Characterization of beta-endorphin- and alpha-MSH-related peptides in rat heart.

POMC-derived peptides and mRNA have been identified in heart tissue, although POMC processing has not been fully characterized. In the present study, we found that beta-lipotropin and ACTH were localized in rat heart, although they were almost entirely converted to beta-endorphin- and alpha-MSH-related peptides. Ion exchange HPLC analysis revealed that beta-endorphin(1-31) was further processed to alpha-N-acetyl-beta-endorphin(1-31), which comprised 35.9 +/- 0.1% of total immunoreactivity, and smaller amounts of beta-endorphin(1-27), beta-endorphin(1-26), and their alpha-N-acetylated derivates. The predominant alpha-MSH immunoreactive peptides coeluted with alpha-MSH and N,O-diacetyl-alpha-MSH by reverse-phase HPLC, although small amounts of ACTH(1-13)-NH2 were also present. Thus, multiple forms of beta-endorphin and alpha-MSH are localized in rat heart. beta-Endorphin(1-31) is a minor constituent, however, indicating that nonopioid beta-endorphin peptides predominate.