IMMUNOREACTIVE β-MSH IN HUMAN PLASMA AND IN A CORTICOTROPHIC ADENOMA CULTURE MEDIUM. ITS RELATION TO THE LIPOTROPHINS

ABSTRACT In order to characterize more accurately the relationship between immunoreactive β-MSH ("β-MSH") and the lipotrophins (LPH) we attempted to investigate the gel filtration and the immunological characteristics of "β-MSH" in the plasma of patients with Nelson's syndrome and Addison's disease as well as in the culture medium from a human corticotrophic adenoma using a sensitive radioimmunoassay from human β-MSH. When added either to hormone free plasma or to a plasma from a patient with Nelson's syndrome all the human β-MSH (hβ-MSH) elutes from a Sephadex G-50 column as a single peak in a volume corresponding to its molecular weight. In contrast plasma "β-MSH" in 3 patients with Nelson's syndrome and one patient with Addison's disease almost completely elutes in a volume corresponding to a molecular weight range of 6000– 10 000; no "β-MSH" can be detected in its normal elution volume. Drastic pH change (8.2 to 2.3) does not significantly alter the elution pattern. Chromatography of a corticotrophic adenoma culture medium gave a similar pattern of "β-MSH" with a main peak in the molecular weight range of 6000–10 000. In our radioimmunoassay the culture medium and purified hβ-LPH gave parallel displacement curves for [125I]hβ-MSH. It is suggested that hβ-LPH or a closely related substance is the main material responsible for "β-MSH" immunoactivity.