Overview
PT-141 (Bremelanotide) and Melanotan II are both cyclic synthetic analogs of α-MSH (alpha-melanocyte-stimulating hormone) that activate melanocortin receptors (MCRs). They share structural similarities — both are derived from the MT-II scaffold — but have distinct receptor selectivity profiles that result in meaningfully different biological and research applications.
Melanotan II: Broad Melanocortin Receptor Agonism
Melanotan II (cyclo[Nle4,D-Phe7]-α-MSH) is a non-selective melanocortin agonist binding MC1R, MC3R, MC4R, and MC5R. Its MC1R activity drives eumelanin synthesis and skin pigmentation — the distinguishing effect not shared by PT-141. MC4R activity mediates centrally mediated effects studied in appetite, energy homeostasis, and autonomic regulation research. Melanotan II is highly potent and contains a light-sensitive Trp residue requiring protection from UV exposure during storage and handling.
PT-141 (Bremelanotide): MC3R/MC4R Selective Profile
PT-141 (Bremelanotide) was derived from Melanotan II through structural optimization to reduce MC1R activity, effectively eliminating the pigmentation effect while retaining MC3R and MC4R agonism. It became the first FDA-approved melanocortin-based compound when approved as Vyleesi (bremelanotide) in June 2019. Its research applications center on hypothalamic-pituitary-gonadal (HPG) axis modulation, autonomic cardiovascular effects, and central nervous system melanocortin pathway research.
Key Differences
| Parameter | Melanotan II | PT-141 (Bremelanotide) |
|---|---|---|
| MC1R activity | Yes (pigmentation) | Minimal |
| MC3R/MC4R activity | Yes | Yes (primary) |
| Skin pigmentation | Yes | No |
| Light sensitivity | High (Trp residue) | Moderate |
| FDA status | Research only | Approved as Vyleesi (2019) |
| Vial size | 10mg | 10mg |
Research Applications
Melanotan II is used in pigmentation research (MC1R/melanogenesis pathway), energy balance studies, and broad melanocortin system investigations. Its MC1R activity makes it the primary compound for studying the melanocortin system’s role in skin biology. PT-141 is used in HPG axis research and central melanocortin pathway studies where pigmentation effects would confound endpoints. PT-141’s FDA-approved status as Vyleesi provides extensive published clinical data for research reference.
Laboratory Considerations
Both peptides are lyophilized and reconstituted with bacteriostatic water. Melanotan II must be protected from light during reconstitution and storage — amber vials or foil wrapping are recommended. Both are sensitive to oxidation; reconstituted solutions should be stored at 4°C and used within 3–4 weeks. Do not vortex. The 10mg vial size for both reflects higher dosing requirements in animal studies relative to other peptides in the melanocortin class.
Research Disclaimer: All compounds discussed are intended exclusively for laboratory and research purposes. This content is not medical advice. Bastion Peptides products are not approved for human use, consumption, or therapeutic application.
