HGH 191 (Somatropin / rhGH) – 15 IU

What is HGH 191?

Human growth hormone in its native 191-amino acid form represents the gold standard for GH receptor research. Produced through recombinant DNA technology in E. coli or mammalian cell expression systems, this bioidentical somatotropin is structurally indistinguishable from endogenous pituitary-derived GH. Unlike secretagogues that stimulate indirect GH release, HGH 191 enables direct investigation of growth hormone receptor binding, signal transduction, and downstream metabolic effects.

The 191-amino acid sequence forms a four-helix bundle structure with two disulfide bonds critical for receptor binding and biological activity. This tertiary structure allows GH to bind its receptor as a sequential dimer—first engaging site 1 of the receptor with high affinity, then recruiting a second receptor molecule through site 2 interactions to initiate JAK2-STAT5 signaling. With over five decades of research characterizing GH's effects on IGF-1 production, lipolysis, protein synthesis, and linear growth, HGH 191 remains central to endocrinology and metabolic research.

Mechanism of Action

Growth hormone exerts its effects through direct and indirect mechanisms. Direct effects occur via GH receptor (GHR) binding on target tissues. Upon GH binding, the receptor undergoes conformational changes that activate associated JAK2 tyrosine kinases, phosphorylating intracellular domains and recruiting STAT proteins. This JAK2-STAT5 pathway drives transcription of GH-responsive genes including IGF-1, SOCS proteins, and metabolic enzymes.

Indirect effects are mediated primarily through insulin-like growth factor-1 (IGF-1) production. GH stimulates hepatic and peripheral IGF-1 synthesis, which then acts through the IGF-1 receptor (a receptor tyrosine kinase) to promote anabolic processes. The GH-IGF-1 axis demonstrates complex feedback regulation: IGF-1 inhibits pituitary GH secretion while amplifying peripheral GH actions. GH also exhibits anti-insulin metabolic effects—promoting lipolysis in adipose tissue, stimulating hepatic glucose production, and antagonizing insulin's glucose uptake in muscle.

Key Research Findings

• GH administration increases lean body mass by 2.1 kg and decreases fat mass by 2.0 kg over 6-month periods in GH-deficient adults, with effects mediated through both direct lipolysis and IGF-1-mediated protein synthesis (Salomon et al., 1989)
• Physiological GH replacement restores IGF-1 levels to normal range and improves lipid profiles, reducing LDL cholesterol by 8-15% through upregulation of LDL receptors (Cuneo et al., 1991)
• GH demonstrates biphasic effects on glucose metabolism: acute administration causes insulin resistance through free fatty acid elevation, while chronic exposure improves insulin sensitivity via body composition changes (Davidson et al., 1988)
• Pulsatile GH administration produces superior anabolic effects compared to continuous infusion, highlighting the importance of secretory patterns in physiological GH action (Clark et al., 1985)
• Supraphysiological GH doses increase muscle protein synthesis rates by 50-100% but with diminishing returns above replacement levels, demonstrating receptor saturation kinetics (Fryburg et al., 1991)

Research Applications

• GH receptor binding and signal transduction studies
• IGF-1 pathway and somatomedin hypothesis research
• Metabolic effects: lipolysis, gluconeogenesis, protein synthesis
• JAK2-STAT5 signaling cascade investigations
• Dose-response and receptor saturation experiments
• GH vs. secretagogue comparison studies
• Pulsatile vs. continuous GH delivery pharmacodynamics
• GH resistance and receptor mutation models
• Body composition and metabolic research
• Skeletal growth plate and linear growth mechanisms

Reconstitution

Reconstitute with bacteriostatic water to desired concentration (supplied with order). GH is stable when reconstituted but sensitive to agitation—add water slowly down the side of the vial and allow to dissolve naturally without shaking. Use our peptide calculator to determine optimal reconstitution volume.

Storage & Handling

Store lyophilized powder at 2-8°C (refrigerated) or -20°C (frozen) for maximum stability. After reconstitution, maintain at 2-8°C and use within 14 days. Do not freeze reconstituted product. Protect from light and avoid repeated freeze-thaw cycles.