What is HGH?Complete Somatropin Research Reference — QSC Peptides

Human Growth Hormone (HGH), also known as somatropin, is a 191-amino-acid, single-chain polypeptide hormone with a molecular weight of 22,124 daltons. It is synthesized and secreted by somatotroph cells in the anterior pituitary gland and is the primary anabolic and metabolic hormone of the GH axis.

The somatropin molecule adopts a characteristic four-helix bundle structure (helices 1, 2, 3, 4) that defines its receptor binding geometry. The molecule contains two disulfide bridges: Cys53-Cys165 and Cys182-Cys189. The full molecular formula is C₉₉₀H₁₅₂₈N₂₆₂O₃₀₀S₇.

QSC Peptides offers research-grade recombinant somatropin — identical to the endogenous 191-amino-acid sequence — in 10 IU, 24 IU, and 36 IU vial strengths.

IU to mg Conversion

Per WHO International Standard for Somatropin: 1 mg ≈ 3 IU. This means:

• 10 IU vial = ~3.33 mg somatropin
• 24 IU vial = ~8.00 mg somatropin
• 36 IU vial = ~12.00 mg somatropin

QSC Peptides labels all HGH products in IU per vial for consistency with research standards.

Mechanism of Action — GHR Binding and JAK2-STAT5

Somatropin binds the growth hormone receptor (GHR), a transmembrane class I cytokine receptor expressed in liver, adipose tissue, muscle, and many other tissues. Binding occurs as a sequential 1:2 complex — one HGH binds two GHR molecules (site 1 then site 2), inducing receptor dimerization.

Dimerization transactivates receptor-associated JAK2 (Janus Kinase 2), which phosphorylates STAT5 (Signal Transducer and Activator of Transcription 5). Phospho-STAT5 dimerizes, translocates to the nucleus, and drives transcription of IGF-1, IGFBP-3, and ALS genes.

In parallel, GHR activates ERK1/2 via Grb2-SOS-Ras-RAF-MEK signaling, and PI3K-Akt for anti-apoptotic and metabolic effects.

Direct vs. IGF-1-Mediated Effects

• Direct effects: Lipolysis (HSL activation in adipocytes), insulin antagonism (IRS-1 inhibition), gluconeogenesis upregulation
• IGF-1-mediated effects: Protein synthesis (PI3K-Akt-mTOR), cellular proliferation (Ras-MAPK), anti-apoptosis

Pulsatile Secretion

Endogenous GH is released in 4–8 discrete pulses per 24 hours, controlled by the balance between hypothalamic GHRH (stimulatory) and somatostatin (inhibitory). The largest pulse occurs ~1 hour after sleep onset during slow-wave sleep (SWS). Between pulses, GH levels fall to near-undetectable levels. This pulsatile pattern is important for research using QSC Peptides GHRH analogs vs direct somatropin.

Somatopause — Age-Related GH Decline

Somatopause refers to the progressive decline in GH secretory amplitude beginning in the third decade of life, with pulse amplitude falling ~14% per decade. By the seventh decade, IGF-1 levels are typically 50–80% below peak. This decline forms the basis for research into GH axis restoration using QSC Peptides somatropin, GHRH analogs, and GH secretagogues.

HGH Storage in Research

• Lyophilized (freeze-dried): Store at 2–8°C (shelf life) or −20°C (long-term). Stable for labeled shelf life when refrigerated.
• Reconstituted: Store at 2–8°C, use within 3–5 days. Do not freeze reconstituted solution.
• Stability notes: Avoid repeated freeze-thaw cycles, light exposure, and vigorous agitation — all degrade the 191-aa polypeptide chain.