Selective processing of beta-endorphin in regions of porcine pituitary

The prohormone of β -endorphin is unusual in that it is the precursor of more than one biologically active peptide 1–3 (Fig. 1). The activation of this prohormone, to produce corticotropin (ACTH), α -melanotropin ( α -MSH) and β -endorphin, would seem to be relatively complex as its processing pattern is known to differ between tissues. Thus ACTH is produced in the anterior pituitary whereas α -MSH is formed in the pars intermedia 4,5 ; similarly, lipotropin and β -endorphin seem to predominate in the anterior pituitary whereas β -endorphin alone has been thought to be the principal component in the pars intermedia. We report here a study of the distribution of β -endorphin-related peptides in various regions of porcine pituitary. The main products in the anterior pituitary were lipotropin and the potent analgesic form of β -endorphin, whereas the main products in the pars intermedia were the inactive lipotropin C′-fragment and its N -acetyl derivative. Thus the processing of the C-terminal region of the β -endorphin prohormone differs markedly between the two regions of porcine pituitary.