melanocortin receptor raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2025-11-13 and is reviewed periodically as new material appears.
Melanotan II is a synthetic cyclic heptapeptide that acts as an agonist at melanocortin receptors. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, the endogenous peptide involved in pigment production. The analogue carries a lactam bridge that constrains the ring and slows enzymatic breakdown relative to the native hormone. In research literature it appears under several abbreviations, and naming conventions are not fully standardized. Published descriptions usually place it within the broader melanocortin agonist family.
Receptor binding at MC1R on melanocytes raises intracellular cyclic AMP and increases expression of tyrosinase and related enzymes. The downstream result is greater synthesis of eumelanin, the dark pigment, without ultraviolet exposure acting as the trigger. The compound is not selective, however, and also engages MC3R, MC4R and MC5R, which are expressed in the central nervous system and elsewhere. That lack of selectivity is the explanation usually offered for effects reported outside pigmentation, including appetite suppression and nausea. Selectivity remains a central theme in comparative studies of related peptides.
Human data remain limited and mostly short-term. Reports describe small trials and observational accounts rather than large controlled studies, so questions about dose-response relationships and long-term effects on melanocytes stay open. Whether repeated exposure alters naevus behaviour is not settled in the published record. Researchers also note that self-administered use outside clinical settings makes actual exposure difficult to quantify. Statements about efficacy and safety should therefore be read as preliminary rather than established.
Lyophilised melanotan-2 is supplied as a solid, which is more stable than a solution. The material is hygroscopic, so weighing is done quickly, in low humidity, with the container kept sealed. Reconstitution usually uses water for injection or bacteriostatic water, added down the wall of the vial to limit foaming. A reconstituted solution is held at 2 to 8 °C and kept away from light. Repeated freezing and thawing of the same vial is avoided because ice crystal formation and concentration effects degrade the peptide.
Reversed-phase high-performance liquid chromatography is the routine method for purity assessment. Peptides absorb near 214 nm because of the peptide bond, and a gradient of acetonitrile in water separates the intact peptide from deletion sequences, oxidised products, and earlier-eluting fragments at neutral pH. Electrospray ionisation mass spectrometry provides an orthogonal check: the measured mass must agree with the theoretical value. Amino acid analysis and peptide mapping confirm structure but are used less often. Reference standards remain scarce because the peptide is not described in any pharmacopoeia.
Regulatory treatment varies by country. In the United States the peptide is not approved as a medicine, and products offered for human use may be treated as unapproved new drugs; some states also restrict sale. Australia, the United Kingdom, and European Union member states apply comparable restrictions to unapproved peptide products. Border agencies have seized shipments labelled as research chemicals. Classification may change over time, and the legal position for personal importation is not clearly settled in most published guidance.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic cyclic heptapeptide | Melanocortin receptor agonist |
| Molecular formula | C50H69N15O9 | Neutral form, mass near 1024.2 g/mol |
| Primary targets | MC1R, MC3R, MC4R, MC5R | Binding is non-selective across subtypes |
| Related compounds | Alpha-MSH, melanotan I, afamelanotide | Structurally or functionally related peptides |
| Common abbreviations | MT-II, MT-2 | Naming in the literature is not uniform |
Melanotan-2, also written Melanotan II, is a synthetic cyclic heptapeptide designed as an analogue of alpha-melanocyte-stimulating hormone. Its sequence is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, and the lactam bridge between the aspartate and lysine side chains constrains the peptide into a ring. This structural change increases receptor affinity and metabolic stability relative to the native hormone. The compound was created in the 1980s as a research tool for studying pigmentation biology.
Melanocytes are the pigment-producing cells of the skin, and they carry melanocortin-1 receptors on their surface. When the receptor is activated, cyclic adenosine monophosphate rises inside the cell and raises the activity of enzymes such as tyrosinase, which increases melanin output. Melanotan-2 binds melanocortin-1 receptors in vitro and in animal models, and this binding is generally described as the basis for the tanning effect. Other receptors account for different effects: melanocortin-4 receptors contribute to appetite and erectile signalling, while melanocortin-3 and melanocortin-5 receptors contribute to energy balance and exocrine function.
Lyophilized peptide powder is generally stored frozen, protected from light and moisture. Tryptophan residues are susceptible to oxidation, and the lactam bridge can hydrolyze under strongly acidic or basic conditions. Solutions prepared for laboratory work degrade faster than dry powder, and repeated freeze-thaw cycles accelerate loss. Common practice is to aliquot solutions before freezing and to avoid alkaline buffers. Reported stability windows vary with concentration, buffer, and temperature, so exact shelf lives are method-specific rather than universal.
Regulatory status differs by country, and in many places supplying the compound for human consumption is unlawful. Vendors frequently label material as intended for research use only, a designation that shifts stated purpose but does not create a legal pathway for personal use. Certificates of analysis accompanying such products vary widely in detail and provenance. Third-party testing exists but is voluntary, and results are rarely linked to a specific lot in a publicly verifiable way.
==== Intact ring system ==== Steroids can be classified based on their chemical composition. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples of this classification include:
=== Foreign policy === Moore supports Israel's right to defend itself and a two-state solution to the Israeli–Palestinian conflict. In December 2022, he attended the Jewish Community Relations Council of Greater Washington's legislative breakfast, where he said he would be "very aggressive" in promoting trade between Maryland and Israel and promised that one of his first overseas visits would be to Israel. He expressed solidarity with Israel amid the October 7 attacks, and later supported an immediate ceasefire in the Gaza war. In October 2024, Moore criticized a Students for Justice in Palestine event at the University of Maryland, College Park held on the one-year anniversary of the October 7 attack to honor Palestinian civilians killed in the Gaza war, saying that he felt that it was an "inappropriate date for such an event". In May 2026, Moore told Politico that he believed Israeli Prime Minister Benjamin Netanyahu had committed war crimes in the Gaza war, citing his use of food as a negotiating tool. In April 2026, Moore criticized U.S. involvement in the 2026 Iran war, likening it to the war in Afghanistan and fearing it would evolve into "another forever war". He also criticized President Donald Trump for not clearly addressing the American people on what the U.S. is doing in Iran or what success looks like.
Partial smooth muscle differentiation of a fibroblastic cell Activation of a stellate cell (e.g. hepatic Ito cells or pancreatic stellate cells). Loss of contractile phenotype (or acquisition of "synthetic phenotype") of a smooth muscle cell. Direct myofibroblastic differentiation of a progenitor cell resident in a stromal tissue. Homing and recruitment of a circulating mesenchymal precursor which can directly differentiate as above or indirectly differentiate through the other cell types as intermediates. Epithelial to mesenchymal transdifferentiation (EMT) of an epithelial cell. Perhaps the most studied pathway of myofibroblast formation is TGF-beta1 dependent differentiation from fibroblast cells. Activation of the TGF-beta receptor 1 and TGF-beta receptor 2 leads to induction of the canonical SMAD2/SMAD3 pathway. Together with the co-activation of the non-canonical EGFR pathway, these events lead to upregulation of the ACTA2 gene and subsequent alpha smooth muscle actin protein production. Several regulators of the myofibroblast differentiation pathway have been described, including hyaluronan and CD44 co-receptor activation of EGFR.
Sources: en.wikipedia.org
John Lilley states, "...neutron-induced fission generates extra neutrons which can induce further fissions in the next generation and so on in a chain reaction. The chain reaction is characterized by the neutron multiplication factor k, which is defined as the ratio of the number of neutrons in one generation to the number in the preceding generation. If, in a reactor, k is less than unity, the reactor is subcritical, the number of neutrons decreases and the chain reaction dies out. If k > 1, the reactor is supercritical and the chain reaction diverges. This is the situation in a fission bomb where growth is at an explosive rate. If k is exactly unity, the reactions proceed at a steady rate and the reactor is said to be critical. It is possible to achieve criticality in a reactor using natural uranium as fuel, provided that the neutrons have been efficiently moderated to thermal energies." Moderators include light water, heavy water, and graphite. According to John C. Lee, "For all nuclear reactors in operation and those under development, the nuclear fuel cycle is based on one of three fissile materials, 235U, 233U, and 239Pu, and the associated isotopic chains. For the current generation of LWRs, the enriched U contains 2.5~4.5 wt% of 235U, which is fabricated into UO2 fuel rods and loaded into fuel assemblies." Lee states, "One important comparison for the three major fissile nuclides, 235U, 233U, and 239Pu, is their breeding potential.
=== Preclinical === AB-300 (AB300) – non-hallucinogenic serotonin 5-HT2A and 5-HT2C receptor agonist AB-5006 (AX-5006) – Escherichia coli csgA protein aggregation inhibitor and gastrointestinal microbiome modulator [96] AEX-23 – orexin OX1 receptor agonist and α-synuclein aggregate/modulator [97] Afamelanotide ([Nle4,DPhe7]-α-MSH; CUV-1647; EPT-1647; Melanotan I; Melanotan; MT-I; Prenumbra; Scenesse) – melanocortin receptor agonist [98] Alpha-synuclein aggregation inhibitor (ACI-5755; morphomer α-synuclein) – α-synuclein inhibitor [99] BEBT-758 – RNA interference and α-synuclein expression inhibitor [100] Bevemipretide (SBT-272) – cardiolipin ligand and stabilizer [101] BSC-3301 – receptor-interacting serine/threonine-protein kinase 1 (RIPK1) inhibitor [102] BXQ-350 (SapC; SapC-DOPS; sphingolipid activator protein C) – sphingomyelin phosphodiesterase stimulant and sphingosine 1-phosphate stimulant [103] Cannabidiol (CBD) – cannabinoid receptor modulator and other actions [104] Carbon monoxide (CO; HBI-002) – heme oxygenase 1 modulator [105] CB-401 – amyloid β-protein modulator [106] CBT-102 – undefined mechanism of action [107] CJRB-301 (MRx-0005) – bacteria replacement and microbiome modulator [108] CJRB-302 (MRx-0029) – bacteria replacement and microbiome modulator [109] CK-0803 – regulatory T-lymphocyte replacement [110] CU-13001 – 15-lipoxygenase (15-LOX/ALOX15) inhibitor [111] EHP-102 (VCE-003.2) – cannabinoid CB2 receptor agonist and peroxisome proliferator-activated receptor alpha (PPARα) modulator (cannabigerol (CBG) derivative) [112] Estianeptine ((S)-tianeptine; TNX-4300) – peroxisome proliferator-activated receptor PPARβ/δ and PPARγ agonist [113] FHL-401 – toll-like receptor 2 antagonist [114] FHL-701 – interleukin-12 (IL-12) subunit p40 inhibitor [115] FKK-01PD (FKK-01PD; TGHW-01AP; apomorphine prodrug) – non-selective dopamine receptor agonist and other actions [116] HT-4403 – leucine-rich repeat kinase 2 (LRRK2) inhibitor [117] IC-100 (ICCN-100) – various actions [118] KFRX-05 (BK-40195) – leucine-rich repeat kinase 2 (LRRK2) inhibitor and protein tyrosine kinase inhibitor [119] KP-405 – undefined mechanism of action [120] LB-P4 – bacteria replacement and microbiome modulator [121] Mbiotix – bacteria replacement and microbiome modulator [122] ML-021 – muscarinic acetylcholine M4 receptor antagonist [123] MP-201 – 2,4-dinitrophenol (DNP) prodrug and various actions [124] NB-003 – gene transference and parkin protein replacement [125] NB-129 – undefined mechanism of action [126] NLY-02 – glial cell inhibitor [127] NLY-03 – undefined mechanism of action [128] NNI-362 – 70 kDa ribosomal protein S6 kinase modulator [129] NRG-5051 – mitochondrial permeability transition pore inhibitor [130] PMN-442 – monoclonal antibody against α-synuclein [131] PP-003 – α-synuclein degrader [132] Research programme: 3100 programme - DigmBio/Daegu Catholic University – G protein-coupled receptor (GPCR) modulators [133] Research programme: enzyme targeted therapeutics - Nitrase Therapeutics – enzyme modulators and α-synuclein inhibitors [134] Research programme: neurodegenerative disease therapeutics - Caraway Therapeutics – autophagy stimulants and MCOLN1 stimulants [135] RGL-193 – undefined mechanism of action [136] ST-502 – gene therapy and α-synuclein genetic transcription inhibitor [137] Tomaralimab (NM-101; NM-102; NM-103; OPN-305) – monoclonal antibody against toll-like receptor 2 [138] Zervimesine (CT-1812; Elayta) – sigma σ2 receptor antagonist [139]
This time, the internet amplified the proposition and spawned a hundred frauds and scams. However, their adoption of the "HGH" term has provided an easy way to distinguish the hype from the evidence. In 2003, growth hormone hit the news again, when the US FDA granted Eli Lilly approval to market Humatrope for the treatment of idiopathic short stature. The indication was controversial for several reasons, the primary one being the difficulty in defining extreme shortness with normal test results as a disease rather than the extreme end of the normal height range Recombinant growth hormone available in the U.S. (and their manufacturers) include Nutropin (Genentech), Humatrope (Eli Lilly and Company), Genotropin (Pfizer), Norditropin (Novo Nordisk), Tev-Tropin (Teva) and Saizen (Merck Serono). The products are nearly identical in composition, efficacy, and cost, varying primarily in the formulations and delivery devices. Somapacitan-beco (Sogroya) is the first once-per week subcutaneous human growth hormone (hGH) therapy that was approved in the United States. It was approved for medical use in the United States in August 2020.
Sources: en.wikipedia.org
== Nazi Germany (1933–1945) == Soon after Adolf Hitler was appointed as chancellor in 1933, the German Reichstag (parliament) passed the Enabling Act (German: Ermächtigungsgesetz), officially titled "Law for Removing the Distress of People and Reich" (German: Gesetz zur Behebung der Not von Volk und Reich), which effectively gave the chancellor the power of a dictator. This event marked the end of the Weimar Republic and the beginning of Nazi Germany. Hitler thereupon destroyed all democratic systems and consolidated all power to himself. After the death of president Paul von Hindenburg in 1934, Hitler merged the offices of chancellor and president in his own person and called himself Führer und Reichskanzler. Political parties: NSDAP
== S == Sac6 Sla1p Srv2 (CAP) S-adenosyl-L-homocysteine hydrolase, (SAHH) Sla2p Synaptopodin Scinderin (adseverin) Synapsins Scruin Spectrin Severin Spectraplakins SVSII Shot (Short stop) Spire Shroom Smitin (Smooth Musc.Titin) Supervillin SipA Smoothelin Sucrose synthetase SipC Sra-1 Spinophilin Ssk2p Swinholide
Until the Renaissance, the vast majority of drugs in Western medicine were plant-derived extracts. This has resulted in a pool of information about the potential of plant species as important sources of starting materials for drug discovery. Botanical knowledge about different metabolites and hormones that are produced in different anatomical parts of the plant (e.g. roots, leaves, and flowers) are crucial for correctly identifying bioactive and pharmacological plant properties. Identifying new drugs and getting them approved for market has proved to be a stringent process due to regulations set by national drug regulatory agencies.
A number of former Wildcats have gone on to pursue successful professional NBA careers (especially during the Lute Olson era), including Gilbert Arenas, Richard Jefferson, Mike Bibby, Jason Terry, Sean Elliott, Damon Stoudamire, Khalid Reeves, Luke Walton, Hassan Adams, Salim Stoudamire, Andre Iguodala, Channing Frye, Brian Williams (later known as Bison Dele), Sean Rooks, Jud Buechler, Michael Dickerson, Chase Budinger, Jordan Hill, Jerryd Bayless, Derrick Williams, Kadeem Allen, Aaron Gordon, Solomon Hill, Rondae Hollis-Jefferson, Stanley Johnson, T.J McConnell, Lauri Elias Markkanen, Kobi Simmons, Steve Kerr, Deandre Ayton, Rawle Alkins, and Allonzo Trier. Kenny Lofton, now best known as a former Major League Baseball star, was a four-year letter winner as a Wildcat basketball player (and was on the 1988 Final Four team), before one year on the Arizona baseball team. Another notable former Wildcat basketball player is Eugene Edgerson, who played on the 1997 and 2001 Final Four squads, and spent some of his professional careers as one of the Harlem Globetrotters as "Wildkat" Edgerson.
Sources: en.wikipedia.org
It is a synthetic cyclic heptapeptide and a non-selective melanocortin receptor agonist. Structurally it is modelled on alpha-melanocyte-stimulating hormone, a peptide that occurs naturally in the body.
Activation of MC1R increases pigment synthesis independently of ultraviolet exposure, which is the mechanism usually cited for darkening without sun exposure. Ultraviolet light still influences skin response through separate biological pathways.
Because the peptide binds several melanocortin receptor subtypes, its effects are not confined to pigmentation. This complicates interpretation of both intended and unintended outcomes reported in studies.
Low temperature slows hydrolysis and oxidation, the two main routes by which the peptide backbone and side chains are modified. A lyophilised powder stored at −20 °C is more stable than one kept at room temperature, and once the material is dissolved the degradation rate rises, making refrigeration more important.