GLP-3 RT is a supplier shorthand for retatrutide (listed on this site as RT-GLP3, CAS 2381089-83-2): a single synthetic peptide that acts as an agonist at three receptors in vitro, the GLP-1 receptor (GLP-1R), the GIP receptor (GIPR) and the glucagon receptor (GCGR). There is no "GLP-3" hormone and no "GLP-3 receptor"; the name is a catalog label, not a receptor class.
If you searched for "GLP-3 RT", "GLP 3rt", "GLP3RT" or "GLP-3 RT peptide", this guide explains what those strings refer to, what the molecule is, which receptors it engages in cell-based assays, and how a lab can confirm that a vial labelled this way is the compound it claims to be. It is written for laboratory researchers and stays on identity, nomenclature and in vitro pharmacology.
What does "GLP-3 RT" mean?
"GLP-3 RT" combines two pieces. "RT" is the abbreviation for retatrutide. "GLP-3" is a numbering convention some suppliers use to line up their catalog (GLP-1, GLP-2, GLP-3) by product tier; it does not come from receptor or hormone nomenclature. The same compound is sold under several spellings, which is why search results for these terms look inconsistent. The store's catalog code for it is RT-GLP3 (retatrutide).
| Spelling you may see | What it refers to | Note |
|---|---|---|
| GLP-3 RT, GLP 3 RT, GLP-3RT, GLP3RT, GLP 3rt | Retatrutide | Hyphen and spacing variants of one label |
| RT-GLP3 | Retatrutide (Happy Peptides catalog code) | RT = retatrutide; GLP3 = the supplier numbering |
| GLP-3 peptide, GLP3 peptide, GPL3 peptide | Retatrutide (GPL3 is a transposition typo) | Not a distinct molecule |
| GLP-3R, GLP3R, GLP 3R peptide | Usually the same label with R for retatrutide | Read literally as "GLP-3 receptor" it names nothing; no such receptor is defined |
| Retatrutide, LY3437943 | Chemical (nonproprietary) name and development code | CAS 2381089-83-2 |
| Reta | Informal abbreviation of retatrutide | Colloquial only |
Because supplier labels are not standardized, the name on a vial is not evidence of identity. The CAS number and the batch analytical report are.
What is retatrutide chemically?
Retatrutide is a synthetic, linear peptide of 39 amino-acid residues (per the PubChem record and the supplier specification) carrying a C-terminal amide. The PubChem structure record (CID 171390338) lists non-coded residues (including alpha-aminoisobutyric acid and an alpha-methylated amino acid) and a lysine side chain bearing a C20 fatty diacid attached through a linker. Its sequence combines features that resemble the N-terminus of GIP, the central region shared by glucagon and GLP-1, and a proline-rich C-terminal tail similar to that of exendin-4. It is supplied as a lyophilized powder.
| Property | Value |
|---|---|
| Chemical name | Retatrutide (development code LY3437943) |
| CAS number | 2381089-83-2 |
| Molecular formula (free peptide) | C221H342N46O68 |
| Average molecular weight | about 4731 g/mol (4731.33) |
| Length and termini | 39 residues, C-terminal amide |
| Key modifications | Non-coded residues; C20 fatty-diacid side chain via linker |
| PubChem | Compound CID 171390338 |
| Vial sizes at Happy Peptides | 10 mg, 20 mg, 30 mg (lyophilized) |
One practical trap: some listings quote a higher molecular weight than 4731. A trifluoroacetate counter-ion adds roughly 114 Da per TFA, so a salt-form figure near 4845 is not a different molecule. When you compare a measured mass to a listing, check whether the listing is a free-peptide or a salt-form value.
How can one compound act on three receptors in vitro?
GLP-1R, GIPR and GCGR are all class B1 G-protein-coupled receptors that signal mainly through Gs and cyclic AMP (cAMP). A single engineered peptide can carry enough of each native ligand's binding determinants to activate all three. In the laboratory this is measured receptor by receptor, usually in cells that express only one of them, with the native ligand run alongside as a reference.
| Receptor | Native ligand | Main signal | Typical in vitro readout |
|---|---|---|---|
| GLP-1R | GLP-1 (7-36 amide) | Gs / cAMP; also beta-arrestin recruitment | cAMP accumulation in cells expressing human GLP-1R; insulin-secretion readouts in beta-cell lines |
| GIPR | GIP (1-42) | Gs / cAMP | cAMP accumulation in cells expressing human GIPR; adipocyte-line readouts |
| GCGR | Glucagon (29 residues) | Gs / cAMP; Gq coupling reported in some systems | cAMP accumulation in cells expressing human GCGR; hepatocyte-culture readouts |
Potency is not assumed to be equal across the three receptors, so each assay needs its own concentration-response curve and its own parental-cell counter-screen.
Why is "GLP-3" not a receptor class?
The glucagon-like peptides that exist as hormones are GLP-1 and GLP-2, both cleaved from proglucagon alongside glucagon, and each acts on its own receptor. GIP is a separate incretin with its own precursor. No peptide hormone or receptor is defined as "GLP-3" in standard nomenclature, so the label cannot describe a receptor class. The full classification, including where the supplier numbering came from, is in Is There Such a Thing as GLP-3? The Incretin Classes Explained, and the narrower naming question is answered in Is Retatrutide a GLP-3?
How do you confirm a "GLP-3 RT" vial is retatrutide?
Match the evidence, not the label:
- CAS number: 2381089-83-2 should appear on the specification and the report.
- Batch-specific report: a lot number that matches the vial, with HPLC purity, identity, net peptide content and endotoxin results. Recent RT-GLP3 batch reports on the product page list identity, purity, net content and endotoxin results.
- Mass-spectrometry identity: a deconvoluted mass near 4731 Da for the free peptide. In electrospray data, multiply-charged ions fall near m/z 1578 (3+), 1184 (4+), 947 (5+) and 790 (6+).
- Consistent formula and weight: C221H342N46O68 and about 4731 g/mol on the free-peptide basis.
The step-by-step version, with the red flags to look for in a report, is in Sourcing GLP-3 RT as a Research Material.
Common questions about GLP-3 RT
Is GLP-3 RT the same as retatrutide? Yes. GLP-3 RT, GLP3RT, GLP 3rt and RT-GLP3 are spellings of one supplier label for retatrutide. Confirm by CAS number and a batch mass-spectrometry result.
What is the difference between GLP-1 and GLP-3 RT? GLP-1 is a native 30-residue hormone that activates one receptor, GLP-1R. GLP-3 RT is retatrutide, a 39-residue engineered peptide with a fatty-diacid side chain that activates GLP-1R, GIPR and GCGR in vitro.
Related research guides
Research-use note
All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use.
