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proopiomelanocortin (adrenocorticotropin/ beta-lipotropin/ alpha-melanocyte stimulating hormone/ beta-melanocyte stimulating hormone/ beta-endorphin)
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 or intermedins) are a class of peptide hormones that in nature are produced by cells in the intermediate lobe of the pituitary gland. They were first isolated by the Yale professor Aaron B. Lerner.[1] Synthetic analogs of these naturally occurring hormones have also been developed and researched.

Contents

Function

They stimulate the production and release of melanin (melanogenesis) by melanocytes in skin and hair. MSH signals to the brain have effects on appetite and sexual arousal.

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.

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 for more information.

Structure of MSH

proopiomelanocortin derivatives
POMC
     
γ-MSH ACTH β-lipotropin
         
  α-MSH CLIP γ-lipotropin β-endorphin
       
    β-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:

α-MSH: Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val
β-MSH (human): Ala-Glu-Lys-Lys-Asp-Glu-Gly-Pro-Tyr-Arg-Met-Glu-His-Phe-Arg-Trp-Gly-Ser-Pro-Pro-Lys-Asp
β-MSH (porcine): Asp-Glu-Gly-Pro-Tyr-Lys-Met-Glu-His-Phe-Arg-Trp-Gly-Ser-Pro-Pro-Lys-Asp
γ-MSH: Tyr-Val-Met-Gly-His-Phe-Arg-Trp-Asp-Arg-Phe-Gly

Synthetic MSH

Synthetic analogs of alpha-MSH have been developed for human use. Two of the better known are afamelanotide (melanotan-1) in testing by Clinuvel Pharmaceuticals in Australia and bremelanotide by Palatin Technologies, a New Jersey company.

  • 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.[3] Bremelanotide (formerly PT-141) which stemmed from Melanotan II research was previously under development by the New Jersey company for its aphrodisiac effects. These effects are mediated by actions in the hypothalamus on neurons that express MC3 MC3R and MC4 MC4R receptors.

References

  1. ^ "Professor Aaron Lerner. Dermatologist who discovered melatonin" (Obituary). Times Online. 19 March 2007. http://www.timesonline.co.uk/tol/comment/obituaries/article1538930.ece. Retrieved 2009-03-31. 
  2. ^ Clinuvel FAQs
  3. ^ Hadley ME (Oct 2005). "Discovery that a melanocortin regulates sexual functions in male and female humans". Peptides 26 (10): 1687–9. doi:10.1016/j.peptides.2005.01.023. PMID 15996790. 

Further reading

External links








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