HGH Fragment 176-191 is a synthetic peptide corresponding to amino acids 176–191 of the C-terminal region of human growth hormone (hGH). This region was identified in the 1980s and 1990s as the minimal sequence required to reproduce the fat-mobilizing (lipolytic) effects of full-length growth hormone — without stimulating IGF-1 production, cell proliferation, or the broader endocrine cascade associated with hGH. For Canadian research laboratories studying adipose tissue biology, metabolic signaling, or hGH pharmacology, Fragment 176-191 serves as a precise tool for isolating lipolytic mechanisms from the confounding effects of intact growth hormone.
All information in this guide is provided for research purposes only. HGH Fragment 176-191 is not approved for human consumption or therapeutic use.
What Is HGH Fragment 176-191?
HGH Fragment 176-191 is a 16-amino acid peptide fragment of human growth hormone with the sequence Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe-Leu-OH. It represents the core lipolytic domain of hGH, stripped of the receptor-binding regions responsible for the hormone’s growth-promoting and IGF-1–stimulating activities.
The discovery of this fragment’s biological activity traces to foundational work by Ng and colleagues (1987) and subsequent structure-activity mapping at Monash University, which systematically truncated the hGH C-terminus to define the minimal active sequence for lipolysis. The 176–191 region emerged as the shortest fragment retaining full lipolytic potency in adipocyte assays.
Mechanism of Action
Lipolytic Pathway Activation
HGH Fragment 176-191 stimulates lipolysis through a mechanism that parallels — but is not identical to — full-length growth hormone:
- Beta-adrenergic pathway potentiation: Fragment 176-191 increases intracellular cAMP in adipocytes, activating protein kinase A (PKA) and downstream hormone-sensitive lipase (HSL). This leads to hydrolysis of stored triglycerides into free fatty acids and glycerol.
- Anti-lipogenic effect: The fragment suppresses expression of lipoprotein lipase (LPL) and acetyl-CoA carboxylase (ACC), reducing the capacity for fatty acid uptake and de novo lipogenesis in adipose tissue.
- Direct adipocyte signaling: Unlike full-length hGH, which signals through the hGH receptor (GHR) and JAK2/STAT5 pathway, Fragment 176-191 appears to act through a distinct membrane-binding site on adipocytes. The exact receptor identity remains an area of active investigation.
What Fragment 176-191 Does NOT Do
The scientific importance of Fragment 176-191 lies as much in what it does not activate as in what it does:
- No IGF-1 upregulation: Multiple studies confirm that Fragment 176-191 does not increase hepatic or systemic IGF-1 levels
- No mitogenic activity: The fragment does not stimulate cell proliferation in sensitive cell lines
- No insulin resistance: Unlike hGH, the fragment does not impair glucose uptake or insulin sensitivity
- No organomegaly: Chronic administration in animal models does not produce heart, liver, or kidney enlargement
These properties make Fragment 176-191 indispensable for researchers who need to study hGH’s metabolic effects in isolation from its growth-promoting actions.
Key Research Studies
Foundational Lipolysis Research
- Ng et al. (1987): First demonstrated that the C-terminal region of hGH (residues 177–191) retained lipolytic activity in isolated rat adipocytes. This discovery established that hGH’s lipolytic and growth-promoting domains were structurally separable.
- Heffernan et al. (2001): Conducted structure-activity studies on hGH fragment variants, confirming that the 176–191 fragment stimulated lipolysis without affecting IGF-1 or glucose metabolism in obese rodent models.
- Fridkin et al. (1997): Extended these findings to human adipose tissue preparations, demonstrating dose-dependent lipolytic responses to the synthetic fragment.
Metabolic Studies in Animal Models
- Obesity models: Chronic administration of Fragment 176-191 in diet-induced obese mice reduced body fat percentage by 15–20% over 4–6 weeks, with no change in lean body mass, food intake, or IGF-1 levels.
- Metabolic rate: Indirect calorimetry studies showed increased fat oxidation rates in treated animals, as evidenced by decreased respiratory exchange ratios (RER).
- Insulin sensitivity: Fragment 176-191 did not impair glucose tolerance or insulin sensitivity — in some models, modest improvements were observed, consistent with reduced visceral adiposity.
Comparative Studies
Fragment 176-191 has been directly compared against full-length hGH, AOD9604, and adrenergic lipolytic agents in multiple experimental paradigms. These comparisons consistently show that Fragment 176-191 retains the lipolytic potency of hGH while eliminating its endocrine side effects.
For broader context on hGH-derived peptides and their research applications, see our HGH peptides guide.
Research Protocols
Reconstitution and Handling
HGH Fragment 176-191 is supplied as a lyophilized powder for laboratory research use:
1. Allow vial to equilibrate to room temperature before reconstitution.
2. Reconstitute with sterile bacteriostatic water. Typical volume: 2 mL per vial (yielding a concentration dependent on vial size).
3. Swirl gently until fully dissolved. Do not vortex.
4. Store at 2–8°C post-reconstitution; use within 14–21 days.
5. Avoid freeze-thaw cycles, which can compromise peptide integrity.
Our peptide calculator provides convenient concentration and volume calculations for research reconstitution protocols.
In Vitro Research Concentrations
- Adipocyte lipolysis assays: 0.1–10 μM (acute, 2–4 hour incubation)
- Lipogenesis inhibition studies: 100 nM – 1 μM (24–48 hour treatment)
- Receptor binding studies: 1 nM – 100 nM for membrane-binding characterization
In Vivo Research Dosing (Animal Models)
Published preclinical literature reports:
- Acute lipolysis: 0.05–0.5 mg/kg subcutaneous injection
- Chronic metabolic studies: 0.25–1 mg/kg/day subcutaneous injection over 4–12 weeks
- Twice-daily protocols: Some labs use divided doses (e.g., 0.25 mg/kg bid) for more sustained lipolytic activity
All animal research must comply with institutional ethics committee protocols and CCAC guidelines.
Fragment 176-191 vs. Related Compounds
Fragment 176-191 vs. AOD9604
AOD9604 is a closely related peptide derived from the same C-terminal hGH region (amino acids 177–191 with an added tyrosine). Both compounds share the same lipolytic mechanism and IGF-1 independence. The primary differences are:
- Structural: AOD9604 includes an N-terminal tyrosine and lacks the Leu-176 present in Fragment 176-191
- Pharmacokinetic: AOD9604 was specifically developed for oral bioavailability; Fragment 176-191 is administered via subcutaneous injection
- Research literature: AOD9604 has more extensive clinical trial data; Fragment 176-191 has a larger preclinical literature base
For a detailed AOD9604 analysis, see our AOD9604 research guide.
Fragment 176-191 vs. Full-Length hGH
Full-length hGH (191 amino acids) activates the complete spectrum of growth hormone signaling through the GHR/JAK2/STAT5 pathway, including IGF-1 upregulation, cell proliferation, gluconeogenesis, and lipolysis. Fragment 176-191 isolates only the lipolytic signal. Researchers studying the relative contribution of each hGH domain to metabolic outcomes can use Fragment 176-191 as a precision tool.
For comprehensive information on hGH peptide variants, consult our HGH peptides guide.
Safety and Regulatory Considerations
Research-Only Status
HGH Fragment 176-191 is classified as a research peptide. It is not approved by Health Canada, the FDA, or any other regulatory authority for therapeutic, cosmetic, or dietary use. All products from Webber Science are labeled for research purposes only and are not for human consumption.
Preclinical Safety Profile
The available safety data from animal studies include:
- No changes in IGF-1, glucose, insulin, or thyroid function markers
- No evidence of organomegaly or tissue hyperplasia at research doses
- No observed impact on cardiac structure or function
- Injection site tolerability comparable to saline control
No human clinical trial data are available for Fragment 176-191. The safety profile should not be extrapolated from AOD9604 clinical data, as the two peptides, while related, have distinct pharmacokinetic properties.
Canadian Regulatory Notes
HGH Fragment 176-191 is not a scheduled substance under the Controlled Drugs and Substances Act. As a research chemical, it is subject to standard laboratory chemical handling and importation requirements. Canadian research institutions must maintain documentation verifying research-use intent and comply with Health Canada guidelines for investigational compounds.
Frequently Asked Questions
Is HGH Fragment 176-191 the same as growth hormone?
No. Fragment 176-191 is a 16-amino acid portion of the 191-amino acid human growth hormone molecule. While it retains the lipolytic (fat-mobilizing) property of hGH, it does not stimulate IGF-1 production, cell growth, or the other endocrine effects of full-length growth hormone.
How does Fragment 176-191 compare to AOD9604?
Both peptides derive from the C-terminal lipolytic region of hGH. Fragment 176-191 corresponds to amino acids 176–191, while AOD9604 is based on amino acids 177–191 with an added tyrosine. They have similar lipolytic mechanisms but different pharmacokinetic profiles. See our AOD9604 research guide for detailed comparison.
Can HGH Fragment 176-191 be used for fat loss?
HGH Fragment 176-191 is available for research purposes only and is not approved for fat loss, weight management, or any therapeutic application. While preclinical studies demonstrate lipolytic activity in animal models, no human clinical trials have been completed. This peptide should be used exclusively as a laboratory research tool.
What is the recommended reconstitution procedure?
Reconstitute with sterile bacteriostatic water using gentle swirling. Typical ratio is 2 mL per vial. Do not vortex. Store at 2–8°C and use within 14–21 days. Use the peptide calculator for precise concentration calculations.
Where can Canadian researchers purchase HGH Fragment 176-191?
Webber Science supplies HGH Fragment 176-191 as a research-grade peptide for qualified Canadian laboratories. View HGH Fragment product page for specifications, certificates of analysis, and ordering information.
Summary
HGH Fragment 176-191 is one of the most well-characterized tools available for studying isolated lipolytic signaling in adipose tissue. Its precise derivation from the hGH C-terminus — and its documented inability to activate IGF-1, mitogenic, or insulin-antagonist pathways — make it uniquely valuable for researchers who need to decouple growth hormone’s metabolic and growth-promoting effects.
Key takeaways:
- Fragment 176-191 is the minimal hGH lipolytic fragment (amino acids 176–191), confirmed in more than three decades of research
- It stimulates adipocyte lipolysis without activating IGF-1, cell proliferation, or insulin resistance
- Preclinical data demonstrate fat mass reduction in obese animal models without lean tissue loss
- Available from Webber Science for qualified Canadian research laboratories
All products are sold for research purposes only. Not for human consumption or therapeutic use.
For broader context, explore our weight loss peptides guide and HGH peptides guide for related compounds, and use the peptide calculator for reconstitution and dosing calculations.