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

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Abstract
The amino-terminal region of the common ACTH/.beta.-lipotropin (.beta.-LPH) precursor was identified in the AtT-20 mouse tumor cell as a glycopeptide with an apparent MW of 16,000 (the 16K fragment). A 3rd 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. The mouse 16K fragment has 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. 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 is reported.