Morphine-like substances exist in brain or the pituitary of various species. Beta-lipotropin (beta-LPH) was found to contain within its C-terminal sequence the primary structure of these peptides.
Identity between the sequence of isolated fragments and thecarboxy terminal portion of the corresponding beta-lipotropins hasalso been observed in human and in porcine pituitary and hypothalamic-neurohypophysis extracts.