HGH Fragment 176-191 Research Guide: The hGH C-Terminal Lipolytic Domain
By UK Peptide Lab Research Team•19 September 2026•8 min read
Key Takeaways
- HGH Fragment 176-191 is the native C-terminal 16-mer of the 191-residue human growth hormone: sequence YLRIVQCRSVEGSCGF, molecular weight 1817.09 g/mol, CAS 66004-57-1.
- The Cys7-Cys14 intrachain disulfide bridge, corresponding to Cys182 and Cys189 of intact hGH, closes the native C-terminal loop characterised by Ogru et al. (J Pept Res, 2000).
- Because hGH residue 176 is a tyrosine, the fragment is sequence-identical to AOD-9604 (Tyr-hGH(177-191)); the names carry different literatures, the chain is the same.
- Rodent work on the same sequence reported lipolysis and reduced body fat without IGF-1-mediated growth or glucose-handling effects (Ng et al., J Mol Endocrinol, 2000; Heffernan et al., Endocrinology, 2001).
- The human evidence is thin: the AOD-9604 trials showed safety without established efficacy, the programme was wound down, and the unmodified fragment has essentially no direct human literature. Supplied for in-vitro laboratory research only.
What is HGH Fragment 176-191?
HGH Fragment 176-191 is the native C-terminal sixteen residues of the 191-residue human growth hormone, amino acids 176 through 191 exactly as they occur in the parent protein: sequence Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, written YLRIVQCRSVEGSCGF. The molecular formula is C₇₈H₁₂₅N₂₃O₂₃S₂, the molecular weight 1817.09 g/mol and the CAS number 66004-57-1. The two cysteine residues, at fragment positions 7 and 14, form an intrachain disulfide bridge, so the fragment carries the small loop that closes the C-terminus of the native hormone. UK Peptide Lab supplies HGH Fragment 176-191 5mg as lyophilised powder for in-vitro laboratory research only.
The C-Terminus of hGH and the Lipolytic Domain
The research interest in this fragment comes from the division of labour within the intact hormone. Human growth hormone is a 191-residue protein whose growth-promoting actions run through receptor dimerisation and the IGF-1 axis, while its lipid-mobilising activity was traced early on to the C-terminal region. The founding work is the synthetic fragment programme of Ng and Bornstein (Am J Physiol, 1978), who reported hyperglycaemic activity for synthetic C-terminal fragments, and Bornstein and colleagues (Acta Endocrinol, 1983), who reported that a carboxyl-terminal part sequence inhibited acetyl-CoA carboxylase, acting through a second messenger. The design logic ever since has been separation: study the lipolytic domain without the growth and diabetogenic actions of the intact hormone.
Sequence Chemistry: the Disulfide-Bridged Loop
The chemistry worth knowing before experimental work is the disulfide. The two cysteines of the fragment correspond to Cys182 and Cys189 of the intact hormone, and their intrachain bridge closes the small C-terminal loop. Ogru and colleagues characterised the bridged structure of the C-terminal peptide by NMR, describing it as a cyclic anti-obesity peptide (J Pept Res, 2000). The two molecular weight conventions in circulation follow from this: 1817.09 g/mol is the formula weight of the reduced 16-mer (C₇₈H₁₂₅N₂₃O₂₃S₂), while sources that quote the disulfide-closed form, deducting the two bridging hydrogens, give approximately 1815.1 g/mol, the convention used on our AOD-9604 page. Oxidation of that bridge is the degradation route to design against.
The Lipolysis Literature
The metabolic literature on this sequence is built on the developed AOD-9604 candidate, which is sequence-identical to the native fragment. Ng and colleagues reported the molecular and cellular actions of the structural domain AOD9401 on lipid metabolism in Zucker fatty rats (J Mol Endocrinol, 2000). Heffernan and colleagues reported that oral administration of the fragment altered lipid metabolism in rodents (Am J Physiol Endocrinol Metab, 2000), and their chronic treatment study in obese mice and β3-adrenergic receptor knock-out mice (Endocrinology, 2001) is the most cited in the field: treatment reduced body weight and body fat, restored β3-adrenergic receptor expression toward lean levels, and did so without raising IGF-1 or impairing glucose handling. The knock-out data are the mechanistic crux, since mice lacking the β3 receptor showed no lipolytic response, implicating β3-adrenergic signalling in the fragment's activity.
HGH Fragment 176-191 vs AOD-9604
The relationship is easy to state precisely. Because residue 176 of human growth hormone is itself a tyrosine, the native fragment 176-191 and AOD-9604, written Tyr-hGH(177-191), are sequence-identical: YLRIVQCRSVEGSCGF in both cases. What separates them is provenance and the literature attached to each name. The unmodified fragment appears in the early synthetic fragment work and in modern drug-delivery studies, while AOD-9604 5mg is the developed candidate that Metabolic Pharmaceuticals carried through phase 2b clinical development, six randomised trials summarised by Stier, Vos and Kenley (J Endocrinol Metab, 2013). Laboratories selecting between the two names are choosing between the native-sequence framing and the clinically characterised one; the peptide chain is the same.
A Modern Line: Fragment 176-191 in Drug Delivery
The unmodified fragment also has its own current literature. Habibullah and colleagues (Drug Des Devel Ther, 2022) reported that hGH fragment 176-191 enhanced the toxicity of doxorubicin-loaded chitosan nanoparticles against MCF-7 breast cancer cells. It is a single in-vitro study, but it shows the fragment being used as a research reagent in its own right rather than as the unmodified mirror of AOD-9604.
Reading the Evidence Honestly
Here is the honest position, stated plainly. The human clinical literature belongs to AOD-9604, not to the unmodified fragment, and even there the story is thin: six randomised, placebo-controlled trials reported safety and tolerability indistinguishable from placebo, with no effect on serum IGF-1 and no adverse effect on carbohydrate metabolism, but efficacy in obesity was never established, the development programme was discontinued, and no marketing authorisation exists in the UK or any other jurisdiction. For HGH Fragment 176-191 itself there is essentially no direct human literature at all, and the preclinical findings are rodent and in-vitro results that have not been replicated at clinical scale. This guide therefore carries no dosing information, no human-use claims and no therapeutic promises. The material is supplied for in-vitro laboratory research only.
Laboratory Handling, Reconstitution and Storage
Store lyophilised vials at -20°C, protected from light and moisture. To reconstitute, allow the vial to reach room temperature, swab the stopper, and inject bacteriostatic water slowly down the inner glass wall rather than onto the cake, then swirl gently until clear and colourless; never shake or vortex. Because the fragment carries an intrachain disulfide bridge, treat oxidation as the failure mode to design against: keep headspace minimal, re-seal promptly and avoid repeated freeze-thaw cycles. Reconstituted solution held at 2-8°C should be used within approximately four weeks, or aliquoted into single-use volumes at -20°C. See the peptide storage guide for fuller methodology.
Sourcing Research-Grade HGH Fragment 176-191 in the UK
UK Peptide Lab supplies HGH Fragment 176-191 5mg at £29.99 as lyophilised powder, supplier-tested, batch UKPL-9505 at 99.57% purity by HPLC, with the supplier certificate of analysis published on this page and independent third-party verification pending; the independent certificate will be published once complete. Orders placed before 2pm GMT dispatch the same day, with free Royal Mail Tracked shipping on UK orders over £45. Supplied strictly for in-vitro laboratory research use, not a licensed medicine anywhere, and purchasers must be 18 or over.
Related Products
Disclaimer: This article is for research and educational purposes only. All information provided is not intended as medical advice. UK Peptide Lab products are not for human consumption and are sold strictly for laboratory research use only.
Frequently Asked Questions
What is HGH Fragment 176-191?
HGH Fragment 176-191 is the native C-terminal sixteen residues of human growth hormone, sequence YLRIVQCRSVEGSCGF, molecular weight 1817.09 g/mol and CAS number 66004-57-1. The two cysteines form the intrachain disulfide bridge of the native C-terminal loop. It is supplied as lyophilised powder for in-vitro laboratory research only and holds no marketing authorisation in any jurisdiction.
Is HGH Fragment 176-191 the same as AOD-9604?
In primary structure, yes. Because residue 176 of human growth hormone is a tyrosine, the native fragment 176-191 and the developed hexadecapeptide AOD-9604, written Tyr-hGH(177-191), are sequence-identical. The names carry different literatures, with the phase 2b clinical programme belonging to AOD-9604 (Stier et al., J Endocrinol Metab, 2013), but the peptide chain is the same sixteen residues.
Does HGH Fragment 176-191 raise IGF-1?
The fragment is not a growth hormone secretagogue and does not act through the growth signalling of the intact hormone: it is a piece of the hormone itself, carrying the C-terminal lipolytic region rather than the receptor binding sites that drive IGF-1 production. Consistent with that, the clinical literature on the sequence-identical AOD-9604 reports no change in serum IGF-1 and no adverse effect on carbohydrate metabolism (Stier et al., J Endocrinol Metab, 2013), and the preclinical work reported lipolysis without IGF-1-mediated growth effects (Heffernan et al., Endocrinology, 2001).
How should HGH Fragment 176-191 be stored and reconstituted?
Store lyophilised vials at -20°C protected from light and moisture. Reconstitute by injecting bacteriostatic water slowly down the inner glass wall and swirling gently until clear and colourless; never shake or vortex. Hold the solution at 2-8°C and use within approximately 4 weeks, minimising headspace because the intrachain disulfide bridge makes oxidation the main degradation route. Supplied for in-vitro laboratory research only.
References
- [1] Hyperglycemic action of synthetic C-terminal fragments of human growth hormone. American Journal of Physiology (1978). View →
- [2] Metabolic actions of pituitary growth hormone. I. Inhibition of acetyl CoA carboxylase by human growth hormone and a carboxyl terminal part sequence acting through a second messenger. Acta Endocrinologica (1983). View →
- [3] Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats. Journal of Molecular Endocrinology (2000). View →
- [4] The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice. Endocrinology (2001). View →
- [5] The conformational and biological analysis of a cyclic anti-obesity peptide from the C-terminal domain of human growth hormone. Journal of Peptide Research (2000). View →
- [6] Safety and tolerability of the hexadecapeptide AOD9604 in humans. Journal of Endocrinology and Metabolism (2013). View →
- [7] Human growth hormone fragment 176-191 peptide enhances the toxicity of doxorubicin-loaded chitosan nanoparticles against MCF-7 breast cancer cells. Drug Design, Development and Therapy (2022). View →