oxyntomodulin and Adenoma--Islet-Cell

Gastrointestinal hormones (GI hormones) have received growing interest in endocrinology, gastroenterology and neuroendocrinology. Because of new methodological techniques, they can be measured in plasma and therefore be related to different pathophysiological conditions. In childhood, our present knowledge is as yet limited to the physiological rôle of gastrin at different ages and in some diseases (gastrinoma; Verner-Morrison syndrome) caused by humoral dysfunction. The present review relates the clinical important GI hormones to chemically classified families. The diagnostic value of determining endogenous hormone concentration in plasma and the validity of function tests carried out by administration of exogenous hormones are pointed out. Particular emphasis is given to the trophic action of GI hormones in the development and function of the gastrointestinal tract during childhood. More speculatively, GI hormones are involved in the complex function of the central nervous system, thus making food intake a trophotropic action in a broader sense.

Topics: Adenoma, Islet Cell; Bombesin; Ceruletide; Child; Cholecystokinin; Gastric Inhibitory Polypeptide; Gastrins; Gastrointestinal Hormones; Glucagon-Like Peptides; Humans; Motilin; Neurotensin; Pancreatic Neoplasms; Pancreatic Polypeptide; Secretin; Somatostatin; Substance P; Vasoactive Intestinal Peptide

Topics: Acromegaly; Adenoma, Islet Cell; Cholestasis; Diverticulitis; Esophageal Achalasia; Esophageal Perforation; Glucagon; Glucagon-Like Peptides; Glycogen Storage Disease; Hepatitis; Humans; Hypoglycemia; Molecular Weight; Osteitis Deformans; Pancreas; Pheochromocytoma; Thyroid Neoplasms

Endocrine tumors of the pancreas may produce characteristic syndromes attributable to the increased secretion of one or more hormones. These tumors provide valuable opportunities for the analysis of hormone biosynthesis and secretion in the neoplastic human endocrine cell. The authors studied a pancreatic endocrine tumor obtained from a patient with classical glucagonoma syndrome. Characterization of plasma and tumor glucagon-like immunoreactivity (GLI) by high-performance liquid chromatography and radioimmunoassay for GLI showed different chromatographic profiles, with glucagon the major molecular form in the tumor, and glicentin and oxyntomodulin predominating in plasma. Although immunocytochemical staining of the tumor showed only focal weak positivity for glucagon, tumor extracts contained large amounts of immunoreactive GLI peptide. Northern blot analysis of tumor RNA demonstrated that abundant glucagon mRNA transcripts were present, just slightly larger in size than those detected in normal pancreas and intestine. Electron microscopic analysis of the tumor cellular ultrastructure revealed only occasional small electron dense secretory granules. A large number of complex lysosome-like structures of variable size and electron density were detected throughout the cytoplasm and ringing the nucleus of most cells, a feature atypical of endocrine tumors of the pancreas. Primary cultures of dispersed tumor cells were established and, in contrast to previous results, were obtained using normal or neoplastic islet cell models, GLI secretion was found to be stimulated eightfold by incubation with 5 mM dibutyryl cyclic adenosine monophosphate. Phorbol myristate acetate, the calcium ionophore A23187, and sodium butyrate had no effect on GLI secretion in vitro. These observations indicate that neoplastic human A cells may have abnormalities at different points in the biosynthesis and secretion of glucagon.

Topics: Adenoma, Islet Cell; Blotting, Northern; Chromatography, High Pressure Liquid; Culture Techniques; Cytoplasm; Glicentin; Glucagon; Glucagon-Like Peptides; Glucagonoma; Humans; Immunohistochemistry; Insulin; Microscopy, Electron; Oxyntomodulin; Pancreatic Neoplasms; Peptide Fragments; Proglucagon; Protein Precursors; RNA, Neoplasm; Somatostatin

125I-Labelled glucagon-like peptide-1(7-36)amide was cross-linked to a specific binding protein in plasma membranes prepared from RINm5F rat insulinoma-derived cells using disuccinimidyl suberate. Consistent with the presence of a single class of binding site on the surface of intact cells, only a single radiolabelled band at Mr63,000 was identified by SDS-PAGE after solubilization of the ligand-binding protein complex. The band was not observed when 10nM glucagon-like peptide-1(7-36)amide was included in the binding assay, but 1 microM concentrations of glucagon-like peptide-1(1-36)amide, glucagon-like peptide-2 and glucagon did not decrease the intensity of labelling. No change in the mobility of the band was observed under reducing conditions, suggesting that the binding protein in the receptor is not attached to other subunits via disulphide bonds. In control incubations using plasma membranes from pig intestinal epithelial cells, which do not contain specific binding sites for glucagon-like peptide-1(7-36)amide, no cross-linked ligand-binding protein complex was observed.

Topics: Adenoma, Islet Cell; Animals; Cell Line; Cell Membrane; Cross-Linking Reagents; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucagon-Like Peptides; Insulinoma; Peptides; Rats; Receptors, Cell Surface; Receptors, Glucagon

Glucagon-like peptide-1(7-36)amide [GLP-1(7-36)amide], probably representing an important incretin, binds to receptors on RINm5F cells resulting in an adenosine 3',5'-cyclic monophosphate increase. Guanine nucleotides (GTP, GTP-gamma-S, GDP-beta-S) decreased the binding of GLP-1(7-36)amide to receptors on RINm5F cell membranes. Further analysis revealed that GTP (10(-4) M) decreased the receptor affinity with an increase of the Kd from 2.5 +/- 0.99 x 10(-10) M to 9.43 +/- 2.16 x 10(-10) M. In cross-linking experiments the amount of labeled peptide linked to receptors was reduced in the presence of GTP (10(-4) M). Further studies investigated the involvement of membrane depolarization or changes in the cytosolic free calcium level in the intracellular signaling of GLP-1(7-36)amide-induced insulin secretion. In contrast to fuel and nonfuel secretagogues, GLP-1(7-36)amide did not cause a depolarization of the membrane potential. This was unaffected by various glucose concentrations (0-20 mM) or by previous cell depolarization by D-glyceraldehyde. Similarly, the cytosolic calcium concentration remained unchanged after addition of GLP-1(7-36)amide (10(-12)-10(-8) M). The effect of guanine nucleotides on binding of GLP-1(7-36)amide indicates that the action of the peptide is mediated by the adenylate cyclase system. GLP-1(7-36)amide binding neither changed the membrane potential nor altered the intracellular calcium concentration, making an involvement of the inositol 1,4,5-trisphosphate pathway or an activation of protein kinase C in the postreceptor signaling after GLP-1(7-36)amide binding unlikely.

Topics: Adenoma, Islet Cell; Animals; Calcium; Cell Line; Cell Membrane; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptides; Insulinoma; Membrane Potentials; Peptide Fragments; Peptides; Rats; Signal Transduction; Tumor Cells, Cultured

Glucagon-like peptide-1(7-36)amide [GLP-1(7-36)amide] is supposed to be an important physiologic incretin. Recently, high affinity receptors for GLP-1(7-36)amide have been demonstrated on rat insulinoma-derived RINm5F cells. The present study examined the internalization and degradation of the GLP-1-receptor complex. Internalization of the peptide was time- and temperature-dependent. At 37 degrees C binding and internalization was rapid. At 60 min 35% of 125I-labeled GLP-1(7-36)amide was internalized. Incubation in the presence of increasing concentrations of non-labeled GLP-1(7-36)amide resulted in a decrease of internalization of 125I-labeled peptide indicating that this process is saturable. Incubation in the presence of 0.2 mM chloroquine, an inhibitor of intracellular hormone degradation, resulted in intracellular accumulation of 125I-GLP-1(7-36)amide. HPLC-supported analysis of cell content after internalization of 125I-GLP-1(7-36)amide during a 60-min incubation period at 37 degrees C revealed an elution profile showing two maxima of radioactivity: one represented intact labeled GLP-1(7-36)amide, the other an intracellular degradation product of the peptide. Chloroquine caused a 5-fold increase of the peak representing intact 125I-GLP-1(7-36)amide thus demonstrating inhibition of degradation of labelled peptide. Furthermore, a 4-fold increase of the other peak occurred possibly mirroring a delay of release of degradation products by chloroquine. It was excluded that chloroquine is able to interfere with GLP-1(7-36)amide-binding to its receptor.

Topics: Adenoma, Islet Cell; Animals; Chloroquine; Chromatography, High Pressure Liquid; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucagon-Like Peptides; Insulinoma; Kinetics; Pancreatic Neoplasms; Peptides; Rats; Receptors, Cell Surface; Receptors, Glucagon; Temperature; Tumor Cells, Cultured

Topics: Adenoma; Adenoma, Islet Cell; Adrenal Cortex; Female; Gastrins; Glucagon-Like Peptides; Humans; Hydrocortisone; Hyperplasia; Middle Aged; Multiple Endocrine Neoplasia; Pancreatic Neoplasms; Parathyroid Neoplasms; Peptides; Thyroid Gland; Thyroid Hormones

Glucagon-like peptide-1(7-36)amide [GLP-1(7-36)amide], a new important incretin candidate, binds to specific high-affinity receptors on rat insulinoma-derived beta-cells (RINm5F). In the present study, the effect of somatostatin-14 on the GLP-1(7-36)amide-induced insulin release and cAMP generation in this cell line was investigated. Somatostatin did not decrease basal insulin release of RINm5F cells. The GLP-1(7-36)amide-induced insulin release was decreased concentration dependently by somatostatin. Somatostatin, 1 microM reduced the maximally GLP-1(7-36)amide-stimulated (0.1 microM) insulin release to basal insulin levels. The GLP-1(7-36)amide-induced cAMP production was significantly decreased by somatostatin in a concentration-dependent manner. The GLP-1(7-36)amide concentration causing half-maximal cAMP production was 2.98 +/- 1.56 nM. Somatostatin left the EC50 unaltered but decreased the maximal GLP-1(7-36)amide effect for 32% in the presence of 1 nM somatostatin and for 50% at 1 microM. In additional experiments, the interaction of both hormones was evaluated in the perfused pancreas as a nontumor model. Somatostatin (1 nM, 1 microM) inhibited the glucose-induced (6.7 mM) and GLP-1(7-36)amide-potentiated (0.05, 0.5, and 5 nM) insulin release dose dependently. The biphasic pattern of insulin release remained preserved. The GLP-1(7-36)amide-induced insulin release is potently inhibited by somatostatin-14. This effect was demonstrated in different model systems for beta-cell function studies. The present data allow the conclusion that the somatostatin action upon GLP-1(7-36)amide effects is at least partly related to regulation of intracellular cyclic nucleotides.

Topics: Adenoma, Islet Cell; Animals; Cell Line; Cyclic AMP; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptides; Insulin; Insulinoma; Male; Pancreas; Peptide Fragments; Peptides; Rats; Somatostatin; Tumor Cells, Cultured

Specific binding of 125I-labelled glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) to rat insulinoma-derived RINm5F cells was dependent upon time and temperature and was proportional to cell concentration. Binding of radioactivity was inhibited in a concentration-dependent manner by GLP-1(7-36) amide consistent with the presence of a single class of binding site with a dissociation constant (Kd) of 204 +/- 8 pmol/l (mean +/- S.E.M.). Binding of the peptide resulted in a dose-dependent increase in cyclic AMP concentrations (half maximal response at 250 +/- 20 pmol/l). GLP-1(1-36)amide was approximately 200 times less potent than GLP-1(7-36)amide in inhibiting the binding of 125I-labelled GLP-1(7-36)amide to the cells (Kd of 45 +/- 6 nmol/l). Binding sites for GLP-1 (7-36)amide were not present on dispersed enterocytes from porcine small intestine.

Topics: Adenoma, Islet Cell; Animals; Binding, Competitive; Cell Line; Cyclic AMP; Glucagon; Glucagon-Like Peptide 1; Glucagon-Like Peptide-1 Receptor; Glucagon-Like Peptides; Insulinoma; Intestinal Mucosa; Jejunum; Pancreatic Neoplasms; Peptide Fragments; Peptides; Rats; Receptors, Cell Surface; Receptors, Glucagon

The glucagon RIA measures several molecular components in human plasma. Clinical disorders have been described associated with abnormal elevations of certain of these components. This report documents another clinical disorder, the idiopathic postprandial syndrome, which also appears associated with excessive circulating large molecular weight immunoreactive glucagon (IRG) components. During studies of glucose homeostasis in subjects with apparent idiopathic postabsorptive hypoglycemia, 80 subjects were evaluated using oral glucose tolerance tests; 18 subjects were found to have clinical and laboratory findings consistent with the disorder, and of these, 3 had markedly elevated basal total plasma IRG levels. Plasma IRG responses in the subjects after oral glucose or mixed meals were variable. Physical characterization of the excessive large molecular weight IRG components revealed molecular weight estimates of 300,000 and 345,000 daltons in 2 subjects and of more than 200,000 daltons in the third subject. The origin and chemical nature of this material is uncertain. None of these subjects had evidence for a glucagonoma, as supported by the virtual absence of detectable levels of native (3500-dalton) glucagon after gel filtration. Since the origin of the idiopathic postprandial syndrome as well as the origin and chemical nature of large molecular weight IRG components are unknown, the association of these two findings remains unclear but is clinically important in the differential diagnosis of the glucagonoma syndrome.

Topics: Adenoma, Islet Cell; Chromatography, Gel; Food; Glucagon; Glucagon-Like Peptides; Glucose Tolerance Test; Humans; Hypoglycemia; Molecular Weight; Peptides; Syndrome

The heterogeneity of glucagon and insulin in plasma and tissue extracts from a 57-year-old female with glucagonoma syndrome with surgically and autopsy verified islet-cell tumors was studied by Bio-Gel P-10 filtration. The preoperative plasma immunoreactive glucagon (IRG) level was 20.2 ng/ml, and plasma glucagon-like immunoreactivity(GLI) 25.8 ng/ml. The column chromatography of the preoperative plasma revealed three or four IRG components and four GLI components. Among these, peak II, the large glucagon immunoreactivity (LGI) peak, considered a candidate for proglucagon, was prominent, along with peak III. The resected metastatic liver tumor contained an enormous amount of IRG and an appreciable amount of immunoreactive insulin (IRI), indicating that the elevated plasma IRG was mainly of tumor origin. The IRG pattern of the tumor tissue extract revealed a small quantity of IRG in peaks I and II, and a large amount in peak III; control pancreatic tissue extract manifested a similar elution pattern. The IRI elution pattern of the tumor tissue extract revealed two major IRI peaks which migrated close to the elution volume of cytochrome C and insulin, respectively. This is a quite different pattern from the control pancreatic tissue extract in which the RI peak was localized in the elution volume of the insulin. We conclude that the present metastatic liver tumor produced not only enormous amounts of glucagon but heterogeneous peptides which contained immunological insulin determinants within their.

Topics: Adenoma, Islet Cell; Female; Glucagon; Glucagon-Like Peptides; Humans; Insulin; Liver Neoplasms; Middle Aged; Peptides; Radioligand Assay

Topics: Adenoma, Islet Cell; Adult; Female; Gastrins; Gastrointestinal Hormones; Glucagon-Like Peptides; Humans; Male; Middle Aged; Multiple Endocrine Neoplasia; Pancreatic Neoplasms; Somatostatin; Vasoactive Intestinal Peptide; Zollinger-Ellison Syndrome

Pancreas and gut hormones are involved in many endocrine and gastrointestinal diseases. Radioimmunoassays for these hormones have proved particularly valuable in diagnosis, localisation and control of treatment of endocrine tumours, of which many are mixed. An estimate based on ten years experience in a homogenous population of 5 million inhabitants (Denmark) suggests, that endocrine gut tumour-syndromes on an average appear with an incidence of 1 patient per year/syndrome/million. At present six different syndromes are known: 1) The insulinoma syndrome, 2) The Zollinger-Ellison syndrome.3) The Verner-Morrison syndrome. 4) The glucagonoma syndrome. 5) The somatostatinoma syndrome, and 6) the carcinoid syndrome. Accordingly diagnostically valuable RIAs for pancreas and gut hormones include those for insulin, gastrin, VIP, HPP, glucagon, somatostatin, and presumably also substance P. It is probably safe to predict that the need for gut and pancreas hormone RIAs within the next decade will increase greatly in order to assure proper management of tumours producing gastroentero-pancreatic hormones.

Topics: Adenoma, Islet Cell; Carcinoid Tumor; Cholecystokinin; Gastric Inhibitory Polypeptide; Gastrins; Gastrointestinal Hormones; Glucagon; Glucagon-Like Peptides; Humans; Insulin; Intestinal Neoplasms; Motilin; Pancreatic Hormones; Pancreatic Neoplasms; Pancreatic Polypeptide; Radioimmunoassay; Secretin; Somatostatin; Substance P; Vasoactive Intestinal Peptide; Zollinger-Ellison Syndrome