Beta-endorphin is present in active and inactive forms in rat gastric antrum.

Lipotropin, beta-endorphin and a series of peptides related to beta-endorphin were extracted from rat antrum and resolved by gel filtration, ion exchange chromatography and high pressure liquid chromatography; the concentrations of the peptides were determined by radioimmunoassay. The major peptide with beta-endorphin immunoreactivity present in the antrum was lipotropin but it was accompanied by substantial quantities of beta-endorphin in its biologically active form; in addition there were minor quantities of a number of inactive beta-endorphin related peptides. The experiments demonstrate that in rat antrum gastrin can be accompanied by both active and inactive forms of beta-endorphin. The implications of post-translational processing mechanisms common to gastrin and beta-endorphin are discussed.