Evidence for gamma-MSH-like immunoreactivity in ectopic ACTH-producing tumors.

Using a specific radioimmunoassay for gamma-MSH, a predicted peptide in the cryptic N-terminal portion of the adrenocorticotropin-beta-lipotropin precursor, gamma-MSH-like immunoreactivity (gamma-MLI) was detected in two ectopic ACTH producing tumors. Gel chromatographic studies on Bio-Gel P-60 revealed one or two peaks of gamma-MLI; one was eluted near th elution position of beta-LPH, compatible with gamma-MLI in human pituitary and the other emerged near the position of beta-endorphin. These results indicate that ectopic ACTH-producing tumors eleborate not only ACTH, beta-endorphin but also gamma-MLI.