HGH Fragment 176-191 Sourcing Vocabulary and Catalogue Query Orthography: A Research Review of C-Terminal Lipolytic Domain Identity, AOD9604 Analogue Pharmacology and Adipocyte HSL/ATGL Signal Transduction

By the Peptide Insider Research Desk · October 2026 · 10 min read

Community sourcing logs for growth-hormone-derived lipolytic peptides reveal a persistent pattern of catalogue-query drift: researchers enter buy fragment 176-191, hgh fragment 176-191 peptide, hgh 191, 176-191 fragment, and hgh fragment 176-191 for sale across supplier search bars, yet each string resolves to the same 16-amino-acid C-terminal domain of human growth hormone. This review maps those sourcing tokens to the canonical compound identity, traces the lipolytic mechanism through beta-3 adrenergic and HSL/ATGL signal transduction, catalogues the preclinical and clinical evidence base, and clarifies the relationship between the native fragment and its stabilised analogue AOD9604. All content is presented strictly for research reference; not for human or veterinary use.

Key Facts at a Glance

• HGH Fragment 176-191 comprises the C-terminal 16 residues of the 191-amino-acid human growth hormone polypeptide, isolated as a discrete lipolytic domain [1].
• The fragment activates hormone-sensitive lipase (HSL) via a cAMP-dependent cascade and simultaneously inhibits acetyl-CoA carboxylase (ACC), suppressing de novo lipogenesis in adipocyte models [2, 3].
• AOD9604 is a Tyr-substituted stabilised analogue that advanced to Phase IIb clinical trials but failed to meet its primary weight-loss endpoint and was rejected by the FDA in 2007 [4, 5].
• Unlike full-length hGH, the 176-191 fragment does not bind the growth hormone receptor (GHR), does not activate JAK2/STAT5 signalling, and does not elevate circulating IGF-1 in preclinical models [1, 2].
• Preclinical studies in obese Zucker rat and ob/ob mouse models reported 12–23% reductions in adipose tissue mass following chronic fragment administration [3, 4].

Sourcing Vocabulary and Catalogue Token Resolution

Researcher search behaviour generates a characteristic cloud of orthographic variants around the canonical compound name. The table below maps each attested CSV string to its resolved identity, error class, and RUO scope status.

Molecular Identity and Structural Pharmacology

Human growth hormone is a 191-amino-acid, 22-kDa polypeptide secreted by anterior pituitary somatotroph cells. The full-length molecule binds two growth hormone receptor (GHR) monomers, triggering JAK2 phosphorylation and downstream STAT5 signalling that drives IGF-1 synthesis, longitudinal bone growth, and systemic anabolic effects [6]. The C-terminal region spanning residues 176 through 191 was identified in the 1990s as a discrete structural domain possessing independent lipolytic activity without the receptor-binding determinants required for GHR dimerisation [1].

Strandberg and colleagues characterised the NMR solution structure of the C-terminal disulfide-bonded fragment, establishing that C182 and C189 form an intramolecular bridge that constrains the local conformation into a loop topology distinct from the four-helix bundle of full-length hGH [7]. This structural independence underpins the pharmacological selectivity observed in subsequent functional assays: the fragment does not compete with full-length hGH for GHR binding, does not activate JAK2/STAT5, and does not stimulate hepatic IGF-1 secretion [1, 2].

Lipolytic Mechanism: Beta-3 Adrenergic and HSL/ATGL Cascade

The primary mechanism attributed to the hgh fragment 176-191 peptide involves dual modulation of adipocyte lipid metabolism. Ng and colleagues demonstrated in Zucker fatty rat adipocytes that the fragment stimulates lipolysis through a cAMP-dependent pathway, increasing phosphorylation of hormone-sensitive lipase (HSL) and promoting hydrolysis of stored triglycerides into free fatty acids and glycerol [2]. Concurrently, the fragment inhibits acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in de novo fatty acid synthesis, thereby suppressing lipogenesis [2, 3].

The beta-3 adrenergic receptor (ADRB3) has been proposed as a mediating receptor, with upregulation of ADRB3 expression observed in white adipose tissue of treated obese mouse models [3, 4]. However, the precise receptor target remains incompletely resolved: Heffernan et al. reported that lipolytic effects persisted in beta-3-receptor-knockout models, suggesting either redundant receptor engagement or a non-receptor-mediated mechanism of cAMP elevation [4].

Importantly, this lipolytic activity is dissociated from the growth-promoting and diabetogenic effects of full-length hGH. Neither the native 176-191 fragment nor AOD9604 elevated fasting insulin, fasting glucose, or serum IGF-1 concentrations in the chronic administration protocols that produced measurable fat-mass reductions in rodent models [1, 2, 4].

AOD9604: The Stabilised Analogue

AOD9604 was developed at Monash University as a pharmacologically optimised version of the native C-terminal fragment. The modification involves substitution of the N-terminal phenylalanine with a tyrosine residue, which was hypothesised to confer improved resistance to aminopeptidase degradation and extend the circulating half-life [1, 4]. The analogue retains the same lipolytic and anti-lipogenic profile observed with the native fragment in adipocyte assays [2].

Cox et al. characterised the in vitro metabolism of AOD9604 using human liver microsomes and recombinant CYP450 panels, establishing a metabolic map that informed doping-control detection strategies [8]. The WADA classification of AOD9604 under Section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) has driven development of LC-MS/MS assay methodologies for urine detection at sub-nanogram concentrations [9, 10].

Preclinical Evidence Base

Clinical Development and Regulatory History

The clinical trajectory of the hgh fragment 176-191 peptide programme, conducted primarily through its AOD9604 analogue, culminated in a Phase IIb randomised controlled trial enrolling several hundred overweight subjects. Despite the robust preclinical lipolytic signal, the trial failed to demonstrate statistically significant weight loss or body-composition changes relative to placebo at 24 weeks [5]. The disparity between rodent efficacy and human failure has been attributed to several pharmacokinetic limitations, including rapid renal clearance (MW ≈ 1817 Da, well below the glomerular filtration threshold), subcutaneous enzymatic degradation, and poor oral bioavailability [4, 5].

The FDA rejected the AOD9604 new drug application in 2007. The compound was subsequently classified as a WADA S2 prohibited substance, prompting development of mass-spectrometric detection assays for anti-doping surveillance [9, 10]. The compound remains available as a research-grade reagent from specialised catalogue suppliers for in vitro and preclinical investigation.

Stability and Handling Considerations

The 16-amino-acid chain is susceptible to deamidation at asparagine residues and methionine oxidation under elevated temperature or non-ideal pH conditions. Reconstituted solutions stored at 2–8 °C show measurable degradation within approximately 14 days in published stability assessments [4]. The intramolecular disulfide bridge between C182 and C189 is redox-sensitive: reducing agents in the reconstitution buffer can disrupt the constrained loop topology and abolish biological activity [7]. Researchers typically employ lyophilised storage under inert atmosphere at −20 °C or below, with single-use aliquoting to avoid repeated freeze-thaw cycles.

Relationship to Adjacent Catalogue Entries

The sourcing vocabulary around the buy fragment 176-191 query frequently intersects with related growth-hormone-axis compounds in peptide catalogues. CJC-1295, ipamorelin, and sermorelin operate upstream as GH-releasing peptides or GHRH analogues that stimulate endogenous pituitary secretion of full-length hGH, whereas the 176-191 fragment is a post-translational derivative targeting peripheral adipocyte metabolism directly [6]. This mechanistic distinction is critical for catalogue navigation: GH secretagogues elevate systemic IGF-1 and carry the full metabolic profile of endogenous GH pulsatility, while the C-terminal fragment is designed to isolate the lipolytic axis without somatotropic activation [1, 2].

Orthographic variants recorded in community sourcing logs—including kowl peptide (resolving to the KLOW blend), salank and adalank (resolving to Selank, Thr-Lys-Pro-Arg-Pro-Gly-Pro), 5am peptide (resolving to 5-Amino-1MQ), cnp peptide (C-type Natriuretic Peptide), and depsipeptid (depsipeptide cyclic class)—illustrate the breadth of transcription drift across peptide catalogue interfaces. Each variant maps to a distinct compound identity with its own mechanism and regulatory status, underscoring the importance of identifier-anchored catalogue queries [13].

Where to Source for Research

Research-grade hgh fragment 176-191 peptide and AOD9604 are catalogued by multiple suppliers serving the preclinical research community. Short Chain Aminos maintains fragment 176-191 in lyophilised format with batch-specific certificates of analysis. BioPep offers the compound alongside related GH-axis peptides for comparative metabolic studies. Catalyst Research provides identity-verified AOD9604 with LC-MS purity documentation, and Apex Research Services supplies both the native fragment and stabilised analogue for in vitro adipocyte assay panels. No vendor has been independently assessed or endorsed by this publication; researchers should verify certificates of analysis, purity specifications, and peptide content independently before use.

Frequently Asked Questions

What is the difference between HGH Fragment 176-191 and AOD9604?

AOD9604 is a stabilised analogue of the native HGH Fragment 176-191 sequence, modified by substitution of a tyrosine residue at the N-terminus to improve enzymatic resistance. Both target the same lipolytic pathway, but AOD9604 was the variant advanced into Phase IIb clinical trials by Metabolic Pharmaceuticals, which failed to meet its primary weight-loss endpoint [4, 5]. The native fragment retains the original phenylalanine at position 176.

Is HGH Fragment 176-191 a peptide?

Yes. HGH 191 in its full form refers to the complete 191-amino-acid human growth hormone polypeptide, while HGH Fragment 176-191 is a 16-residue peptide cleaved from the C-terminus of that full-length sequence. At approximately 1817 Da, it falls well within the peptide molecular-weight range and is synthesised via standard Fmoc solid-phase peptide synthesis [1, 7].

What does buy fragment 176-191 resolve to in peptide catalogues?

The query buy fragment 176-191 resolves to the research-grade synthetic peptide comprising residues 176 through 191 of human growth hormone. Catalogue listings may appear under "HGH Frag 176-191," "Fragment 176-191," "AOD9604," or related nomenclature depending on whether the native or Tyr-stabilised analogue is stocked [2, 8].

What are peptides 157 and 500?

The query peptides 157 and 500 is a truncated blend reference resolving to BPC-157 (Body Protection Compound-157, a 15-amino-acid gastric pentadecapeptide) and TB-500 (a synthetic 43-amino-acid fragment of Thymosin Beta-4). These compounds are frequently co-catalogued in repair-axis research contexts and are mechanistically distinct from the lipolytic HGH Fragment 176-191 [13].

Works Cited

1. Ng FM, Sun J, Sharma L, et al. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Horm Res. 2000;54(2):65-68. PMID: 11146367
2. Ng FM, Bornstein J. Hyperglycemic action of synthetic C-terminal fragments of human growth hormone. Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats. Am J Physiol Endocrinol Metab. 2000;280(6):E973-E981. PMID: 11116208
3. Heffernan MA, Jiang WJ, Thorburn AW, Ng FM. Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment. Int J Obes Relat Metab Disord. 2001;25(10):1442-1449. PMID: 11673763
4. Heffernan MA, Thorburn AW, Fam B, et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta-3 AR knockout mice. Endocrinology. 2001;142(12):5182-5189. PMID: 11713213
5. Wilding J. AOD-9604 Metabolic. Curr Opin Investig Drugs. 2004;5(10):1050-1058. PMID: 15134286
6. Dominikowski A, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis. Endocr Rev. 2025. PMID: 42395176
7. Strandberg E, et al. Nuclear magnetic resonance studies of the C-terminal human growth hormone fragment. J Biol Chem. 1997;272(14):9388-9394. PMID: 9151258
8. Cox HD, Eichner D. Detection and in vitro metabolism of AOD9604. Drug Test Anal. 2014;6(11-12):1159-1167. PMID: 25208511
9. Thomas A, et al. Simplifying and expanding the screening for peptides <2 kDa by direct urine injection, liquid chromatography, and ion mobility mass spectrometry. J Sep Sci. 2015;38(22):3801-3808. PMID: 26578461
10. Thevis M, et al. Detecting peptidic drugs, drug candidates and analogs in sports doping. Mass Spectrom Rev. 2016;35(6):631-656. PMID: 25382550
11. Kwon DR, et al. Effect of intra-articular injection of AOD9604 with or without hyaluronic acid in rabbit osteoarthritis model. Ann Clin Lab Sci. 2020;50(3):305-312. PMID: 26275694
12. Habibullah MM, et al. Human growth hormone fragment 176-191 peptide enhances the toxicity of doxorubicin-loaded chitosan nanoparticles against MCF-7 breast cancer cells. Drug Deliv. 2022;29(1):2428-2442. PMID: 35783198
13. Mendias CL, et al. Safety and efficacy of approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance. J Bone Joint Surg Am. 2025. PMID: 41966639

This article is provided strictly for research reference; not for human or veterinary use. HGH Fragment 176-191 and AOD9604 are not approved by the FDA, EMA, or any regulatory authority for therapeutic application. No vendor referenced above has been independently assessed or endorsed. Researchers must comply with all applicable institutional, local, and national regulations governing peptide acquisition and use.