Alpha MSH is a 13 amino acid peptide (1665 kD) with serine at the N terminal end and amidated valine at the C terminal end. Alpha MSH is derived from pro-opiomelanocorticotropin, a precursor protein which contains within its structure, the sequence of ACTH, beta MSH and gamma MSH. The amino acid sequence of alpha MSH is identical to ACTH 1-13 in humans. Alpha MSH stimulates melanosome dispersion within dermal melanocytes and melanin biosynthesis within epidermal melanocytes. It also stimulates aldosterone synthesis. Plasma alpha MSH increases in humans with high fever due to endotoxin. Average plasma alpha MSH has been found higher in AIDS patients and also in obese men with insulin resistance.