Circulating human pituitary pro-gamma-melanotropin enhances the adrenal response to ACTH.

The amino-terminal region of the common corticotropin/beta-lipotrophin (beta-LPH) precursor has been identified in the AtT-20 mouse tumor cells as a glycopeptide with an apparent molecular weight of 16,000 (the '16K fragment'). A third melanotropin core sequence or gamma-MSH similar to that found in ACTH and beta-LPH was predicted to occur in this glycopeptide from the complementary DNA sequence of mRNA isolated from bovine pituitary intermediate tissue. Recently, the mouse of 16K fragment has been found to have a small but significant potentiation on the corticosteroidogenesis elicited by ACTH in a static cell system, an effect that could be enhanced when the glycopeptide was pretreated with trypsin. This synergism could also be mimicked by synthetic gamma-MSH peptides in vitro and in vivo. We report here the potentiating properties of a naturally occurring human pro-gamma-MSH glycopeptide on the ACTH-induced steroidogenic response of isolated perfused rat and human adrenocortical cells.