Alpha-MSH

Alpha-melanocyte-stimulating hormone (alpha-MSH) is the prototypical melanocortin peptide, derived from the POMC (proopiomelanocortin) precursor protein through enzymatic processing. This endogenous tridecapeptide activates all five melanocortin receptor subtypes (MC1R-MC5R), mediating diverse physiological functions including pigmentation, inflammation, appetite, and sexual behavior.

MC1R activation in melanocytes stimulates cAMP production and subsequent eumelanin synthesis, producing skin and hair pigmentation. This protective pigmentation response to UV exposure represents alpha-MSH's most recognized function. However, the peptide's effects through other MC receptors are equally significant physiologically.

Alpha-MSH demonstrates potent anti-inflammatory activity through MC1R and MC3R in immune cells, suppressing NF-kB activation and reducing production of pro-inflammatory cytokines. Central MC4R activation in the hypothalamus regulates appetite and energy expenditure, while MC3R/MC4R activation influences sexual function and social behavior.

As the endogenous reference compound for the melanocortin system, alpha-MSH is essential for receptor characterization studies and as a comparator for evaluating synthetic analogs. Its relatively short half-life in vivo (minutes) drove development of more stable synthetic analogs like afamelanotide and setmelanotide for therapeutic applications.