Melanocyte-stimulating hormone
From Wikipedia, the free encyclopedia
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proopiomelanocortin (adrenocorticotropin/ beta-lipotropin/ alpha-melanocyte stimulating hormone/ beta-melanocyte stimulating hormone/ beta-endorphin)
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| Identifiers | |
| Symbol | POMC |
| Entrez | 5443 |
| HUGO | 9201 |
| OMIM | 176830 |
| RefSeq | NM_000939 |
| UniProt | P01189 |
| Other data | |
| Locus | Chr. 2 p23 |
The melanocyte-stimulating hormones (collectively referred to as MSH) are a class of peptide hormones produced by cells in the intermediate lobe of the pituitary gland.
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[edit] Function
They stimulate the production and release of melanin (melanogenesis) by melanocytes in skin and hair. MSH is also produced by a subpopulation of neurons in the arcuate nucleus of the hypothalamus. MSH released into the brain by these neurons has effects on appetite and sexual arousal.
[edit] In amphibians
In some animals (such as the claw-toed frog Xenopus laevis) production of MSH is increased when the animal is in a dark location. This causes pigment to be dispersed in pigment cells in the toad's skin, making it become darker, and harder for predators to spot. The pigment cells are called melanophores and therefore, in amphibians, the hormone is often called melanophore-stimulating hormone.
[edit] In humans
An increase in MSH will cause a darkening in humans too. Melanocyte-stimulating hormone increases in humans during pregnancy. This, along with increased estrogens, causes increased pigmentation in pregnant women. In Addison's disease high levels of adrenocorticotropic hormone (ACTH) production also leads to high MSH levels, which cause an abnormal darkening.
Different levels of MSH are not the major cause of racial variation in skin colour. In many red headed people, and other people who do not tan well, there are variations in their hormone receptors, causing them to not respond to MSH in the blood.
See: Melanocortin receptor.
[edit] Structure of MSH
Melanocyte-stimulating hormone belongs to a group called the melanocortins. This group includes ACTH, alpha-MSH, beta-MSH and gamma-MSH; these peptides are all cleavage products of a large precursor peptide called pro-opiomelanocortin (POMC). Alpha-MSH is the most important melanocortin for pigmentation.
The different melanocyte-stimulating hormones have the following amino acid sequences:
| alpha-MSH: | Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2 |
| beta-MSH (human): | Ala-Glu-Lys-Lys-Asp-Glu-Gly-Pro-Tyr-Arg-Met-Glu-His-Phe-Arg-Trp-Gly-Ser-Pro-Pro-Lys-Asp |
| beta-MSH (porcine): | Asp-Glu-Gly-Pro-Tyr-Lys-Met-Glu-His-Phe-Arg-Trp-Gly-Ser-Pro-Pro-Lys-Asp |
| gamma-MSH: | Tyr-Val-Met-Gly-His-Phe-Arg-Trp-Asp-Arg-Phe-Gly |
[edit] Synthetic MSH
Two synthetic analogs of alpha-MSH are being developed for human use. The first called Melanotan (referred to by the proprietary name CUV1647), by Clinuvel Pharmaceuticals in Australia and the second called Bremelanotide by Palatin Technologies, a New Jersey company.
- Alpha-MSH topical cream is being investigated as a possible therapeutic aid in the treatment of melanoma.[citation needed]
- Melanotan one (CUV1647) is being investigated as a method of photoprotection in patients with erythropoietic protoporphyria, polymorphous light eruption, actinic keratosis and squamous cell carcinoma (a form of skin cancer).[1]
- An additional analog called Melanotan II causes enhanced libido and erections in most male test subject and arousal with corresponding genital involvement in most female test subjects.[citation needed] Bremelanotide (formerly PT-141) which is based upon Melanotan II is being developed by the New Jersey company for its aphrodisiac effects and is currently in clinical trials to treat erectile dysfunction and sexual arousal disorder. These effects are mediated by actions in the hypothalamus on neurons that express MC3 MC3R and MC4 MC4R receptors.
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