Size Heterogeneity ofβ-MSH in Ectopic ACTH-Producing Tumors: Presence ofβ-LPH-Like Peptide

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Abstract
Gel chromatographic, immunologic and biologic properties of β-melanocyte-stimulating hormone (β-MSH) in tumor tissues obtained from eight patients with the ectopic ACTH syndrome were studied and compared to those of pituitary β-MSH. Size heterogeneity of immunoreactive β-MSH was found in all the tumors studied as well as in normal human pituitaries. Both the tumors and pituitaries contained immunoreactive β-MSH of a larger molecular size than the well-characterized β-MSH of small molecular size. The large molecular weight β-MSH also predominated in the plasma. It was found to be bioactive by an in vitro MSH assay, immunologically indistinguishable from human β-MSH, and chromatographically very similar to β-lipotropic hormone β-LPH) Tryptic digestion of the large molecular weight β-MSH under controlled conditions promptly produced bioactive β-MSH of small molecular size, followed by the appearance of immunologically active but biologically inert fragments. These results suggest that the ectopic ACTH-producing tumor as well as the pituitary elaborate β-LPH-like peptide which might be the predominant component of immunoreactive β-MSH in man.