HGH 191AA (Somatropin)

Where secretagogues nudge the body's own pituitary, HGH 191AA supplies the hormone itself: a somatropin made by recombinant DNA technology whose 191 amino acids match the endogenous form exactly. That identity is what makes it the standard against which bioassays and immunoassays are calibrated.

Research fields and findings:

• Structural biology: the 1992 crystal structure shows how a single GH molecule binds two receptor molecules at once.
• Signalling: in 2014 it was worked out how the GH receptor switches on the kinase JAK2 after binding, the starting point of the JAK/STAT cascade with STAT5 as the key factor.
• IGF-1 axis: mice whose livers make no IGF-1 grew normally despite sharply lowered blood levels, pointing to locally produced IGF-1 as the real mediator (1999).
• Metabolism: the Endocrine Reviews article (2009) describes increased lipolysis and reduced insulin sensitivity under GH in humans.
• Ageing: a systematic review (2007) of randomized trials in healthy older people found small changes in body composition but more frequent edema, joint complaints and carpal tunnel syndrome.

Preclinical work also covers bone density, muscle physiology, lipid metabolism, regenerative pathways and cell proliferation. The pharmacological difference from CJC-1295 or ipamorelin is fundamental: GH given directly bypasses pulsatile secretion and the feedback of the axis, something every study design has to account for. The protein ships lyophilized; the amount per vial is stated in international units.

The molecule is pharmacologically well characterized and largely well tolerated in studies. Because the hormone arrives from outside, its effects are stronger and less tied to natural feedback than with secretagogues.

• Injection site: redness, pressure, brief irritation.
• Fluid retention, joint complaints and tingling or numbness in the hands, dose-dependent in the literature.
• Fasting glucose goes up and insulin sensitivity goes down, more markedly with direct supply than with secretagogues.
• Natural pulsatility is lost and the regulation of the body's own axis may shift.
• Human data over long periods are missing; the profile rests on short studies and anecdotal reports.

This summary is no substitute for medical advice.

• Human growth hormone and extracellular domain of its receptor: crystal structure of the complex - crystal structure of the hormone-receptor complex.
• Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects - review of metabolic effects in humans.
• Systematic review: the safety and efficacy of growth hormone in the healthy elderly - pooled look at randomized trials in older people.