Chapter 16 – Proopiomelanocortin Family

POMC is a precursor for melanocortins (MCs), such as ACTH and MSH, which contains α-MSH, β-MSH, and γ-MSH, and for β-endorphin (β-END), an opioid peptide. MCs exhibit their roles via MC receptors, and β-END exerts its role via μ-opioid receptors. Primarily, ACTH is involved in corticosteroid production, MSHs are involved in pigment stimulation, and β-END is involved in analgesia. Both the pars distalis and pars intermedia of the pituitary are major sources of POMC, where different peptides are generated by tissue-specific posttranslational processing. The main products in the pars distalis are ACTH and β-END, whereas the main end-products in the pars intermedia are α-MSH and β-END. Therefore, the POMC system is multifunctional; that is, in addition to the generation of several peptides, various modifications could diversify the biological functions of POMC-derived peptides. Moreover, their receptors are widely distributed in bodies.