Maple Melanotan vs PT-141 research centers on melanocortin receptor selectivity. Melanotan I (afamelanotide) is a linear alpha-MSH analogue with preference for MC1R, Melanotan II is a cyclic analogue active across MC1R, MC3R, MC4R and MC5R, and PT-141 (bremelanotide) is a related cyclic analogue studied mainly at MC3R and MC4R in preclinical models. For research purposes only. Not for human consumption. Not for diagnostic or therapeutic use.
Research comparison of melanocortin system peptides: Melanotan I (afamelanotide), Melanotan II, and PT-141 (bremelanotide). Covers the five melanocortin receptors (MC1R-MC5R), structural differences between linear and cyclic analogues, receptor selectivity profiles, and the relationship between these compounds.
The Melanocortin Receptor System
The melanocortin system consists of five G protein-coupled receptors (MC1R through MC5R) that are activated by endogenous peptides derived from proopiomelanocortin (POMC) processing, primarily alpha-MSH. Each receptor has a distinct tissue distribution and functional profile:
| Receptor | Primary Location | Function | Key Agonist |
|---|---|---|---|
| MC1R | Melanocytes (skin, hair follicles) | Melanogenesis (eumelanin production), UV-protective pigmentation | MT-I (afamelanotide) |
| MC2R | Adrenal cortex | Cortisol synthesis (ACTH receptor) | ACTH only |
| MC3R | Hypothalamus, GI tract | Energy homeostasis, feeding behavior | Gamma-MSH |
| MC4R | Hypothalamus, brainstem, spinal cord | Appetite regulation, energy expenditure, autonomic/sexual function | PT-141 (bremelanotide) |
| MC5R | Exocrine glands, adipose tissue | Sebaceous gland regulation, immune function | Alpha-MSH |
Three Compounds, One System
Melanotan I, Melanotan II, and PT-141 are structurally related but pharmacologically distinct. PT-141 is actually a metabolite of Melanotan II, discovered when researchers observed that MT-II’s melanocortin effects included CNS-mediated signaling through MC4R that was independent of its pigmentation effects via MC1R.
| Parameter | Melanotan I (Afamelanotide) | Melanotan II | PT-141 (Bremelanotide) |
|---|---|---|---|
| Structure | Linear 13-amino acid peptide | Cyclic 7-amino acid peptide (lactam bridge) | Cyclic 7-amino acid peptide (free acid C-terminus) |
| Derived From | Alpha-MSH analogue (linear) | Alpha-MSH core with cyclization | Active metabolite of Melanotan II |
| Receptor Selectivity | MC1R-preferring (relatively selective) | Non-selective (MC1R, MC3R, MC4R, MC5R) | MC4R-preferring (MC3R, MC4R) |
| Primary Research Activity | Melanogenesis (pigmentation) | Melanogenesis + MC4R CNS effects | MC4R CNS-mediated signaling |
| Pigmentation Effect | Strong (EMA-approved for this purpose) | Strong | Weak to moderate |
| CNS MC4R Activity | Minimal (poor BBB penetration, MC1R preference) | Significant | Primary mechanism |
| Regulatory Status | EMA approved (Scenesse, 2014, erythropoietic protoporphyria) | Research only | FDA approved (Vyleesi, 2019) |
| Key Structural Feature | Linear (no lactam bridge) | Lactam bridge (Asp5-Lys10), amide C-terminus | Lactam bridge, free acid C-terminus (from MT-II metabolism) |
Linear vs Cyclic: Why Structure Determines Selectivity
The structural difference between MT-I (linear) and MT-II/PT-141 (cyclic) directly determines receptor selectivity:
Melanotan I retains the linear peptide structure of alpha-MSH, which gives it relatively selective MC1R binding. The linear conformation presents the pharmacophore (His-Phe-Arg-Trp core) in an orientation that preferentially engages MC1R’s binding pocket. This MC1R selectivity is why MT-I’s primary effect is pigmentation without significant CNS signaling.
Melanotan II and PT-141 contain a lactam bridge that constrains the peptide into a cyclic conformation. This cyclization locks the His-Phe-Arg-Trp pharmacophore into a more rigid orientation that engages multiple melanocortin receptor subtypes, particularly MC4R. The cyclic structure increases metabolic stability (resistance to peptidases) and alters receptor selectivity from MC1R-preferring to broadly active (MT-II) or MC4R-preferring (PT-141).
Cardiovascular and Autonomic Considerations
MC4R activation in the central nervous system engages autonomic signaling pathways, which has implications for cardiovascular parameters in research settings. PT-141 (bremelanotide) produces transient increases in blood pressure and decreases in heart rate in preclinical and clinical studies. This autonomic activation is a direct consequence of central MC4R signaling, not a peripheral vascular effect, and is unique to the MC4R-active compounds (MT-II and PT-141) but not MC1R-selective compounds (MT-I).
Research Selection Guide
| Research Focus | Recommended | Rationale |
|---|---|---|
| MC1R/melanogenesis pathway | Melanotan I | MC1R-preferring, minimal MC4R confounding |
| MC4R CNS signaling | PT-141 | MC4R-preferring, FDA-approved reference |
| Broad melanocortin system | Melanotan II | Non-selective, activates MC1R + MC3R + MC4R + MC5R |
| Pigmentation without CNS effects | Melanotan I | Linear structure, poor BBB penetration |
| Autonomic/cardiovascular MC4R effects | PT-141 | Cleanest MC4R signal, clinical BP/HR data available |
| Structure-activity relationships | All three | Linear vs cyclic comparison, free acid vs amide C-terminus |
Research Products
Available at Maple Research Labs
Third-party COA verification | Same-day dispatch by 2 PM PT, Mon–Fri
Melanotan 1 10MG |
Melanotan 2 10MG |
PT-141
Deep-Dive Research Pages
Melanotan (Melanocortin System) Research | MT-I vs MT-II, full MC receptor pharmacology
PT-141 (Bremelanotide) Research | MC4R mechanism, CNS signaling, FDA approval data
Frequently Asked Questions
What is the difference between Melanotan 1 and Melanotan 2?
Melanotan I is a linear 13-amino acid peptide that preferentially activates MC1R (the melanogenesis receptor), producing pigmentation effects with minimal CNS signaling. Melanotan II is a cyclic 7-amino acid peptide with a lactam bridge that activates multiple melanocortin receptors non-selectively (MC1R, MC3R, MC4R, MC5R), producing both pigmentation and CNS-mediated effects via MC4R. The structural difference (linear vs cyclic) is what determines their different receptor selectivity profiles.
What is the relationship between Melanotan II and PT-141?
PT-141 (bremelanotide) is an active metabolite of Melanotan II. When MT-II is processed enzymatically, its C-terminal amide is converted to a free acid, producing PT-141. This metabolite retains the cyclic structure and MC4R activity but has shifted receptor preference toward MC4R and away from MC1R. PT-141 was developed as a standalone compound after researchers recognized that MT-II’s CNS-mediated effects via MC4R were pharmacologically distinct from its pigmentation effects via MC1R.
Where can I buy melanocortin peptides for research in Canada?
Maple Research Labs supplies Melanotan 1, Melanotan 2, and PT-141 within Canada, with third-party purity verification via HPLC and mass spectrometry. All products include batch-specific COAs. Orders placed by 2 PM PT (Mon–Fri) ship the same business day, from BC with tracking. These compounds are supplied exclusively for in-vitro and preclinical research use.
For peer-reviewed research on this topic, visit PubMed.
Related research resources: research documentation, batch Certificates of Analysis and Melanotan I vs Melanotan II pharmacology.