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Human -Lipotropin Radioimmunoassay: Identification of Immunoreactive -Lipotropin in Human Plasma and Tissue^*

RONALD E. WILSON, DAVID N. ORTH, WENDELL E. NICHOLSON, CHARLES D. MOUNT and XAVIER Y. BERTAGNA

Department of Medicine and Cancer Research Center, Vanderbilt University School of Medicine Nashville, Tennessee 37232

Address all correspondence to: Dr. David N. Orth, Division of Endocrinology, A-4215 Vanderbilt Medical Center, Nashville, Tennessee 37232.

Disagreement exists concerning the relative contributionsto total plasma immunoreactive human lipotropin(hLPH) made by hβLPH and its amino-terminal fragment,hLPH [hβLPH-(l-58)]. Using an antiserum (R1547) whichrequires the free COOH-terminal Asp⁵⁸ residue of hLPH for fullaffinity and reacts only 1% as well with hβLPH and antisera (R3and G106) that react with both LPHs, we examined gel chromatographyeluate fractions of plasma extracts from one normalsubject under basal conditions and another after metyraponeadministration, of plasma or plasma extracts from patients withACTH/LPH hypersecretion of various causes, of an extract twonormal pituitary glands, and an extract of an ectopic ACTH/LPH-secreting tumor. Immunoreactive hLPH was always amajor, frequently the predominant, and sometimes the onlyimmunoreactive LPH observed. We also observed in plasma ortissue of two patients with ectopic ACTH/LPH syndrome apeptide whose immunoreactivity and apparent molecular sizewere consistent with those of octadecapeptide human /?MSH, amolecule that is not thought to exist in normal man. Thesestudies demonstrate that hLPH is a major LPH component inplasma and tissues and indicate that the hLPH RIA providesa reliable estimate of the hLPH concentration in plasma withoutprior chromatography.

^* This work was supported in part by NCI Research Grants 5-R01-CA-11685 and 5-R25-CA-19429 and Grant-in-Aid 5-M01-RR-00095 from the NIH, USPHS.

Recipient of IndividualResearch Fellowship Grant 1-F32-AM-05974 from the NIH during the course of these studies.Present address: Centre de Recherches Endocrinologiques (Prof. Bricaire), Hopital Cochin,27 rue du Faubourg St. Jacques, F75674 Paris, Cedex 14,France.

Received December 9, 1980.