The term melanocortins refers to a group of small protein hormones that develop from the gene product proopiomelanocortin (POMC).
The hormones affect physiological activity in the body by binding with specific receptors; the melanocortin receptors, of which there are currently five identified: MC1R - MC5R. These receptors are prolific within the human body and present in virtually every organ, making the effects of the melanocortins widespread and varied. Known physiological activity influenced by the melanocortins includes pigmentation, inflammation, energy homeostasis, appetite and sexual function.
Melanocortins expressed in the brain, or those which cross the Blood Brain Barrier (BBB) and bind with MC3R and MC4R (the third and fourth melanocortin receptors) are thought to play a fundamental role in feeding and body weight.
Melanocortin hormones are also expressed in peripheral tissues including testis, ovary, placenta, duodenum, liver, kidney and skin, where they can have a more localised (autocrine or paracrine) response.