A practical reference on MC4R: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-10-08. Anything still debated is marked as such rather than presented as settled.
The molecular backbone consists of seven amino acid residues joined into a ring through a disulfide bridge. This cyclic conformation is critical for receptor binding. The sequence includes an acetylated N-terminus and an amidated C-terminus, modifications that improve resistance to enzymatic breakdown. One residue is in the D-configuration, a feature that further stabilizes the peptide against protease activity. Together, the ring structure and specific stereochemistry determine selectivity among melanocortin receptor subtypes.
Across literature and commercial listings, the substance appears under several names, including bremelanotide, PT-141, and various brand designations. A CAS registry number provides a unique identifier for the compound, aiding retrieval from chemical databases. Synonym lists may also contain early development codes and descriptive chemical names. When consulting sources, researchers need to confirm that the cited names refer to the same molecular structure to avoid confusion. Naming consistency matters especially when comparing analytical data across publications.
PT-141 is a synthetic cyclic heptapeptide whose development code is bremelanotide. It belongs to the class of melanocortin receptor agonists and acts by mimicking endogenous peptide hormones. The compound originated from research on melanotan II, where investigators exploring derivatives found distinct pharmacological features. Unlike the parent compound, PT-141 showed effects on pathways related to sexual desire and function in early studies, prompting its development as a separate candidate. Its molecular design aimed to separate receptor activity from pigmentary effects.
How receptor activation translates into a change in desire is not established in detail. Proposed steps include modulation of dopaminergic signalling in reward circuits and downstream effects on autonomic tone. Human data consist mainly of clinical trials measuring self-reported outcomes rather than direct measurements of brain activity or transmitter release. The transient rise in blood pressure sometimes observed after administration is likewise reported consistently but explained only partly by known melanocortin pathways.
Melanocortin receptors form a family of five G-protein-coupled proteins, labelled MC1R through MC5R, that respond to peptides derived from pro-opiomelanocortin. Alpha-melanocyte-stimulating hormone and adrenocorticotropic hormone are the best-known endogenous ligands. The receptors are distributed differently across tissues, so a single agonist can produce effects in the brain, skin, adrenal gland and vasculature. This distribution explains why one peptide can influence both pigmentation and motivated behaviour.
Bremelanotide is a cyclic heptapeptide that binds several melanocortin receptors rather than one. In vitro assays report agonist activity at MC1R, MC3R, MC4R and MC5R, with MC4R generally treated as the subtype most relevant to sexual effects. MC4R is expressed in hypothalamic nuclei involved in appetite, energy balance and motivated behaviour, which provides a plausible route for central action. Selective MC4R agonists studied in animals produce comparable behavioural changes, supporting that interpretation.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Cyclic peptide | Melanocortin receptor agonist family |
| Molecular weight | Approximately 1025 Da | Free base form |
| Appearance | White to off-white powder | Lyophilized product |
| Solubility | Soluble in water | Also dissolves in polar organic solvents |
| Storage temperature | -20 degrees Celsius | Dry and protected from light |
After subcutaneous administration, plasma concentrations rise within roughly thirty minutes and the elimination half-life is short, on the order of two to three hours. Reported physiological responses include transient increases in blood pressure and nausea, which tended to diminish with repeated dosing in trial settings. Because the peptide clears quickly, effects are not expected to persist long after a dose. Absorption from non-injected routes is poorly characterised, and nasal delivery produced variable plasma levels in older work.
Clinical research typically uses randomised, double-blind, placebo-controlled designs. The most common primary endpoint is the desire domain score of the Female Sexual Function Index, sometimes paired with a distress measure. Secondary outcomes include arousal, satisfaction, and event-based counts of satisfying sexual episodes. Across trials, average improvements are modest and individual responses vary widely. Whether benefits persist beyond a few months, and whether they depend on baseline hormone status, remain open questions rather than settled findings.
Identity and purity testing for this peptide typically relies on reversed-phase high-performance liquid chromatography with ultraviolet detection, reported as area-percent purity. Mass spectrometry, usually in tandem mode, confirms molecular mass and supports quantification in biological matrices. Sequence confirmation may use peptide mapping after enzymatic digestion, while nuclear magnetic resonance and circular dichroism supply supplementary structural detail. No single technique establishes identity alone, so laboratories compare retention time, mass, and fragment pattern against a verified reference standard.
The lactam ring that closes the peptide backbone improves resistance to exopeptidase attack, but the molecule stays susceptible to hydrolysis and oxidation once dissolved. Degradation accelerates with temperature, extreme pH, and light exposure, and repeated freeze-thaw cycles promote aggregation and material loss. Lyophilized powder held desiccated at or below minus twenty degrees Celsius is the common way to keep reference material. Reconstituted solutions are generally kept cold and used within a short window because their stability is far lower than that of the dry solid.
Early research on PT-141 grew out of work on melanotan II, a related cyclic peptide studied for pigmentation. Investigators observed that centrally acting melanocortin agonists also influenced sexual behaviour in animal models, and the programme shifted toward that endpoint. A nasal formulation was evaluated in clinical trials but showed inconsistent absorption, and later studies used subcutaneous administration instead. Regulatory approval in the United States followed in 2019 for a defined population of premenopausal women with acquired, generalised hypoactive sexual desire disorder. That approval was specific to that group rather than a broad indication.
Bremelanotide acts as a non-selective agonist at melanocortin receptors, with reported activity at MC1R, MC3R, MC4R and MC5R. The proposed basis for its central effects is activation of MC4R populations in the hypothalamus, a region associated with appetite and reproductive signalling. Because the peptide carries a net positive charge and polar side chains, it does not cross biological membranes freely, which is one reason oral administration is not the standard route. Effects generally appear within an hour of parenteral administration and are described as centrally mediated rather than peripheral.
Bremelanotide, developed under the code PT-141, is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone. Its structure is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, with a lactam bridge joining the aspartate and lysine side chains. The molecule has the formula C50H68N14O10 and a monoisotopic mass near 1025 daltons. It is commonly prepared as the acetate salt and appears as a white to off-white lyophilised powder in solid form. The free acid is the pharmacologically relevant species, while the counter-ion improves handling and dissolution.
=== Lebanon === The Parliament of Lebanon is the Lebanese national legislature. It is elected to a four-year term by universal adult suffrage in multi-member constituencies, apportioned among Lebanon's diverse Christian and Muslim denominations. Its major functions are to elect the president of the republic, to approve the government (although appointed by the president, the prime minister, along with the Cabinet, must retain the confidence of a majority in the Parliament), and to approve laws and expenditure. The name of a deputy in Arabic is Naeb (نائب). The plural of Naeb is Nuwab (نواب).
This is caused by an atheroma or plaque in the artery wall and is a build-up of cell debris, that contain lipids, (cholesterol and fatty acids), calcium and a variable amount of fibrous connective tissue. Accidental intra-arterial injection either iatrogenically or through recreational drug use can cause symptoms such as intense pain, paresthesia and necrosis. It usually causes permanent damage to the limb; often amputation is necessary.
== Clinical trials == Clinical trials for muscular dystrophy have not proven successful in generating functional improvements compared to placebo. Gains of muscle mass were small to non-existent in this population. Research is ongoing on the potential use of myostatin inhibitors for motor neuron diseases like spinal muscle atrophy and amyotrophic lateral sclerosis. Due to myostatin's effect as a negative regulator of bone, its inhibition has also been considered for orthopedic diseases such as rheumatoid arthritis. Myostatin inhibitors were generally able to increase lean body mass and reduce body fat in people with sarcopenia, but the extent to which this translated into functional improvements varied. Bimagrumab showed effectiveness in increasing lean mass and reducing fat mass in obese individuals in a clinical trial.
== History == 1979-1988: Research scientist and Senior research scientist of First Institute of Biochemistry, Semmelweis University Medical School and Hungarian Academy of Sciences 1988-1994: Head of Peptide Research Laboratory, Associate Professor of Biochemistry, Joint Research Organization of the Hungarian Academy of Sciences and Semmelweis University Medical School, The First Institute of Biochemistry 1994-2008: Head of Peptide Biochemistry Research Group and Rational Drug Design Laboratory, Professor of Biochemistry, Department of Medicinal Chemistry, Semmelweis Medical University 1992-1999: Scientific advisor of Sugen 1999-2005: Scientific advisor of Axxima Pharmaceuticals 1999–present: CEO and CSO of Vichem Chemie Research Ltd. 2001-2012: Chairman of Rational Drug Design Laboratories Co-operation Research Center, Semmelweis University 2002-2008: Curator of Office for Subsidised Research Units of Hungarian Academy of Sciences 2008-2012: Head of Signal Transduction Therapy Laboratory at Semmelweis University 2012–present: Head of Pathobiochemistry Research Group of Hungarian Academy of Sciences at Semmelweis University, Department of Medical Chemistry
==== Reticular region ==== The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue, and receives its name from the dense concentration of collagenous, elastic, and reticular fibres that weave throughout it. These protein fibres give the dermis its properties of strength, extensibility, and elasticity. Also located within the reticular region are the roots of the hairs, sebaceous glands, sweat glands, receptors, nails, and blood vessels. Tattoo ink is held in the dermis. Stretch marks, often from adolescent growth spurts, weight gain, pregnancy and obesity, are also located in the dermis.
Sources: en.wikipedia.org
Studies show that the EPOC effect exists after both aerobic exercise and anaerobic exercise. In a 1992 Purdue study, results showed that high intensity, anaerobic type exercise resulted in a significantly greater magnitude of EPOC than aerobic exercise of equal work output. For exercise regimens of comparable duration and intensity, aerobic exercise burns more calories during the exercise itself, but the difference is partly offset by the higher increase in caloric expenditure that occurs during the EPOC phase after anaerobic exercise. Anaerobic exercise in the form of high-intensity interval training was also found in one study to result in greater loss of subcutaneous fat, even though the subjects expended fewer than half as many calories during exercise. Whether this result was caused by the EPOC effect has not been established, and the caloric content of the participants' diet was not controlled during this particular study period. Most researchers use a measure of EPOC as a natural part of the quantification or measurement of exercise and recovery energy expenditure; to others this is not deemed necessary. After a single bout or set of weight lifting, Scott et al. found considerable contributions of EPOC to total energy expenditure. In their 2004 survey of the relevant literature, Meirelles and Gomes found: "In summary, EPOC resulting from a single resistance exercise session (i.e., many lifts) does not represent a great impact on energy balance; however, its cumulative effect may be relevant".
== Paralogs == Escherichia coli (E. coli) expresses two different forms of shikimate dehydrogenase, AroE and YdiB. These two forms are paralogs of each other. The two forms of shikimate dehydrogenase have different primary sequences in different organisms but catalyze the same reactions. There is about 25% similarity between the sequences of AroE and YdiB, but their two structures have similar structures with similar folds. YdiB can utilize NAD or NADP as a cofactor and also reacts with quinic acid. They both have high affinity of their ligands as shown by their similar enzyme (Km) values. Both forms of the enzyme are independently regulated.
=== Partial === Partial tears are seemingly even less common than complete tears. They are more likely to arise from overuse from activities like daily running. The bottom of the foot may be swollen or bruised.
== Contraindications == Methamphetamine is contraindicated in individuals with a history of substance use disorder, heart disease, or severe agitation or anxiety, or in individuals currently experiencing arteriosclerosis, glaucoma, hyperthyroidism, or severe hypertension. The FDA states that individuals who have experienced hypersensitivity reactions to other stimulants in the past or are currently taking monoamine oxidase inhibitors should not take methamphetamine. The FDA also advises individuals with bipolar disorder, depression, elevated blood pressure, liver or kidney problems, mania, psychosis, Raynaud's phenomenon, seizures, thyroid problems, tics, or Tourette syndrome to monitor their symptoms while taking methamphetamine. Owing to the potential for stunted growth, the FDA advises monitoring the height and weight of growing children and adolescents during treatment.
Sources: en.wikipedia.org
It belongs to the melanocortin receptor agonist family of peptides. Its cyclic structure distinguishes it from linear peptides and shapes its receptor binding profile.
It emerged from research on melanotan II. Investigators exploring derivatives observed distinct pharmacological features related to sexual function.
Common names include bremelanotide and PT-141. Chemical databases may also list early development codes and descriptive names.
Bremelanotide binds several melanocortin receptors, and MC4R is the subtype most often cited as responsible for its behavioural effects. Activity at MC1R, MC3R and MC5R is also reported. Selectivity is therefore described as limited rather than precise.