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Melanocortin 4 receptor (MC 4 R) is a melanocortin receptor that in humans is encoded by the MC4R gene highly expressed in paraventricular nucleus of the hypothalamus. [5] [6] [7] It encodes the MC 4 R protein, a G protein-coupled receptor (GPCR) that binds α-melanocyte stimulating hormone (α-MSH).
Melanocortin receptors are members of the rhodopsin family of 7-transmembrane G protein-coupled receptors. There are five known members of the melanocortin receptor system [ 1 ] each with differing specificities for melanocortins : [ 2 ] [ 3 ] [ 4 ]
MC2R is activated exclusively by ACTH, whereas the other 4 receptors can be activated by ACTH, α-MSH, β-MSH, and γ-MSH, although the binding affinities differ. For all the melanocortin receptors, binding of an agonistic ligand activates the receptor, leading to dissociation of the G protein and activation of the enzyme adenyl cyclase.
Proopiomelanocortin has been shown to interact with melanocortin 4 receptor. [21] [22] The endogenous agonists of melanocortin 4 receptor include α-MSH, β-MSH, γ-MSH, and ACTH. The fact that these are all cleavage products of POMC should suggest likely mechanisms of this interaction. [citation needed]
Stimulation of the melanocortin-4 receptor causes a decrease in appetite and an increase in metabolism of fat and lean body mass, even in a relatively starved state. [21] Conversely, damage to this receptor has been shown to result in morbid obesity, and is the most commonly known cause of monogenic morbid obesity. [22]
LB54640 is a small molecule melanocortin 4 receptor agonist developed by LG Chem Life Sciences for hypothalamic obesity. Unlike the older drug with the same mechanism of action, setmelanotide, it can be taken by mouth. [1] [2] [3]
[2] [4] Common side effects include nausea, pain at the site of injection, and headache. [2] It may also cause a temporary increase in blood pressure and decrease in heart rate after each dose, and darkening of the gums, face, and breasts. [4] The medication is a peptide and acts by activating the melanocortin receptors. [1] [5]
THIQ is a drug used in scientific research, which is the first non-peptide agonist developed that is selective for the melanocortin receptor subtype MC 4. [1] [2] In animal studies, THIQ stimulated sexual activity in rats, [3] but with little effect on appetite or inflammation. [4]