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

The amino-terminal region of the common corticotropin/ β -lipotropin ( β -LPH) precursor has been identified in the AtT-20 mouse tumour cell as a glycopeptide with an apparent molecular weight of 16,000 (the ‘16K fragment’) 1,2 A third melanotropin core sequence or γ -MSH similar to that found in ACTH and β -LPH was predicted to occur in this glycopeptide from the complementary DNA sequence of mRNA isolated from bovine pituitary intermediate tissue 3 . Recently, the mouse 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 4 . This synergism could also be mimicked by synthetic γ -MSH peptides in vitro and in vivo 5 . We report here the potentiating properties of a naturally occurring human pro- γ -MSH glycopeptide 6 on the ACTH-induced steroidogenic response of isolated perfused rat and human adrenocortical cells.