PT-141 (Bremelanotide) — Cyclic Heptapeptide Melanocortin MC3R/MC4R Receptor Agonist
Research-Grade Compound
PT-141 (bremelanotide) is a synthetic cyclic heptapeptide that acts as a melanocortin receptor agonist, with its principal research activity at the MC3R and MC4R subtypes expressed in the central nervous system. Molecular formula C50H68N14O10, molecular weight 1,025.2 Da, CAS 189691-06-3. Structure: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH.
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What is PT-141?
PT-141 (bremelanotide) is a synthetic cyclic heptapeptide that acts as a melanocortin receptor agonist, with its principal research activity at the MC3R and MC4R subtypes expressed in the central nervous system. Molecular formula C50H68N14O10, molecular weight 1,025.2 Da, CAS 189691-06-3. Structure: Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH.
The compound descends directly from Melanotan II. Compare the two structures and the difference is a single functional group at the C-terminus: MT-II ends in a carboxamide, PT-141 in a free acid. One atom of chemistry, and the mass gap between them is about 1 Da — 1,024.2 versus 1,025.2. That small change shifted the receptor selectivity profile enough to send the two molecules down separate development paths, which is a useful illustration of how sensitive melanocortin binding is to C-terminal chemistry.
Bremelanotide is one of a small number of compounds in this catalog with a completed FDA approval record. It was approved under the brand name Vyleesi for hypoactive sexual desire disorder in premenopausal women, delivered as a prefilled autoinjector. That approval concerns a specific finished pharmaceutical product, not the lyophilized research-grade material sold here. Peptide.Express supplies PT-141 for in-vitro laboratory research only.
How Does PT-141 Work? Mechanism of Action
The melanocortin system runs on five G protein-coupled receptors, MC1R through MC5R, all of which couple to Gs and signal through adenylate cyclase. Receptor occupancy raises intracellular cAMP, cAMP activates protein kinase A, and PKA phosphorylates the downstream transcriptional and channel targets that differ by cell type. PT-141 engages this system with a preference for MC3R and MC4R.
Receptor distribution is what makes the compound interesting as a research tool. MC4R is dense in the hypothalamus — the paraventricular nucleus in particular — and in the medial preoptic area and spinal autonomic nuclei. MC3R sits largely in the arcuate nucleus and limbic structures. Both are central, not peripheral. PT-141 has no meaningful activity on vascular smooth muscle, which is the entire mechanistic separation from PDE5 inhibitors such as sildenafil and tadalafil: those compounds work by blocking cGMP breakdown in peripheral vasculature, and PT-141 does not touch that pathway at all.
Downstream of MC4R the picture gets less resolved. Rodent work implicates oxytocinergic projections from the paraventricular nucleus and dopaminergic signalling in the medial preoptic area, but the circuit-level account is inferred from lesion studies, receptor-null animals and pharmacological blockade rather than measured directly. MC4R is also a central node in the leptin-melanocortin energy-balance pathway, so appetite and feeding readouts move alongside the arousal-pathway endpoints in the same animals. Study designs that fail to separate those two outputs will conflate them.
Selectivity is relative, not absolute. PT-141 retains measurable affinity for MC1R, so at high concentrations a melanogenic signal can appear in preparations containing melanocytes. Researchers attributing an effect to MC4R specifically should include a selective antagonist arm or a receptor-null control rather than relying on the compound to sort the receptors out on its own.
Research Applications of PT-141
Melanocortin Receptor Pharmacology
- Selectivity profiling: cAMP accumulation assays in cell lines expressing single recombinant receptors (MC1R through MC5R) are the standard way to place PT-141 on the melanocortin selectivity map.
- Structure-activity work: the C-terminal free acid of PT-141 against the carboxamide of Melanotan II is one of the cleanest single-variable comparisons available in this receptor family.
- Antagonist blockade: SHU9119 and related MC3R/MC4R antagonists are used to confirm that an observed cAMP or behavioural signal is receptor-mediated rather than off-target.
Central Nervous System Signalling Models
- Hypothalamic circuit research: paraventricular nucleus MC4R activation and its oxytocinergic projections are the most studied downstream branch in rodent preparations.
- Central versus peripheral mechanism separation: PT-141 activity is independent of vascular smooth-muscle signalling, so it functions as the CNS-side reference compound when PDE5 inhibitors supply the peripheral arm.
- Receptor-null comparisons: MC4R knockout models are the strongest available control for attributing a CNS readout to that subtype.
Energy Balance and Feeding Circuit Research
- Leptin-melanocortin pathway modelling: MC4R sits downstream of POMC neurons in the arcuate nucleus, making melanocortin agonists standard tools in food-intake studies.
- Endpoint deconfounding: feeding and arousal endpoints both run through MC4R, so protocols measuring one need a design that accounts for the other.
- Cross-compound comparison: running PT-141 alongside Melanotan II isolates the contribution of MC1R and MC5R activity that PT-141 largely lacks.
PT-141 vs Melanotan II
| Feature | PT-141 (Bremelanotide) | Melanotan II |
|---|---|---|
| Structure | Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 |
| C-terminus | Free acid | Carboxamide |
| Molecular formula | C50H68N14O10 | C50H69N15O9 |
| Molecular weight | 1,025.2 Da | 1,024.2 Da |
| CAS number | 189691-06-3 | 121062-08-6 |
| Receptor profile | Preferential MC3R / MC4R | Non-selective: MC1R, MC3R, MC4R, MC5R |
| MC1R pigmentation pathway | Residual affinity only | Direct agonism — melanogenesis is a primary readout |
| Site of action studied | Central nervous system | Central and peripheral (melanocytes, exocrine tissue) |
| FDA status | Approved as Vyleesi for HSDD in premenopausal women | Not approved for any indication |
| Research framing | CNS melanocortin circuit pharmacology | Multi-receptor melanocortin pharmacology, melanogenesis |
These two molecules are close enough structurally that suppliers and secondary sources routinely blur them. They are not interchangeable. Swapping Melanotan II into a protocol designed around PT-141 adds MC1R and MC5R activity that the original design never accounted for, and any pigmentation-linked readout in that experiment becomes uninterpretable.
PT-141 Technical Specifications
| Compound Name | PT-141 (bremelanotide) |
|---|---|
| Common Synonyms | PT141, bremelanotide, PT-141 peptide |
| FDA-Approved Brand (finished drug product) | Vyleesi |
| Classification | Cyclic heptapeptide melanocortin receptor agonist |
| Amino Acid Sequence | Ac-Nle-cyclo(Asp-His-D-Phe-Arg-Trp-Lys)-OH |
| Receptor Targets | MC3R, MC4R (residual MC1R affinity) |
| CAS Number | 189691-06-3 |
| Molecular Formula | C50H68N14O10 |
| Molecular Weight | 1,025.2 Da |
| Parent Compound | Melanotan II — PT-141 differs at the C-terminus (free acid vs carboxamide) |
| Purity | ≥99% by HPLC |
| Purity Confirmation | LC-MS/MS molecular weight verification |
| Endotoxin Testing | LAL (Limulus Amebocyte Lysate) method |
| Physical Form | Lyophilized powder |
| Appearance | White to off-white powder |
| Reconstitution | Bacteriostatic water or sterile 0.9% sodium chloride |
| Storage (lyophilized) | -20°C, desiccated, protected from light |
| Storage (reconstituted) | 2–8°C, use within 14–28 days |
| Shelf Life | 24 months from manufacture (lyophilized) |
| Testing Methods | HPLC, LC-MS/MS, LAL Endotoxin |
| Documentation | Certificate of Analysis (CoA) per batch |
| Intended Use | In-vitro laboratory research only |
How to Reconstitute PT-141 for Research
PT-141 is a small cyclic peptide and goes into solution readily. The ring structure makes it more resistant to mechanical stress than a long linear peptide, but that is not licence to shake it — the standard slow-wall technique applies.
- Bring the vial to room temperature before opening so condensation does not form on the septum.
- Draw the calculated volume of bacteriostatic water. For the 10 mg vial, 2 mL yields 5 mg/mL and 5 mL yields 2 mg/mL.
- Swab the septum with alcohol and allow 30 seconds to dry.
- Inject the diluent slowly against the inner vial wall rather than directly onto the lyophilized cake. Spraying the powder causes foaming.
- Swirl gently for 60–90 seconds until dissolution is complete. Do not shake or vortex.
- Confirm the solution is clear and colorless. Discard if cloudy, discolored, or if particulate matter is visible.
- Label the vial with the reconstitution date and the resulting concentration.
- Store at 2–8°C, use within 14–28 days, and avoid repeated freeze-thaw cycles.
Diluent: bacteriostatic water for peptide reconstitution. Full protocol: step-by-step peptide reconstitution guide. Concentration maths: peptide reconstitution calculator.
Frequently Asked Questions — PT-141
What is PT-141 (bremelanotide)?
What melanocortin receptors does PT-141 target?
How does PT-141 differ from PDE5 inhibitors mechanistically?
What is the difference between PT-141 and Melanotan II?
Is PT-141 the same as Vyleesi?
Is PT-141 FDA approved?
Does PT-141 activate MC1R and affect pigmentation pathways?
What is known about the half-life of PT-141?
What purity standard does Peptide.Express use for PT-141?
What testing does PT-141 undergo before shipping?
How should PT-141 be stored before and after reconstitution?
How do I reconstitute PT-141 and what concentration results?
Where is the Certificate of Analysis for PT-141?
Research References
- Molinoff PB, Shadiack AM, Earle D, Diamond LE, Quon CY. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003. Read Molinoff et al. on PT-141 as an MC3R/MC4R melanocortin agonist
- Mountjoy KG, Mortrud MT, Low MJ, Simerly RB, Cone RD. Localization of the melanocortin-4 receptor (MC4-R) in neuroendocrine and autonomic control circuits in the brain. Mol Endocrinol. 1994. Read Mountjoy et al. on MC4R distribution in hypothalamic and autonomic circuits
- Vyleesi (bremelanotide) injection, FDA-approved prescribing information via DailyMed. Bremelanotide is approved for hypoactive sexual desire disorder in premenopausal women; the approval covers the finished drug product only. Read the Vyleesi (bremelanotide) FDA prescribing information
All products are sold for in-vitro laboratory research use only. Not intended for human consumption, clinical use, or veterinary use. Peptide.Express makes no medical claims. Consult the published literature for research application guidance.