH deficiency in children and adults), making the human evidence base for those uses robust.45 Two caveats temper how that grade transfers to a research-product context. First, the strong data apply to GH-deficient populations under medical supervision; efficacy and especially the risk-benefit balance in healthy or GH-replete subjects are not established by these trials. Second, somatropin is a prescription biologic in most jurisdictions, and any material obtained for laboratory work is research-use-only and not an approved drug. Long-term safety signals (insulin resistance, fluid retention, and the theoretical IGF-1-related concerns) remain part of the published discussion and should not be understated.4
Reconstitution & storage
Reconstitute with bacteriostatic water for laboratory handling. Store lyophilised material frozen and reconstituted material refrigerated. Use Peptigo’s reconstitution calculator and storage cheat sheet for working figures.
References
- UniProt Consortium. Somatotropin (GH1), Homo sapiens — entry P01241. Mature chain residues 27-217 (191 aa); disulfide bonds 79-191 and 208-215 in precursor numbering (Cys53-Cys165 and Cys182-Cys189 in mature numbering). https://www.uniprot.org/uniprotkb/P01241/entry
- Ayyar VS. History of growth hormone therapy. Indian J Endocrinol Metab. 2011;15(Suppl 3):S162-S165. PMC3183530. https://pmc.ncbi.nlm.nih.gov/articles/PMC3183530/
- Brooks AJ, Waters MJ, et al. The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects. Front Endocrinol (Lausanne). 2018;9:35. https://www.frontiersin.org/articles/10.3389/fendo.2018.00035/full
- Salomon F, Cuneo RC, Hesp R, Sönksen PH. The effects of treatment with recombinant human growth hormone on body composition and metabolism in adults with growth hormone deficiency. N Engl J Med. 1989;321(26):1797-1803. PMID 2687691. https://pubmed.ncbi.nlm.nih.gov/2687691/
- Milner RD, et al. United Kingdom multicentre clinical trial of somatrem. Arch Dis Child. 1987;62(10):1029-1032. PMID 3310915. https://pmc.ncbi.nlm.nih.gov/articles/PMC1778484/
- Genotropin (somatropin) prescribing information, Pfizer — Clinical Pharmacology: mean terminal half-life ~0.4 h after IV and ~3.0 h after subcutaneous administration; subcutaneous bioavailability ~80%. https://www.pfizermedical.com/genotropin/clinical-pharmacology
- Laursen T, Jorgensen JO, Susgaard S, Moller J, Christiansen JS. Subcutaneous absorption kinetics of two highly concentrated preparations of recombinant human growth hormone. Ann Pharmacother. 1993;27(4):411-415. PMID 8477114. https://pubmed.ncbi.nlm.nih.gov/8477114/