Comparative assessment of ACTH and lipotropin plasma levels in the diagnosis and follow-up of patients with Cushing's syndrome: a study of 210 cases.

PURPOSE: A series of 210 patients with Cushing's syndrome was evaluated at a single center to assess the relative values of adrenocorticotropic hormone (ACTH) and lipotropin (LPH) plasma levels in the etiologic diagnosis of Cushing's syndrome and in the follow-up of treated Cushing's diseases. PATIENTS AND METHODS: These patients included 149 patients with Cushing's diseases, 20 with adrenal tumors, and 41 with ectopic ACTH/LPH syndromes. Hormone levels were measured before therapy and during the follow-up of treated Cushing's diseases. RESULTS: ACTH and LPH plasma levels were moderately elevated in Cushing's diseases, low or undetectable in adrenal tumors, and highly elevated in ectopic ACTH/LPH syndromes, but the overlap between the three etiologic groups was less for LPH than for ACTH. LPH appeared to be as sensitive as ACTH in evaluating the outcome of trans-sphenoidal surgery and in detecting the occurrence of Nelson's syndrome after bilateral adrenalectomy. CONCLUSION: Therefore, plasma LPH determinations provide a better index than ACTH measurements, probably for technical reasons as well as because of the greater stability of LPH in blood.

Human gamma-lipotropin radioimmunoassay: identification of immunoreactive gamma-lipotropin in human plasma and tissue.

Disagreement exists concerning the relative contributions to total plasma immunoreactive human lipotropin (hLPH) made by h beta LPH and its amino-terminal fragment, h gamma LPH [h beta LPH-(1-58)]. Using an antiserum (R1547) which requires the free COOH-terminal Asp58 residue of h gamma LPH for full affinity and reacts only 1% as well with h beta LPH and antisera (R3 and G106) that react with both LPHs, we examined gel chromatography eluate fractions of plasma extracts from one normal subject under basal conditions and another after metyrapone administration, of plasma or plasma extracts from patients with ACTH/LPH hypersecretion of various causes, of an extract two normal pituitary glands, and an extract of an ectopic ACTH/LPH-secreting tumor. Immunoreactive h gamma LPH was always a major, frequently the predominant, and sometimes the only immunoreactive LPH observed. We also observed in plasma or tissue of two patients with ectopic ACTH/LPH syndrome a peptide whose immunoreactivity and apparent molecular size were consistent with those of octadecapeptide human beta MSH, a molecule that is not thought to exist in normal man. These studies demonstrate that h gamma LPH is a major LPH component in plasma and tissues and indicate that the h gamma LPH RIA provides a reliable estimate of the h gamma LPH concentration in plasma without prior chromatography.

Simultaneous assay of immunoreactive beta-lipotropin, gamma-lipotropin, and beta-endorphin in plasma of normal human subjects, patients with ACTH/lipotropin hypersecretory syndromes, and patients undergoing chronic hemodialysis.

We have studied the relative concentrations of the human immunoreactive (IR) peptides gamma-lipotropin (hgammaLPH, [1-58]hbetaLPH), beta-lipotropin (hbetaLPH), and beta-endorphin (hbetaEND, [61-91]hbetaLPH) using gel exclusion chromatography together with a specific radio-immunoassay (RIA) for hgammaLPH and a RIA that (because hbetaEND is the COOH-terminus of the hbetaLPH molecule) measures both hbetaEND and hbetaLPH on an equimolar basis. In normal subjects, basal plasma IR-hgammaLPH was often undetectable (<12.5 fmol/ml), but ranged up to 21 fmol/ml, and IR-hbetaEND/hbetaLPH was 10.8+/-0.7 fmol/ml; previous studies by others suggest that most of the IR-hbetaEND/hbetaLPH was probably hbetaLPH. Both IR-hgammaLPH and IR-hbetaEND/hbetaLPH were significantly elevated (P < 0.001) in patients undergoing chronic hemodialysis (101.5+/-12.7 and 23.8+/-2.0 fmol/ml, respectively). Their IR-hgammaLPH coeluted with standard hgammaLPH as a single peak, and IR-hbetaEND/hbetaLPH coeluted with hbetaLPH; no distinct peak of IR-hbetaEND was observed. In patients with ACTH/LPH hypersecretion due to Addison's disease, Nelson's syndrome, or ectopic ACTH syndrome, IR-hgammaLPH and IR-hbetaEND/hbetaLPH were both elevated, and IR-hbetaEND/hbetaLPH eluted as two peaks, one coeluting with hbetaLPH and the other with hbetaEND. The molar concentrations of all three peptides were significantly correlated with one another. The lower concentrations of endogenous IR-hbetaEND observed may be due in part to its apparent shorter plasma half-life, as estimated in an Addison's patient given a cortisol infusion. The biologic significance of these three peptides in circulating blood is still unknown. The increased levels of hbetaLPH and hgammaLPH in plasma of patients with chronic renal failure suggest that the kidney may be an important organ for their metabolism.

Molecular weight forms of immunoreactive calcitonin in a patient with medullary carcinoma of the thyroid: dynamic studies with calcium, pentagastrin and somatostatin.

We have examined the characteristics of circulating immunoreactive human calcitonin (IR-hCT) by studying its different molecular weight (MW) forms under various secretory conditions in a patient with medullary carcinoma of the thyroid. Plasma IR-hCT (318 mg/l basal) increased 9 and 12 times, respectively, after calcium (0 . 3 mg/kg/min over 10 min i.v.) and pentagastrin (3 . 2 microgram i.v.) administration. Somatostatin infusion (500 microgram/h) caused a 41% decrease in plasma IR-hCT and markedly diminished the responses to both pentagastrin and calcium. Sephadex G50 chromatography separated different IR-hCT forms: hCT itself predominated after stimulation with either calcium or pentagastrin (52% and 62%, respectively), while it was reduced in the basal state (33%) and following somatostatin (11%); reciprocal changes were observed for the higher MW forms. Under denaturing conditions, with or without reducing agent, total plasma IR-hCT was resolved into one major peak co-eluting with 125I-hCT. Thus, the hCT monomer appears to be the major secretory product of the medullary carcinoma of the thyroid studied here. The predominance of higher MW forms in the basal state reflects their slower plasma disappearance rate. These high MW forms are mainly the result of aggregation or non-covalent protein binding of the hCT monomer.

Ectopic production of high molecular weight calcitonin and corticotropin by human small cell carcinoma cells in tissue culture: evidence for separate precursors.

The DMS-79 continuous line of human small cell lung carcinoma cells, which produces immunoreactive (IR)-corticotropin (ACTH), -lipotropin (LPH), and -beta-endorphin (beta END), was found to produce IR-calcitonin (CT). Two major high molecular weight (HMW) forms of IR-CT were observed after gel exclusion chromatography under denaturing conditions (mol wt. approximately 7,000 and approximately 14,000), as well as a minor HMW IR-CT component (mol. wt. approximately 70,000). None of these IR-CT materials was extracted from DMS-79 medium by affinity chromatography using an ACTH antibody covalently bound to agarose. These results demonstrate ectopic production of HMW forms of CT and ACTH/LPH/beta END by human lung tumor cells in tissue culture, but do not support the existence of a common CT/ACTH/LPH/beta END precursor molecule.

Corticotropin, lipotropin, and beta-endorphin production by a human nonpituitary tumor in culture: evidence for a common precursor.

A continuous line (DMS-79) of human pulmonary small cell carcinoma cells was shown to secrete immunoreactive adrenocorticotropin (ACTH), lipotropin, and beta-endorphin concomitantly into the culture medium. Gel filtration of the culture medium demonstrated at least five components: high molecular weight material(s) that had ACTH, lipotropin, and beta-endorphin immunoreactivities and materials similar to ACTH, beta-lipotropin, gamma-lipotropin, and beta-endorphin in their immunoreactivities and apparent molecular weights. The same components were observed when gel filtration was carried out in 6 M guanidine-HCl, and the high molecular weight material(s) appeared to consist of more than one component, with molecular weights in the range of 15,000-40,000. Immune affinity chromatography of the high molecular weight component(s) from gel filtration with a specific anti-(1-24)ACTH serum demonstrated that the ACTH, lipotropin, and beta-endorphin immunoreactivities were possessed by the same molecule(s), suggesting that ACTH, lipotropins, and beta-endorphin were derived from a common, high molecular weight precursor.