Radioimmunoassay of beta-MSH in human plasma and tissues

Pro-opiocortin: the multiple adrenal hormone precursor. Review

Corticotropin (ACTH) is biosynthesized in the human pituitary gland as a long polypeptide precursor (pro-opiocortin) of some 240 residues. When ACTH is secreted in response to stress, the peptides derived from the rest of this precursor, pro-gamma-melanotropin (gamma-MSH) and beta-lipotropin (beta-LPH), are also secreted (Fig. 1). This article will describe the search for a biological significance for this phenomenon.

Receptor mechanisms in fish chromatophores--V. MSH disperses melanosomes in both dermal and epidermal melanophores of a catfish (Parasilurus asotus)

1. Synthetic alpha-MSH was tested for its action on dermal and epidermal melanophores of the siluroid catfish. Parasilurus asotus. 2. MSH did not produce melanosome aggregation in these melanophores. 3. It was, however, very effective in bringing about pigment dispersion in dermal melanophores. 4. Epidermal melanophores were also responsive to MSH, although the rate and the degree of the response was smaller than those of the dermal melanophores. 5. A possible role of MSH in skin color changes in vivo is discussed.

The endocrinology of the opiates and opioid peptides

Since the isolation of the enkephalins five yr ago, there has been an explosive increase in knowledge concerning the effects of the opiates and opioid peptides. This review deals with the interactions of opiates with the endocrine system in rat and man. The opioid peptides have been demonstrated to exert a variety of effects on pituitary hormone secretion in rat and man. In the rat, opiates stimulate growth hormone, prolactin and ACTH release and inhibit the release of the glycoprotein hormones. In man, the physiologic role of the endogenous opiates appears to be involved predominantly in ACTH and gonadotrophin regulation. Opiate effects are mainly exerted at the level of the hypothalamus but further modulating effects may occur at the pituitary and at end-organs. Opiate-induced hormonal effects appear to be mediated through dopaminergic and/or serotonergic mechanisms. Recent studies have also suggested a possible local neuromodulatory role for the opioid peptides in the control of carbohydrate metabolism and reproductive processes.

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.

Ultrastructure, immunohistochemistry and hormone release of pituitary adenomas in relation to prolactin production

Fifteen cases of pituitary adenoma, 14 of which were associated with hyperprolactinemia, were studied by observation and granule morphometry of electron micrographs, immunohistochemistry and sequential observation of in vitro release with regard to hormone production, storage and secretion. Adenoma cells of 6 cases with marked elevation of plasma prolactin were sparsely granulated, showed characteristic ultrastructures including the presence of small secretory granules, well developed Golgi and rough membranes, misplaced exocytosis, and positive or negative immunostaining for prolactin. These adenomas also showed vigorous release of the hormone into the circulation and/or culture medium. In vitro studies showed that negative immunostaining of adenoma cells did not preclude the production and secretion of the hormone. One densely granulated adenoma containing cells with numerous lactotroph type granules showed moderate release of prolactin into the circulation. In an acromegalic case associated with both high plasma growth hormone and prolactin, some cells were shown by immunohistochemistry to store both hormones There were 4 adenomas which could not be shown to produce, store and secrete prolactin by any method available.

Cushing's syndrome: a review of diagnostic tests

This review presents an analysis and interpretation of the published experimental data that form the basis for laboratory tests commonly used for screening, definitive diagnosis, and differential diagnosis in Cushing's syndrome. The single-dose overnight dexamethasone suppression test is excellent for screening outpatients since this test has a very low incidence of false-negative results (1.9% of 154 patients with Cushing's syndrome). The definitive diagnosis of Cushing's syndrome is best established by combining basal state measurements of the daily urine-free cortisol excretion and late evening plasma cortisol levels with the 2-mg low-dose dexamethasone suppression test. The etiology of Cushing's syndrome is best determined by combining measurements of basal state plasma adrenocorticotropin (ACTH) levels with the 8-mg high-dose dexamethasone suppression test. Under certain conditions, the basal state daily urine excretion of 17-hydroxycorticosteroids and 17-ketogenic steroids, the insulin tolerance test, and the metyrapone test may be useful in the definitive or differential diagnosis of Cushing's syndrome.

Ectopic production of lipotropin by cancer

Lipotropin (LPH) has been evaluated as a potential tumor marker using a sensitive beta melanocyte-stimulating hormone (beta MSH) radioimmunoassay. All 79 acetic acid extracts of carcinomas of lung, colon, stomach, esophagus and breast contained LPH in concentrations greater than blood; 61 of 79 extracts contained LPH in larger amounts than control tissues from patients without cancer. In a blind prospective study, plasma LPH was quantified in 107 patients admitted for work-up because of an abnormality on a chest roentgenogram. Thirty-one of 33 patients subsequently diagnosed as having benign lesions had plasma LPH within the 95 per cent confidence limits of normal subjects whereas 28 (36 per cent) of the 74 patients subsequently diagnosed histologically as having primary lung carcinoma had elevated levels. In control studies, 13 of 100 patients with chronic obstructive pulmonary disease had elevated plasma LPH levels; three of the 13 with elevated levels and four with normal levels have been diagnosed, during the two years of follow-up, as having lung carcinoma. In control studies of 23 patients with granulomatous lung disease, 22 had normal levels of LPH. In those with carcinoma of the colon elevated plasma LPH levels were observed in two of 21 untreated patients and in 11 of 61 patients receiving noncurative chemotherapy. Elevated plasma LPH levels were also observed in 10 of 59 patients with breast cancer, eight of 28 with pancreatic cancer, eight of 22 with gastric or esophageal cancer, six of 16 with renal cancer, four of eight with prostatic cancer, one of seven with cervical cancer and one of six with ovarian cancer. We conclude, an elevated LPH level is frequently observed in blood and tumor tissue from patients with various types of carcinoma.

Sensitive new in vitro bioassay for melanocyte-stimulating activity using the skin of Anolis carolinensis

An accurate, highly reproducible and sensitive bioassay for melanocyte-stimulating hormone (MSH) using the skin of Anolis carolinensis in vitro is described. The time taken for green Anolis skin fragments to change to a specific, visually assessed, green-brown color is dose-related, and this forms the basis of the new assay. The method is simple to perform, and 1 person may assay 20 samples in a day using the dorsal skin from a single adult lizard. The mean dose-response ranges between 48 X 10(-12) and 375 X 12(-12) M (38 to 625 pg/ml). Using the assay, alpha-MSH, beta-MSH, ACTH (4-10), and ACTH (1-10) were equipotent on a molar basis. For repeated bioassay of rat pituitary extracts, the dose-response curves were highly significant, and only 1 of the 9 pituitary dose-response curves deviated significantly from the slope of the standard alpha-MSH curve. The index of precision, lambda, for the 9 pituitary bioassays ranged between 0.037 and 0.081, while the mean 95% fiducial limits were -6.6 and 7.1% on either side of the estimated potency. The new rate method is compared with an earlier quantal method which also uses the isolated skin of Anolis carolinensis. The quantal method does not have dose-response characteristics and is therefore less accurate and reproducible than the new method; the coefficient of variation for repeated bioassay of the same pituitary extracts ranged from between 12 to 20% for the quantal method and between 2.9 to 5.7% for the new rate method.

Coordinate control of corticotropin, beta-lipotropin, and beta-endorphin release in mouse pituitary cell cultures

Hypothalamic extract stimulates the release of corticotropin (ACTH) and endorphins 2.5- to 30-fold in mouse pituitary tumor cell cultures (AtT-20/D(16v) line) and primary cell cultures from mouse anterior pituitary. ACTH and endorphin activities were measured by radioimmunoassay and immunoprecipitation. Pretreatment of tumor cell cultures with 1 muM dexamethasone reduced the stimulatory effect of the extract on release of ACTH and endorphins. Pretreatment of primary cell cultures with 10(-6) M dexamethasone reduced the stimulatory effect of both vasopressin and the extract on the release of ACTH and endorphins. Release of ACTH and endorphin was coupled in both kinds of cultures in the basal, stimulated, and inhibited states. The molecular weight forms of ACTH and endorphin in tumor cell culture medium were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Radioimmunoassay and immunoprecipitation show that the 13,000-dalton and 4500-dalton forms of ACTH were present in about equal amounts in medium from cultures incubated with or without hypothalamic extract for 15 min, 30 min, or 2 hr. Smaller amounts of the high molecular weight forms of ACTH (20,000- to 23,000-dalton and 31,000-dalton ACTH) were observed in the culture medium at these times. The predominant forms of endorphin released after 20 min or 3 hr of incubation had molecular weights of 31,000, 11,700 (beta-lipotropic hormone-size material) and 3500 (beta-endorphin-size material). No degradation of the forms of endorphin released into the culture medium was observed after incubating the culture medium for 1.5 hr in the absence of cells. The proportions of the different forms of endorphin and ACTH present in the culture medium resembles that seen in cell extracts.

The nature of the immunoreactive lipotropins in human plasma and tissue extracts

This study was designed to establish definitively the nature of immunoreactive lipotropin (IR-LPH) in human plasma and tissue extracts. Using gel filtration, gel filtration under denaturing conditions, cationic exchange chromatography, immunoprecipitation, and radioimmunoassay, we have studied normal and tumorous human pituitaries, ectopic ACTH- and LPH-secreting tumors, plasma from normal subjects before and after dexamethasone administration, and plasma from patients with primary adrenal insufficiency and pituitary and nonpituitary ACTH- and LPH-secreting tumors. Except in the plasma and tumors of occasional patients with ectopic ACTH syndrome, the smallest IR-LPH appears to be lambda-lipotropin (lambdaLPH), which is often the predominant and occasionally the only IR-LPH present. The other major peptide appears to be betaLPH, a 91-amino acid molecule that contains lambdaLPH as its 1-58 sequence. Larger immunoreactive materials were observed in some specimens, but the "big" LPH in one plasma was shown to be lambdaLPH bound to IgG.The weak melanocyte-stimulating activity of LPH suggests that ACTH may be the principal pigmentary hormone in man. The fact that lambdaLPH, rather than betaLPH, is the predominant form in plasma suggests that the enkephalin-endorphin opiate peptides, which are contained in the "missing" 59-91 sequence from the betaLPH precursor of lambdaLPH, may be secreted in parallel with ACTH under both physiological and pathological conditions in man.

Characterization of a common precursor to corticotropin and beta-lipotropin: identification of beta-lipotropin peptides and their arrangement relative to corticotropin in the precursor synthesized in a cell-free system

Radioactive proteins synthesized in an mRNA-dependent reticulocyte cell-free system under the direction of mRNA from AtT-20/D-16v mouse cells were isolated by specific immunoprecipitation using antiserum to either alpha(1-24) corticotropin or beta-endorphin [beta(61-91) lipotropin]. Each immunoprecipitate was fractionated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and shown to contain only one labeled protein with an apparent molecular weight of 28,500. Tryptic peptide analysis of the Mr 28,500 corticotropin and beta-lipotropin molecules isolated from the gels demonstrated that the two proteins had the same lysine, methionine, and tryptophan peptides. Four tryptic peptides from the cell-free product exhibited the same electrophoretic and chromatographic mobilities as marker tryptic peptides from bovine beta-melanotropin and porcine beta-endorphin. The identification of these peptides was confirmed by amino acid composition studies with a variety of labeled amino acids. The beta-lipotropin tryptic peptides were also shown to be located carboxy terminal to the corticotropin tryptic peptides.

The immunolocalization of ACTH and alpha MSH in human and rat pituitaries

Human and rat pituitaries were investigated immunohistochemically for ACTH and alpha MSH activity by means of the enzyme-labeling technique. In rat pituitaries cells present in both the anterior and intermediate lobes were reactive with the anti-ACTH antibodies, the cells from the intermediate lobe were also reactive with anti-alpha MSH antibodies. In human pituitaries, ACTH-immunoreactivity was found in cells from the anterior lobe and cells invading the posterior lobe. In 5 out of 15 pituitaries ACTH-immunoreactive cells located at or invading the posterior lobe were also reactive with the anti-alpha MSH antibodies. It is concluded that the human pituitary cells that invade the posterior lobe represent a population which is at least immunohistochemically identical with the intermediate lobe cells of the rat. The ACTH-immunoreactivity of intermediate lobe cells may be explained by the presence of a corticotropin-like intermediate lobe peptide (CLIP) which has been suggested to be a prohormonal fragment of alpha MSH.

Ultrastructural, histochemical, and biochemical studies of two cases with amylase, ACTH, and beta-MSH producing tumor

Two cases of intrathoracic tumor, different in histology and accompanied by hyperamylasemia, were studied ultrastructurally, histochemically, and biochemically. The ultrastructure of the tumor cell cytoplasm showed many zymogen granules in case 1 and smaller cored granules in addition to zymogen granules in case 2. Both tumors contained not only a large amount of amylase, which was electrophoretically of saliva type with three components, but also significant amounts of immunoreactive ACTH and beta-MSH. Starch film and immunofluorescence showed that the tumor cells stored amylase. It was concluded from these findings that the tumor cells ectopically producing amylase, which showed differentiation toward the cells with zymogen production, could differentiate toward the cells of ACTH-MSH system at the same time.

Effects of melanocyte stimulating hormone and theophylline on human melanocytes in vitro

The effects of MSH on the human melanocyte in vitro were studied. The addition of MSH up to the concentration of 40 mug/ml into the culture medium did not produce appreciable change on the morphology of the melanocyte. The melanocyte, however, responded to the simultaneous addition of MSH and theophylline with marked increase in the length and complexity of the dendritic process. Melanin synthesis, as indicated by the uptake of tyrosine in the presence of an inhibitor of protein synthesis, was remarkably activated by the simultaneous addition of MSH and theophylline. MSH alone activated the melanin synthesis only slightly, but the increase in the uptake of tyrosine was significant statistically. These results were discussed in terms of the MSH-cyclic AMP cascade in which theophylline worked as an inhibitor of cyclic AMP phosphodiesterase, and increased the intracellular level of cyclic AMP by inhibiting catabolism of cyclic AMP.

Gastric carcinoid with ectopic production of ACTH and beta-MSH

A 51-year-old woman with typical Cushing's syndrome of about 9 years duration was shown to have a gastric carcinoid tumor. Plasma levels of ACTH and cortisol were elevated and lacked the normal diurnal rhythm. Urinary excretion of steroids was unaffected by the administration of either metyrapone or dexamethasone. Fluctuation in urinary steroid excretion, as well as transient hypokalemic alkalosis and glycosuria suggested periodic hormonogenesis. The extirpated gastric carcinoid was shown to contain immunoreactive ACTH and beta-MSH. However, the biologic ACTH activity was undetectable by in vivo steroidogenic assay. By gel filtration, it was demonstrated that both tumor and plasma ACTH was predominately "big" ACTH. Although postoperatively she developed hypoadrenocorticism severe enough to require ACTH treatment, her pituitary-adrenal function was gradually restored. This is the first documented case of ectopic ACTH syndrome caused by gastric carcinoid in which successful cure was achieved by surgery.

Ectopic adrenocorticotrophic hormone production and neoplasm

Three patients presented with severe hypokalaemic, hypochloraemic alkalosis, muscle weakness and later cutaneoud pigmentation. There were few signs of Cushing's syndrome. Two had bronchial and one pancreatic neoplasm. Plasma cortisol and urinary steroid metabolites were extremely elevated and synacthen stimulation showed significant adrenal capacity even with adrenal metastases. Aminoglutethamide reduced plasma cortisol in two patients.

Plasma immunoreactive beta-melanocyte-stimulating hormone and skin pigmentation in chronic renal failure

Plasma immunoreactive beta-melanocyte stimulating hormone (beta-MSH) concentrations were greatly increased in patients with chronic renal failure. There was no correlation between the severity of the renal failure or the degree of pigmentation and the plasma beta-MSH levels.

Cutaneous manifestations of internal malignancy

Skin changes may result from metastases to skin or from chemicals or hormones that are secreted by the tumor, resulting in identifiable cutaneous syndromes, or may be inflammatory dermatoses, benign or malignant proliferative lesions, or nevoid states whose association is recognized but the mechanisms of which are unexplained.

Fine structure of the pars intermedia in the rhesus monkey, Macaca mulatta

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Adrenocorticotrophic and melanocyte-stimulating peptides in the human pituitary

The adrenocorticotrophic and melanocyte-stimulating peptides of the human pituitary were investigated by means of radioimmunoassay, bioassay and physicochemical procedures. Substantial amounts of adrenocorticotrophin and a peptide resembling beta-lipotrophin were identified in pituitary extracts, but alpha-melanocyte-stimulating hormone, beta-melanocyte-stimulating hormone and corticotrophin-like intermediate lobe peptide, which have been identified in the pars intermedia of pituitaries from other vertebrates, were not found. The absence of beta-melanocyte-stimulating hormone appears to contradict previous chemical and radioimmunological studies. Our results suggest, however, that it is not a natural pituitary peptide but an artefact formed by enzymic degradation of beta-lipotrophin during extraction.

Biologic and immunologic characterization and physical separation of ACTH and ACTH fragments in the ectopic ACTH syndrome

Extracts of tumors from 32 patients with the ectopic ACTH syndrome were subjected to simultaneous bioassay and radioimmunoassays for ACTH. Radioimmunoassays were performed using three antisera, one of which reacts with the extreme N-terminal 1-13 amino acid sequence of ACTH, the second with the N-terminal 1-23 sequence of the ACTH molecule, and the third with the C-terminal 25-39 amino acid sequence of ACTH. There was, in general, good correlation between bioactivity and N-terminal ACTH immunoreactivity. However, there were large excesses of both extreme N-terminal and C-terminal immunoreactive materials in most tumor extracts, which were not found in extracts of three human pituitaries. Three tumor extracts were subjected to molecular sieve chromatography on Sephadex G-50 fine resin. The bioactive ACTH eluted in the same fractions as pituitary ACTH (mol wt approximately 4,500 daltons) and reacted equally in all three ACTH radioimmunoassay systems. The bioactive tumor ACTH was neutralized by incubation with the C-terminal antiserum, indicating it has an intact C-terminal sequence of amino acids. The next several fractions from the Sephadex column contained a material, mol wt approximately 3,100, which was biologically inactive and had C-terminal immunoreactivity but no N-terminal or extreme N-terminal immunoreactivity. Incubation with the N-terminal 1-23 ACTH antiserum did not adsorb these C-terminal fragments, indicating they lacked an intact sequence of amino acids in this region. A smaller ACTH fragment (mol wt approximately 1,800 daltons) eluted in still later fractions and reacted with the extreme N-terminal antiserum but not with the N-terminal or C-terminal antisera. It had no steroidogenic activity, but appeared to have significant melanocyte-stimulating activity. It is concluded that, in addition to an ACTH similar, if not identical, to pituitary ACTH, tumors of patients with the ectopic ACTH syndrome contain both N-terminal and C-terminal ACTH fragments.