Melanin-concentrating hormone (MCH) is a 19 amino acid peptide originally isolated from the salmon pituitary gland (in fish the length of the peptide is 17 amino acids). In rodents and humans the peptide is synthesized in the brain and is involved in a number of physiological effects, although it is best known for its central role in the control of appetite control. For example, central administration of MCH in mice leads to obesity and conversely, knockout of the MCH gene in mice yields lean animals with an increased metabolic rate and reduced body fat.